A crazy optical setup

soldevilla · Post by **soldevilla** » Mon Oct 09, 2017 7:50 am

Tired of take micro minerals pictures with very little working distance that do not allow me to work with diffusers and reflectors like I want, I've been testing "crazy" optical settings to increase working distance.

At the end I found an interesting optical layout and it will make me to machine a special adapter. But I have no knowledge of optical ray tracing, and I propose if someone can test in the computer this idea. In my practical tests it have worked and creates image, with it seems that good quality, now I have to mechanize a piece that ensures the correct optical centering.

I have placed a microscope objective x4 or x10. Back, located about 30mm I have placed a Nikon x20, and approximately 160mm further away is the camera chip. The magnification varies greatly by slightly varying the distance between the two lenses.

Pau · Post by **Pau** » Mon Oct 09, 2017 8:35 am

A priory your idea really sounds crazy, a recipe of disaster I would say...but I'm very curious of see your results, even your preliminary tests.

If I understand well you want to take the first objective aerial image with the second objective that projects the further amplified image onto the sensor, but using them well outside their specification (30mm...varying the distance between the two lenses ...)

Sorry, I am not able to perform your calculations

rjlittlefield · Post by **rjlittlefield** » Mon Oct 09, 2017 10:48 am

Well, "disaster" may be too strong, but I agree there is not much to recommend this scheme except for increased working distance. For resolution, you will not even get the full NA of the front lens, because you have moved it farther away from the subject without making its aperture wider. The rear objective will be stopped down to the NA of the front objective, so even though it is nominally 20X NA 0.40 or similar, it will act like NA 0.20 or less (depending on the front objective and spacings). In addition to the loss of NA, there will be added aberrations due to pushing the front lens so far away from its design point.

Accurate calculations will not be practical due to missing information about the lenses involved. Your best bet is to just try it and see if the image quality is high enough to make you happy.

--Rik

soldevilla · Post by **soldevilla** » Mon Oct 09, 2017 11:47 am

Pau wrote:If I understand well you want to take the first objective aerial image with the second objective that projects the further amplified image onto the sensor, but using them well outside their specification (30mm...varying the distance between the two lenses ...)

exactly, Pau, that's the idea.

The rear objective will be stopped down to the NA of the front objective, so even though it is nominally 20X NA 0.40 or similar, it will act like NA 0.20 or less (depending on the front objective and spacings). In addition to the loss of NA, there will be added aberrations due to pushing the front lens so far away from its design point.

Well, I can not measure NA, but I can get an idea by looking at how many diaphragms I've lost. And at the moment it does not seem too light.

The objectives sometimes behave a little rebellious. I have sometimes obtained better results using finite microscope objectives in front of a telephoto lens, as if it were infinite ... When I have time I will turn that piece in my lathe and do the tests.