In-camera focus shifting--down the rabbit hole

[leonardturner]

I wondered if the focus shift function incorporated into the Nikon 850 would function with the addition of their TC 17EII teleconverter, and whether this might be useful. I chose a small section of a wing from a long deceased Luna moth taped to a glass slide, featuring the prominent “eye” as a test subject. The focus shifting functionality was there, and a reasonably good image was obtained using it, but with a more or less central area that appeared blurred. This is the region immediately above the imaginary iris of the imaginary eye, and led to more than a week’s worth of additional images of the same subject, taken with four different lenses and multiple different approaches to lighting and even polarization. I thought about localized trash in the system, relative motion of part of the wing (which did break up some further during the week), lighting being too flat, or the polarization film over the Tronds in the first image having an adverse effect. I now have an idea of what I'm seeing, but would be interested in the thoughts of others.

Images were all "auto" processed in Photoshop Bridge, but were not sharpened, etc.

Nikon 850, 105 macro with 17EII teleconverter, f8, arbitrary spacing of images "3" two Trond lights

reversed Companon 50, short extension tube, f5.6, Trond
Here the overall image looks a bit sharper at about 2.5X, but the area in question still looks "wrong"

5X Mitty on Raynox, Trond. Here the subject is placed higher in relation to the camera.

10X Mitty on Raynox, Trond

I think that what I have learned from this is that there are several populations of scales; in addition to the brown and (a little) blue, there is a more ivory scale to the immediate left of the white scales in the last image. I think that the white scales are more translucent, showing confusing detail from behind, and they are catching the light from the main Trond on the left in a different way because of curvature in the specimen. There is also the matter of white on white, with little of the contrast that provides a sense of sharpness.

But is that all there is? Am I missing something?

Thanks,

Leonard

[rjlittlefield]

What you have found is consistent with what I've seen with other moths.

I have not looked at a Luna moth eyespot. But I do know that some other groups have quite different types of scales on various spots. For example at viewtopic.php?t=699 , I discovered that the prominent satin-textured "Y" of the Autographa and Anagrapha months 'is actually composed of many layers of individually almost transparent scales, lying very close together instead of coarsely shingled like the rest of the wing." Similarly, at viewtopic.php?t=8203 , I learned that the ventral side of the glassy spot on a skipper wing is composed of very shiny transparent scales aligned at an assortment of almost random angles. The stereo images at viewtopic.php?p=50395#p50395 are revealing. There are some animations farther down that may be helpful also.

I don't think you've missed anything in your explanation.

--Rik

[leonardturner]

Thanks for your thoughts and references, Rik. All informative and very interesting, but the stereo especially so. Not only different populations of scales, but differing characteristics within individual examples!

Leonard

[MarkSturtevant]

I suppose it must be as suggested -- very translucent 'ghost - like' of scales.