68degrees
Well-known
I see spotting scopes 30x power and 60x power, not much dimensionally bigger than a big 300 or 600 telephoto. Why arent there any slr lenses be made with this power and dimensions?
30x spotting scopes but no 30x slr lenses. Why?
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mervynyan
Mervyn Yan
projected film size
68degrees
Well-known
can you elaborate? How big do you estimate the image size is from a spotting scope? I mean how big would the film need to be?
Gregoyle
Well-known
They make spotting scope adapters.
I used a surveillance kit that had a Kowa spotting scope with adapter a few years ago. I forget what the equivalent F-stop is on the spotting scopes, but with the ISO capabilities of today's cameras they are entirely usable.
-Greg
I used a surveillance kit that had a Kowa spotting scope with adapter a few years ago. I forget what the equivalent F-stop is on the spotting scopes, but with the ISO capabilities of today's cameras they are entirely usable.
-Greg
Phil_F_NM
Camera hacker
The scope only needs to illuminate an area a bit larger than the size of your pupil at a given eye relief.
The human eye can adjust to lighting conditions as well and can see far more than the most sensitive films can, with properly adjusted eyes which are used to the dark. So the optic doesn't need to be as fast with regard to maximum aperture since the eye can accommodate for darker viewing in the case of such an optic.
Phil Forrest
The human eye can adjust to lighting conditions as well and can see far more than the most sensitive films can, with properly adjusted eyes which are used to the dark. So the optic doesn't need to be as fast with regard to maximum aperture since the eye can accommodate for darker viewing in the case of such an optic.
Phil Forrest
Gregoyle
Well-known
One thing I just thought of,
Most lens designs came around when film was the only "sensor." Also, autofocus needs f/8 or larger, even today. I don't remember what the F-stop equivalent was on the spotting scope we used, but it was much smaller than f/8. You would have needed hyper-speed films for anything but the brightest sunlight.
-Greg
Most lens designs came around when film was the only "sensor." Also, autofocus needs f/8 or larger, even today. I don't remember what the F-stop equivalent was on the spotting scope we used, but it was much smaller than f/8. You would have needed hyper-speed films for anything but the brightest sunlight.
-Greg
68degrees
Well-known
so its basically because the maximum fstop would be unusable under anything less than EV 17? What do you estimate the fstop would be? f64 or such?
Those adapters must have some kind of aperture control on them then right or are they just they are what they are?
Those adapters must have some kind of aperture control on them then right or are they just they are what they are?
Phil_F_NM
Camera hacker
There are a few lenses out there which are essentially mirror telescopes with a refracting element. Based upon the Gregorian and Cassegrain telescope designs, they are catadioptric lenses and usually 1000mm or less.
They have fixed max apertures and a bunch have no aperture control at all as they are intended to be used at their stated "max" or only aperture. One of the fastest 1000mm lenses I've seen was an f/8 but most are f/11 from the ones I've had a chance to use.
These are the only real super telephoto options past 1000mm but still they don't collect light as efficiently as your typical tessar or double-gauss design. Their folded optics enable someone to have a 3 meter telescope in their living room though as a hobby as such a refractive optic would be huge.
I'm digressing but basically taking a telescope or field scope design which is built with the sensitivity of the human eye in mind and transferring it to photographic use with an effective maximum aperture of f/8 or lower just makes them ungainly and inefficient despite their ability to reach out well past what a normal lens could do. This is the reason that astrophotographers use geosynchronous tripod heads which track a fixed point in the sky. Hooking a camera up to a telescope means the working max aperture is quite small for an image which is 97% black with bright points here and there.
Phil Forrest
They have fixed max apertures and a bunch have no aperture control at all as they are intended to be used at their stated "max" or only aperture. One of the fastest 1000mm lenses I've seen was an f/8 but most are f/11 from the ones I've had a chance to use.
These are the only real super telephoto options past 1000mm but still they don't collect light as efficiently as your typical tessar or double-gauss design. Their folded optics enable someone to have a 3 meter telescope in their living room though as a hobby as such a refractive optic would be huge.
I'm digressing but basically taking a telescope or field scope design which is built with the sensitivity of the human eye in mind and transferring it to photographic use with an effective maximum aperture of f/8 or lower just makes them ungainly and inefficient despite their ability to reach out well past what a normal lens could do. This is the reason that astrophotographers use geosynchronous tripod heads which track a fixed point in the sky. Hooking a camera up to a telescope means the working max aperture is quite small for an image which is 97% black with bright points here and there.
Phil Forrest
68degrees
Well-known
This all started yesterday while observing an Eagles nest at 680 feet. (the park forbids gettting closer than the observation site). My 300mm (7x) wasnt cutting it. I took a few shots but couldnt see much of the eagles. Nice shot of the huge nest though.
Next I looked with 10x 10x50 binoculars were better, brighter for observing.
Earlier in the month we looked at Jupiter with a cheap 36x (900m with 25mm eyepiece) taiwan telescope bought back in the 80s or 90s that I found in a storage closet and forgotten about.
I mused at using it to look at the eagles nest, then yestereday I actually tried it. The image was pretty good at least compared to the other devices I tried. I could see the chicks, the bird feeding its chicks, all clear and close up, really filled the frame with the action.
I thought, why are there no 36x slr lenses. Even a 1000mm lens is only 23x. Spotting scopes Ive seen go up to 60x no problem. That would be about 2500mm lens. Ive seen 60x spotting scopes for a couple hundered dollars.
Next I looked with 10x 10x50 binoculars were better, brighter for observing.
Earlier in the month we looked at Jupiter with a cheap 36x (900m with 25mm eyepiece) taiwan telescope bought back in the 80s or 90s that I found in a storage closet and forgotten about.
I mused at using it to look at the eagles nest, then yestereday I actually tried it. The image was pretty good at least compared to the other devices I tried. I could see the chicks, the bird feeding its chicks, all clear and close up, really filled the frame with the action.
I thought, why are there no 36x slr lenses. Even a 1000mm lens is only 23x. Spotting scopes Ive seen go up to 60x no problem. That would be about 2500mm lens. Ive seen 60x spotting scopes for a couple hundered dollars.
Texsport
Well-known
I use a Zoomar 1000/8 CAT lens attached to an OM-D to get 2000mm equivalent.
I find that the factor limiting wide use is the f8.
Great moon pics however!
Texsport
I find that the factor limiting wide use is the f8.
Great moon pics however!
Texsport
bwcolor
Veteran
60x spotting scopes for a couple of hundred dollars are of poor optical quality.
Look for better optics:
Look for better optics:
68degrees
Well-known
ya but im saying, 60x slr lenses dont even exist at all to my knowledge.
Phil_F_NM
Camera hacker
Like I said, you'd need a 3 meter telescope at that point. It's all about the light at the exit pupil, it's luminance and coverage. You just can't get that in a lens without going to an optic the size of a trashcan or greater.
Phil Forrest
68degrees
Well-known
trashcan diameter front element. hahaha. think Im gonna need a bigger boat... uh I mean a bigger tripod. Grab and end will ya? ahha
Sejanus.Aelianus
Veteran
Phil_F_NM
Camera hacker
It can be done and you can do it by hand.
Look up hand grinding optics online or homemade telescope.
Back when I was in the Navy, one of my chiefs was in a "club" of a few folks on the ship who would sit around drinking coffee and hand grinding elements for their homemade telescopes.
A few folks made refractive scopes and one was making a Cassegrain reflector. That reflector chassis was probably 18" in diameter with a 15" wide primary mirror element that he was grinding himself and was going to have drilled then coated for reflectivity.
The final telescope design was about 5'x18." I didn't see the finished telescope but there is no reason he couldn't do it. With an optic that big, he could fill the eyepiece with the lunar surface or get good detail of Jupiter and the rings of Saturn.
That's what I mean by "trashcan" sized. When your tripod is a 2.5T truck.
Phil Forrest
Look up hand grinding optics online or homemade telescope.
Back when I was in the Navy, one of my chiefs was in a "club" of a few folks on the ship who would sit around drinking coffee and hand grinding elements for their homemade telescopes.
A few folks made refractive scopes and one was making a Cassegrain reflector. That reflector chassis was probably 18" in diameter with a 15" wide primary mirror element that he was grinding himself and was going to have drilled then coated for reflectivity.
The final telescope design was about 5'x18." I didn't see the finished telescope but there is no reason he couldn't do it. With an optic that big, he could fill the eyepiece with the lunar surface or get good detail of Jupiter and the rings of Saturn.
That's what I mean by "trashcan" sized. When your tripod is a 2.5T truck.
Phil Forrest
68degrees
Well-known
Thats amazing! Thanks!
68degrees
Well-known
I like DIY but thats taking it to a whole new level. Did you actually do this yourself?
Phil_F_NM
Camera hacker
No, I didn't have the patience back then but I watched with fascination at the work these guys were doing. Hand grinding a precision optic is a slow process that can be very easily screwed up. One aberration and you have to start the whole thing over again. I've seen a bunch of homemade telescopes and looked through them. There are a lot of amateur astronomers out in the high desert of New Mexico with years invested into custom optics that are truly priceless. The patience and skill which is demonstrated in creating a homemade telescope is really amazing.
Phil Forrest
micromontenegro
Well-known
Almost any good telescope can be used with your camera using a T adapter and a T ring. I routinely use both Celestron C8 (2000mm) and C90 (1250mm). To get really REALLY high magnifications, you will need an eyepiece projection adapter. Then, the light is the limit.
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