06-24-2015 06:12 PM
So I finally got a good consumer DLSR, the T6i. My T mount adaptor comes in friday. I didn't get a shutter release yet but with the T6i I think the remote control through my cell phone will keep the vibrations down.......I guess. I've always wanted to get into astrophotography but never had a camera that could do it. I've read quite a bit about it over the years but I'll be new to it just as I'm new to anything other than a point and shoot and cell phone cameras.
I have an old school (no electronics but I know how to use it very well) Meade 8" Schmidt–Cassegrain that I've had for years. I do have an off axis corrector and a very good tripod. I'm just looking for some hints and tips from the astrophotography buffs here if there are any. What I think I'll try first is planetary pictures and pictures of the moon. After I get the hang of the basics I'll get more ambitious. Anything would be much appreciated.
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06-26-2015 04:51 PM
Most LX200 scopes are f/10, but there were some f/6.3 models and the new LX600 and LX850 models are f/8. You'll want to know what focal ratio you have because when you use a camera with a telescope there's no adjustable f-stops like there is for a lens. You'll be doing manual exposures and you'll want to know what your native focal ratio is.
When you connect the camera, connect it "straight through" (no 90º diagonal). I have a 14" LX200 ACF -- which has longer forks and I have a LOT of clearance behind the optical tube. My scope can point straight up through the fork arms with an electric focus and my Canon 60Da attached and still have plenty of room so that there's no danger of the camera hitting the base if the optical tube tries to point straight up.
Check the clearance on your scope (with camera attached) to make sure you are comfortable knowing that you have enough clearance -- as this will avoid potential damage if you slew to a new target in the dark and the camera crashes into the base.
My LX200 has an electric focus with visual back (standard 2" tube opening for a 2" eyepiece or 2" diagonal) and so my camera uses a 2" diameter nosepiece with the EOS t-ring. I don't use the SCT T-mount.
When focusing the scope, always "finish" turning the focuser into focus in the counter-clockwise direction. The LX200 has mirror-shift when you reverse the direction of focus. This is because the focus knob either pushes or pulls on the primary mirror at the back of the scope and the mirror rides on a central baffle that has to allow at least a tiny bit of slop so that it can slide easily. When you "push" the mirror forward, it gets the best support from the bottom and also forces the mirror to rest in a properly collimaged position. When you "pull" the mirror back, it slightly de-collimates your optics and ALSO the mirror may eventually settle on you in mid-exposure (that would ruin the image being captured at the time). By finishing focus while rotating the knob in the counter-clockwise direction, you give the primary mirror the best support, collimation, and it reduces the potential for the mirror to settle and move after you finish the focus.
The LX200 has a mirror-lock knob and when I do visual astronomy I don't use it. But when I do imaging, I DO use it. My scope has an electric focuser on the visual back. That means I can adjust the main focus, lock the mirror, then use the electric focuser to fine-focus the telescope to my satisfaction.
I prefer to point the scope to a pinpoint star to focus. Focusing on the moon or a planet is is not quite as easy to see if you achieved perfect focus. But when you've minimized the size of a pinpoint star, you'll have more accurate focus.
There is an application called "Backyard EOS" which is built for astronomy astro-imaging using Canon EOS cameras. It has focus aids as well as both planetary imaging modes and deep-sky imaging modes. It controls the camera and performs image acquisition for you (it's basically "tethered" remote shooting control of the camera.)
I normally use a Bahtinov focusing mask on my scope to achieve fine focus for deep-sky images. But a lot of imagers I know have electric focusers and use a program called FocusMax which is exceptionally accurate focus. FocusMax deliberately de-focuses a star (you see the donut shape) and starts focusing and imaging and focusing and imaging. It measure the size of the donut and does several runs creating plots. It mathematicaly determines where the perfect focus point must be located (even if sky conditions are horrible.)
Both "Backyard EOS" and "FocusMax" require Windows (I use a Mac so I don't use them, but they are popular.)
The moon is a VERY easy target... the correct exposure for the moon follows the "Loony 11 Rule". That rule says that at f/11 (and it only works at f/11) you can set the shutter speed to the inverse of the ISO sensitivity. So at f/11 and ISO 100, it'd be 1/100th sec. At ISO 400 it would be a 1/400th sec exposure, etc.
If your scope is really an f/10, it's close enough... f/10 is approximately 1/3rd stop more light than f/11 (it's not a significant difference) but it means the moon will be slightly bright. You can adjust the shutter speed 1/3rd stop faster to compensate. E.g. instead of 1/100th sec you should shoot at 1/125th sec. and be bang-on the accurate exposure again. If you have an f/6.3 scope then you are 1.6 stops faster (almost, but not quite 2 stops). That means insead of ISO 100 and 1/100th, you'd want to shoot at ISO 100 and 1/320 sec.
Planets are slightly more difficult... they are dimmer than the moon so you'll use a higher ISO setting. But they are typically imaged by shooting about a minute's worth of video frames. Stacking software is then used to identify the best frames out of the video and those are combined to create a composite image.
If you happen to image Jupiter, note than Jupiter has a fairly fast rotational speed... the surface changes enough in MERELY 10 minutes that if you try to combine images shot more than 10 minutes apart you'll get blur. All the data you capture for Jupiter needs to be captured within that 10 minute window of time. There is a program called Registax that is particular popular (and free) for planetary image stacking.
If you image Saturn, it's low in the sky this year (because it's an "outer" planet and our northern polar axis is pointed toward the sun. That puts saturn low relative to the horizon for astronomers who live in northern latitudes.) This means you'll get some atmosphereic dispersion when you view it. Atmospheric dispersion is a form of chromatic aberration -- except it's caused by our atmosphere working like a lens. The atmosphere splits "white" light into the rainbow spectra of light. You'll see a "red fringe" on one edge of the planet and it's rings... and a "blue fringe" on the opposite edge. Not to worry... one of the features of Registax is that it can separate the single color image into red, green, and blue color channels and it lets you "shift" them back on top of each other. This greatly improves the focus quality of your image.
Deep sky objects are particularly difficult. This may cause you to lose all your hair. You have been warned. :-)
To detail how to take deep-sky images would take a while... but I can sum up:
The scope needs to be mounted on a "wedge" (e.g. such as a Meade Superwedge). The wedge is moutned to the tripod and the scope is then mounted to the wedge. The wedge is tilted so that the tilt angle is adjusted for YOUR viewing latitude. If the scope is merely on an alt-az mount then you'd get field rotation as you imagine and that would create blurred results.
You mentioned your scope does not have "electronics" but it would need to minimally have an RA drive that can track at sidereal speed. Do you have this?
The mount needs a "precise polar alignment" (which takes a bit of effort.)
You take numerous long exposure images (e.g. 5-10 minutes would be typical).
You also need to capture "dark" frames, and it's also helpful to grab "flat" frames and "bias" frames. I can explain what these are if you haven't heard of them.
The images are then stacked using image registration and integration stoftware (for deep sky objects there's a free program called "Deep Sky Stacker". I use something called PixInsight do do my registration & integration (stacking) but PixInsight isn't free.
You mention this is an "old school" LX-200 with "no electronics". Are the electronics fried? I've seen a number of LX200 models and some have very old primitive electronics, but I've never seen one that doesn't have any electronics. There are places that will either repair or refit the scope so that it does have working electronics. Finding the very old original boards in working order is tough. There were some bad capacitors used which would dry out over time and then blow. The guys that service the scopes know which ones blow and they replace them with modern equivalent capacitors that wont blow BUT it's critical that they do it BEFORE the scope has a problem. If the capacitors blow before being replaced they often take out other electornics on the board and now it's a more serious repair. Those "more serious" repairs can involve trying to find replacement boards that aren't made anymore, haven't been made in years, and are becoming increasingly rare.
So... now there are services that simply pull the original boards and replace them with completely new boards, but the refit kits give you electronics that work like an LX90 (not an LX200). LX90's dont' have PEC -- so they aren't as precise as LX200's, but it's still better than nothing.
Moon shots are easy (no elecronics needed.)
Planetary shots are fairly easy but it helps to at least have a working RA drive that can track at sidereal speed (clock-drive) even if there are no computerized go-to electronics.
Deep-sky objects, however... will really need working electronics and an autoguider. This are the most complicated images by far --- because they require such long exposure times. And during those very long exposures, you can tolerate any movement or tracking errors -- otherwise it ruins the image.
06-28-2015 11:23 AM
Thanks for the great information. I guess I should have given more information about my scope.
Like I said it's a very old school manual unit. I cannot locate the manual at this time so I don't have the model number handy but I know it's not a LX model. I’ll post some pictures of it the next time I set it up. No electronics at all and when I mean no electronics I mean it never came with any so nothing is broken or anything like that. I have an equatorial mount (wedge) on my tripod and it does have an RA motor so drift will not be much of an issue. I know how to polar align it very well too, been doing it for years. The eyepiece is 1.25". Thanks also about the focus mechanism. I have noticed that over the years and without really thinking about it I’ve always made my final focus counter-clockwise as you mentioned.
It is indeed an f/10 scope. Also imprinted on the ring is F=2000mm, D=203.2mm and of course f/10.
Thanks for the information on the software as well. I’ll download your suggestions. RIght now I'm not really interested in deep sky objects but mainly the moon and planets at this time. I'll try to get out in the field soon and start experimenting. Can't wait.
06-28-2015 12:13 PM - edited 06-28-2015 12:13 PM
"I'm just looking for some hints and tips from the astrophotography buffs ..."
Tim Campbell is all you need to know!
06-28-2015 12:18 PM
Here's an image I shot of the moon (this image has been posted previously), but it's an example of the "Loony 11" rule.
This wasn't shot through my LX-200... instead it was shot through a TeleVue NP101is -- a 101mm aperture, 540mm focal length apochromatic refractor (so this is an f/5.4 scope). EXCEPT... this image had TeleVue 2x Powermate in the path, making this effectively a 1080mm f/11 scope. As your scope is 2000mm f/10, you'll get a closer shot (more on that in a moment.)
This is ISO 100 and 1/100th sec.
I avoid photographing the moon near a "full" moon only because the surface appears flat (two-dimensional) due to the lack of shadows. When it's anywhere near 1st or 3rd quarter you get the sun lighting the moon from the side and tremendous shadow detail of the mountains and craters (particularly near the day/night terminator).
This shot is slightly cropped in (about 30%) using a Canon 60Da (APS-C size sensor).
The moon is almost exactly 1/2º (angular dimension) from edge to edge and varies by a tiny amount from perigee to apogee (around 29 arc-minutes near perigee and around 33 arc-minutes near apogee.) With a 2000mm scope and a Canon DSLR camera with an APS-C size sensor (such as your T6i) you can calculate the angular dimensions of the frame (I use the "angular field of view" calculator on this website: http://www.tawbaware.com/maxlyons/calc.htm )
That gets dimensions of .4º in the narrow dimension and .6º in the long dimension of the frame. This means if you were to shoot the moon in a horizonal frame as I did for the image above, you wont quite be able to fit the moon in from top to bottom. But if you rotate the camera to take the image vertically, you WILL be able to fit the moon in if you shoot near a 1st quarter or 3rd quarter moon phase (or you can always just take a few images and stitch them together.
Since the moon doesn't require a very long exposure, such an image can be created even with a mount that isn't tracking at all.
You have a couple of choices as to how you'd like to attach the camera. Depending on your scope model, there may be a SCT t-mount (threads onto the rear cell of the telescope and provides a standard "t-thread") then attach the t-adapter (aka "t-ring") designed for Canon EOS mount. The other method is to use a "nosepiece" This is a tube that drops into the eyepiece seat -- just like any other eyepiece you own -- except it has the t-threads on it so you can attach the camera-specific t-adapter. Since eyepieces are mostly commonly available in 1.25" and 2" sizes, you can get these nosepieces in 1.25" and 2" sizes as well.
I use 2" size to avoid vignetting. With a full-frame DSLR camera I think a 2" is essential. With an APS-C camera you can get away with a 1.25".
One more thing... you can also get a Meade f/6.3 focal reducer. Technically this is a ".63x" focal reducer (meaning whatever focal ratio you have, just multiple it by .63) but since SCTs are most commonly made in f/10 focal ratios, Meade calls it a an "f/6.3" focal reducer. This is opposite of using a focal mulitplier (like a teleconverter or barlow).
The Meade reducer has SCT threads on both the front and back. It's intended to thread directly onto the rear of your scope, you then use the Meade T-mount (you can attach a visual back, but there is one issue you need to be aware of.) And then of course you attach the camera t-ring and camera to the t-mount. This drops the focal ratio of your scope down to f/6.3 and also increases the angular field of view (multiple your 2000mm focal length by .63 and you get 1260mm focal length). That makes it MUCH easier to frame the moon however you want.
The thing about the focal reducers is that they have an optimized back-focus distance. The Meade f/6.3 reducer/flatener is optimized for a back-focus distance of 110mm (that's the distance from the rear-most element of the reducer to the camera's imaging plane.) Your camera has a 44mm "flange to focal plane" distance (that's the distance from the lens mounting flange on the front of the body to the image plane inside the camera (there's a focus-mark on the top of your camera body which resembles a circle with a straight line drawn through the center of it -- that indicates the precise position of the sensor inside the body.) So you'd want to subtract that 44mm from the 110 and that gets a a "working distance" of 66mm. But everything component in the path will take up some of that space... the t-ring itself will probably take up about 5mm. That means you want a tube that's about 60mm (rounding) long. Anyway, you hopefully get the idea. The distance does not have to be perfect, because you do get to play with focus -- that's just the optimal distance.
06-28-2015 01:07 PM - edited 06-28-2015 01:33 PM
Here's a planetary image. This is NOT MY IMAGE. This was taken by a friend of mine, Greg Knekleian, using the 14" Celestron C14 at an observatory that our astronomy club maintains and operates for a local school district. This scope has a 3910mm focal length (14" f/11 scope).
To capture this image, Greg used a Canon EOS Rebel T1i camera at ISO 3200 (which is max ISO for that camera) and shot 600 frames. He fed the frames into "Registax" (a free planetary image stacking program). There are numerous YouTube videos that explain how to use Registax. He had Registax search for the best 60 out of 600 frames and those 60 frames were then stacked.
Here's a blog article showing the result of the first attempt at stacking:
Notice a problem... if you inspect the planet near the rings at the bottom vs. the rings at the top, you'll notice the "bottom" has a red color fringe and the "top" has a blue color fringe. This is caused by atmospheric dispersion. The atmosphere itself is acting like a prism and splitting light into a rainbow. It would be as if you took three images of the planet... one red, one green, and one blue, and then stacked them on top of each other but shifted the "red" copy of the image down just a few pixels and shifted the "blue" copy of the image up just a few pixels.
Registax has a built-in feature that can help correct for this. It literally does just what I described above... in reverse. It splits the image into a red, green, and blue color channel version of the image and then allows you to shift the color channels to reconverge them -- resulting in a slightly sharper image that does not have any color bleeding (the color bleeding or "fringing" is a form of "chromatic aberration", but since the "lens" that causes the chromatic aberration is our atmosphere it is called "atmospheric dispersion".
Here's the corrected version of the image (I've cropped this to a square format).
Notice that in this image you no longer see the red/blue color fringing at the top & bottom of the planet.
Finding a correct exposure... a little math:
Knowing that the moon gets a perfect exposure at f/11 using the any shutter speed which is the recipricol of the ISO setting (e.g. 1/100th at ISO 100, or 1/200th at ISO 200, etc.) you can do some math to find the correct exposure for Saturn.
The moon is 1 A.U. (https://en.wikipedia.org/wiki/Astronomical_unit) from the Sun. Saturns "mean" distance from the Sun is 9.6 A.U. (it's 9 A.U. at it's closest (perihilion) and 10.1 A.U. at it's farthest (aphelion.)) We'll just use the "mean" distance.
According to the inverse-square law (https://en.wikipedia.org/wiki/Inverse-square_law) light becomes less intense as distance from the light source increases proportional to the inverse of the square of the distance. If the moon is 1 and Saturn is 9.6 then the square of 1 is still 1, but the square of 9.6 is roughly 92. That means the Saturn gets 92x less light more light than the moon gets (per unit of surface area).
But there's more... the surfaces of objects have different amounts of reflectivity. The moon is actually quite poor -- it's about as reflective as a worn black asphalt road (both the surface of the moon and a worn (not freshly paved) black asphalt road have a surface albedo of 0.12 (12%). Saturn, however, is a bit more reflective. It has a surface albedo of 47%. It is nearly 4x more reflective than the moon.
That means if you divide the 92x value (difference in how much light reaches the object) by the difference in reflectivity (about 4x) you get a value of 23x. So the moon is 23x brighter than Saturn. That's about 4.5 stops.
If you can get a correct exposure of the moon at ISO 100 and 1/100th, then you can bump up the ISO to ISO 1600 (4 stops) then slow the shutter down to about 1/60th (assuming a steady mount) and you've got enough light to image Saturn.
Jupiter is brighter than Saturn.
Jupiter's distance is only 5.2 A.U. (which mean the moon is only about 27x brighter ... vs. the Saturn where the moon is 92x brigher.) Jupiter is also a bit more reflective -- not by much -- it's surface albedo is 0.52 (52% reflective -- or 4.3x more reflective than the moon). Divide 27 by 4.3 and you get about 6.28. That's a difference of only about 2.5 stops (vs the 4.5 stops for Saturn.) That means you could shoot Jupiter at ISO 400 and 1/60 (vs. Saturn at ISO 1600 and 1/60th).
BTW, I didn't adjust Greg's image of Saturn. But I think it's a bit dim. I'm guessing the T1i's ISO 3200 is not quite a 'true' ISO 3200 and could stand to have it's exposure boosted a bit more. I find that if I boost his image by somewhere around 1 to 1.5 stops it looks pretty good in terms of exposure levels.
06-29-2015 03:01 PM
Yep - that's old. (The 2080 scopes were introduced back in 1980.) I never trust the bubble-levels for leveling out my scope (I use a large 2-axis spirit level). I've lined up three bubble-levels side-by-side on the same flat surface and can't get any two of them to agree on the level point.
Also... not all 2080's have the same thread on the rear-cell. Some models had a thread that looked like a standard SCT thread, but if you attemped to thread-on something that uses SCT threads you'd discover you wouldn't get very far before the threads would bind.
If you pick up the Meade t-adapter for your scope, make sure it threads on ok. If it does thread on without binding, then your 2080 does have SCT threads and you'll be fine if you want to put a focal reducer on the scope. If it does bind, don't buy a focal-reducer because you wont be able to attach it (it requires standard "SCT threads").
You can attach the camera into the visual back (Meade calls this an "eyepiece-holder") using the 1.25" Nosepiece and a T-ring for your camera. That would work regardless of whether your scope has "SCT threads" or not. If your scope DOES have standard SCT threads, then you can use a Meade #62 T-adapter and the T-ring for an EOS camera (Meade doesn't specifically sell the T-rings for camera-specific mounts... but it's an industry standard so you can literally buy ANY t-ring made to fit Canon EOS mount and it will have the standard "t-thread" size to attach to the Meade #62 T-adapter. If your scope does have standard "SCT-threads" then you can use the Meade f/6.3 Reducer/Flattener to create a wider field of view and also reduce the focal ratio of the scope.
Note that Meade also makes an f/3.3 reducer/flattener... you do NOT want that (it wont get good results with an EOS camera). The adapter can only produce a decent image in the very center of the field and optical quality degrades rapidly as you get to the outer edges of the frame. For this reason, people who use it tend to use it only with imagers that have extremely tiny imaging sensors -- not the larger imaging sensor that your Canon camera will have.
06-29-2015 06:38 PM
Thanks again Tim. I told you it was old. I bought it new in 1991. I'm kind of glad I got it before all the computer controlled units came out as I know how to star hop, use star charts etc. to find objects manually.
I do have SCT threads and I bought a cheap (not cheaply made) t adaptor that fits my EOS as well. I was playing with it last night but had to go to bed as I work early in the morning. I took some not so good shots of Jupiter but is was shortly after sunset and seeing was terrible. Everything worked fine I just have to get some more time to play with the camera settings etc. I used the Canon software with remote shooting on my laptop. Now I need to get a longer USB cable for those cold nights in the winter LoL. Again thanks and I'll be sure to post some picture once I get good enough I won't embarrass myself.