Luminous Landscape Forum
Equipment & Techniques => Medium Format / Film / Digital Backs – and Large Sensor Photography => Topic started by: theguywitha645d on December 01, 2011, 09:23:31 pm
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Ray had asked to see a results from the Pentax 645D for astrophotography. I am relatively new to astrophotography and I really enjoy wide-field work. This is a single 3-minute exposure at ISO 1600 and, if I remember correctly, 35mm lens at f/6.7. This was on an AstroTrac mount.
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Thanks! I had asked you via PM, but it's even better that you shared it publically.
That's a great result for such a relatively small amount of signal integration!
Let's see...3 minutes at f6.7 is equivalent to 2 minutes at f5.6; 1 minute at f4; 30 seconds at f2.8.
I'm doing that exposure conversion because all of our digital backs/cameras can shoot 30 sec at f2.8, and in 30 seconds the sky turns little enough that with a wideangle or normal lens, you hardly need a tracking mount; a fixed tripod will do. Anyone can take such an image. I'd love to see more people share an image?
Ray
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Ray, sorry. I was not sure I could send an image via PM. But I also thought there might be some other crazy folks doing astro with MDF. I can't believe there are only two of us trying this kind of work.
I have a question which you may know the answer. I occasionally get a sensor split with astro photos, but not always--a green/magenta split. And it is only apparent with a great contrast shift applied with a histogram or a curve. Usually, it is a star field with one side closer to sky glow from a neighboring city. Is the sensor just looking at each half differently and trying to WB balance? I am not sure this is something to worry about. I never see this in normal daylight conditions. Thoughts?
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Is it a straight-line split, down or across the middle? That would indicate slightly different gain/LCC calibrations for different sides of a stitched chip (as in, the manufacturing process used stitching). There have been threads on this phenomenon, I believe, for other backs. IIRC, a fresh LCC image taken when shooting would correct it.
Or is it more wavy, like my attachment below? If I really level-torture a file with a fairly strong vignetting gradient from centre to edge (wide open lens) and low background counts, I can get colour banding from my DCS645M back. My educated guess is that this is because it produces a 12-bit output RAW file; 12 bits could be undersampling the noise and thus quantizing the gradient. 14 bits would prevent that (ha! see the "Why are only MF 16 bit?" (http://www.luminous-landscape.com/forum/index.php?topic=59856.0) thread!). That's given me an idea - I think I can simulate this pretty easily.
Ray
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Is it a straight-line split, down or across the middle? That would indicate slightly different gain/LCC calibrations for different sides of a stitched chip (as in, the manufacturing process used stitching). There have been threads on this phenomenon, I believe, for other backs. IIRC, a fresh LCC image taken when shooting would correct it.
That is the one. The interesting thing is it is not consistent--I can take several different astro photos in one session, but it only shows in a few. I will have to look into that more.
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Hey, your turn to post an image (without the rings). :)
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That is the one. The interesting thing is it is not consistent--I can take several different astro photos in one session, but it only shows in a few. I will have to look into that more.
I believe the Pentax uses dual readout so each side of the sensor is being read separately and either the camera or the software puts the data together and normalises the exposure readings to get a uniform image.
It could be that consecutive long exposures and the accumulation of noise causes some slight errors in the process
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I believe the Pentax uses dual readout so each side of the sensor is being read separately and either the camera or the software puts the data together and normalises the exposure readings to get a uniform image.
It could be that consecutive long exposures and the accumulation of noise causes some slight errors in the process
Yaya, thanks. That would seem to make sense.
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I'll try and throw a IQ180 image on, if I am up and about tonight..
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Hey, your turn to post an image (without the rings). :)
Here we go. Using the wonderful removable IR filter feature of the DCS645M, to boost signal sensitivity (it now picks up more IR than visible light, so the colours tend to white).
Mamiya 645AFD, 200mm APO at f2.8, 30 seconds, untracked.
Comet Hartley is the greenish fuzzball left of centre (green from its Cyanogen emission).
As much as I love MFD, it really is not that well suited for astrophotography...I discovered that too late! :( But now I also use my Mamiya lenses on a 5DII as well ;D .
The MFD sensors are huge, but noisy...but at least they're slowly getting better. That's why I'd love to see some examples, and I'm encouraged by your 645D shot.
Ray
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Ray, thanks. I knew of a guy working in telescope instrumentation that had the same conclusion about medium-format sensor. But I am encouraged by the 645D.
I will try to post some more. But like I said, I am just starting and I am also trying to figure out my 645D--and why do the stars come out so late at night. :)
I would like to play some more with stacking to see if I can reduce noise--the noise at 1600 is not really bad, but when you push the contrast with things like the Milky Way, the noise obviously get pushed as well. I have also been playing with moon-lit landscapes, but I am really waiting for this winter to try some snow scenes at night. But all in all, I have been impressed with what Pentax has done with the sensor. I just came back from Japan with a 300mm lens I would like to play more with.
I will see if I can post a few more tonight--jet lag is still with me.
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As much as I love MFD, it really is not that well suited for astrophotography...I discovered that too late! :( But now I also use my Mamiya lenses on a 5DII as well ;D .
Ray
Perhaps not!
Hi,
I am not an expert, but over the last few years I have learned some very interesting things about digital astrophotography. There are some wonderful techniques that can be used to tame the noise generated in sensors during longer exposures. Much astrophotography is done with CCDs that can be pretty noisy. With the right techniques, you can get rid of the noise!
If you have not looked into this topic I can recommend the book:
The New CCD Astronomy by Ron Wodaski.
It is amazing what stacking a few image frames can do to reduce noise. Four stacked will make a significant difference in reducing noise. After 16 frames, the gains diminish quickly. Also, if you take the time and create a series of calibration frames (dark, bias, and flats) and apply them your image, quality will improve even more.
There are some fantastic software tools for both Mac and PC users that are free, or very inexpensive, that make processing digital images easy. One favorite is Nebulosity by Craig Stark of Stark Labs.
As an overview: you shoot your image files and put them in a folder. Shoot your dark frames, put them in a folder. And so on with your flat and bias frames (if you elect to use them). Then fire up a program like Nebulosity. The software will ask you to point to your dark frames. It will then stack them into a master dark frame (with low noise) and save it. You do the same thing with your flat frames and your bias frames. You end up with a master frame for dark, flat field, and bias.
Next, you tell the program the folder for your image files. Typically you will shoot 4 or more frames of a single subject on rig tracking the sky accurately like the AstoTrack mentioned in the original post. The program will work with you to align and stack the image frames. At this point the stacked photos will be nice. But then you tell the software to apply the master calibration frames for dark, flat, and bias, and everything gets even better. Noise should be all gone. Your image should be free of any natural vignetting. You will still have work to in order to stretch the image, correct color, sharpen, and so on, but your starting point should be massively better than if you had made single frame of the night sky.
One final point. It is important to keep the sensor as cool / cold as possible. Heat equals more noise recorded. Dedicated astro imaging cameras use active cooling systems to manage the heat. Big observatories will use liquid Nitrogen cooling. I have found shooting on cooler / colder nights vs on a warm summer night makes a difference in image noise.
Ray, I bet you can do some terrific asto work with your MFDB. With accurate tracking, good focus, and some free / inexpensive software I think you will be as surprised.
Cheers,
Paul
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My twin does a lot of astro stuff using a CCD and a 5DII. I think there is a contact link on his site if you have any questions. I'm sure he'd be happy to help with any questions.
http://sanjeevsivarulrasa.com/
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As promised here is a set of 8 images I took with my IQ180 in my backyard tonight. They were taken using the PhaseOne 645DF with my IQ180 and the Mamiya 55mm f/2.8 lens. I took images starting at ISO800 @ f/2.8 and 60.0s like recommended above. However this was over exposed since their was light spill from Bridgeport (closest major city) near by. Exposure was adjusted and images were taken full-frame 80mp at ISO400 and ISO800. Then for comparison I flipped into Sensor+ (20mp Images) and took images from ISO400, ISO800, ISO1600 for comparisons. I was generally pleased with the results surprisingly well handled noise, this was my first time trying out the camera with long exposures at night. Methodology is better explained in the descriptions.
http://www.flickr.com/photos/brianhirschfeldphotography/sets/72157628255284141/
Some notes: A few planes etc flew by because apparently in this distance is part of JFK's flight path for its 9:00 PM international flights heading up towards Greenland before cutting over. In most of the images Orion's Belt is visible. If anyone wants to see the full-res images PM or e-mail me montblanc100years@mac.com and I'll put them in a dropbox or something.
Enjoy
~BH
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My twin does a lot of astro stuff using a CCD and a 5DII. I think there is a contact link on his site if you have any questions. I'm sure he'd be happy to help with any questions.
http://sanjeevsivarulrasa.com/
WOW! Those are really excellent. I don't want to post now.
Actually, if you could ask your twin, the landscapes with stars, are those fixed tripod shots? At the image scale it is hard to see if the stars are trailing and I would really be interested in focal length, ISO, and exposure information. And please pass along my complements.
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Thanks Brian.
Here are some other tests and mucking about at night. The painting with light image is the longest at five plus minutes. All of these are stopped down to f/5.6 or f/6.7. I think all were at ISO 1600. Focal length are a combination of 35mm, 55mm, and 120mm (Big Dipper).
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I was checking out that Astotrac mount, how does that work?
also edited one of my Astrophotography Images, so you can only see the stars, just Levels and B&W
http://www.flickr.com/photos/brianhirschfeldphotography/6448480871/in/photostream
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Brian, I mount mine on a Gitzo tripod with a Manfrotto geared head--the geared head make polar alignment easier. Basically, there is a polar scope (which unfortunately is optional) which aligns the mount to the North star. I simply attach the camera to the mount with a ball head. You turn on the drive and it slowly rotates the camera to counter the Earth's rotation. You have about an hour before you need to reset the drive. This mount will also works in the Southern hemisphere. It is very light and compact and runs off AA batteries--the mount comes with a cigarette lighter adapter; I went to an electronic parts store and fashioned two battery packs for about $6; the AstroTrac battery pack is about $15.
Getting used to polar alignment takes a bit of doing--it is amazing how stars all look the same. You actually use the north star and one or two others whose position is marked in the reticle of the polar scope. The better aligned, the longer the tracking and/or the longer the focal length. Polar alignment for a 35mm lens is easy, tricky with a 120mm.
The AstroTrac is one of the most compact equatorial mounts available, but there are others including mounts for telescopes.
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WOW! Those are really excellent. I don't want to post now.
Actually, if you could ask your twin, the landscapes with stars, are those fixed tripod shots? At the image scale it is hard to see if the stars are trailing and I would really be interested in focal length, ISO, and exposure information. And please pass along my complements.
Brian,
I have no idea. All I know is that he goes off in the middle of the night for hours on end and spends quality time with his telescope! I mostly do landscapes and compared to my efforts, his are monumental investments in time and patience. What you are looking at is likely multiple stacks on an automated mount. Drop him a note, he's quite geeky about explaining what he does :)
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This might not be astro photography but I did a 10 minute+ long exposure test with the 645D, the image is here on my blog: http://blog.dominik.ca/2012/01/20/salvation-mountain/
The raw is still under exposed so it got a boost in Lightroom which brings out more noise. I will try to open the lens more or increase the ISO to let more light in quicker for my next test.
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Looks pretty damn good to me, got to say.
Nice picture too, I'm a little confused as to the scale of the foreground subject, but I like that, makes you stop and look.
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WOW! Those are really excellent. I don't want to post now.
Actually, if you could ask your twin, the landscapes with stars, are those fixed tripod shots? At the image scale it is hard to see if the stars are trailing and I would really be interested in focal length, ISO, and exposure information. And please pass along my complements.
whilst i am not his twin,
here is one of my latest images using three images. one for the foreground,sky and then the stars.
bear in mind the 500 rule, divide your focal lenght by 500 to find out the longest exp time you can use before trailing shows. looking north or south an absolute max is 30 secs, i prefer 20 or less. if you look to the horizon or away from the poles times will be significantly shorter.
simon
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Here we go. Using the wonderful removable IR filter feature of the DCS645M, to boost signal sensitivity (it now picks up more IR than visible light, so the colours tend to white).
Mamiya 645AFD, 200mm APO at f2.8, 30 seconds, untracked.
Comet Hartley is the greenish fuzzball left of centre (green from its Cyanogen emission).
As much as I love MFD, it really is not that well suited for astrophotography...I discovered that too late! :( But now I also use my Mamiya lenses on a 5DII as well ;D .
The MFD sensors are huge, but noisy...but at least they're slowly getting better. That's why I'd love to see some examples, and I'm encouraged by your 645D shot.
Ray
I tried to clean that up a bit with deconvolve, NR, curves. It becomes a decent looking star field.
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Perhaps not!
Hi,
I am not an expert, but over the last few years I have learned some very interesting things about digital astrophotography. There are some wonderful techniques that can be used to tame the noise generated in sensors during longer exposures. Much astrophotography is done with CCDs that can be pretty noisy. With the right techniques, you can get rid of the noise!
If you have not looked into this topic I can recommend the book:
The New CCD Astronomy by Ron Wodaski.
It is amazing what stacking a few image frames can do to reduce noise. Four stacked will make a significant difference in reducing noise. After 16 frames, the gains diminish quickly. Also, if you take the time and create a series of calibration frames (dark, bias, and flats) and apply them your image, quality will improve even more.
There are some fantastic software tools for both Mac and PC users that are free, or very inexpensive, that make processing digital images easy. One favorite is Nebulosity by Craig Stark of Stark Labs.
As an overview: you shoot your image files and put them in a folder. Shoot your dark frames, put them in a folder. And so on with your flat and bias frames (if you elect to use them). Then fire up a program like Nebulosity. The software will ask you to point to your dark frames. It will then stack them into a master dark frame (with low noise) and save it. You do the same thing with your flat frames and your bias frames. You end up with a master frame for dark, flat field, and bias.
Next, you tell the program the folder for your image files. Typically you will shoot 4 or more frames of a single subject on rig tracking the sky accurately like the AstoTrack mentioned in the original post. The program will work with you to align and stack the image frames. At this point the stacked photos will be nice. But then you tell the software to apply the master calibration frames for dark, flat, and bias, and everything gets even better. Noise should be all gone. Your image should be free of any natural vignetting. You will still have work to in order to stretch the image, correct color, sharpen, and so on, but your starting point should be massively better than if you had made single frame of the night sky.
One final point. It is important to keep the sensor as cool / cold as possible. Heat equals more noise recorded. Dedicated astro imaging cameras use active cooling systems to manage the heat. Big observatories will use liquid Nitrogen cooling. I have found shooting on cooler / colder nights vs on a warm summer night makes a difference in image noise.
Ray, I bet you can do some terrific asto work with your MFDB. With accurate tracking, good focus, and some free / inexpensive software I think you will be as surprised.
Cheers,
Paul
Thanks, Paul. This is all excellent advice; the sort I've been dispensing for a number of years :D - I guess you didn't realise my background (research and lecturing in observational astronomy and astronomical data analysis; and over 20 years as an amateur astrophotographer).
I don't regret for a moment getting my MFDB, which I use for most of my photography; but I do berate myself for not doing better homework on my S/N expectations of MFDB-CCD vs. DSLR-CMOS. I'm afraid I took manufacturers' ISO claims much too literally :-[ - not realising that they can correspond to any arbitrary S/N in the shadow intensities. All those years I'd spent shooting film, where ISO was defined rigidly with respect to threshold detectability of density above base fog - and hence a minimum S/N - lulled me into this. And the concept of ISO sensitivities doesn't exist in research CCDs; we work directly with the sensor parameters for calculating S/N.
Well, what do you do when you get a result which is poorer than expected? You get to the bottom of the reason(s). I've plotted up noise models which explain exactly what's going on, for all sorts of sensors and exposure times. I find this really fascinating.
What these models show is that with high readnoise cameras (MFD systems), you really need very long exposures - to accumulate lots of light per pixel, which pushes you above the lower intensities where readnoise dominates. The problem is that hardly any MFD systems allow exposures longer than 1 minute! But one scenario where you get high pixel intensities, even in 1 minute or less, is the high background of moonlit/twilit skies: this explains why MFD moonlight and deep twilight shots can be competitive with DSLR ones.
But OTOH, longer exposures also build up more thermal dark noise, which again is higher in MFD systems (especially the older generation CCDs with bigger pixels) than DSLRs. While this can be subtracted with dark frames (in-camera or afterwards), two particularly egregious issues can arise:
(1) the temperature of the sensor can keep rising as first the photo and then the dark frame are taken, so the dark frame subtracts too much dark intensity;
(2) there are many cameras whose firmware subtracts the "bias level" before writing out the RAWs, and which rely on a masked border of reference pixels to measure that bias level in each exposure; the problem is that these reference pixels also accumulate their own dark noise or amp glow in long exposures, which skews the estimated bias level upwards! As a result, too much bias offset is subtracted, and if the sky pixels had low counts, some or all of them can go negative, which means they are set to zero in the RAW file. I've seen all this happen with my Kodak back, and a Kodak DCS720x too.
Some active thermal control would make a huge difference: keep the temperature low, or at least keep it relatively stable. I gather that keeping it stable is the secret to the PhaseOne Xpose+ backs.
Not subtracting any Bias level (the Canon way) would also make a huge difference: no pixels end up being zeroed, and even if the sensor was hot, separate dark frames can always be matched to the photos for post-exposure dark subtraction in software. I've been trying to get sample RAW frames from people with different MFD backs/cameras, in order to see which ones subtract the bias and which don't. (Message to all: please PM me if you'd like to contribute a sample RAW!).
So you see, there are so many "gotchas" with MFD systems and astrophotography - I sometimes think they were put there deliberately to thwart it! ;)
In contrast, it is absolutely effortless with my 5DII: true RAWs with no bias subtraction, really low readnoise, really low darknoise...
That doesn't stop me from keeping on trying to improve results with my Kodak though!
Ray
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I tried to clean that up a bit with deconvolve, NR, curves. It becomes a decent looking star field.
Thanks. I'd go with the NR and curves, but the deconvolution introduces strong artefacts in this example, in my view.
Ray
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whilst i am not his twin,
here is one of my latest images using three images. one for the foreground,sky and then the stars.
bear in mind the 500 rule, divide your focal lenght by 500 to find out the longest exp time you can use before trailing shows. looking north or south an absolute max is 30 secs, i prefer 20 or less. if you look to the horizon or away from the poles times will be significantly shorter.
simon
Beautiful image! But before anyone rushes out to reproduce it with a MFD camera, bear in mind that the EXIF says it was taken with a 1ds MkII - as I said, it's so easy with those Canons!
The constellations (Taurus with the Pleiades and Hyades star clusters are in the centre) tell me that the stars were shot with an ultrawide lens - I'm guessing between 14mm - 17mm; but the boat doesn't seem to have ultrawide distortion to my eyes. Did you use two different lenses?
Ray
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This might not be astro photography but I did a 10 minute+ long exposure test with the 645D, the image is here on my blog: http://blog.dominik.ca/2012/01/20/salvation-mountain/
The raw is still under exposed so it got a boost in Lightroom which brings out more noise. I will try to open the lens more or increase the ISO to let more light in quicker for my next test.
That's astrophotography, in my book! :) Lovely. You have the Cancer-Gemini-Canis Minor region there. The dense clump of trails on the left is the M45 (Praesepe/Beehive) star cluster in Cancer. The bright star in the middle is Procyon in Canis Minor.
Tell me please - was there dark frame subtraction done? I see a few bright specks which look like hot pixels. If that's all the dark noise you get in 10 minutes without dark subtraction, then the P645D Kodak sensor is absolutely outstanding!
Ray
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As promised here is a set of 8 images I took with my IQ180 in my backyard tonight. They were taken using the PhaseOne 645DF with my IQ180 and the Mamiya 55mm f/2.8 lens. I took images starting at ISO800 @ f/2.8 and 60.0s like recommended above. However this was over exposed since their was light spill from Bridgeport (closest major city) near by. Exposure was adjusted and images were taken full-frame 80mp at ISO400 and ISO800. Then for comparison I flipped into Sensor+ (20mp Images) and took images from ISO400, ISO800, ISO1600 for comparisons. I was generally pleased with the results surprisingly well handled noise, this was my first time trying out the camera with long exposures at night. Methodology is better explained in the descriptions.
http://www.flickr.com/photos/brianhirschfeldphotography/sets/72157628255284141/
Some notes: A few planes etc flew by because apparently in this distance is part of JFK's flight path for its 9:00 PM international flights heading up towards Greenland before cutting over. In most of the images Orion's Belt is visible. If anyone wants to see the full-res images PM or e-mail me montblanc100years@mac.com and I'll put them in a dropbox or something.
Enjoy
~BH
Brian, those are very good. The huge sensor area of the 80MP chip is certainly apparent! They look like full-645 film shots with my manual focus 55/2.8 lens. The wide open lens aberrations even look the same.
The S/N should be better in the Sensor+ 20MP shots, but since these were taken under bright moonlight, you're not really in the readnoise-limited regime anyway (see my notes above). It would be more illuminating (pardon the pun!) to compare Sensor+ on/off under a darker sky.
Its is evident that the P645D is not the only sensor with a "split personality"! There's a very mild difference between the left and right halves of your IQ180.
The horizontal banding lines are more troubling. They tend to be stronger in the right-hand half of your photos; they are semi-random insofar as their positions move around; and some frames [the Sensor+ ones?] seem to be virtually free of them while others have them strongly. I never get them when I let my Kodak back do in-camera dark frame subtraction, but I sometimes get something similar to them if I try to subtract a "matching" dark frame in software post-exposure, and it wasn't a good match. My guess is that something is a bit awry in your IQ180's readout or dark handling. This is surprising to say the least, for a new PhaseOne product! Worth checking out with your dealer or PhaseOne support, I think!
Ray
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If that was an astro CCD camera, I'd say poor shielding leading to EMF intereferences when the data is read. Could be that is caused by heat buildup because of the relatively long exposure and that it doesn't matter in normal photographic operations. Would test if that occurs in hand made dark frames as well and then eventually run a FFT analysis on the RAW data. Wouldn't be surprised to find a couple of peaks and a link with the CCD read frequency.
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If that was an astro CCD camera, I'd say poor shielding leading to EMF intereferences when the data is read. Could be that is caused by heat buildup because of the relatively long exposure and that it doesn't matter in normal photographic operations. Would test if that occurs in hand made dark frames as well and then eventually run a FFT analysis on the RAW data. Wouldn't be surprised to find a couple of peaks and a link with the CCD read frequency.
Good insights, Pierre.
However, AFAIK, PhaseOne don't allow you to get "hand made dark frames" - you'd set the camera for say a 1 minute dark frame with the lens cap on, and then it would immediately subtract off another 1 minute internal dark frame! So [dark] minus [dark] = random component of dark noise only. And probably only the positive half of those noise residuals, by way of a further kick in the nads. ;)
As I said, MFD long exposure stuff is riddled with "gotchas" than other cameras just don't impose.
Ray
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yes you are correct shot on a 1dsmk2. the principles are the same though. iso 200 was used for the boat and sky at 20mm as was the star image at 2.8 iso1600
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Thanks, Paul. This is all excellent advice; the sort I've been dispensing for a number of years :D - I guess you didn't realise my background (research and lecturing in observational astronomy and astronomical data analysis; and over 20 years as an amateur astrophotographer).
Could you please give a bit of info on using a reflector telescope for wildlife @100-200 yds? I like going to the big parks in Canada and the US to photograph wildlife. I've been ready to go with an APO refractor to replace a basic spotting scope that I tried for the job. The distributor is not recommending their $600-1000 range, they want to sell a $1600 TMB . I replied asking about some astro-tech products.
8" newt @f4
http://www.canadiantelescopes.com/Shop-By-Brand/Telescopes_8/Astro-Tech-8-f-4-imaging-Newtonian-OTA_2#.Tx5iLW9up8E (http://www.canadiantelescopes.com/Shop-By-Brand/Telescopes_8/Astro-Tech-8-f-4-imaging-Newtonian-OTA_2#.Tx5iLW9up8E)
or
http://www.telescope.com/Astrophotography/Astrophotography-Telescopes/Orion-8-f39-Newtonian-Astrograph-Reflector-Telescope/pc/-1/c/4/sc/57/p/101450.uts (http://www.telescope.com/Astrophotography/Astrophotography-Telescopes/Orion-8-f39-Newtonian-Astrograph-Reflector-Telescope/pc/-1/c/4/sc/57/p/101450.uts)
I would also buy the field flattener/ coma corrector
http://www.canadiantelescopes.com/Shop-By-Brand/Accessories_20/Astro-Tech-photo-visual-Coma-Corrector-and-field-flattener_2#.Tx5rp29up8E (http://www.canadiantelescopes.com/Shop-By-Brand/Accessories_20/Astro-Tech-photo-visual-Coma-Corrector-and-field-flattener_2#.Tx5rp29up8E)
That would give me a great 800mm fl f4 with few optical problems in an awkward 32" long tube.
If it's a fail optically with poor imaging of fur or feathers I would bite the bullet for an RC design
http://www.canadiantelescopes.com/Shop-By-Brand/Telescopes_8/Astro-Tech-8-f-8-Ritchey-Chrtien-astrograph_2#.Tx5sf29up8E (http://www.canadiantelescopes.com/Shop-By-Brand/Telescopes_8/Astro-Tech-8-f-8-Ritchey-Chrtien-astrograph_2#.Tx5sf29up8E)
Apart from the smaller form in the wind, would it provide better looking photos for more than twice the price? Is it really worth it for terrestrial shots?
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That's astrophotography, in my book! :) Lovely. You have the Cancer-Gemini-Canis Minor region there. The dense clump of trails on the left is the M45 (Praesepe/Beehive) star cluster in Cancer. The bright star in the middle is Procyon in Canis Minor.
Tell me please - was there dark frame subtraction done? I see a few bright specks which look like hot pixels. If that's all the dark noise you get in 10 minutes without dark subtraction, then the P645D Kodak sensor is absolutely outstanding!
Ray
Yea, it was all default settings so dark frame subtraction was on. I will try to do one without it assuming I can turn it off.
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Could you please give a bit of info on using a reflector telescope for wildlife @100-200 yds? I like going to the big parks in Canada and the US to photograph wildlife. I've been ready to go with an APO refractor to replace a basic spotting scope that I tried for the job.
Don't forget that, unlike in spotting scopes, you'll get images that are upside-down, left to right, or eventually only upside down depending on the optical combination used (refractor, cassegrain, newtonian...). That will take some time getting used to. Apos are worth the extra money, as achromats will show severe purple and blue fringing. Triplets are not necessarily essential, a good doublet should be enough. No chromatic aberration in reflecting scopes, but a coma corrector will be mandatory in most cases. I own a TMB triplet (115/805), among other scopes, and find it inconvenient for day use/bird watching, etc... It is quite heavy, and very top heavy. I also have a Synta apo, similar optically to that one, but of an older model (http://www.skywatcher.com/swtinc/product.php?id=29&class1=1&class2=101) and that one is definitely usable with an erecting (porro) prism. It's also affordable.
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Could you please give a bit of info on using a reflector telescope for wildlife @100-200 yds? I like going to the big parks in Canada and the US to photograph wildlife. I've been ready to go with an APO refractor to replace a basic spotting scope that I tried for the job. The distributor is not recommending their $600-1000 range, they want to sell a $1600 TMB . I replied asking about some astro-tech products.
8" newt @f4
http://www.canadiantelescopes.com/Shop-By-Brand/Telescopes_8/Astro-Tech-8-f-4-imaging-Newtonian-OTA_2#.Tx5iLW9up8E (http://www.canadiantelescopes.com/Shop-By-Brand/Telescopes_8/Astro-Tech-8-f-4-imaging-Newtonian-OTA_2#.Tx5iLW9up8E)
or
http://www.telescope.com/Astrophotography/Astrophotography-Telescopes/Orion-8-f39-Newtonian-Astrograph-Reflector-Telescope/pc/-1/c/4/sc/57/p/101450.uts (http://www.telescope.com/Astrophotography/Astrophotography-Telescopes/Orion-8-f39-Newtonian-Astrograph-Reflector-Telescope/pc/-1/c/4/sc/57/p/101450.uts)
I would also buy the field flattener/ coma corrector
http://www.canadiantelescopes.com/Shop-By-Brand/Accessories_20/Astro-Tech-photo-visual-Coma-Corrector-and-field-flattener_2#.Tx5rp29up8E (http://www.canadiantelescopes.com/Shop-By-Brand/Accessories_20/Astro-Tech-photo-visual-Coma-Corrector-and-field-flattener_2#.Tx5rp29up8E)
That would give me a great 800mm fl f4 with few optical problems in an awkward 32" long tube.
If it's a fail optically with poor imaging of fur or feathers I would bite the bullet for an RC design
http://www.canadiantelescopes.com/Shop-By-Brand/Telescopes_8/Astro-Tech-8-f-8-Ritchey-Chrtien-astrograph_2#.Tx5sf29up8E (http://www.canadiantelescopes.com/Shop-By-Brand/Telescopes_8/Astro-Tech-8-f-8-Ritchey-Chrtien-astrograph_2#.Tx5sf29up8E)
Apart from the smaller form in the wind, would it provide better looking photos for more than twice the price? Is it really worth it for terrestrial shots?
I've never heard of someone using a Newtonian layout for wildlife. The image quality, with the coma corrector, would be excellent (APO-like chromatism, but lower contrast due to the large central obstruction of the secondary mirror). But the handling would be frustrating. Just aiming the scope at an animal (which may be moving) would be difficult, as you must stand near the front and look in perpendicularly from the side. The range of focus is also very limited with a Newtonian - you can't go much inside infinity - and since the tube supporting the weight of the camera and coma corrector has to move in and out to achieve focus, it takes a beefy focuser to be mechanically rigid. I'm not saying what you want to do can't be done, just that it is not the easiest way to do things.
If you want a reflecting design for its lower cost with respect to an equivalent aperture APO refracting design, then I suggest you go for one with a Cassegrain layout - i.e. a convex secondary mirror sends the light straight to the back of the telescope. You get that regular photographer's viewpoint (behind the lens, looking up the length of it) on your target - much easier to aim and adjust than a Newtonian, and more compact too. And focusing usually varies the spacing between the mirrors, so combined with the amplification effect of the convex secondary mirror, this layout has a much larger range of focus.
Conventional photographic "mirror lenses" are the sort I mean - these are often based on Maksutov or Schmidt optics with additional internal field-correction lenses, and a Cassegrain focal layout. In medium format, there was a Mamiya 645 500/8 and a massive Pentax 67 1000/8. Some Rubinar 500/5.6 mirror lenses were modified from T2 to P6 (Pentacon Six) fitting as well (though vignetting would be higher, as this was originally a 35mm format design).
You didn't say whether this had to be for medium format or not, so I'll give you some options for 35mm and DSLRs. (The 800/4 Newtonian would also only cover 35mm max).
There are also many well-known brands of visual Maksutov-Cassegrain (MCT) and Schmidt-Cassegrain telescopes (SCT), which are good for photography as long as you add an extra field-flattening/coma-correcting lens unit - the f6.3 reducer-corrector lenses are great for SCTs as they combine image correction with focal reduction (f/10 Meade/Celestron SCTs become f/6.3; and f6.3 Meade SCTs become f/4), the tradeoff being that they increase vignetting on the 35mm format. MCTs tend to have slower f-ratios than SCTs (f/12 to f/15 but there are a few f/10 models - e.g. Intes Micro). A 5-inch Celestron SCT with a Celestron f6.3 reducer-corrector would be a sharp, compact and affordable 775mm f/6.3 "tele-lens", and you could correct the vignetting in Photoshop. If you need more reach, and can handle more weight and bulk, an 8-inch + reducer would be 1260mm f/6.3. I don't think Meade make f/6.3 SCTs anymore, but an 8 inch one of those + reducer would be 800mm f/4 - the same spec as the Newtonian you were thinking of, and much easier to use.
The RC design you mention (Ritchey-Chretien) is another Cassegrain layout, but one which does not need a full-aperture glass element at the front, and is said to deliver a good off-axis images without extra correcting lenses - considerably better than an uncorrected Newtonian or SCT. With an additional field flattening lens, they move up a further notch and are the choice for large format astronomical imaging. The Astrotech one you linked to would be excellent, and it has the option of the field flattening lens too.
Ray
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Don't forget that, unlike in spotting scopes, you'll get images that are upside-down, left to right, or eventually only upside down depending on the optical combination used (refractor, cassegrain, newtonian...). That will take some time getting used to.
You only get inverted images when using the telescopes visually, with eyepieces. When you have an SLR camera attached in place of an eyepiece, image orientiation is normal with Cassegrain types and refractors. They're just like camera lenses, after all - the SLR mirror and pentaprism sort out the orientation.
Apos are worth the extra money, as achromats will show severe purple and blue fringing. Triplets are not necessarily essential, a good doublet should be enough.
True, an ED or Fluorite doublet is "APO enough" for prime-focus imaging (no additional magnification).
What matters most for photography with APOs is field flatness. Very few APOs have inherently good flatness - most require additional field-flattening lenses. Some exceptions (self contained flat-field designs) are the Petzval-design APOs from Televue, and the Takahashi FSQ line (the creme de la creme!). Also pay attention to the image circle (with field flattener if required): some only cover 35mm (Televue, Synta, Astrotech); some cover and have adapters for Medium Format up to 6x7cm (Takahashi, Astro-Physics, Borg, some TMB, some William Optics).
If you're the kind of person who insists on Leica S2 lenses, wait till you look through or image with a Tak FSQ-106ED!
Ray
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Yes you are of course correct if he uses prime focus photography. I was thinking in terms of afocal photography because of the spotting scope replacement. While I am aware of several spotting scopes adapters for cameras, I haven't seen spotting scopes used at prime focus. I am leaving for a trip right now, but will try to post samples taken in afocal mode with both the synta and tmb and the special eyepiece and adapter I bought for that purpose (40mm extremely large exit pupil). At prime focus, one will be undersampling and sacrificing a lot of what can be gained (provided there is enough light) in terms of reach and resolution compared to a standard tele. Also, chances are that he'll want to use a diagonal, (that will flip the image again, at least in one direction) so he can focus in a relative comfort and an extremely sturdy tripod and that will require some coordination. But of course both approaches are possible.
As far as the focal reducer is concerned on the Cx line, without flat fields, that will be hard to correct cleanly imho. The 6.3 should be better than the 3.3, but the good FOV is really too narrow. At least it was on the C11.
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Ray,
You are correct, I did not know your background. I does seem that MFDB and astrophotography are at odds with one another. And here I thought preprocessed Nikon RAW files were a bit of a hassle. It is nothing like the challenges you list.
Overall I am just blown away with what amateur imagers can achieve from their backyards today. It is amazing.
For fun, attached is a non-MF shot I did with my gear.
All the best,
Paul
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Hi,
To amplify what the others stated, I think your biggest challenge will be working in the field with a telescope. I am sure I can be done, but you should not underestimate the challenges of:
Transporting
Setting up
Focusing
Keeping everything steady
The size and length of a telescope makes stability an issue. A telescope needs very solid tripod and a strong head to keep it from shaking. This will be especially true of the 8” reflector or a long refractor. When you mount a DSLR, even a small and light one, the balance and stability issues get much, much more challenging.
Your second biggest challenge is optically telescopes are designed to look at stars and planets not take pictures of moose. Getting good contrast, a flat field, and good optical correction across the sensor will be tricky.
A good APO with a flat field will be your best bet. You can achieve this with a refractor that was designed from the beginning for use in wide field astro imaging such as the aforementioned Takahashi FSQ 106 or a Tele Vue NP101 or Tele Vue NP127. These scopes also have sturdy focusers designed from the beginning to hold photographic gear. So that is good. However, they are expensive and only provide very modest 500 -600mm focal lengths.
If you take the second route and purchase an APO doublet or triplet, you will need to add a field flattener. This extra part can add flex to your system resulting in images that are not sharp top to bottom.
Most cassegrain systems for photography and astronomy have very large central obstructions. This mirror in the front of the scope is big and it kills contrast. Take a look at how big the mirror is on the front of the RC you listed. I bet its central obstruction is at least 40%. Anything above 25% and the impact of a large secondary mirror really kicks in.
The RC has off axis aberrations. The aberrations are somewhat different from other compound systems but the image is still of value to some professional astronomers for measurements. Without a corrector of some kind, this will be a poor fit for terrestrial imaging. Outside of the center, the image will get soft.
Also, without going off on the deep end, the RC is one of the most difficult scopes to design and build. The conic shapes of both mirrors are very, very tricky to figure. They also can be very, very challenging to align. I have not used the one you list, but it is very hard for me to imagine that you are getting a good RC at this price. It is like trying to buy a cheap high bypass turbofan engine for your 747. There is just too much going on to make one work well for little money.
One more point, as your imaging focal length increases and you shoot across large distances, you have a very good chance of getting soft images from the bubbly turbulent air over the ground. If I put a converter and shoot a subject far away with my long lens, I see significant softness if the sun has been out warming the ground and the air above it. Trying to bridge a long distance with a telescope may work against you if you want sharp photos.
I am not sure what system you use, but I would look at getting or renting a long telephoto lens and learn how to work with it to shoot your subjects. A 600 F4 with a 1.4 converter, and a strong tripod or monopod would be a good start. If you have Nikon gear there is an old manual focus 800mm 5.6 that is very nice and sharp wide open. Nikon and Cannon both have 500mm F4 lenses that are light and easy to carry. The Nikon 500mm F4 P manual focus lens is very nice.
I think you have an interesting idea, however I think using a telescope for shooting wildlife would be like trying to swat a fly with a howitzer. I can be made to work, but things are going to be messy.
Good luck and have a great trip.
Paul
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Thanks to all for the information, its good stuff.
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I'll be using tilt screen live view so the strange camera angle of a newtonian is not a big deal. I'd expect to use it like the waist level ground glass of my Mamiya RB67 on tripod with cable release. I will have to consider the options.
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Most cassegrain systems for photography and astronomy have very large central obstructions. This mirror in the front of the scope is big and it kills contrast. Take a look at how big the mirror is on the front of the RC you listed. I bet its central obstruction is at least 40%. Anything above 25% and the impact of a large secondary mirror really kicks in.
You are right, the manual said 47% by diameter, 22% by area which is a massive diffraction hit. Not worth it at this price level IMO. If it was a 30% i'd be all over it.
I have no problem with pointing a 32" tube. If the distributor tells me the lower end refractors arn't up to the challenge so be it. It's much easier to correct reflector problems that color problems in a raw conversion.
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I wanted to get back to this with a practical example, but the weather has not been cooperating to say the least. Still, these extremely poor pictures show the issues to expect. Wide field shows the area in front of my house, with uncorrected vignetting. The white spot is the area we are aiming at. 1st zoom level is taken with the Canon 300 2.8 + TC 1.4 (420mm) 2nd zoom is the TMB 805/115 at prime focus. The two flat fields (that's the plus of bad weather, you can take flat fields ;-)) show that the amount of vignetting is, expectedly, much higher with the TMB than it is with the Canon Zoom. This being said, compared to the wide angle shot, which can be corrected in lightroom, it remains quite acceptable. The problem is of course that you'll have to make a model of the vignetting yourself if you care. The second image shows a roof on the edge of the field of view and, imho, distortion is kept well under control in the TMB (no need for a field flattener).
Now, about the constraints... The Canon + TC was handheld with IS on (I made sure exposure was quick enough so vibration wouldn't impact the image too much) The TMB was on a 26kg mount, quite unpractical to catch a bird in flight, and I had to take 5 shots around teh focus point to be sure I would hit something decent (can't trust my eyes too much).
With even more constraints, I can bet better results with afocal images because the camera (using a macro lens in my case) is doing the autofocus on the image that gets out of the eyepiece, but the conditions weren't worth the trial
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This is not clear to me. The TMB is about 800mm focal vs the canon with 1.4 at 420mm.
So the 1st zoom at 100% is the TMB not the canon. Correct? I can see some color fringing on the smaller canon shot. The TMB looks like a real APO.
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Correct, relative sizes were preserved: bigger magnification equals TMB. I meant "second image", but had a slip of the mind and keyboard.
Yes, the TMB is a triplet. And in fact it is even better than the Canon than the images show because the edge of the roof was quite close to the edge in the TMB shot, and a bit less so in the Canon shot (because both shots were centered on the same location and, of course, the field is wider on the shorter focal length.
I'll try the Skywatcher doublet as well when the weather clears a bit.