I remember some discussion threads sometime back about what focus setting (minimum or infinity) to chose on the host lens when using a reversed enlarger lens in front, but have been unable to find them. So I would like to ask the question again.
Is there any advantage to image quality (other than the obvious change in magnification) in choosing the minimum focus setting or the infinity setting (or something in between) when coupling a reversed enlarger lens with a normal lens?
The set up I am currently using is a Nikon D80 with a Nikkor 200mm Micro lens as a host lens coupled with various enlarger lenses (50mm to 150 mm) reversed. The change in focus results in approximately a 50% change in magnification on a 120 mm enlarger lens for example. I am still working to determine the best combination of F-stops between the host lens and the reversed lens, but was wondering if there is an optimum focus setting for the host lens.
If someone can remember the previous discussion, could someone point me to the thread?
Thanks
JD
Host lens focus setting
Moderators: rjlittlefield, ChrisR, Chris S., Pau
Hi JD
I'm going to wimp out of diggng all the links out, but point you to
Rik's own page of links
If you use your browser "Edit" to look for "combo" you'll find several relevant ones. "Stopping down a lens on a combo" (ish), is one of the most revealing.
A casual consideration of the ray paths shows that both the lenses expect their subjects to be at infinity, or closer. If you focus the biggun to something less, the rays from the littlun have to be diverging, which it's not designed for. But you have to suck it and see.
I've tried a few dozen combinations or so over a period, I suppose. While some are OK, the edge performance is usually less than perfect.
Just today I was combining lenses which by themselves are quite respectable. Almost all the combinations, using a variety of 40 - 50mm lenses on the front, reversed, gave fairly nasty CA at the edges.
Some worked better - when I've found a reportworthy pattern I'll publish, but in the meantime, try every lens you have!
Using an "Infinity Corrected" microscope objective on a 200mm telephoto as "tube" lens, the tele should also be focused at infinity. However, Rik's test of that combination using the focus adjustment on the tele lens to achieve the focus steps, showed no drastically bad effect.
I'm going to wimp out of diggng all the links out, but point you to
Rik's own page of links
If you use your browser "Edit" to look for "combo" you'll find several relevant ones. "Stopping down a lens on a combo" (ish), is one of the most revealing.
A casual consideration of the ray paths shows that both the lenses expect their subjects to be at infinity, or closer. If you focus the biggun to something less, the rays from the littlun have to be diverging, which it's not designed for. But you have to suck it and see.
I've tried a few dozen combinations or so over a period, I suppose. While some are OK, the edge performance is usually less than perfect.
Just today I was combining lenses which by themselves are quite respectable. Almost all the combinations, using a variety of 40 - 50mm lenses on the front, reversed, gave fairly nasty CA at the edges.
Some worked better - when I've found a reportworthy pattern I'll publish, but in the meantime, try every lens you have!
Using an "Infinity Corrected" microscope objective on a 200mm telephoto as "tube" lens, the tele should also be focused at infinity. However, Rik's test of that combination using the focus adjustment on the tele lens to achieve the focus steps, showed no drastically bad effect.
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rjlittlefield
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I think it has a lot to do with how much different the focal lengths are.
This is based mostly on gut feeling and vague theory, rather than actual data, but I have the feeling that combinations work better if a) the rear lens is much longer than the one reversed on front, and b) the aperture is set by the front lens.
A symmetric combination like two 50's face to face can be good, but apparently only if you keep them close together and stick a new aperture stop right in the middle.
At the bottom of FAQ: Stopping down a lens combo is my comment that "Sometime I would be interested to see an unbiased accounting of combos: try all pairs of a zillion different long and short lenses, tabulate the results -- all the results -- and see at least what the odds are. My prediction is that most of them won't work very well. But I could be wrong, and that would be an interesting thing to know." That was written over 3 years ago, and I still think it would be interesting.
I agree with ChrisR's analysis that infinity on the rear lens probably puts the front lens nearer to its sweet spot.
--Rik
This is based mostly on gut feeling and vague theory, rather than actual data, but I have the feeling that combinations work better if a) the rear lens is much longer than the one reversed on front, and b) the aperture is set by the front lens.
A symmetric combination like two 50's face to face can be good, but apparently only if you keep them close together and stick a new aperture stop right in the middle.
At the bottom of FAQ: Stopping down a lens combo is my comment that "Sometime I would be interested to see an unbiased accounting of combos: try all pairs of a zillion different long and short lenses, tabulate the results -- all the results -- and see at least what the odds are. My prediction is that most of them won't work very well. But I could be wrong, and that would be an interesting thing to know." That was written over 3 years ago, and I still think it would be interesting.
I agree with ChrisR's analysis that infinity on the rear lens probably puts the front lens nearer to its sweet spot.
--Rik
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Firephoto798
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Rik,
I've read many of the threads regarding stopping down lens combos and was wondering if you believe that having the right F-stop relationship between the reversed lens and the host lens is more important than how the host lens is focused or what the host lens is?
Or do you believe that it's an "all of the above" issue, and a matter of changing combinations of lenses until finding a pair that work?
JD
I've read many of the threads regarding stopping down lens combos and was wondering if you believe that having the right F-stop relationship between the reversed lens and the host lens is more important than how the host lens is focused or what the host lens is?
Or do you believe that it's an "all of the above" issue, and a matter of changing combinations of lenses until finding a pair that work?
JD
A specific example of a combo is alluded to on this page of Evaluations By Bjørn Rørslett
where he suggests two identical lenses (Nikkor 105mm f/4) back to back, work rather well.
If they were both made to focus at infinity with a diaphragm at the focal plane in the middle, it would make a Bilateral Telecentric Lens.
Schneider and others suggest this is a happy arrangement from the point of view of the sensor because the rays arrive from a narrow angle about normal to it. I have 2 x el Nik 63mms, and 2 x R'gon 75mm 1:1s, I always intended to try that with. Must eat more Pringles..
where he suggests two identical lenses (Nikkor 105mm f/4) back to back, work rather well.
If they were both made to focus at infinity with a diaphragm at the focal plane in the middle, it would make a Bilateral Telecentric Lens.
Schneider and others suggest this is a happy arrangement from the point of view of the sensor because the rays arrive from a narrow angle about normal to it. I have 2 x el Nik 63mms, and 2 x R'gon 75mm 1:1s, I always intended to try that with. Must eat more Pringles..
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ray_parkhurst
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Here's one:
http://www.opto-engineering.com/telecen ... orial.html
simpler (see fig 5)
http://www.schneideroptics.com/pdfs/ind ... Lenses.pdf
http://www.opto-engineering.com/telecen ... orial.html
simpler (see fig 5)
http://www.schneideroptics.com/pdfs/ind ... Lenses.pdf