Problem with setting up this test is that these lenses were designed for a particular piece of equipment, presumably a microfiche reader, and I have no data on the way they were set up. I'm pretty sure the extensions used were quite large, possibly with additional optics to project onto a viewscreen, but that's not what I bought them for. To be practical, I decided to test them with the maximum extension I could get from my bellows, plus the adapters and of course whatever mechanics they are mounted in. Testing them all the same way, I can get an idea of their useful mag range in such a system, and how well they can work on FF to show the types of photos I want to take.
I ended up testing 11 different lenses, from two series. The majority were from the "cone" series similar to the 18.25x sold by Surplus Shed. These include the following magnifications: 15.7x; 18.25x; 20.78x; 23x; and 29x. Also included in this series were the 8.05x and 10.6x, which also have a cone-shaped mechanic but are a smaller maximum diameter and thus won't fit on the 48.5mm adapter (from Raf) I used for the others.
The remaining 4 lenses were from the "objective" series. I presume they were used on a projection system as well, but with a different extension requirement. They have longer focal lengths for the same nominal magnification. These look more like regular microscope objectives, except the mount is smaller, around 16mm if I remember correctly. I have taped them all up to allow threading into RMS for testing and will measure the thread later. I'll also publish pics of all the lenses themselves. I may end up putting all this on my website and link to it here, haven't decided. Anyway, these lenses are marked: 15x-1; 23x-1; 35x-2; and 40x-2.
The test subject is a 1955-S RPM-004 that I found in a recent BU roll search. The coin has a small dust spec near the center, so I cropped to that spec for my "center" shots. This was only for convenience since the mags are different for each lens, so it's impossible to pixel peep for comparisons. Quality must be judged on absolute basis. For the "corner" shots, since the FOV is different for each lens, there is no fixed reference.
Each image was composited from a 12-shot stack with ~18um steps. This is another practical convention since the NAs on these objectives vary. It seemed to be OK for the highest powers, and thus overkill for the lower powers, but oh well.
Because I shot stacks, I can show something for LoCA, but have not sifted through the images to do this yet. Again, perhaps I will upload this info to my website later.
I'll show the Cone series first, Overall / Center / Corner, then the Objective series.
8.05x
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10.6x
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15.7x
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18.25x
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20.78x
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23x
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29x
Edited to add Objective series images
15x-1
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23x-1
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35x-2
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40x-2
Edited to add some comments about the lenses
8.05x: Center is sharp with low LaCAs. Does not cover FF well but covers APS-C based on my earlier tests.
10.6x: Center is sharp with visible LaCAs. Does not cover FF well but probably covers APS-C well.
15.7x: Center is sharp with visible LaCAs. Covers FF reasonably well. Nice presentation of the "money shot".
18.25x: Center shows some diffraction softening, visible LaCAs. Covers FF well.
20.78x: Center shows some diffraction softening with low LaCAs. Covers FF well. Probably covers "money shot" well.
23x: Center shows some diffraction softening with low LaCAs. Covers FF well. May cover "money shot" well.
29x: Center shows strong diffraction softening. Covers FF well.
15x-1: Center and Corner are soft but consistent across FF
23x-1: Center is sharp with low LACAs. Covers FF well.
35x-2: Center shows some diffraction softening, some visible LaCAs. Does not cover FF.
40x-2: Center is sharp with low LaCAs. Covers FF well. Nice presentation of the "money shot".
Edited to add examples of low (23x) versus visible (18.25x) LoCA animations:
23x Cone showing relatively low levels of Longitudinal Chromatic Aberrations (LoCA). Little if any hue shift on spectral highlights is apparent.
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18.25x Cone objective showing visible levels of LoCA
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Would like to hear feedback on this method of showing LoCA
