Thanks all for your interest in this topic and for the benefit of your knowledge of the subject. All this is very informative and helpful.
More of the same (with pictures, if possible) would be appreciated.:-)
So stick an extension tube or tubes behind a longer lens and get the best of both worlds. When I used Leica R3s, my favorite was 180mm Elmar.
Here is a web-page with an interesting alternative viewpoint to Macro technique:
Measure it, and you'll see. You lose some light due to reflections, even with multicoating, and some is transmissive loss due to the glass itself, even with a converter of excellent quality made by one of the major manufacturers. Most people don't notice, because they are using TTL metering, but meter a uniformly illuminated plain surface like a gray card with the lens focused at infinity (the surface should not be in focus) the lens stopped down two stops and no teleconverter, and then with the lens wide open and the teleconverter, and you'll get different readings--up to a half stop in transmissive loss in my experience.
Originally Posted by Q.G.
Still photographers often ignore transmissive loss in general, because it's compensated for automatically with in-camera metering. State of the art modern multicoated cine lenses that cost more than a luxury car, though, are often marked in T-stops, rather than f:stops, because there is less room for exposure error and more money at stake on a film set, and handheld metering is the norm.
An interesting fact that might be relevant: A camera lens is optimized for a specific lens-to-object distance. Even if a lens were perfectly corrected for all aberrations at that one specific distance (which is not possible by the way) it will not be perfectly corrected at other distances. I think there is even a rigorous theorem to this effect that someone proved long ago. I think it might have been Maxwell or someone famous like that.
What are the implications of this? Basically, one should not necessarily assume that using an ordinary camera lens with extension tubes or bellows (i.e. far from its ideal conjugate ratio) will produce better close up results than alternative techniques that use additional optical components, such as tele-converters and/or diopters. It is all going to depend on the specific details of the lens designs.
By the way, if I am not mistaken, spherical aberration and coma tend to be particularly bad actors when one changes the conjugate ratio.
Last edited by alanrockwood; 03-02-2009 at 11:04 PM. Click to view previous post history.
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Here is another interesting link on comparing different close-up techniques.
I do that every time i use my lenses, process the film, and see the results.
Originally Posted by David A. Goldfarb
The aperture values on them are calculated. F-stops, not T-stops.
I never noticed anything that would make me think it is anything but negligible.
Originally Posted by alanrockwood
But not all lens designs are equally sensitive to this. And most do quite well covering a wide range.
Things can get iffy when the conjugate ratio changes from long-short to just about equal, and from just about equal to short-long.
The upshot is that, though their performance does change, most standard lenses are excellent performers from infinity to close-up. Some even still when going beyond 1:1.
Q.G. You are right that some lenses perform better with change of conjugate ratio than others.
Just for fun I ran some lens trace calculations using WinLens. I tried all 14 lenses in the "double gauss" library that is distributed with the program. This library includes a wide range of lenses, such as biotar types, dogmar, some that look like plasmats, etc. I ran them at conjugate ratios of infinity and at 1:1 and eyeballed the spot diagrams to see how well the lenses did.
Basically all or almost all the lenses gave much better spot diagrams at infinity than at 1:1 conjugate ratio. By eye I would say that most of the lenses were at least twice as bad at 1:1 as at infinity. Some were better than others. For example, one of the lenses described as a "Biotar F/5.6 HFOV 20deg USP 2117252 " wasn't too bad at 1:1. Others, such as the one labeled "DG F/1.5 HFOV 23deg Leica Xenon L" were truly horrible at 1:1. Part of the difference between these extremes two may relate to the aperture used in the simulations. However, the point is that the lenses performed much differently at infinity compared to 1:1.
Interestingly, most of these lenses are based on symmetrical or near-symmetrical types. This general class of lenses is generally considered to be better behaved with respect to changes in conjugate ratios than highly unsymmetrical lenses, yet in general there were big changes in performance when going from infinity to 1:1.
One lesson is that an ordinary camera lens is probably not going to perform particularly well when used with extension for extreme closeups . Of course, there are probably lenses for which this rule of thumb would fail. I think that modern macro lenses using internal focusing would likely fall into this class because the designer could arrange the focusing to adjust for aberrations while it is focusing.
One final note: stopping the lens down should cover a variety of faults, except for lateral color. Most closeups are probably shot at small apertures anyway in order to maximize depth of field, so here is a case where mother nature wants to work with us instead of against us.
But then, there are lenses, and lens simulations.
Try a Planar on a bellows, and you will be amazed how well it holds up, even when compared to a Makro-Planar.