I have just bought a Kaiser Digital Slide Duplicator in order to digitise 35mm slides (mostly positives), since this is something I need to do fairly often.
In general, I have seen lots of people advising the use of real macro lenses for this type of use, since they have a flat field and that should help avoid blurring around the edges; the answers in this DPReview thread, for example. I use a full-frame Canon 5DS R and already have a Canon 100mm 2.8L IS USM macro lens, and since the product page for the duplicator says full-frame sensors should be used with lenses of about 80–120mm to get full-size reproductions, I figured that should be a perfect match.
But the results so far have been… disappointing, to say the least. Horribly blurry edges. The narrower I set the aperture, the less noticeable it gets, but even at its very narrowest (32), there’s very noticeable blurring. When taking regular pictures, the lens is very sharp all the way out to the edges, so it’s not a general lens issue.
I note that the Kaiser product page actually – and rather mysteriously to me – says, “Not suited for use with macro lenses”. I can’t figure out how this statement could be true of a duplicator (how can a flat field be a disadvantage?), but then I’m dreadful at physics, so perhaps there’s a logical reason?
Here is an example of a slide shot at F11 (first) and F29 (second). You can see that F29 is better, but still not in any way usable (ignore the pink – there’s a thin sheet of plastic with pink writing on the back of the duplicator’s diffusor, and I haven’t taken it off in case I want to return the duplicator):
I tried taking off the “Detachable achromatic 10 dioptre macro lens”, just in case that was the issue, but that only, unsurprisingly, made the lens completely unable to focus, so clearly it wasn’t.
To test, I’ve tried with the only non-macro lens I have that goes to between 80 and 120mm and has a diametre I can work with (I have a 67–52mm stepdown ring and a 52–58mm step-up ring), which is a 70–200mm F4.0. Not sure if it’s the step-down ring, but the result is heavily barrelled and no sharper (at F32):
Is there something I’m missing here? What does it mean when Kaiser state their duplicate is not suited for macro lenses, when macro lenses are generally exactly what you want for duplicators? Is there something I can do to achieve slides that are actually in focus, or is this just the wrong product for my lens and body?