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Photo Forum / Digital Photography / DSLR Cameras / August 2006D200 on telescope?
I've got a Meade 4" Schmidt-Cassegrain telescope which (in theory) can be used as a 1000mm lens (if I did the math right, it should be just about f/11). Adapter mounts are available at quite reasonable prices to hook it up to a Nikon lens mount (I'm ordering one today). Any hidden gotchas when I hook it up to my D200? My interest d'jour is a fruit tree about 200 feet from my back porch which is attracting a nice collection of birds. That's too far for my 200 mm lens to shot them as anything but little specs. I haven't the foggiest idea what the closest focus distance is for the 'scope (it was designed with astronomy as the primary use). > I've got a Meade 4" Schmidt-Cassegrain telescope which (in theory) can be > used as a 1000mm lens (if I did the math right, it should be just about [quoted text clipped - 8 lines] > idea what the closest focus distance is for the 'scope (it was designed > with astronomy as the primary use). All you can do is try it and see what happens. I have all the adaptors to attach my D70 to a Meade I've got, but I've been disappointed with the results. Part of the problem is keeping everything rock solid when you shoot, and focusing can also be difficult as the light entering the camera can be pretty low. Your 200mm lens should be acting as a 300mm lens (x1.5), so you might be better off just moving in slowly or making some kind of blind. I've shot hummingbirds on a feeder with a 200mm and moving in doesn't seem to bother them at all. >>I've got a Meade 4" Schmidt-Cassegrain telescope which (in theory) can be >>used as a 1000mm lens (if I did the math right, it should be just about [quoted text clipped - 14 lines] > shoot, and focusing can also be difficult as the light entering the camera > can be pretty low. I have a Celestron 6" newtonian which is very heavy and the mount and tripod aren't that strong so I get a lot of shake. I've never used it for terrestrial purposes but have taken a few photos of the moon. The T adapter is builtin so I just needed to get a Canon t-ring. This was my first attempt and I haven't managed to get anything better: http://www.photo.net/photodb/photo?photo_id=3803100&size=lg Greg  Signature"All my time I spent in heaven Revelries of dance and wine Waking to the sound of laughter Up I'd rise and kiss the sky" - The Mekons > I've got a Meade 4" Schmidt-Cassegrain telescope which (in theory) can be > used as a 1000mm lens (if I did the math right, it should be just about [quoted text clipped - 8 lines] > idea what the closest focus distance is for the 'scope (it was designed > with astronomy as the primary use). Give it a shot. The more frame you can fill, the better. However, if you camera has a mirror lock up and delay mechanism, use it! You need to counteract any vibration. >I've got a Meade 4" Schmidt-Cassegrain telescope which (in theory) can be >used as a 1000mm lens (if I did the math right, it should be just about [quoted text clipped - 8 lines] >idea what the closest focus distance is for the 'scope (it was designed >with astronomy as the primary use). I use my D70 on a slightly bigger scope, 1350mm f13 I think... I also like to aim it at a birdhouse at the edge of my yard, about 50 feet or so... Don't expect great pictures! You need to shoot at the fasted shutter speed, and use a remote control as well. Also you can drape a large coat over the scope to dampen vibrations. I find 2 problems, 1 is it's very hard to focus! The other is the large dust bunny's that can fall out of the scope onto your sensor... You need to check your sensor for dust after each time you use the scope and blow the dust out before it sticks. Get a small hand bulb. You really would be better off finding an old 500mm mirror lens at a flea market or something. That's my plan anyway! But hey - have fun - it can be entertaining. But the photos probably won't make Nat Geo. > >I've got a Meade 4" Schmidt-Cassegrain telescope which (in theory) can be > >used as a 1000mm lens (if I did the math right, it should be just about [quoted text clipped - 25 lines] > You really would be better off finding an old 500mm mirror lens at a flea market > or something. That's my plan anyway! Mirror lenses have the problem of lack of contrast compared to some refractive optics. The best ones (current high quality Maksuvtovs from Meade, Intes, Intes Micro, TEC, etc) are pretty decent. Old ones had poor quality coatings and the larger the central obstruction, the lower the contrast. A telescope is a telephoto lens, functionally. What you have to be concerned about is: -Vibration. Anything with a f.l. longer than about 400mm will need a strong support (telescope mount or tripod) and some mechanism to dampen mirror slap, especially with some DSLRs. Also, a remote release. Touching the camera during the exposure is a no-no. -Heat waves. The larger the front of the lens or lens aperture, the worse this problem is. The further away the object is (great atmospheric depth) the worse they effect the image. Shooting on a hot day over a distance, you will surely lose sharpness and contrast because of it. The higher the magnification (focal length) the worse the problem appears. -Thermal equalibrium of the telescope. Larger telescopes (mirrors over 4" across) need to be at the same temp as the outside air. Changing temp = changing optics and it screws up the quality of the image. It's not so much a problem with refractive optics. >>I've got a Meade 4" Schmidt-Cassegrain telescope which (in theory) can be >>used as a 1000mm lens (if I did the math right, it should be just about [quoted text clipped - 8 lines] >>idea what the closest focus distance is for the 'scope (it was designed >>with astronomy as the primary use). >I use my D70 on a slightly bigger scope, 1350mm f13 I think... >I also like to aim it at a birdhouse at the edge of my yard, about 50 feet or >so... >Don't expect great pictures! You need to shoot at the fasted shutter speed, and >use a remote control as well. Also you can drape a large coat over the scope to >dampen vibrations. >I find 2 problems, 1 is it's very hard to focus! The other is the large dust >bunny's that can fall out of the scope onto your sensor... You need to check >your sensor for dust after each time you use the scope and blow the dust out >before it sticks. Get a small hand bulb. >You really would be better off finding an old 500mm mirror lens at a flea market >or something. That's my plan anyway! >But hey - have fun - it can be entertaining. But the photos probably won't make I've tried this with my Canon 300D and my son-in-law's telescope. Or rather, I should say, he tried it. The biggest problem was focus. Even in aiming at the moon because the stop at infinity is a bit beyond infinity. My camera, and I suspect many others, was simply not meant to be focussed this way. Too bad. Perhaps one of those special focussing screens at Katzeye (did I get that right) would help? --- Paul J. Gans > >>I've got a Meade 4" Schmidt-Cassegrain telescope which (in theory) can be > >>used as a 1000mm lens (if I did the math right, it should be just about [quoted text clipped - 36 lines] > My camera, and I suspect many others, was simply not meant to be > focussed this way. Too bad. It's not the camera, it's the system. In days of yore SLRs had dozens of focusing screens to choose from, depending on the kind of lens you specialized in using. A nearly clear glass screen is almost best for long, slow lenses, but the best focusing is achieved with a dedicated "null focuser" that has center portion that blacks out right at the point of best focus. It's also called a "knife-edge" focusing screen. The Katzeyes make the image superficially brighter, but do not (IMO) aid in focusing that much. > It's not the camera, it's the system. In days of yore SLRs had dozens > of focusing [quoted text clipped - 5 lines] > The Katzeyes make the image superficially brighter, but do not (IMO) > aid in focusing that much. Maybe some day you'll actually own a DSLR and you'll realize what stupid sh.t you post. Greg Signature"All my time I spent in heaven Revelries of dance and wine Waking to the sound of laughter Up I'd rise and kiss the sky" - The Mekons > > It's not the camera, it's the system. In days of yore SLRs had dozens > > of focusing [quoted text clipped - 10 lines] > > Greg Don't comment on what you don't understand, dunce http://www.astropix.com/HTML/I_ASTROP/I08/I0815/I0815.HTM > -- > "All my time I spent in heaven > Revelries of dance and wine > Waking to the sound of laughter > Up I'd rise and kiss the sky" - The Mekons >>>It's not the camera, it's the system. In days of yore SLRs had dozens >>>of focusing [quoted text clipped - 13 lines] > Don't comment on what you don't understand, dunce > http://www.astropix.com/HTML/I_ASTROP/I08/I0815/I0815.HTM Of the DSLRs you own which has a knife-edge focusing screen? And more importantly of the DSLRs you own which has a Katzeye? Greg Signature"All my time I spent in heaven Revelries of dance and wine Waking to the sound of laughter Up I'd rise and kiss the sky" - The Mekons > >>>It's not the camera, it's the system. In days of yore SLRs had dozens > >>>of focusing [quoted text clipped - 18 lines] > > Greg None. But I've used cameras equipped with both for taking astronomical shots. I've also used the knife-edge technique for testing some optics. >>>> It's not the camera, it's the system. In days of yore SLRs had dozens >>>> of focusing [quoted text clipped - 17 lines] > > Greg Rich is 100% correct in what he has described for focusing. (My qualifications: I have made my own telescopes, including grinding and polishing mirrors, and testing them using "knife-edge" techniques (it is called a Foucault test), see http://en.wikipedia.org/wiki/Amateur_telescope_making , I have written papers on optical design, and I am a professional astronomer.) The problem is that most DSLRs do not have interchangeable screens. Knife-edge focusing is extremely accurate on stars. I installed screens in SLRs where I polished the ground glass to give a clear view, and placed a knife edge on the glass surface, then used the knife edge for focusing. I am currently modifying a Canon right angle finder to give accurate focusing. Roger > >>>> It's not the camera, it's the system. In days of yore SLRs had dozens > >>>> of focusing [quoted text clipped - 24 lines] > http://en.wikipedia.org/wiki/Amateur_telescope_making , I have > written papers on optical design, and I am a professional astronomer.) Yes, I understand a little about Focault testing and I have to say I didn't know you were a professional astronomer. My issue with Rich was his statement: "The Katzeyes make the image superficially brighter, but do not (IMO) aid in focusing that much." After using my friend's Digital Rebel (actually, my old Rebel I sold to him a couple of years ago) with a Katz Eye Optics focusing screen installed I think Rich is full of sh.t. I don't know where he comes up with the "superficially brighter" and it's a reach to say that they don't "aid in focusing that much", especially over the OEM focusing screens in DSLRs. > The problem is that most DSLRs do not have interchangeable > screens. Knife-edge focusing is extremely accurate on stars. [quoted text clipped - 3 lines] > I am currently modifying a Canon right angle finder to > give accurate focusing. That sounds cool. Greg > > >>>> It's not the camera, it's the system. In days of yore SLRs had > dozens [quoted text clipped - 38 lines] > "superficially brighter" and it's a reach to say that they don't "aid in > focusing that much", especially over the OEM focusing screens in DSLRs. It's similar to the old Beattie "Intenscreen" which achieved similar results. > My issue with Rich was his statement: "The Katzeyes make the image > superficially brighter, but do not (IMO) aid in focusing that much." After [quoted text clipped - 3 lines] > "superficially brighter" and it's a reach to say that they don't "aid in > focusing that much", especially over the OEM focusing screens in DSLRs. Again, I have to agree with Rich. The focusing in such cameras is pretty poor compared to the micro-prism systems in SLR cameras pre auto-focus era. Perhaps it's an aging factor now that I'm in my 50's, but I have a very hard time manual focusing a DSLR, and a lot of other people complain about the same thing. Hopefully we'll see this issue addressed in upcoming camera announcements. Roger >> My issue with Rich was his statement: "The Katzeyes make the image >> superficially brighter, but do not (IMO) aid in focusing that much." After [quoted text clipped - 13 lines] > > Roger Remember the diagonal split screen you used to see in a film camera's viewfinder? Your image was either in focus...or not. > >> My issue with Rich was his statement: "The Katzeyes make the image > >> superficially brighter, but do not (IMO) aid in focusing that much." After [quoted text clipped - 16 lines] > Remember the diagonal split screen you used to see in a film camera's > viewfinder? Your image was either in focus...or not. They tended to black out completely beyond f11, but lower than that they worked well. Most people I knew eventually moved to fine mattes for everything. But your dioptric correction had to be accurate if your eyesight was "off" otherwise focusing was difficult. A slow lens in low light could be a problem. >>>> My issue with Rich was his statement: "The Katzeyes make the image >>>> superficially brighter, but do not (IMO) aid in focusing that much." After [quoted text clipped - 22 lines] > otherwise focusing was difficult. > A slow lens in low light could be a problem. Yeah, you're right. But in those days, my Nikkor lenses were either F1.8, or F2.0, or F2.5, and aperture was set manually. I never liked the fine matte screens, probably for the reason you suggest. > >>>> My issue with Rich was his statement: "The Katzeyes make the image > >>>> superficially brighter, but do not (IMO) aid in focusing that much." After [quoted text clipped - 27 lines] > > I never liked the fine matte screens, probably for the reason you suggest. I think most people preferred things that were absolute, like split screens and the little prisms that surrounded them. You knew exactly how they behaved and when the image was in-focus with them. They tended to bother me, seemingly always being "in the way" of the image. > > My issue with Rich was his statement: "The Katzeyes make the image > > superficially brighter, but do not (IMO) aid in focusing that much." After [quoted text clipped - 9 lines] > I'm in my 50's, but I have a very hard time manual focusing > a DSLR, and a lot of other people complain about the same thing. I thought the Katz Eye split prism is a big step up from the focus screens in current DSLRs. They may not be as good as the screens in pre-autofocus cameras but the Katz Eye helped me considerably over my standard Rebel XT. It's all relative. Greg > Again, I have to agree with Rich. The focusing in such cameras > is pretty poor compared to the micro-prism systems in SLR cameras [quoted text clipped - 3 lines] > Hopefully we'll see this issue addressed in upcoming camera > announcements. Hi Roger, Now that we have the "dandelion" for using manual focus, non-electronic lenses on Canon by enabling the internal focus confirmation, does this obsolete the katz-eye screens? And would this work for focusing very long focal lengths such as telescopes? My T-mount adaptor doesn't have a nice flat area to mount one like my M42 does, but I presume a T-mount adaptor could be made with space for the Dandelion. I find manual focus to be difficult on my Rebel XT. If the depth of field is very shallow so I can really see the plane of best focus, then I do ok, but if not, then sometimes I can see that I am off a bit when I enlarge the image. For my Peleng 8mm M42 lens, I just guess the distance and set the focus from the distance scale with good results, but for longer lenses think that the autofocus confirmation would be adequate without having to actually see that focus has been achieved. Stop down metering is not difficult, but manual focussing is. There are some amazing bargains on M42 lenses and in-camera focus confirmation would make these very usable. Is there something similiar for Nikon users? Dandelion home page: http://www.filmprocess.ru/oduvanchik/ an EOS to M42 adaptor with it pre-installed: http://www.rugift.com/photocameras/canon-eos-adapter-focus-confirm.htm A kind of a review here: http://www.digit-life.com/articles2/digimage/oduvan.html > Now that we have the "dandelion" for using manual focus, non-electronic > lenses on Canon by enabling the internal focus confirmation, does this > obsolete the katz-eye screens? And would this work for focusing very long > focal lengths such as telescopes? My T-mount adaptor doesn't have a nice > flat area to mount one like my M42 does, but I presume a T-mount adaptor > could be made with space for the Dandelion. While an interesting device, there are still problems with the electronics detecting a signal. Sometimes the light level is just too low for the focusing electronics to give a good enough signal. This is the case for high f/ratio optics, like f/11 or f/16 telescopes, or low light levels (try focusing on a star). > I find manual focus to be difficult on my Rebel XT. If the depth of field > is very shallow so I can really see the plane of best focus, then I do ok, [quoted text clipped - 9 lines] > > Is there something similiar for Nikon users? I do not know. > Dandelion home page: > http://www.filmprocess.ru/oduvanchik/ [quoted text clipped - 4 lines] > A kind of a review here: > http://www.digit-life.com/articles2/digimage/oduvan.html A very interesting device. I wonder if you used a T-mount and the EOS to M42 adapter if focus confirmation would work on a telescope? Still, low light would be a roblem. There are also these devices for focusing DSLRs or film SLRs on a telescope: http://www.stellar-international.com I have their top-end model and it works. But it is a hassle to remove the camera to focus. Roger According to Roger N. Clark (change username to rnclark) <username@qwest.net>: > > Now that we have the "dandelion" for using manual focus, non-electronic > > lenses on Canon by enabling the internal focus confirmation, does this [quoted text clipped - 9 lines] > f/ratio optics, like f/11 or f/16 telescopes, or low light > levels (try focusing on a star). In part, this is because the built-in autofocus, like the various focus assists on various focusing screens (with the exception of the clear with cross-hair and the matte) depend on the light rays coming from opposite edges of the lens at maximum aperture. This is why (using the split-image as an example) when you stop a lens down below a certain maximum aperture (usually using the preview button on an auto-aperture lens) you will find one or both of the halves of the split will black out. At a certain aperture, you can very carefully position your eye and get both to work at the same time, but below that, nothing that you do will make it work. This is why Nikon (and probably Canon too, once they offered interchangeable finder screens) offered several variants of the same basic focusing screen, each tailored for a certain maximum aperture, so you could swap in an alternate screen when using something like a 1000mm f11 or so. These were in the G and H series (center microprism and full-screen microprism) The G1 and H1 were mostly for short focal lengths f3.5 or faster. The G2 tops out at 200mm f4 and starts at 24mm f2.8 The G3 tops out at 1000mm f11 reflex and is considered "excellent" at 180mm f2.5 The G4 tops out at 1200mm f11 and is considered "usable" at 180mm f2.5 These are from a table in a 1968 edition of _Nikon F Nikormat Handbook of Photography_ There were later screens for the Nikon F, but it is too much trouble to dig up the tiny sheets which accompanied the screens. Enjoy, DoN. SignatureEmail: <dnichols@d-and-d.com> | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- > In part, this is because the built-in autofocus, like the > various focus assists on various focusing screens (with the exception of [quoted text clipped - 6 lines] > and get both to work at the same time, but below that, nothing that you > do will make it work. While I agree, there are things you can do. For example, on a split image screen, you can unglue the split lens and re-glue it at a different angle of the split. I did that once with an Exakta screen for focusing the camera on a telescope. Lowering the angle changes the f/ratio where it blacks out, but it also changes the sensitivity to best focus. Roger > This is why Nikon (and probably Canon too, once they offered > interchangeable finder screens) offered several variants of the same [quoted text clipped - 20 lines] > Enjoy, > DoN. > A very interesting device. I wonder if you used a T-mount > and the EOS to M42 adapter if focus confirmation would work > on a telescope? Still, low light would be a roblem. I would think that if you screwed a M42 to T-mount adaptor into a EOS to M42 with the dandelion device that focus comfirmation would work fine if the telescope was faster than f/8 or f/5.6. > There are also these devices for focusing DSLRs or film SLRs > on a telescope: > http://www.stellar-international.com > I have their top-end model and it works. But it is a hassle > to remove the camera to focus. Are stars and other astronomical items always found at exactly infinity focus? Is it adequate to focus on something big, bright and far away like the moon and then point to the stars without refocussing or are there other effects than just thermal that have to be compensated out by focussing off infinity? btw, the articles on your website are excellent. > Are stars and other astronomical items always found at exactly infinity > focus? Is it adequate to focus on something big, bright and far away like > the moon and then point to the stars without refocussing or are there other > effects than just thermal that have to be compensated out by focussing off > infinity? Yes, all astronomical objects can be considered infinity for focusing. I do use the moon or a bright planet when they are up, but they are not always up. Then you get set up on a subject and start exposing, the temperature changes and the focus shifts. So you need to check focus every 20 to 30 minutes. It is a real pain. > btw, the articles on your website are excellent. Thanks, Roger > I've got a Meade 4" Schmidt-Cassegrain telescope which (in theory) can be > used as a 1000mm lens (if I did the math right, it should be just about > f/11). Adapter mounts are available at quite reasonable prices to hook it > up to a Nikon lens mount (I'm ordering one today). > > Any hidden gotchas when I hook it up to my D200? Check out various astronomy sites. > My interest d'jour is a fruit tree about 200 feet from my back porch which > is attracting a nice collection of birds. That's too far for my 200 mm > lens to shot them as anything but little specs. I haven't the foggiest > idea what the closest focus distance is for the 'scope (it was designed > with astronomy as the primary use). Point it at something near (like the tree) and find out. Signature-- r.p.e.35mm user resource: http://www.aliasimages.com/rpe35mmur.htm -- r.p.d.slr-systems: http://www.aliasimages.com/rpdslrsysur.htm -- [SI] gallery & rulz: http://www.pbase.com/shootin -- e-meil: Remove FreeLunch. > > I've got a Meade 4" Schmidt-Cassegrain telescope which (in theory) can be > > used as a 1000mm lens (if I did the math right, it should be just about [quoted text clipped - 12 lines] > > Point it at something near (like the tree) and find out. Distance, heat waves and the effect on images. This are E-1 shots through a 1000mm telescope. The first one at 1 mile, the second about 6 miles. Not the effect of heat waves on the building's finer details. You also have to deal with atmospheric extinction where blue scattering and haze cut contrast and detail. http://www.pbase.com/andersonrm/image/65044718 http://www.pbase.com/andersonrm/image/65044728 >> I've got a Meade 4" Schmidt-Cassegrain telescope which (in theory) can be >> used as a 1000mm lens (if I did the math right, it should be just about [quoted text clipped - 12 lines] > >Point it at something near (like the tree) and find out. The focus of the scope with it's eyepiece is vastly different from the camera at prime. I have to spin the little wheel a few dozen times to get from eyepiece focus to camera focus. I guess it has to do with the distance to the focal plane... So it's possible you could get focus with the eyepiece but not with a camera, depending on what limit runs out first. > >> I've got a Meade 4" Schmidt-Cassegrain telescope which (in theory) can be > >> used as a 1000mm lens (if I did the math right, it should be just about [quoted text clipped - 20 lines] > So it's possible you could get focus with the eyepiece but not with a camera, > depending on what limit runs out first. SCTs or Schmidt-Cassegrain Telescopes usually have wide focus ability compared to other types of telescopes of such focal lengths. A 4" should focus from about 10' to infinity with a camera, camera and eyepiece. |
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