Use stereomicroscope lens without a microscope?

rjlittlefield · Post by **rjlittlefield** » Wed Feb 06, 2019 1:12 pm

Lou Jost wrote:exaggerated perspective that I noted on the aerial image from my Leica objective

I know that you've written this several times, but I've never been sure that I know what you're talking about.

Is this "exaggerated perspective" an effect that you see when you're looking through the lens with both eyes (and thus inferring perspective from stereo disparity)?

Or is it an effect that you see when you're looking through the lens with just one eye (and thus inferring perspective from monocular clues like relative motion and focus)?

--Rik

Lou Jost · Post by **Lou Jost** » Wed Feb 06, 2019 1:36 pm

Pau, even a flat-field lens can have exaggerated perspective, making an image that is stretched in the z direction. This would make no difference in a normal stack but I am guessing it should be visible in stereo images.

Lou Jost · Post by **Lou Jost** » Wed Feb 06, 2019 1:39 pm

Rik, if I recall correctly, it was visible as I moved my loupe around to examine the aerial image. Thus, visible with a single eye. It was much like the experience of moving around in Google Earth with the 'Exaggerated Elevation" option set to a high number. That effect is visible on a normal flat monitor. It was a very weird experience to see my butterfly wing looking like the Rocky Mountains through this lens.

viktor j nilsson · Post by **viktor j nilsson** » Wed Feb 06, 2019 2:01 pm

Could this be an optical illusion caused by the very shallow DOF of high NA lenses? In our daily life, we are used to the fact that things that are out of focus tend to be located further away (or closer) than things in focus. So when we look through a lens with unusually high NA, maybe our brains (or at least those of some of us!) may perceive the rapid loss of focus with distance as exaggerated perspective?

Pau · Post by **Pau** » Wed Feb 06, 2019 2:11 pm

Lou, do you refer to something like looking though a wide angle lens like a phone camera at close objects?

Lou Jost · Post by **Lou Jost** » Wed Feb 06, 2019 2:38 pm

No Pau and Viktor. If you do what I suggested in Google Earth and move your viewpoint around, you will see it. It is simply stretching everything in the z direction.

rjlittlefield · Post by **rjlittlefield** » Wed Feb 06, 2019 6:35 pm

Lou Jost wrote:Pau, even a flat-field lens can have exaggerated perspective, making an image that is stretched in the z direction. This would make no difference in a normal stack but I am guessing it should be visible in stereo images.

Optical images are always stretched by a relative factor of m. That is, the image is m times wider than the subject, but m^2 times deeper. It falls out of 1/f = 1/o + 1/i when you take the derivatives.

This makes no difference in stereography because you just choose separation angles that are appropriate when referenced back to the original subject.

The increased depth is also not normally perceived as such when examining optical images because the images are only viewed on-axis. We do "see" it all the time in one sense, but that's when we look through a microscope and complain that there is so little DOF. The reason that even young eyes can only focus such a shallow slab on the subject is that it becomes an impossibly deep slab after magnification.

But perhaps with such a large diameter lens, Lou is able to look far enough off axis to directly perceive the enhanced depth at say m=2.

--Rik

Lou Jost · Post by **Lou Jost** » Wed Feb 06, 2019 6:47 pm

Maybe that's the explanation. I've never seen this effect when examining the aerial images of other lenses, but this is an exceptionally broad lens.