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    <title>topic Re: Rebel T6 Astrophotgrphy with Telescope Settings Assistance in EOS DSLR &amp; Mirrorless Cameras</title>
    <link>https://community.usa.canon.com/t5/EOS-DSLR-Mirrorless-Cameras/Rebel-T6-Astrophotgrphy-with-Telescope-Settings-Assistance/m-p/264409#M29163</link>
    <description>&lt;P&gt;Do you have specific targets in mind? &amp;nbsp; The problem is the lack of tracking. &amp;nbsp;Also, both scopes you listed are achromatic refractors.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;An "achromatic" refractor is one that uses a very simple achromatic "doublet" configuration (two lens elements). &amp;nbsp;It will have color fringing or color bleeding near the edges of the frame. &amp;nbsp;The more expensive "apochromatic" refractors use a combination of better "glass" (typically an ultra-low dispersion glass) and usually at least 3 elements (and sometimes 4) and produce noticeably sharper results ... but cost a lot more (typicaly these things start at around $1000 for *just* the optical tube -- no mount.) &amp;nbsp;An "achromatic" refractor will still look good in the center of the field.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;The moon is an easy exposure using something called the "Looney 11" rule. &amp;nbsp;At f/11, the exposure duration should be set to the inverse of the ISO. &amp;nbsp;So ISO 100 means use 1/100th sec. &amp;nbsp;Or ISO 200 then use 1/200th sec. etc. &amp;nbsp;That's fairly easy and it will nail the moon.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;ISO 800 is typically the highest ISO I would use on that camera. &amp;nbsp;&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;For any deep-sky object ... the mount needs to be tracking and you need an equatorial mount. &amp;nbsp;The 70EQ is equatorial ... but doesn't track (and it's not a solid mount so vibration is likely to be an issue). &amp;nbsp;The 80LCM is motorized ... but not equatorial.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;The Earth is spinning from west to east at 15 arc-seconds of angular rotation per second of time.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;If we pick the 900mm focal length, you get a field of view 1.4° wide in the horizontal direction and the camera has 5184 pixels per how. &amp;nbsp;It turns out 1.4° x 60 (minutes) x 60 (seconds) = 5040. &amp;nbsp;In other words 1 pixel = about 1 arc-second of sky. &amp;nbsp;If not tracking, a star would travel 15 pixels every second. &amp;nbsp;So you can imagine how you'd end up with a smeared image if it doesn't track (tracking is requried -- not optional).&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;The reason it needs to be an "equatorial" mount instead of the simpler alt/az mount is becuase on an equatorial mount, the axis of the mount is parallel to Earth's axis of rotation ... that means they neatly cancel each other out and the star is held in place even for a very long exposure. &amp;nbsp;On an alt/az type mount the computer can move both axes to compensate ... but the field rotates (it appears to "twist" over time becuase the axes aren't parallel). &amp;nbsp;This causes a twisted smeared image in a long exposure.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;A minimum mount from Celestron would be their Advanced VX mount ... and only for very light loads (the CGEM or better yet the CGX are the mounts more often used for imaging). &amp;nbsp;Also, best to keep the focal length short when learning astrophotography (e.g. 500-700mm range). &amp;nbsp;When you get into longer focal lengths (e.g. 2000mm) the tracking accuracy becomes critical and the mount is very unforgiving of tracking errrors caused by alignment errors, vibrations, flexure, periodic errors (basically mechanical imperfection in the worm gear) etc.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;You'll also be contending with high focal ratios (f/10, f/11) which mean you'll need much longer exposure times. (depending on the object it could be 4-8 minutes long at ISO 800).&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;Orion makes a 6" f/4 Newtonian "Astrograph" for about $400 ... an f/4 scope collects light 8x faster than an f/11 scope. &amp;nbsp;That means the light that an f/11 scope would require 8&amp;nbsp;minutes to capture ... it can capture in just 1 minute. &amp;nbsp;It has a 610mm focal length ... which is pretty good as you're starting out because that will be a bit more forgiving when it comes to tracking accuracy.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;An "astrograph" is any class of telescope which has been optimized for astrophotography. &amp;nbsp;In the case of a newtonian-type reflector, the issue with a normal Newtonian scope is that the position of the mirrors is designed to bring the image to focus at the eyepiece ... typically about mid-travel on the focuser. &amp;nbsp;The problem with photography is that a DSLR camera has a t-ring to mount to the scope ... but the image sensor is about 50mm farther back from that t-ring (about 2".) &amp;nbsp;This means in order to focus... the whole camera has to be brought about 2" closer to the scope. &amp;nbsp;So you start focusing inward and you can see the image just starting to come to focus when... the focuser tube hits the limit of travel.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;To get around this... the Newtonian "astrograph" design moves the primrary mirror 2" closer to compensate for that extra 2" the camera needs. &amp;nbsp;This means the image actually comes to focus about 2" beyond the focuser tube (which is perfect for a DSLR camera). &amp;nbsp;But that's farther than where an eyepiece would be located. &amp;nbsp;So they throw in a 2" extension barrel to hold the eyepiece an extra 2" farther away if you want to use it for visual observing. &amp;nbsp;You remove the extension barrel when using the DSLR camera.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;That $400 price is *just* the optical tube assembly (not a mount). You would still need an equatorial Go-To mount. &amp;nbsp;Tip: &amp;nbsp;Get the BEST mount you can afford. &amp;nbsp;This is THE most critical piece of gear for astrophotography.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;Mounts will have either a "Vixen" style or a "Losmandy" style dovetail saddle ... which mounts to the mounting rail on the bottom of the telescope. &amp;nbsp;These are both industry standard mounting rails. &amp;nbsp;The Vixen-style rail is a narrower dovetail bar ... but thick. &amp;nbsp; It is more commonly found on smaller / lighter telescopes. &amp;nbsp; The Losmandy style rail is much widder ... but a little thinner. &amp;nbsp;It is more commonly found on larger / heavier telescopes. &amp;nbsp;As these are industry standards... you can buy a mount from one vendor and a scope from a completely different vendor ... you do not have to buy the scope and mount from the same company.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;I will caution you that a $400 telescope isn't a lot of money for an imaging scope. &amp;nbsp;Newtonians often need a coma corrector for imaging or you may see degradation of the quality of stars near the edge of the field (and coma correctors can cost a few hundred dollars. &amp;nbsp;Baader planetarium makes one that costs about $200.)&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;And keep in mind ... this really is doing things on a budget.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;Meanwhile back to your question on exposure.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;You cannot adjust the f-stop when shooting through a telescope. &amp;nbsp;What you do instead is pretend that you are taking a manual exposure and&amp;nbsp;use the focal ratio of the scope. &amp;nbsp;E.g. if you used that f/4 Newtonian ... then it's f/4. &amp;nbsp;&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;The ISO for *that* particular camera should be ISO 800 (or less). &amp;nbsp;For a moon photo you wont need ISO 800 (I do my moon exposures at ISO 100 becuase it's fairly bright and it's a fast exposure). &amp;nbsp;But for deep-sky objects ... things are much fainter and you have to increase the ISO. &amp;nbsp;The optimal ISO for *that* camera is ISO 800. &amp;nbsp;This has to do with how that camera applies gain. &amp;nbsp;Light is technically analog and the sensor receives it as analog. &amp;nbsp;But because it is a digital camera, it has to run the data through an analog-to-digital conversion (ADC). &amp;nbsp;It can either apply some analog gain before it does the ADC (which we call "upstream gain") or it can apply some gain *after* it goes through the ADC (which we call "downstream gain"). &amp;nbsp;It can actually do a little of both. &amp;nbsp;THAT camera sensor applies mostly "upstream" (analog) gain UNTIL it hits ISO 800 ... at which point it switches to "downstream" (digital) gain. &amp;nbsp;The problem with digital gain is that you lose dynamic range faster. &amp;nbsp;&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;In other words ISO 800 will give the optimum amount of gain possible before you start sacrificing a lot of dynamic range. &amp;nbsp;This is true of any Canon DSLR that has the Canon 18MP sensor. &amp;nbsp;(so this ISO doesn't apply to all Canon cameras but it does apply to the T6).&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;Exposure duration will vary based on the target.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;When I did my Andromeda image ... I was shooting 8-minute exposures at f/5.4 (the f/4 scope could shoot that in 4 minutes ... and maybe 3 minutes would be better). &amp;nbsp;But if you tried to do that with an f/11 scope ... first you'd discover that the galaxy doesn't fit in the frame ... but also you'd have to run very long exposure times because f/11 is "slow").&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;Just a little over a week ago I shot M42 (Orion Nebula) ... which is "easy" becuase it's bright (for a deep-sky object) but "hard" because it requires a lot of dynamic range. &amp;nbsp;So you end up taking several different exposures and using HDR to combine them. &amp;nbsp;My longest exposure times were 4 minutes (the f/4 scope could shoot those in 2 minutes). &amp;nbsp;&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;By the way ... you don't just take one shot. &amp;nbsp; You take lots of them. &amp;nbsp;Ideally shot after shot for at least an hour ... and preferably at least 2 hours. &amp;nbsp;(the guys who are really serious will take 6-8 hours worth of data and sometimes across multiple nights.) &amp;nbsp;This data is combined via image "stacking" software which improves the image quality by reducing image noise.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;Some faint objects can require very long exposures.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;Collecting the data is half the battle... processing the data is the other half of the battle. &amp;nbsp;(Processing usually consumes the most time.)&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;</description>
    <pubDate>Mon, 14 Jan 2019 23:41:09 GMT</pubDate>
    <dc:creator>TCampbell</dc:creator>
    <dc:date>2019-01-14T23:41:09Z</dc:date>
    <item>
      <title>Rebel T6 Astrophotgrphy with Telescope Settings Assistance</title>
      <link>https://community.usa.canon.com/t5/EOS-DSLR-Mirrorless-Cameras/Rebel-T6-Astrophotgrphy-with-Telescope-Settings-Assistance/m-p/264329#M29162</link>
      <description>&lt;P&gt;Have the Rebel T6&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;Going to be trying some astrophotography using a:&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;Celestron Powerseeker 70EQ refractor telescope with specs:Aperture 70mm, Focal length 700mm, Focal ratio - 10&lt;/P&gt;&lt;P&gt;&amp;nbsp;or a&lt;/P&gt;&lt;P&gt;Celestron 80LCM (Compterized) refractor telescope with specs: &amp;nbsp; Aperture 80mm, Focal length 900mm, Focal ratio - 11&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;Will be using a T-ring and T-adaptor (1.25") to attach to the telescopes and a wireless/remote switch/trigger.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;I know to use Manual and RAW or RAW+Lareg/Fine and am looking for some guidance on:&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;F stop&lt;/P&gt;&lt;P&gt;ISO&lt;/P&gt;&lt;P&gt;Shutter Speed/Exposure&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;Have seen numbers all over the place and looking for plain language basic guidance.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;</description>
      <pubDate>Mon, 14 Jan 2019 06:08:50 GMT</pubDate>
      <guid>https://community.usa.canon.com/t5/EOS-DSLR-Mirrorless-Cameras/Rebel-T6-Astrophotgrphy-with-Telescope-Settings-Assistance/m-p/264329#M29162</guid>
      <dc:creator>EddM</dc:creator>
      <dc:date>2019-01-14T06:08:50Z</dc:date>
    </item>
    <item>
      <title>Re: Rebel T6 Astrophotgrphy with Telescope Settings Assistance</title>
      <link>https://community.usa.canon.com/t5/EOS-DSLR-Mirrorless-Cameras/Rebel-T6-Astrophotgrphy-with-Telescope-Settings-Assistance/m-p/264409#M29163</link>
      <description>&lt;P&gt;Do you have specific targets in mind? &amp;nbsp; The problem is the lack of tracking. &amp;nbsp;Also, both scopes you listed are achromatic refractors.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;An "achromatic" refractor is one that uses a very simple achromatic "doublet" configuration (two lens elements). &amp;nbsp;It will have color fringing or color bleeding near the edges of the frame. &amp;nbsp;The more expensive "apochromatic" refractors use a combination of better "glass" (typically an ultra-low dispersion glass) and usually at least 3 elements (and sometimes 4) and produce noticeably sharper results ... but cost a lot more (typicaly these things start at around $1000 for *just* the optical tube -- no mount.) &amp;nbsp;An "achromatic" refractor will still look good in the center of the field.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;The moon is an easy exposure using something called the "Looney 11" rule. &amp;nbsp;At f/11, the exposure duration should be set to the inverse of the ISO. &amp;nbsp;So ISO 100 means use 1/100th sec. &amp;nbsp;Or ISO 200 then use 1/200th sec. etc. &amp;nbsp;That's fairly easy and it will nail the moon.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;ISO 800 is typically the highest ISO I would use on that camera. &amp;nbsp;&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;For any deep-sky object ... the mount needs to be tracking and you need an equatorial mount. &amp;nbsp;The 70EQ is equatorial ... but doesn't track (and it's not a solid mount so vibration is likely to be an issue). &amp;nbsp;The 80LCM is motorized ... but not equatorial.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;The Earth is spinning from west to east at 15 arc-seconds of angular rotation per second of time.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;If we pick the 900mm focal length, you get a field of view 1.4° wide in the horizontal direction and the camera has 5184 pixels per how. &amp;nbsp;It turns out 1.4° x 60 (minutes) x 60 (seconds) = 5040. &amp;nbsp;In other words 1 pixel = about 1 arc-second of sky. &amp;nbsp;If not tracking, a star would travel 15 pixels every second. &amp;nbsp;So you can imagine how you'd end up with a smeared image if it doesn't track (tracking is requried -- not optional).&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;The reason it needs to be an "equatorial" mount instead of the simpler alt/az mount is becuase on an equatorial mount, the axis of the mount is parallel to Earth's axis of rotation ... that means they neatly cancel each other out and the star is held in place even for a very long exposure. &amp;nbsp;On an alt/az type mount the computer can move both axes to compensate ... but the field rotates (it appears to "twist" over time becuase the axes aren't parallel). &amp;nbsp;This causes a twisted smeared image in a long exposure.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;A minimum mount from Celestron would be their Advanced VX mount ... and only for very light loads (the CGEM or better yet the CGX are the mounts more often used for imaging). &amp;nbsp;Also, best to keep the focal length short when learning astrophotography (e.g. 500-700mm range). &amp;nbsp;When you get into longer focal lengths (e.g. 2000mm) the tracking accuracy becomes critical and the mount is very unforgiving of tracking errrors caused by alignment errors, vibrations, flexure, periodic errors (basically mechanical imperfection in the worm gear) etc.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;You'll also be contending with high focal ratios (f/10, f/11) which mean you'll need much longer exposure times. (depending on the object it could be 4-8 minutes long at ISO 800).&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;Orion makes a 6" f/4 Newtonian "Astrograph" for about $400 ... an f/4 scope collects light 8x faster than an f/11 scope. &amp;nbsp;That means the light that an f/11 scope would require 8&amp;nbsp;minutes to capture ... it can capture in just 1 minute. &amp;nbsp;It has a 610mm focal length ... which is pretty good as you're starting out because that will be a bit more forgiving when it comes to tracking accuracy.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;An "astrograph" is any class of telescope which has been optimized for astrophotography. &amp;nbsp;In the case of a newtonian-type reflector, the issue with a normal Newtonian scope is that the position of the mirrors is designed to bring the image to focus at the eyepiece ... typically about mid-travel on the focuser. &amp;nbsp;The problem with photography is that a DSLR camera has a t-ring to mount to the scope ... but the image sensor is about 50mm farther back from that t-ring (about 2".) &amp;nbsp;This means in order to focus... the whole camera has to be brought about 2" closer to the scope. &amp;nbsp;So you start focusing inward and you can see the image just starting to come to focus when... the focuser tube hits the limit of travel.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;To get around this... the Newtonian "astrograph" design moves the primrary mirror 2" closer to compensate for that extra 2" the camera needs. &amp;nbsp;This means the image actually comes to focus about 2" beyond the focuser tube (which is perfect for a DSLR camera). &amp;nbsp;But that's farther than where an eyepiece would be located. &amp;nbsp;So they throw in a 2" extension barrel to hold the eyepiece an extra 2" farther away if you want to use it for visual observing. &amp;nbsp;You remove the extension barrel when using the DSLR camera.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;That $400 price is *just* the optical tube assembly (not a mount). You would still need an equatorial Go-To mount. &amp;nbsp;Tip: &amp;nbsp;Get the BEST mount you can afford. &amp;nbsp;This is THE most critical piece of gear for astrophotography.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;Mounts will have either a "Vixen" style or a "Losmandy" style dovetail saddle ... which mounts to the mounting rail on the bottom of the telescope. &amp;nbsp;These are both industry standard mounting rails. &amp;nbsp;The Vixen-style rail is a narrower dovetail bar ... but thick. &amp;nbsp; It is more commonly found on smaller / lighter telescopes. &amp;nbsp; The Losmandy style rail is much widder ... but a little thinner. &amp;nbsp;It is more commonly found on larger / heavier telescopes. &amp;nbsp;As these are industry standards... you can buy a mount from one vendor and a scope from a completely different vendor ... you do not have to buy the scope and mount from the same company.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;I will caution you that a $400 telescope isn't a lot of money for an imaging scope. &amp;nbsp;Newtonians often need a coma corrector for imaging or you may see degradation of the quality of stars near the edge of the field (and coma correctors can cost a few hundred dollars. &amp;nbsp;Baader planetarium makes one that costs about $200.)&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;And keep in mind ... this really is doing things on a budget.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;Meanwhile back to your question on exposure.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;You cannot adjust the f-stop when shooting through a telescope. &amp;nbsp;What you do instead is pretend that you are taking a manual exposure and&amp;nbsp;use the focal ratio of the scope. &amp;nbsp;E.g. if you used that f/4 Newtonian ... then it's f/4. &amp;nbsp;&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;The ISO for *that* particular camera should be ISO 800 (or less). &amp;nbsp;For a moon photo you wont need ISO 800 (I do my moon exposures at ISO 100 becuase it's fairly bright and it's a fast exposure). &amp;nbsp;But for deep-sky objects ... things are much fainter and you have to increase the ISO. &amp;nbsp;The optimal ISO for *that* camera is ISO 800. &amp;nbsp;This has to do with how that camera applies gain. &amp;nbsp;Light is technically analog and the sensor receives it as analog. &amp;nbsp;But because it is a digital camera, it has to run the data through an analog-to-digital conversion (ADC). &amp;nbsp;It can either apply some analog gain before it does the ADC (which we call "upstream gain") or it can apply some gain *after* it goes through the ADC (which we call "downstream gain"). &amp;nbsp;It can actually do a little of both. &amp;nbsp;THAT camera sensor applies mostly "upstream" (analog) gain UNTIL it hits ISO 800 ... at which point it switches to "downstream" (digital) gain. &amp;nbsp;The problem with digital gain is that you lose dynamic range faster. &amp;nbsp;&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;In other words ISO 800 will give the optimum amount of gain possible before you start sacrificing a lot of dynamic range. &amp;nbsp;This is true of any Canon DSLR that has the Canon 18MP sensor. &amp;nbsp;(so this ISO doesn't apply to all Canon cameras but it does apply to the T6).&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;Exposure duration will vary based on the target.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;When I did my Andromeda image ... I was shooting 8-minute exposures at f/5.4 (the f/4 scope could shoot that in 4 minutes ... and maybe 3 minutes would be better). &amp;nbsp;But if you tried to do that with an f/11 scope ... first you'd discover that the galaxy doesn't fit in the frame ... but also you'd have to run very long exposure times because f/11 is "slow").&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;Just a little over a week ago I shot M42 (Orion Nebula) ... which is "easy" becuase it's bright (for a deep-sky object) but "hard" because it requires a lot of dynamic range. &amp;nbsp;So you end up taking several different exposures and using HDR to combine them. &amp;nbsp;My longest exposure times were 4 minutes (the f/4 scope could shoot those in 2 minutes). &amp;nbsp;&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;By the way ... you don't just take one shot. &amp;nbsp; You take lots of them. &amp;nbsp;Ideally shot after shot for at least an hour ... and preferably at least 2 hours. &amp;nbsp;(the guys who are really serious will take 6-8 hours worth of data and sometimes across multiple nights.) &amp;nbsp;This data is combined via image "stacking" software which improves the image quality by reducing image noise.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;Some faint objects can require very long exposures.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;Collecting the data is half the battle... processing the data is the other half of the battle. &amp;nbsp;(Processing usually consumes the most time.)&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;</description>
      <pubDate>Mon, 14 Jan 2019 23:41:09 GMT</pubDate>
      <guid>https://community.usa.canon.com/t5/EOS-DSLR-Mirrorless-Cameras/Rebel-T6-Astrophotgrphy-with-Telescope-Settings-Assistance/m-p/264409#M29163</guid>
      <dc:creator>TCampbell</dc:creator>
      <dc:date>2019-01-14T23:41:09Z</dc:date>
    </item>
    <item>
      <title>Re: Rebel T6 Astrophotgrphy with Telescope Settings Assistance</title>
      <link>https://community.usa.canon.com/t5/EOS-DSLR-Mirrorless-Cameras/Rebel-T6-Astrophotgrphy-with-Telescope-Settings-Assistance/m-p/264411#M29164</link>
      <description>&lt;P&gt;BTW ... on a budget ... the easier way to start is to use a solid tripod, skip the telescope completely, and just get a decent "tracking" head ... such a a&amp;nbsp;Sky Watcher "Star Adventurer" head or an iOptron SkyGuider Pro head. &amp;nbsp;These run $300-400 price range and you just use your camera and lenses.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;Here's an example of an image captured using a tracking head and a Canon 135mm f/2 lens:&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;&lt;IMG src="https://community.usa.canon.com/t5/image/serverpage/image-id/16871iEFCE90EEFD076884/image-size/original?v=1.0&amp;amp;px=-1" border="0" alt="IMG_2741.JPG" title="IMG_2741.JPG" /&gt;&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;Here's an image captured using the same camera ... but using a 540mm apochromatic refractor and a very good equatorial mount. &amp;nbsp;These were 8-minute exposures at ISO 800 using the f/5.4 scope and I shot a little over an hour's worth of images.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;&lt;IMG src="https://community.usa.canon.com/t5/image/serverpage/image-id/11681i564470385D3AEF59/image-size/original?v=1.0&amp;amp;px=-1" border="0" alt="Andromeda &amp;amp; Companions" title="Andromeda &amp;amp; Companions" /&gt;&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;(note the image does not come out of the camera looking like this ... this is the result of hours and hours of processing.)&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;Images of the moon are fast and easy:&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;&lt;IMG src="https://community.usa.canon.com/t5/image/serverpage/image-id/13241iAAA58CE55E4344E4/image-size/original?v=1.0&amp;amp;px=-1" border="0" alt="IMG_2918.jpg" title="IMG_2918.jpg" /&gt;&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;That's was taken using the 540mm scope ... but with a 2x tele-extender at f/11 and 1/100th sec at ISO 100.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;</description>
      <pubDate>Mon, 14 Jan 2019 23:48:30 GMT</pubDate>
      <guid>https://community.usa.canon.com/t5/EOS-DSLR-Mirrorless-Cameras/Rebel-T6-Astrophotgrphy-with-Telescope-Settings-Assistance/m-p/264411#M29164</guid>
      <dc:creator>TCampbell</dc:creator>
      <dc:date>2019-01-14T23:48:30Z</dc:date>
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      <title>Re: Rebel T6 Astrophotgrphy with Telescope Settings Assistance</title>
      <link>https://community.usa.canon.com/t5/EOS-DSLR-Mirrorless-Cameras/Rebel-T6-Astrophotgrphy-with-Telescope-Settings-Assistance/m-p/264594#M29165</link>
      <description>&lt;P&gt;Beautiful shots, TCampbell.&amp;nbsp;&lt;BR /&gt;&lt;BR /&gt;How many images did you stack for the M31 image?&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;Gorgeous work.&amp;nbsp;&lt;/P&gt;</description>
      <pubDate>Wed, 16 Jan 2019 23:41:05 GMT</pubDate>
      <guid>https://community.usa.canon.com/t5/EOS-DSLR-Mirrorless-Cameras/Rebel-T6-Astrophotgrphy-with-Telescope-Settings-Assistance/m-p/264594#M29165</guid>
      <dc:creator>axepilot</dc:creator>
      <dc:date>2019-01-16T23:41:05Z</dc:date>
    </item>
    <item>
      <title>Re: Rebel T6 Astrophotgrphy with Telescope Settings Assistance</title>
      <link>https://community.usa.canon.com/t5/EOS-DSLR-Mirrorless-Cameras/Rebel-T6-Astrophotgrphy-with-Telescope-Settings-Assistance/m-p/264621#M29166</link>
      <description>&lt;P&gt;&lt;SPAN&gt;The only total lunar eclipse of 2019 will happen on the evening of Jan. 20.&amp;nbsp; It is called the "Wolf Moon." It is a good, pretty easy sky event to photograph.&lt;/SPAN&gt;&lt;/P&gt;&lt;P&gt;&lt;SPAN&gt;I would like to mention the photos Tim Campbell takes are not easy. They take a lot or preparation, a lot of gear and a lot of post editing. Not to mentions a lot of talent and skill.&amp;nbsp; Guys like Tim Campbell make it look easy but it is not.&lt;/SPAN&gt;&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;&lt;SPAN&gt;The Wolf Moon will be far easier to start&amp;nbsp;with and it is a stunning event to photograph.&lt;/SPAN&gt;&lt;/P&gt;</description>
      <pubDate>Thu, 17 Jan 2019 15:28:06 GMT</pubDate>
      <guid>https://community.usa.canon.com/t5/EOS-DSLR-Mirrorless-Cameras/Rebel-T6-Astrophotgrphy-with-Telescope-Settings-Assistance/m-p/264621#M29166</guid>
      <dc:creator>ebiggs1</dc:creator>
      <dc:date>2019-01-17T15:28:06Z</dc:date>
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    <item>
      <title>Re: Rebel T6 Astrophotgrphy with Telescope Settings Assistance</title>
      <link>https://community.usa.canon.com/t5/EOS-DSLR-Mirrorless-Cameras/Rebel-T6-Astrophotgrphy-with-Telescope-Settings-Assistance/m-p/264673#M29167</link>
      <description>&lt;P&gt;Imaging the lunar eclipse is different than imaging the moon under normal conditions only because the moon will dim quite a bit.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;Please see Fred Espinak’s page (aka “Mr. Eclipse”) with guidelines on this: &amp;nbsp;&lt;A href="http://www.mreclipse.com/LEphoto/LEphoto.html" target="_blank"&gt;http://www.mreclipse.com/LEphoto/LEphoto.html&lt;/A&gt;&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;&lt;SPAN&gt;The Moon moves at 14.685 arc-seconds per second. (The Earth spins at 15.04 arc-seconds per second ... but since the moon is orbiting as we spin, it makes the moon appear to move just fractionally slower than the stars.)&lt;/SPAN&gt;&lt;BR /&gt;&lt;BR /&gt;&lt;SPAN&gt;The formula for calculating field of view (assuming you have a calculator that works in Degrees) is:&lt;/SPAN&gt;&lt;BR /&gt;&lt;BR /&gt;&lt;I&gt;Angular field of view&lt;/I&gt;&lt;SPAN&gt; = 2 * arctan(&lt;/SPAN&gt;&lt;I&gt;sensor width&lt;/I&gt;&lt;SPAN&gt; / ( 2 * &lt;/SPAN&gt;&lt;I&gt;focal length&lt;/I&gt;&lt;SPAN&gt;))&lt;/SPAN&gt;&lt;BR /&gt;&lt;BR /&gt;&lt;SPAN&gt;For an APS-C sensor camera (say 22.5mm in the horizontal direction) and a 600mm lens it's:&lt;/SPAN&gt;&lt;BR /&gt;&lt;BR /&gt;&lt;SPAN&gt;2 * arctan( 22.5 / ( 2 * 600))&lt;/SPAN&gt;&lt;BR /&gt;&lt;BR /&gt;&lt;SPAN&gt;This works out to a 2.148° field of view (in the horizontal direction)&lt;/SPAN&gt;&lt;BR /&gt;&lt;BR /&gt;&lt;SPAN&gt;Multiply that by 3600 to convert degrees into arc-seconds and that works out to 7732.8.&lt;/SPAN&gt;&lt;BR /&gt;&lt;BR /&gt;&lt;SPAN&gt;With my Canon 60Da camera, the 18MP sensor is 5184 x 3456.&lt;/SPAN&gt;&lt;BR /&gt;&lt;BR /&gt;&lt;SPAN&gt;Divide 5184 / 7732.8 = .67 arc-seconds per pixel.&lt;/SPAN&gt;&lt;BR /&gt;&lt;BR /&gt;&lt;SPAN&gt;In 1 second, the moon will travel 14.685 arc-seconds. So 14.685 * .67 = 9.84 pixels (per second).&lt;/SPAN&gt;&lt;BR /&gt;&lt;BR /&gt;&lt;SPAN&gt;So if you were to take a photo of the moon at ISO 100, f/11, 1/100th sec (the "Looney 11" guideline)... it would move about .0984 pixels (you could just round that to .1 pixels) during that exposure (without a tracking mount).&lt;/SPAN&gt;&lt;BR /&gt;&lt;BR /&gt;&lt;SPAN&gt;This is why even though the moon does move ... you don't need to worry about it for purposes of most photography &lt;/SPAN&gt;&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;HOWEVER ... during an eclipse the moon gets dark enough to require an exposure which would be quite a bit longer. &amp;nbsp;It’s hard to predict exactly how dark ... it depends on how close the moon will get to the very center of the shadow cone (there’s enough &amp;nbsp;room in the umbra cone to easily fit 3 moons edge to edge). &amp;nbsp; If the moon passes directly through the very center *and* during a perigee moon ... it can get so dark that it nearly goes completely black instead of red and almost vanishes. &amp;nbsp;Imaging the moon in those conditions could be a VERY long exposure (e.g. 30 minutes). &amp;nbsp; &amp;nbsp;But that very rarely happens. &amp;nbsp;Still... the exposure could be a few minutes.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;Use the exposure table on Fred’s page ... instead of shooting f/11 open the aperture to whatever wide-open is for your lens (e.g. if you’re using a 150-600mm and it can do f/5.6 at 600mm... then use f/5.6). &amp;nbsp;You may want to boost ISO a bit too.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;Anyway... with the moon moving at nearly 10 pixels per second (if not on a tracking mount) you need to try to get a faster shutter speed.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;But another trick ... is to just use a shorter focal length. &amp;nbsp;The moon will be smaller in your field of view ... but will move fewer pixels per second.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;Whatever happens with the camera ... just make sure _you_ enjoy the eclipse! &amp;nbsp;&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;Clear skies &amp;amp; good luck!&lt;/P&gt;&lt;P&gt;Tim&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;</description>
      <pubDate>Fri, 18 Jan 2019 00:28:27 GMT</pubDate>
      <guid>https://community.usa.canon.com/t5/EOS-DSLR-Mirrorless-Cameras/Rebel-T6-Astrophotgrphy-with-Telescope-Settings-Assistance/m-p/264673#M29167</guid>
      <dc:creator>TCampbell</dc:creator>
      <dc:date>2019-01-18T00:28:27Z</dc:date>
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      <title>Re: Rebel T6 Astrophotgrphy with Telescope Settings Assistance</title>
      <link>https://community.usa.canon.com/t5/EOS-DSLR-Mirrorless-Cameras/Rebel-T6-Astrophotgrphy-with-Telescope-Settings-Assistance/m-p/264700#M29168</link>
      <description>&lt;P&gt;Another question.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;I heard all the the talk on telescope but they are what we have.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;Questiion on Rebel T6 setting for telescope shooting.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;I tried using Manual mode with T ring and adapter attached and it won't let me set an F aperture as it says no lens attached so with this camera what mode should i use?&amp;nbsp; The T6 has M, AV, TV, P,&amp;nbsp; and all the various auto set up.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;Yes I am green and new to DSLR so any help is useful.&lt;/P&gt;</description>
      <pubDate>Fri, 18 Jan 2019 06:24:56 GMT</pubDate>
      <guid>https://community.usa.canon.com/t5/EOS-DSLR-Mirrorless-Cameras/Rebel-T6-Astrophotgrphy-with-Telescope-Settings-Assistance/m-p/264700#M29168</guid>
      <dc:creator>EddM</dc:creator>
      <dc:date>2019-01-18T06:24:56Z</dc:date>
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      <title>Re: Rebel T6 Astrophotgrphy with Telescope Settings Assistance</title>
      <link>https://community.usa.canon.com/t5/EOS-DSLR-Mirrorless-Cameras/Rebel-T6-Astrophotgrphy-with-Telescope-Settings-Assistance/m-p/264706#M29169</link>
      <description>&lt;P&gt;Almost always you need to be in full manual.&amp;nbsp; That is the M mode on the dial. In this type&amp;nbsp;situation the camera really doesn't have any idea what the exposures should be. You need to tell it.&lt;/P&gt;</description>
      <pubDate>Fri, 18 Jan 2019 14:47:23 GMT</pubDate>
      <guid>https://community.usa.canon.com/t5/EOS-DSLR-Mirrorless-Cameras/Rebel-T6-Astrophotgrphy-with-Telescope-Settings-Assistance/m-p/264706#M29169</guid>
      <dc:creator>ebiggs1</dc:creator>
      <dc:date>2019-01-18T14:47:23Z</dc:date>
    </item>
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      <title>Re: Rebel T6 Astrophotgrphy with Telescope Settings Assistance</title>
      <link>https://community.usa.canon.com/t5/EOS-DSLR-Mirrorless-Cameras/Rebel-T6-Astrophotgrphy-with-Telescope-Settings-Assistance/m-p/264707#M29170</link>
      <description>&lt;P&gt;&lt;EM&gt;"Clear skies &amp;amp; good luck!&lt;/EM&gt;&lt;/P&gt;&lt;P&gt;&lt;EM&gt;Tim"&lt;/EM&gt;&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;Yeah right!&amp;nbsp; We&amp;nbsp; haven't seen the Moon is well over a week and I don't expect it to change Sunday.&lt;img id="smileysad" class="emoticon emoticon-smileysad" src="https://community.usa.canon.com/i/smilies/16x16_smiley-sad.png" alt="Smiley Sad" title="Smiley Sad" /&gt; We were out of electricity for 6 days&amp;nbsp;last week and another winter storm coming tonight. You might have to do the shots for me, Tim.&lt;/P&gt;</description>
      <pubDate>Fri, 18 Jan 2019 14:50:19 GMT</pubDate>
      <guid>https://community.usa.canon.com/t5/EOS-DSLR-Mirrorless-Cameras/Rebel-T6-Astrophotgrphy-with-Telescope-Settings-Assistance/m-p/264707#M29170</guid>
      <dc:creator>ebiggs1</dc:creator>
      <dc:date>2019-01-18T14:50:19Z</dc:date>
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    <item>
      <title>Re: Rebel T6 Astrophotgrphy with Telescope Settings Assistance</title>
      <link>https://community.usa.canon.com/t5/EOS-DSLR-Mirrorless-Cameras/Rebel-T6-Astrophotgrphy-with-Telescope-Settings-Assistance/m-p/264709#M29171</link>
      <description>&lt;BLOCKQUOTE&gt;&lt;HR /&gt;&lt;a href="https://community.usa.canon.com/t5/user/viewprofilepage/user-id/97598"&gt;@EddM&lt;/a&gt;&amp;nbsp;wrote:&lt;BR /&gt;&lt;P&gt;Another question.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;I heard all the the talk on telescope but they are what we have.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;Questiion on Rebel T6 setting for telescope shooting.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;I tried using Manual mode with T ring and adapter attached and it won't let me set an F aperture as it says no lens attached so with this camera what mode should i use?&amp;nbsp; The T6 has M, AV, TV, P,&amp;nbsp; and all the various auto set up.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;Yes I am green and new to DSLR so any help is useful.&lt;/P&gt;&lt;HR /&gt;&lt;/BLOCKQUOTE&gt;&lt;P&gt;A camera lens has an adjustable aperture — but telescopes do not. &amp;nbsp;You have to use the focal ratio of your telescope. &amp;nbsp;Most scope’s have the focal ratio printed somewhere. &amp;nbsp;But you can also just divide the focal ratio by the diameter (in millimeters) to get the focal ratio.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;While it wont be able to detect a lens (there are no electrical contacts to mate to the scope like there is when you connect a camera lens), it will still let you shoot. &amp;nbsp;&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;</description>
      <pubDate>Fri, 18 Jan 2019 15:09:04 GMT</pubDate>
      <guid>https://community.usa.canon.com/t5/EOS-DSLR-Mirrorless-Cameras/Rebel-T6-Astrophotgrphy-with-Telescope-Settings-Assistance/m-p/264709#M29171</guid>
      <dc:creator>TCampbell</dc:creator>
      <dc:date>2019-01-18T15:09:04Z</dc:date>
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      <title>Re: Rebel T6 Astrophotgrphy with Telescope Settings Assistance</title>
      <link>https://community.usa.canon.com/t5/EOS-DSLR-Mirrorless-Cameras/Rebel-T6-Astrophotgrphy-with-Telescope-Settings-Assistance/m-p/264710#M29172</link>
      <description>&lt;P&gt;After i sent that post Ithoughton it and realized I was just not thinking straight but TY for the confirmation.&lt;/P&gt;</description>
      <pubDate>Fri, 18 Jan 2019 15:27:00 GMT</pubDate>
      <guid>https://community.usa.canon.com/t5/EOS-DSLR-Mirrorless-Cameras/Rebel-T6-Astrophotgrphy-with-Telescope-Settings-Assistance/m-p/264710#M29172</guid>
      <dc:creator>EddM</dc:creator>
      <dc:date>2019-01-18T15:27:00Z</dc:date>
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      <title>Re: Rebel T6 Astrophotgrphy with Telescope Settings Assistance</title>
      <link>https://community.usa.canon.com/t5/EOS-DSLR-Mirrorless-Cameras/Rebel-T6-Astrophotgrphy-with-Telescope-Settings-Assistance/m-p/270982#M29173</link>
      <description>This is my first post I created an account just to tell you thank you. I am a noob but aspire to one day take something like your Andromeda photo. I’ve a little success on Orion Nebula..just enough to get me hooked. I have an AVX equatorial mount which I agree is pretty much the minimum for tracking deep sky objects. OTA is a Meade 70mm Apo astrograph quad, and I don’t think I’ll outgrow that anytime soon. Using a Cannon T6 which I think is the first thing I’ll need to upgrade but as there is quite a steep learning curve and so much cool stuff in space, I think the T6 will suffice until I work out all the software, plate solving, basic processing, etc.&lt;BR /&gt;&lt;BR /&gt;Your post was awesome particularly all the info about how the camera sensor applies gain. I’m finding the ISO values to use a bit confusing. I’ve heard there is a certain point on the histo (like 1/3rd or something)...do you think 800 is going to be pretty much always the optimal setting for exposures of to 2 mins? So far from what I’ve seen the AVX will track that long. I have a 50mm off axis guidescope/cam but haven’t gotten into guiding yet but soon will via phd2&lt;BR /&gt;&lt;BR /&gt;Your Andromeda photo is awesome! Thanks for the info and clear skies.</description>
      <pubDate>Mon, 01 Apr 2019 04:41:06 GMT</pubDate>
      <guid>https://community.usa.canon.com/t5/EOS-DSLR-Mirrorless-Cameras/Rebel-T6-Astrophotgrphy-with-Telescope-Settings-Assistance/m-p/270982#M29173</guid>
      <dc:creator>NGC1978</dc:creator>
      <dc:date>2019-04-01T04:41:06Z</dc:date>
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      <title>Re: Rebel T6 Astrophotgrphy with Telescope Settings Assistance</title>
      <link>https://community.usa.canon.com/t5/EOS-DSLR-Mirrorless-Cameras/Rebel-T6-Astrophotgrphy-with-Telescope-Settings-Assistance/m-p/271112#M29174</link>
      <description>&lt;BLOCKQUOTE&gt;&lt;HR /&gt;&lt;a href="https://community.usa.canon.com/t5/user/viewprofilepage/user-id/118749"&gt;@NGC1978&lt;/a&gt;&amp;nbsp;wrote:&lt;BR /&gt;This is my first post I created an account just to tell you thank you. I am a noob but aspire to one day take something like your Andromeda photo. I’ve a little success on Orion Nebula..just enough to get me hooked. I have an AVX equatorial mount which I agree is pretty much the minimum for tracking deep sky objects. OTA is a Meade 70mm Apo astrograph quad, and I don’t think I’ll outgrow that anytime soon. Using a Cannon T6 which I think is the first thing I’ll need to upgrade but as there is quite a steep learning curve and so much cool stuff in space, I think the T6 will suffice until I work out all the software, plate solving, basic processing, etc.&lt;BR /&gt;&lt;BR /&gt;Your post was awesome particularly all the info about how the camera sensor applies gain. I’m finding the ISO values to use a bit confusing. I’ve heard there is a certain point on the histo (like 1/3rd or something)...do you think 800 is going to be pretty much always the optimal setting for exposures of to 2 mins? So far from what I’ve seen the AVX will track that long. I have a 50mm off axis guidescope/cam but haven’t gotten into guiding yet but soon will via phd2&lt;BR /&gt;&lt;BR /&gt;Your Andromeda photo is awesome! Thanks for the info and clear skies.&lt;HR /&gt;&lt;/BLOCKQUOTE&gt;&lt;P&gt;The optimal ISO will vary based on the camera sensor being used. &amp;nbsp;But the T6 uses the same Canon 18MP sensor that my 60Da uses ... so ISO 800 would also be the optimal ISO for that camera assuming you are shooting deep-sky objects.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;The basic idea is that, for deep-sky images, the longer the exposure time, the greater the probability of tracking errors, etc. &amp;nbsp;So it's nice to be able to boost the ISO a little. &amp;nbsp;But ISO is really an application of "gain" (an "amplification" of the information). &amp;nbsp;Your camera knows how to apply both "analog" gain (before the imformation is converted to digital form) as well as "digital" gain (after the conversion has occurred.)&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;The camera sensor collects photons and converts them into electron volts (this is not unlike what a solar panel does). &amp;nbsp;The voltage stored for each photo-site on the sensor can simply go through an analog amplifier to read a higher voltage. &amp;nbsp;&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;The problem is, all camera sensors have to be "powered up" to work. &amp;nbsp;If you simply power up a sensor and then perform a read-out (without actually taking a photo), you'll find that the values in each photo site are not actually zero ... there's something there. &amp;nbsp;This is the bias level of the sensor. &amp;nbsp;The sensor also gets something called "read noise". &amp;nbsp;There are many causes of noise, but read-noise is probably the biggest contributor to overall noise. &amp;nbsp;So one goal of astrophotography processing is to capture "bias" frames and "dark" frames so the computer software can figure out just how much "noise" is on that sensor (and this helps it supress some noise when the images are processed.)&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;If you simply apply ONLY analog gain, you'll amplify that noise. &amp;nbsp;At some point it becomes obnoxious. &amp;nbsp;Canon decided that for this 18MP sensor, that anything beyond ISO 800 is where they consider the noise from analog gain to be unacceptable. &amp;nbsp;So they stop doing analog gain, perform the analog-to-digital conversion (ADC) and now you have digital data.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;In digital form, they can apply more "gain" by simply multiplying the values. &amp;nbsp;Usually there's some stretched algorithm (not just linear multiplication) in an effort to bring up the "signal" (the stuff you want) more than they bring up the "noise" (the stuff you don't want). &amp;nbsp;&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;The problem with the "digital" gain is that the camera has a fixed cap on the largest digital value you can hold (considering it's a 14-bit chip). &amp;nbsp;14-bits means it can hold values between 0 and 16,383. &amp;nbsp;&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;Suppose you multiply everything by 2 (to bring up the exposure by 1 full stop). &amp;nbsp;Anything below the mid-brightness value gets doubled. &amp;nbsp;But anything above the mid-brightness level gets doulbed to a value which is GREATER than the max value the chip can hold. &amp;nbsp;This results in the data getting "clipped". &amp;nbsp; &amp;nbsp;If you had a pixel that was at 15,000 and another pixel at 10,000 (both are less than 16,383) then the pixel which is 15,000 is clearly brigher than the 10,000 value (by about 50% brigher). &amp;nbsp;But when you multiple both by 2x, they both become 16,383 (the max value) because the data "clipped". &amp;nbsp;Now niether is brighter than the other -- they are the same. &amp;nbsp;You lost tonality or the abilty to distinguish between them.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;This basically means you lose dynamic range. &amp;nbsp; &amp;nbsp;The application of digital gain results in a trade-off in that you lose dynamic range.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;But in deep-sky objects, you WANT dynamic range. &amp;nbsp;So you try to resist inching up the ISO too much. &amp;nbsp;A common problem is that the deep-sky object gets a bit brighter ... but the stars all get clipped. &amp;nbsp;Clipped stars will just appear "white". &amp;nbsp;In reality the stars should have some color cast. &amp;nbsp;Some are near-white. &amp;nbsp;Some are yellow. &amp;nbsp;Some are a bit blue. &amp;nbsp;Some are a bit orange. &amp;nbsp;etc. &amp;nbsp;But they shouldn't all be uniform white. &amp;nbsp;If you see that, it usually means the shot was over-exposed.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;Here's an article that may be helpful: &amp;nbsp;&lt;A href="http://dslr-astrophotography.com/iso-dslr-astrophotography/" target="_blank"&gt;http://dslr-astrophotography.com/iso-dslr-astrophotography/&lt;/A&gt;&lt;/P&gt;&lt;P&gt;(the article is about 4 years old ... so it doesn't include the newest camera models, but you can still get the idea of how this works.)&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;As for the histogram and that "1/3rd" point. &amp;nbsp;Generally you'll find the data is down in the lower 1/3rd or lower 1/4 of the histogram.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;Here's an example:&lt;/P&gt;&lt;P&gt;&lt;IMG src="https://community.usa.canon.com/t5/image/serverpage/image-id/19008iC58EFBF80490B300/image-size/medium?v=1.0&amp;amp;px=-1" border="0" alt="Screen Shot 2019-04-02 at 10.31.04 AM.png" title="Screen Shot 2019-04-02 at 10.31.04 AM.png" /&gt;&lt;/P&gt;&lt;P&gt;(the above is from Canon DPP 4)&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;And here's the image it was taken from:&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;&lt;IMG src="https://community.usa.canon.com/t5/image/serverpage/image-id/19007i8EB8092DD3E52F6A/image-size/original?v=1.0&amp;amp;px=-1" border="0" alt="IMG_2700.JPG" title="IMG_2700.JPG" /&gt;&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;The above is a single un-processed frame (on of the frames from the finished photo). &amp;nbsp;I took roughly an hour's worth of data (the above image is an 8-minute exposure). &amp;nbsp;You can see it looks like it is upside-down (it is ... that's how it came out of the camera). &amp;nbsp; Notice the contrast isn't as good. &amp;nbsp;The disk structure is weak. &amp;nbsp;It doesn't even look like there is color in it (but there is). &amp;nbsp;Astrophotography images are usually heavily processed and the data is "stretched". &amp;nbsp;The color in the final image is based on separating the image into separate LRGB channels (L = Luminance channel) and then re-combining such that the luminance applies to saturation (the brighter it is, the more strongly it will be saturated).&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;I primarily used PixInsight to process this ... but I did do a little tweaking in Photoshop and also in Lightroom as well. &amp;nbsp;Learning to process takes a while and frankly is a never-ending quest to learn more (I'm still learning ... and frankly I feel like a beginner. &amp;nbsp;This is one of those ... the more you learn, the more you realize how much you still don't know.)&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;You will need a *precise* polar alignment. &amp;nbsp;I use a gadget by QHY called a "PoleMaster". &amp;nbsp;It's a camera that has roughly a 5° field of view and is usually attached to the mount (not the scope). &amp;nbsp;It takes an image of the sky near the pole and the software prompts you to turn the mount along the RA axis so it can take about 3 different images of the northern sky (each image is rotated a bit more). &amp;nbsp;It has you identify a star in each of the 3 frames (the same star) and it plots a circle through those three positions. &amp;nbsp;From this it can compute the axis of your mount. &amp;nbsp;It also applies a template to the sky to match up against the stars in the image. &amp;nbsp;From here it finds the TRUE pole ... but also finds your telescope's axis. &amp;nbsp;It then draws a circle on your computer screen and tells you to adjust the mount (using only the knobs -- not the electronics) until that star is centered in the circle. &amp;nbsp;At this point you have an extremely precise polar alignment and can do long exposure images without the stars drifting.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;Celestron includes a feature they call "All Star Polar Alignment" (or ASPA). &amp;nbsp;I have not used it. &amp;nbsp;You might try it (they have YouTube videos that explain how to use it). &amp;nbsp;I'm not sure how it compares to the precision alignment you get with a PoleMaster. &amp;nbsp;Nearly every astrophotographer I know who has to setup &amp;amp; take-down the gear each night (no permanent observatory) uses a PoleMaster. &amp;nbsp;It's very popular because it achieves a shockingly accurate alignment in just a couple of minutes.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;An off-axis guider (OAG) is a bit different than what you have. &amp;nbsp;You have a separate guide-scope. &amp;nbsp;An OAG is an adapter that fits on the back of your actual scope (not a separate scope) and has a tiny little pick-off mirror. &amp;nbsp;The guide camera is off at a 90° angle (the "off axis") and the regular imaging camera is still at the back ("on axis"). &amp;nbsp;OAG's are usually used for very long focal length scopes (e.g. big SCTs) to avoid flexure issues. &amp;nbsp;You wont have to worry about that with a 70mm APO.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;The 70mm APO is a great way to start becasue it is more forgiving when it comes to tracking accuracy. &amp;nbsp;I see many frustrated beginners who start with big SCTs ... and if you don't nail the polar alignment, the balance, the flexure issues, tuning the guide-software agressiveness, etc. you lose all your hair trying to learn. &amp;nbsp;Much easier to start with shorter focal lengths, get some early successes ... then work your way up to longer focal lengths.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;I'm not sure what you have as a guide-camera. &amp;nbsp;With your scope you may need minimal guiding. &amp;nbsp;&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;After you balance the weigths on your AVX, slightly "un-balance" them so that the east side of the mount is heavier by just a tiny amount. &amp;nbsp;All mounts have a little gear backlash. &amp;nbsp;By "un-balancing" you keep the weight on one side of the backlash so it doesn't "float" in the backlash (which would result in elongation in stars in the direction of the RA travel).&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;&lt;P&gt;When you start using a guider, one common mistake is to leave the "agressiveness" at 100%. &amp;nbsp;Aggressiveness is the amount of movement it will apply to the mount based on the error in star position. &amp;nbsp;The problem is, stars will "wobble" a bit based on atmospheric "seeing" conditions. &amp;nbsp;If agressiveness is too high, the guider will be "chasing the seeing conditions" (the star didn't *really* move .. it only *appeared* to have moved based on atmospheric distortions. &amp;nbsp;So you don't want to "chase" those subtle movements too agressively. &amp;nbsp;By de-tuning the agressiveness it's willing to let the star move by a tiny amounts without over-reacting. &amp;nbsp;Common agressiveness values are in the 70-85% range.&lt;/P&gt;&lt;P&gt;&amp;nbsp;&lt;/P&gt;</description>
      <pubDate>Tue, 02 Apr 2019 15:10:40 GMT</pubDate>
      <guid>https://community.usa.canon.com/t5/EOS-DSLR-Mirrorless-Cameras/Rebel-T6-Astrophotgrphy-with-Telescope-Settings-Assistance/m-p/271112#M29174</guid>
      <dc:creator>TCampbell</dc:creator>
      <dc:date>2019-04-02T15:10:40Z</dc:date>
    </item>
    <item>
      <title>Re: Rebel T6 Astrophotgrphy with Telescope Settings Assistance</title>
      <link>https://community.usa.canon.com/t5/EOS-DSLR-Mirrorless-Cameras/Rebel-T6-Astrophotgrphy-with-Telescope-Settings-Assistance/m-p/279105#M29175</link>
      <description>Hello everyone I've tried my t6 on my Celestron 127slt and taken good photos ,you need tracking capability to stop motion blur and you can stop movement from touching the shutter button by using the wifi connect app on your phone and tablet remotely shoot picture it's pretty awesome!</description>
      <pubDate>Mon, 12 Aug 2019 20:35:16 GMT</pubDate>
      <guid>https://community.usa.canon.com/t5/EOS-DSLR-Mirrorless-Cameras/Rebel-T6-Astrophotgrphy-with-Telescope-Settings-Assistance/m-p/279105#M29175</guid>
      <dc:creator>Babyzo</dc:creator>
      <dc:date>2019-08-12T20:35:16Z</dc:date>
    </item>
    <item>
      <title>Re: Rebel T6 Astrophotgrphy with Telescope Settings Assistance</title>
      <link>https://community.usa.canon.com/t5/EOS-DSLR-Mirrorless-Cameras/Rebel-T6-Astrophotgrphy-with-Telescope-Settings-Assistance/m-p/279108#M29176</link>
      <description>&lt;A href="https://photos.app.goo.gl/R8PsWK1AbAkofVfw5" target="_blank"&gt;https://photos.app.goo.gl/R8PsWK1AbAkofVfw5&lt;/A&gt;</description>
      <pubDate>Mon, 12 Aug 2019 20:43:28 GMT</pubDate>
      <guid>https://community.usa.canon.com/t5/EOS-DSLR-Mirrorless-Cameras/Rebel-T6-Astrophotgrphy-with-Telescope-Settings-Assistance/m-p/279108#M29176</guid>
      <dc:creator>Babyzo</dc:creator>
      <dc:date>2019-08-12T20:43:28Z</dc:date>
    </item>
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