p.1 #1 · Will Anyone Use the 7D for Astrophotography?
Will anyone be using the 7D for astrophotography? The high resolution, wide ISO range, and hopefully low noise for longer exposures should help.
I believe that I'm going to give it a go with some friends in a few weeks, once my 7D finally arrives. Will try some primefocus and piggyback mounting techniques for starters. Having a stable and accurate mount is essential.
p.1 #2 · Will Anyone Use the 7D for Astrophotography?
I am planning to get 7d later next year for astrophotography. I think it will be a great imager for astrophotography. Depending on the focal length you would need a good mount. I would say Losmandy G8 or better.
Vishnu
Rebel XT unmodified. Just short exposures combined.
I think you can do a lot with 7D as it is. The only thing you will gain is H-alpha response when you have your IR filter out. There are a lot of objects that dont have much emission in H-alpha which you can shoot and get good images with just the camera as is.
p.1 #7 · Will Anyone Use the 7D for Astrophotography?
cameron12x wrote:
Will anyone be using the 7D for astrophotography? The high resolution, wide ISO range, and hopefully low noise for longer exposures should help.
Actually, Canon cameras since 20D hava no longer been a problem, noisewise, for astrophotography. Instead, the limiting factor is the low number of photons that are captured from celestial targets.
The statistical variation in incoming photons causes artifacts that the eye sees as noise. The only cure for this is to capture more photons (faster lenses or longer exposure time).
The only technical thing that would improve the results would be the increase of the quantum efficiency of the sensor, i.e. the percentage of photons that are captured. The improvements in microlenses have a similar effect, but I think Canon has had 100% microlens coverage already before 7D. Regarding other improvements, I don't think they have made any significant changes.
As for clean high ISO images in 7D, you don't benefit from them in astrophotography. In fact, you will lose a significant part of the dynamic range, so it is actually harmful to use high ISO settings. So far I haven't seen the unity ISO value for 7D but for 40D is it around ISO 320. That value (rounded to the next highest real ISO, i.e. 400 in this case) is the highest you should ever use in astrophotography, unless you are forced to limit your exposure length significantly.
It basically means that every photon that is captured is counted, i.e. 1 in the 14-bit RAW file corresponds to 1 photon. If you go any higher, you simply get 2 for 1 photon at ISO 800, 4 for 1 at ISO 1600 etc. You quickly realize that multiplication in the computer would produce exactly the same results - with no added resolution in the dim parts of the image. But all the time you lose at the highlight end as they will overflow to pure white.
Best noise suppression is done in post-processing, which is an art itself. Very different from the post-processing in terrestrial photography, with very different tools as well. See e.g. ImagesPlus at www.mlunsold.com
p.1 #8 · Will Anyone Use the 7D for Astrophotography?
Interesting information... thanks. How would one determine the unity ISO value for 7D? Has this number been published for cameres other than the 40d?
So in the case of the 40D, you'd should at ISO 400 and then do a lot of post-processing (possibly stacking multiple images).
What about using HDR techniques in pre and post-processing? That is, perhaps image using higher ISO to collect light from the faintest objects, then merge these images with ones taken at lower ISO, in order to achieve the highest dynamic range?
p.1 #9 · Will Anyone Use the 7D for Astrophotography?
cameron12x wrote:
Interesting information... thanks. How would one determine the unity ISO value for 7D? Has this number been published for cameres other than the 40d?
So in the case of the 40D, you'd should at ISO 400 and then do a lot of post-processing (possibly stacking multiple images).
What about using HDR techniques in pre and post-processing? That is, perhaps image using higher ISO to collect light from the faintest objects, then merge these images with ones taken at lower ISO, in order to achieve the highest dynamic range?
When a new camera comes to a market, someone soon calculates its gain. There are also programs that perform the calculation for you. Stricly speaking it only applies to the camera it has been measured on, but gain varies a lot less than noise.
Processing in astrophotography does involve stacking multiple images. One reason for that is that if you take a very long exposure, it simply gets overexposed due to light pollution.
When you are able to separate the image histogram from the left side, then you have usable images for stacking. If, for some reason, you cannot get this (by making the exposures longer), only then should you increase the ISO setting.
As for HDR imaging, it's usefulness is limited in astrophotography. The brightness difference between the stars is so huge that HDR imaging cannot help there. Besides, the brighter stars will result in larger blobs in images, so you can distinguish between them in the photos. In HDR imaging you would lose this clue. As for dim nebula parts, most images have always their contrast stretched to reveal the most interesting part - which is the opposite of HDR imaging where contrast is severely reduced.
There are some nebulae that are so bright that HDR imaging is helpful (e.g. M42). However, the main problem is that under light pollution there is a limit as to how dim nebula oarts you can image in practice. That limits the available range for dim nebulae and makes HDR images less useful.
The problem with most astrophotographs is that they are severely underexposed. This changes a lot of rules that apply to ordinary photography - when the last possible photon is squeezed out from the image.
p.1 #10 · Will Anyone Use the 7D for Astrophotography?
Thanks again for the information. I was thinking of HDR imaging mostly for nebulas. I understand where contrast needs to be selectively stretched and, in some cases, the converse. I suppose it just depends on the particular conditions.
For deep space imaging, I believe the challenge is mostly about controlling SNR. We want as much sensitivity (and exposure) as we can without introducing noise or artifacts.
I'm hoping to do some astrophotography within a month or so of getting my 7D. Wish I had it now!
p.1 #11 · Will Anyone Use the 7D for Astrophotography?
cameron12x wrote:
Nice photo. What lens? I'm guessing about 200mm focal length.
What kind of mount did you use for this, what was your exposure, and how many images did you stack?
I used a 600 mm fl 80mm diameter telescope (Orion 80 mm ED) on a Losmandy G8.
Here is the full explanation from another thread.
ISO: 400
Exposure length: 30 seconds
Focus: Manual (Just eye balled it with test exposures)
# of Exposures: 11x30 seconds total 330 seconds or 5.5 mins
Processing: Converted all the raw files to 16-bit Tiff. Created a master dark file to subtract the noise by combining 3x30 sec dark frames. Dark frames are basically same length/temperature as the image files except the front lens cap is left on...so zero signal gets to the sensor. Your measure the thermal noise. Master dark was subtracted from each individual file and then all the 11 exposures were stacked together after aligning the stars.
The final image was manually unsharp masked in photoshop where I created a duplicate of the stack, then blurred it and combined it with the original stack.
Brightness and contrast were adjusted in the end. Although it sounds complex, the whole process takes less than 30 mins.
If someone is seriously interested in getting into astrophotography an inexpensive way (without buy telescope etc) is to get an astrotrac 320x. Its not cheap but it can be used with pretty much all the photogear you have. It can track really well. I am saving up money to buy one...!
Here is a link to some pictures a guy takes with astrotrac.
As far as location...I shot it from Mauna Kea, hawaii. I work there for my school work doing research with the big telescopes up there. So it gives me a lot of free time when I first get there to acclimate. The telescope mount belonged to someone who just happen to be there at the visitor center that night. I borrowed it for 5 mins. But you can take good shots even from inside the city as long as you take a lot of exposures and do flat fields.
p.1 #12 · Will Anyone Use the 7D for Astrophotography?
As an aside, the stars move a considerable amount in a few seconds. You will need to use something that rotates automatically. When I tried taking photos of objects like Venus, Mars, North Star, etc with just a tripod and a long lens (my 55-250 to be exact), I would get trails of all the bright objects.
Also, if you live in a city, you'll want to go WAY out of the bounds of the city. When I lived in Chicago, most of my sky photos were useless. There are lights everywhere and a lot of smog, which reflects all of the light, resulting in a bright lower atmosphere, obscuring the sky. I'd need to go way out, either to the exurbs or further in order to get really good pictures.
p.1 #16 · Will Anyone Use the 7D for Astrophotography?
The Kenko Skymemo is a superb mount with a much higher load capacity than the Astrotrac. It's really a very capable full german equatorial mount. It's just not as portable as the Astrotrac. Its far more accurate in its tracking than the Losmandy mounts. The Losmandy mounts tend to have pretty high periodic error.
As for the 7D, I won't be getting one for astrophotography. As someone else pointed out, since about the 20D, you don't get any noise improvements if you use the camera properly (i.e., shoot at near unity ISO and then take longer exposures). I currently shoot with a XSi modified for better Hydrogen-alpha sensitivity. Most of the really interesting stuff you would want to shoot benefits from this modification (all emission nebula, including the neat ones that provide so much nice color in galaxies). Without the modification, a lot of what should be red nebula come out looking cyan or pink with a cyan cast. The only reason I moved from my 20Da to the XSi was to get better flexibility in the Live View implementation (great for focusing), and a higher megapixel count for my wide field shots.
For those interested in astrophotography, I wrote an article for Naturescapes.net on the topic back in 2007. Here's a link:
It covers everything from lens and camera selection to mount selection, image combining/stacking, and post-stacking editing techniques.
Finally, a recent wide shot of the milky way; one of my favorite views. This was taken with the XSi and a 24mm f/1.4L. If I recall correctly, it was at ISO 400, 12x5 minutes, f/4.
p.1 #17 · Will Anyone Use the 7D for Astrophotography?
scott f wrote:
how does the astrotrac compare to something like the Kenko skymemo? This mount appears to take a heavier load.
I have the Kenko SkyMemo and I feel it is as good as its parameters allow. The polar alignment scope is great and accurate (unlike what I have heard about the optional Astrotrac scope). The mount feels solid and works reliably. The weight limit (5 kg in total) does limit the optics, but it also buys you great portability. Within the weight limit (limiting the focal length indirectly), the mount tracks very well.
p.1 #18 · Will Anyone Use the 7D for Astrophotography?
How do you mount the camera to the German equatorial mount? I'm thinking of getting a Meade Equatorial Mount, which uses worm gears, and sell for around $600.
p.1 #19 · Will Anyone Use the 7D for Astrophotography?
I used my Losmandy G-11(sold) along with my 20D, 5D, 1DMKII, 1DsMKII, now my 50D and 1DsMK3 with my ScopeTronix Digital camera adapter system to mount to Tak tsc225, FS102 and Meade LX200 10" f6.3. I do recommend, if you can find, the 20DA that was made especially for astrophotography. Check B&S. I may be picking up one soon. Overall, I believe it produces a superior image per buck. They are still osed by NASA and Hubble Space lab in Balto.
All with amazing success. You cant go wrong with a Losmandy mount! Also be AWARE that most massed produced mounts(Meade, Celestron-except for the CG series which is Losmandy) and "goto" scopes use plastic gears. Upgrade to metal where possible. Losmandy uses all metal gears and bearings.
Dan
p.1 #20 · Will Anyone Use the 7D for Astrophotography?
rsg_1 wrote:
How do you mount the camera to the German equatorial mount? I'm thinking of getting a Meade Equatorial Mount, which uses worm gears, and sell for around 600.
