06-29-2016 03:31 AM
I've been playing around with my camera and I've been getting better (not good enough to post any pictures yet lol). I also bought a cheap CCD but have not had much time to mess with it yet. I did have it out the other night to capture Saturn but since it's so low in the sky I battled the atmosphere most of the night. I was able to get a decent picture using Registax but nothing to write home about.
I've been thinking of getting a focal reducer to reduce my f10 scope to f6.3. Do you think it's worth it?
06-29-2016 12:26 PM - edited 06-29-2016 12:29 PM
The hard-core astro-imagers tend to use very expensive CCD imaging cameras that have built-in coolers (they can cool the chip to about 40-50ºC colder than ambient temperature) because of the relationship between heat & noise (if the sensor is physically hot then it tends to generate a lot of noise.)
A CCD sensor tends to be better at very long exposure images... but not so good at fast exposures.
A CMOS sensor tends to be better at fast exposures, but not as good as a CCD at very long exposures.
(at least this used to be true... as technology advances the lines are blurred.)
The hard-core astrophotographers will use a monochrome sensor and put color filters in front to take their images... e.g. shoting a set of "luminance" channel images (that's simply the full visible spectrum with the UV (anything <400nm) blocked and the IR (anything >700nm) blocked. These are basically just black & white images. Then they capture another set with "red" filters, another set with "green" filters, another set with "blue" filtes and then they combine them in software to produce the full color image. (Incidentally, while these are "broad band" filters, you can also get "narrowband" filters which selectively allow just a single wavelength of light to pass... i.e. nebulae tend to be composed of specific gases which glow at specific wavelengths so it's a way to capture more data of just the stuff you want ... without over-exposing the rest of the image.
Meanwhile back to your question about the focal reducer.
Your scope has a focal length of roughly 2000mm. (it's probably 2030mm). If you attach a Canon DSLR with an APS-C size sensor to that scope, the angular width of the area of sky that you can see is 38' x 25' (that's in arc-minutes). In other words it's just slightly more than 1/2º wide in one direction and a little less than a 1/2º tall in the other direction.) This is not a big piece of sky.
Here's a simulated (using Starry Night Pro Plus 7) image to show you how, say, the Trifid nebula would fit in the frame if taken with your scope & camera combination (I just picked any 8" Meade f/10 scope to let the software calculate the correct frame dimensions. The orange box represents the size of sky that will fit in the image.
So that works... but the problem is different things in the sky require different sizes... if you point the scope to, say, the Lagoon nebula (which is right next to the Trifid nebula -- just below it in the sky), this is what happens:
You can see this doesn't fit. You'd need to take lots of images and then piece them together as a mosaic (which software can do). OR... you can use a focal reducer. Here's the image with a .62x focal reducer:
This increases the area of sky that will fit in the frame:
You can see that now the frame size is expanded so that it mostly fits (ok, it's a tight fit - but most of it does fit in there.)
That's the point of hte focal reducer... it allows you to capture a larger area of the sky by reducing the focal length of the scope. it is, in effect, the opposite of a tele-converter because it's a focal length reducer rather than a focal length extender.
But you're trying to image Saturn... so let's look at that:
And there you go! That's a simulation of Saturn, as imaged through a simulated scope with the same focal length and properties as yours and using a camera with the same properties as yours... but with a focal reducer.
Do you even see Saturn? It's there... but you wont like this image.
Here it is again, but without the focal reducer (native resolution)
This helps, but not enough...
What's going on?
Saturn doesn't occupy a very large area of the sky. It's only 18" (arc-seconds). Remember I mentioned earlier that the sensor can image an area of the sky which was 38' (arc-minutes) x 25' (arc-minutes)? Well Saturn is so small in the sky that it isn't even 1 arc-minute... it's size is measured in arc-seconds (60 arc-seconds = 1 arc-minute and 60 arc-minutes = 1 degree).
To capture Saturn, put the camera into MOVIE recording mode and IF your camera has this feature, enable 640x480 "CROP" mode. Note that most Canon models don't have "CROP" mode... they may have 640x480, but not "CROP". CROP mode causes the camera to only use the pixels in the middle of the sensor. You get a much bigger image.
If your camera doesn't have "CROP" mode (only found in the menu if the camera is in "movie" mode.) then you can download a utility called "PIPP" (which you want anyway). PIPP = Planetary Image Pre-Processor. It's free software and the guy who wrote it says he initially wrote it because his PC was old & slow and he was trying to use programs like Registax to do planetary image stacking and the planet is so small he only needs the center of the frame. So he could REALLY speed along the processing by croping each single frame of video (making a new video from just the center of the original video) and then sending that reduced size data to the stacking program. So PIPP will let you simulate the crop mode.
You'll need to CAREFULLY focus the telescope on a STAR (do NOT focus on Saturn... find a star nearby), put the camera in 10x zoom mode (on the screen) and carefully focus until you've minimized the size of that star. For better focus, get a Bahtinov focusing mask (I bought one from Spike-A.com). This causes the star to throw diffraction spikes and as you focus the spikes will not necessarily all converge at a common center point.. but when they DO converge, you've nailed focus. Once you've nailed focus, remove the mask, go back to Saturn (as long as you don't touch the focus, the rule is if "anything" in space is focued, then "everything" in space is focused. So accurate focus for both Saturn and a star are the same.
Now you need to record about a minutes' worth of video of Saturn.
The next problem is that regardless of what you use to stack (Registax vs. AutoStakkert2 ... both are free) they want ".AVI" files and your camera doesn't make (nor support) ".AVI" output. It makes ".MOV" files. PIPP to the rescue again... PIPP can not only crop the image size down, it can also create ".AVI" file output from your ".MOV" input.
Now you can feed that into Registax and stack it (numerous YouTube tutorials will help.)
One thing to know about imaging low in the sky is that the Earth's atmosphere behaves like a lens and creates a "chromatic aberration" problem where the red, green, and blue, channels slightly mis-align due to the angle of the atmosphere (this is mostly a problem when shooting things low in the sky... objects near the zenith of the sky don't have this problem.) The effect is called "atmospheric dispersion" and there are even mechanical devices that correct for the problem (it's a prism that can be aligned and tilted to reverse the effect). But it turns out you don't need an "atmospheric dispersion corrector" (ADC) -- you can do it in software. Registax has a feature (used at the very end) that allows you to nudge the red, green, and blue channels back on top of each other so that the channels align and you get a sharper image.
Saturn is low in the sky because it is reaching opposition in the summer. Remember that in mid summer (at the summer solice) Earth's northern polar axis is tilted toward the sun (and away from the outer solar system) at a 23.5º angle. This puts the sun "high" in the sky (making it heat the northern hemisphere more efficiently) but puts objects in the outer solar system "low" in the sky because we are tilted away from those objects. In 15 years saturn will be on the other side of the solar system and we'll see Saturn during the winter months instead of the summer months. At that time, Saturn will be very high in the sky (saturn takes about 30 years to orbit the sun). If you don't want to wait 15 years... the easier option is just fly to the Southern hemisphere (the southern hemisphere is currently tilted "toward" the outer solar system right now ... so for them it is high in the sky.)
This image is a couple of years old (I think this was shot in 2014). This is not "my" image, but this was shot by a personal friend at the observatory that my astronomy club operates for a local school system. That scope is a 14" f/11 SCT (3556mm focal length) and he used a Canon camera (I *think* this was shot with his T1i). The color channels did not align BUT he used the ADC correction feature of Registax to correct it. This is the result:
You DO need a night with good "seeing" conditions... shooting in the middle of a large body of water is ideal (flat surface means smooth laminar air-flow (no turbulance) and no thermals. A large open grassy field is good too (vegitation keeps the Earth surface cooler). AVOID shooting over roof-top (hot roofs will give off heat and distort the atmosphere for several hours after sunset.) Seeing often improves very late at night (e.g. 3am) because things have had a long enough time to cool off that the Earth isn't creating so many thermals that distort the air.
07-02-2016 08:06 AM
Once again Tim you've not failed to impress. I really appreciate you taking the time to write such detailed explanations. I bookmarked this thread and use it a lot as reverence when I'm out under the stars. I can only think that I'll get better with a lot of paintence and your great advice. As soon as I get some good results I'll share but it might take a few years. lol
07-02-2016 09:36 AM
"... shooting in the middle of a large body of water is ideal ..."
Or a mountain top.
07-02-2016 10:57 AM
Download Stellarium (stellarium.org - it's free). It runs on Windows, Mac, or Linux.
In the configuration menu, go into the "plugins" category. You should see a plugin named "oculars" - select that, check the box that says to load the plugin at startup and then click the "configure" button (this is to configure the "oculars" equipment.)
Click the Telescope tab and "add" a new scope... name it for your scope model and enter your scope's focal length and diameter. An 8" f/10 SCT is probably 2080mm focal length with an aperture (diameter) of 208mm. There are some check-boxes for horizontal and vertical flip. This a "straight through" view in a telescope technically results in an image which is upside down & backwards (in other words both horizontal and vertical flip). Your camera also captures the images upside-down and backwards... it just displays them right-side up when you look at them on the LCD screen. The 90º diagonal that you use when visually using the scope (with eyepieces -- not the camera attached) corrects the vertical view (so up is really up and down is really down) but it doesn't correct the horizontal flip (left is really right). This is purely cosmetic so that the occular view provided by stellarium will show the object the way it will appear through the telescope.
Next click the "sensors" tab and enter your camera. You can enter in the info for your T6i. The resolution (for a T6i) can be entered as 6000 x 4000. The chip size should be entered as 22.3 x 14.9 (mm). The pixel height & width should be entered as 3.72 x 3.72 (microns). You can leave the rotation angle alone (this allows you to specific if you've rotated the camera on an angle at the back of the scope ... Stellarium will rotate the orientation of the rectangular box that it draws on the screen to match.) There's also some info about an off-axis guider... unless you have an off-axis guider then leave that box unchecked and don't fill in anything below. (an off-axis guider is a 2nd camera... usually very tiny -- often not much larger than an eyepiece. There is an adapter that attaches between the camera & scope which has a "T" intersection and a very tiny pick-off mirror at the edge of the tube which steals a little light from a tiny box at the edge of the frame and bounces it out to the guide-camera. The idea is to rotate the thing to make sure you have a suitable star visible to the guide-camera. The guide camera takes an image of that star every few seconds and checks to see if it's drifting... if it is drifiting, the software sends a correction to the mount to put the telescope back on target.
There is a tab for "lenses" -- that's for entering focal reducers or focal length multipliers (e.g. a 2x barlow... or a .63x reducer, etc.)
The "eyepieces" tab is to enter the info on all the eyepieces you own (for visual use - not for astrophotography).
With all of that entered, you can set the time of day in Stellarium (e.g. set it to midnight, for example), pick an object (due south near the core of the Milky way (just above) you'll see a red patch if you zoom in slightly... that's probably the Lagoon nebula and above it is the Trifid... a little higher above it is the Omega nebula and slightly higher still is the Eagle nebula.) Anyway you can select an object and if you've set the oculars to always load then in the upper right corner of your screen you'll see a few icons... the rectangular icon represents your camera frame. Click it and Stellarium will draw a red box on the screen representing the area of sky it calculates will fit into your camera frame based on knowing the physical properties of your telescope as well as the physical properties of your camera sensor.
Stellarium is extremely popular because it's free and easy to use (it doesn't do a lot so it's not hard to learn it). I use something called Starry Night Pro Plus 7 -- which is more advanced, but not free.
Whenever I do imaging, I look up the angular dimensions of the object I want to image. For example, set the date & time to midnight in early September and then look for M31 (Andromeda Galaxy). When you select it, a bunch of info will show up in the upper-left corner of your screen. Near the bottom it will list the "size" -- about 3º wide by about 1º tall. You'll see that actually very little of it shows up within the rectangular boundaries of your image sensor. If you toggle on a .63x focal reducer (such as the Meade f/6.3 reducer -- really that's just a .63x reducer but they assume you're using a Meade f/10 scope because most Meade SCTs are f/10 (but not all of them) -- anyway if you toggle on the reducer you'll see the size of the box jump to a larger area of sky. But even still, you'd probably have to shoot at least a 4 panel mosaic to image the thing.
07-02-2016 10:58 AM
"... shooting in the middle of a large body of water is ideal ..."
Or a mountain top.
Or better still... a mountain in the middle of a large body of water. This is why Hawaii is one of the best observatory locations on the planet. ;-)
08-01-2016 04:28 PM
So I am getting better but each time I have the time to go out the clouds and sky have not been cooporating with me. :-(
I'm learning to use AutoStakkert and RegiStax 6 but my biggest problem was focus. My scope is 100% manual (execpt for the RA motor) and when focusing the scope would vibrate no matter how careful I am. I just recieved my JMI motofocus and played with it looking at the communications tower navigation light I use to align my finder scope and it works wonderful. I'm still waiting on my focal reducer which should help with my CCD imager.
Now if only mother nature would be nice.
04-18-2017 05:24 PM
So I've been really working on my method and I'm getting better at it I think. Here is Jupiter at opposition the other night. I used my cheap Orion CCD and my barlow to get this image. It's stacked using Registax6 with a base amount of 1000 frames. My focus is still a little off but I think it's because I am still using the cheap capture software that came with my CCD. I've downloaded SharpCap and will start leaning how to use it. Hopefully I'll get better and better.
04-18-2017 06:33 PM
Focus issues are not necessarily the scope... the atmosphere plays a big role and you'll find that some nights are much better than others.
You can use websites such as Clear Sky Clock ( http://cleardarksky.com/csk/ ) to get an idea of how good the conditions may be near you. The row named "seeing" is the one that indicates atmosphere stability.
04-18-2017 08:33 PM - edited 04-18-2017 08:35 PM
Ya, it was early in the evening and seeing conditions wern't the greatest. I knew the atmosphere was causing most of my focus issues but I pressed on.
I had alloted all night to mess with it but I was having file save problems from the beginning with the Orion capture software and called it a night after only getting two .avi's to save. I was messing with the software more than observing which led to me getting frustrated. I knew I should have spent some time during the day making sure I wouldn't have those kind of problems at night.