03-31-2015 02:25 PM
I have never attempted astrophotography, but would like to learn how to adapt my Canon 6D to My Televue 85 refractor telescope. I'm unfamiliar with even the basics like what adapter is required, how focusing is accomplished, how expsoure is determined, etc. My interest began when I photographed the moon this week with a Tamron 150-600mm lens on my 6D and achieved pretty good, but unexceptional, results. I also took a shot at Jupiter at 600mm and was surprised to resolve two planetary bands on an extreme crop. The results of the moon showed a lot of detail, but lacked the razor sharp crispness of a telescope. It then occured to me that images through a refractor telescope should be amazing by comparison. Anybody who could provide some elementary information of a link to a starter source would helpful. For now, I'm just looking for a starting point, perhaps a basic adapter mount to connect camera to scope, instrucitons on how to focus and expose an image of the moon or jupiter. Thanks for any help that may be forthcoming. Cheers!
03-31-2015 05:40 PM
I found what appears to be an answer to my own question here: http://astro.shoregalaxy.com/dslr_astro.htm#intro
The step by step explanation of the setup and equipment involved seems to be straightforward and may be of use to others who wish to experiment with astrophotography. The author did a good job of explaining the adapter and focussing procedure which I found very helpful personally as a beginner. He also illustrated each point with photos and screenshots to clarify each step of the process so anyone can duplicate each step from beginning to end. Although he goes into detail on how to photograph deep space objects, the information provided appears to be sufficient to get started with the easier task of photographing the moon or nearby planets.
06-04-2015 09:24 PM
You want a 2" diameter "nosepiece" for prime-focus (this means the telescope itself is the camera "lens" and you do not use an eyepiece in the telescope (the camera is directly attached.) The front of the nosepiece is simply a 2" diamter tube that slips into the telescope's focuser just like an eyepiece (you remove the 90º diagonal and attach the camera for a "straight through" shot)).
The opposite end of the nosepiece has a universal male "t-thread" (which will not attach to your camera -- not to worry). The t-thread is "universal" in that it's just a generic thread onto which you will add a camera mount-specific adapter. This is just a roung ring -- the front is a femail t-thread -- so the ring attaches to the prime-focus nosepiece. The back has the EOS specific bayonet mounting ring.
IMPORTANT: These prime-focus nosepieces come in 1.25" diamter barrel size and 2" diamter barrel size. You want the 2" diamter size. If you use the 1.25" it will fit... but will cause vignetting (dark corners) in your images because you have a full-frame sensor camera. You can get away with a 1.25" size for the cameras with APS-C size sensors (although I _always_ prefer a 2" for any scape that can receive 2" barrels and you do own a TeleVue (your scope will take the 2" diamter barrels.)
TeleVue calls this part the ACM-2000 (you can get it from Oceanside Photo & Telescope (OPTcorp.com) for $57). You don't actually need a TeleVue brand adapter... lots of companies make these 2" nosepieces. I think i bought mine from Agena Astro products (agenaastro.com). For example, Agena carries a product they call the "GSO 2" Prime Focus Photography Telescope Adapter with T/T2 thread" for about $25 (half the price) and it's a groved barrel.
The front of the nosepiece has 2" female threads so you can thread on 2" filters if needed. I sometimes thread on an OIII filter, etc.
You will ALSO need a "T-Ring for Canon EOS" (just do a Google search, you'll find lots of them.)
You MIGHT need an extension tube. When you remove the 90º diagonal from the back of the telescope (and you want to) you remove about 2" of total focal length and the telescope was counting on that 2" (it's part of the overall focal length of the scope). Sometimes the camera nosepiece, t-ring, and camera's internal "flange to focal plane distance" (always 44mm on a Canon EOS camera) will make up enough distance that the telscope still focuses. But if you find yourself racking the focus all the way OUT until the focuser hits the limit of travel and wont go out any farther... then you need the 2" extension (and it will DEFINITELY come to focus when the 2" extension is attached.)
For lunar and planetary imaging, you MAY want to buy a TeleVue Powermate. You would only be interested in either their 2x powermate or their 4x powermate. Both the 2x and 4x versions have 2" diameter barrels, but the 2.5x and 5x powermates have 1.25" barrels (which I prefer to avoid). The Powermate can be adapted to work with your camera and it works just like the 2" prime focus nosepiece I mentioned earlier EXCEPT it has optics in it. But you need yet another adapter. The Powermate itself is designed to accept an eyepiece. To attach it to a camera you need TeleVue's adapter. Specifically you need the TeleVue part# PMT-2200 for the TeleVue 2x Powermate, or the TeleVue Part # PMT-4201 for the TeleVue 4x Powermate. On my TeleVue NP101is (540mm focal length f/5.4 scope) I would use the 2x for the moon, and I would use the 4x for smaller objects such as Jupiter or Saturn (well... smaller angular size due to being much farther away than the moon).
The top of the PowerMate is intended for an eyepiece to drop in. You unscrew this, and screw on the camera adapter instead (PMT-2200 or PMT-4201). These still end in T-threads so you still end up needing to add the camera T-Ring. I own both the 2x and 4x Powermate as well as a couple of 2" camera nosepieces so I ordered several camera T-rings and this allows me to just leave the 2x Powermate fully assembled and ready to go as a camera nosepiece with built-in 2x factor as well as a fully assembled 4x Powermate (I don't unthread the t-ring from the prime-focus nosepiece and move it to the Powermate -- I keep the parts fully assembled as a working unit.)
If you get confused, call TeleVue and they'll help you make sure you have the right parts -- but after you get the parts and put it together you'll realize it's pretty easy.
YOU MAY ALSO want to buy either
(a) a remote shutter release with intervalometer (timer) such as the Canon Remote Controller TC-80N3 which allows you to put the camera in "bulb" mode then use the controller to set the number of shots you want to capture, the duration of each frame (shutter speed), and the time interval to wait between each shot. This allows you to capture lots of images for stacking purposes without having to stand at the camera and take each one and more importantly... you don't have to 'touch' the camera to take the shot (which would cause a vibration and harm the image.)
(b) you can control the camera using a computer to do the image acquisition task. The most popular program for this is "Backyard EOS" (note: requires Windows -- no Mac support -- but you can run Windows in a virtual machine on a Mac (which is what I do)).
When imaging the moon you can capture just a single shot. The correct exposure for the moon follows the "Loony 11" rule which suggests that if you use f/11 (and the rule only works at f/11) that the shutter speed should be set to the inverse of the ISO setting. So at ISO 100, you would use 1/100th. At ISO 400, you would use 1/400th, etc. BUT... you don't have an f/11 scope, you have an f/7 scope AND you'll probably want to use the 2x Powermate for the moon (which changes the effective focal length to f/14). That's 2/3rds of a stop darker than f/11. You would compensate by adjusting the shutter speed. E.g. you might try the moon with the 2x Powermate, set the ISO to 100, and set the shutter speed to 1/60th (2/3rds of a stop slower on the shutter.) This should nail the exposure for the moon in just one shot.
For planets, it gets trickier. Jupiter is 5.4x farther away from the sun than the moon. This means it gets about 1/30th of the sunlight as compared to the amount of light that we receive here on Earth (or at the moon) -- and note that's per "unit area" of surface (that's just under 5 stops less. If Jupter were 5.6x farther than the sun then it would be EXACTLY 5 stops less). But there's more... the reflectivity of a body such as a planet or moon is refered to as it's "surface albedo". The moon's surface albedo is 12%. That means that only 12% of the light that strikes the moon is reflected (about 1/8th). Jupiter's surface albedo (technically jupter is a gas giant and has no "solid" surface, but it still has surface reflectivity) is 52%. That means Jupiter reflects about 4x more light than the moon IF they were at the same distance. That's 2 full stops.
Subtract the 5 stops less light (due to Jupiter being farther) and add in the 2 stops more light (because Jupiter is more reflective) and you get a difference of 3 stops.
That means if you were going to shoot the Moon with your TV-85 using a 2x Powermate at ISO 100 and 1/60th sec exposure, then you'd want to shoot Jupiter with a shutter speed 3 stops longer about 1/8th sec.) I think 1/8th is a bit long especially since ideally you'd want to capture video, so I'd bring up the ISO 3 stops instead (e.g. shoot at ISO 800 for Jupiter). If you use the 4x Powermate you'll lose 2 more stops (as compared to the 2x) so you'd want to compensate by bringing the ISO up to ISO 3200 at 1/60th (or maybe you use ISO 1600 and drop the shutter speed to 1/30th).
For planetary imaging, the best thing to do is stack exposures... you'll switch the camera to video mode and capture about 30 seconds worth of video (that'd be about 900 frames at 30 frames per second recording rate. Make sure you have a fast high-quality memory card so it will keep up.) You then scan the frames looking for some decent images (atmospheric instability causes the images to distort -- it's also what causes the stars to "twinkle" -- a bit like trying to look at a coin in the bottom of a pool when someone is making waves in the pool). That means some frames actually will look better than others.
Stacking software will help you find a few hundred similar frames and it will then combine those to make a final master image that will look much better than any single frame. Registax is popular for this (runs only on PCs) and it is free. There are numerous YouTube tutorials that will help you learn to use it.
Deep space objects are more difficult (e.g. nebulae, etc.) These require long exposures -- each usually being many minutes long -- and you typically capture about 16 of them. They are also stacked but you use completely different software to stack them. DeepSkyStacker is free (Windows PCs). There is also a program called "Nebulosity" (Nebulosity can also control your camera to do the image acquisition) which runs on PC or Mac. I use a program called PixInsight (not free - but extremely good and runs on Windows, Mac, or Linux.) I should warn you that PixInisight has a bit of a learning curve (there are books and paid video tutorials to learn to use it.)
Deep space objects require that you have a GOOD quality tracking mount and usually a second scope that you can use for auto-guiding. I piggy-back an Orion ST-80 as a guide-scope with an auto-guider camera. The auto-guider watches a bright star in that region of the sky and takes frequent images (While the main camera is taking an exposure that might run 4 to 20 minutes, etc. the auto-guider camera is snapping a photo every couple of seconds. If the star being tracked by the auto-guider appears to move at all from frame to frame, then the auto-guider sends a corrective movement to the mount to keep the main imaging camera spot-on-target.
Here's a Moon image taken using the exposure rules I described above (the "Loony 11" rule).
Here's a deep-sky object taken with my Canon 60Da. This image is the result of capturing 16 exposures, each of which were 4 minutes long using a telscope that was being controlled by an auto-guider. There are also a number of "dark", "flat", and "bias" frames that went into making this... and a LOT of image processing.
But note that the image above is NOT what comes out of the camera. That's the "combined" image after much processing work. What comes out of the camera from a single frame actually looks like this:
As you can see it's very "muddy" (that's urban light pollution) and you can just barely see the image of the nebula (that happens to be M27 - the "Dumbbell" nebula.) There's a lot of manual processing (e.g. "photoshop" type work) involved to get the final result above.
06-05-2015 11:54 AM - edited 06-05-2015 11:56 AM
One thing more, your Televue 85 Telescope and the Tamron 150-600mm are really not comparable. Although they may look similar in size and outward appearence.
Tim Campbell has explained this very well. Do as he suggests. You may want to join a local astronomy club. All the guys in them are eger to help. At least all the ones I have ever met are.
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