9
\$\begingroup\$

The micro four thirds specifications originally want lenses to be image space telecentric if possible. It seems that some MFT lenses actually follow that recommendation.

Can reversing such a lens yield a usable object-space telecentric optic (for small distances and objects), and which kind of MFT lens would be most suitable?

\$\endgroup\$
3
  • 1
    \$\begingroup\$ I think for a lens to be image space telecentric, its rear element would have to have a diameter at least as large as the diagonal of the sensor. Otherwise the image couldn't cover the whole sensor. So that's the first thing to look for, I guess. \$\endgroup\$
    – Steadybox
    Commented Aug 29, 2023 at 14:19
  • \$\begingroup\$ Also, I can tell from a practical experiment that a basic Lumix Vario kit lens at least doesn't give you object space telecentricity when reversed. But that's not surprising at all, I guess. \$\endgroup\$
    – Steadybox
    Commented Aug 29, 2023 at 14:21
  • \$\begingroup\$ The rear element would certainly be no smaller than the object, that's why it would only be practical at macro scale in any case. \$\endgroup\$ Commented Aug 30, 2023 at 14:39

2 Answers 2

0
\$\begingroup\$

I don't use MFT, but many good lenses can be used reversed with good results on DSLRs. The primary issue with modern lenses is that the aperture is usually controlled electronically, when reversed you lose control of the aperture. Instead, I have used old manual focus lenses reversed. Minolta MD and Canon FD are good choices for this since they aren't used much anymore and can be obtained cheaply or free. I have used 50mm and 28 mm reversed on my DSLR. On an MFT system, the lens is much closer to the sensor, you may need to add an extension tube to compensate. Or, maybe not, experiment.

There are some examples in my presentation here, pages 17-19: http://suncoastcameraclub.org/Tips/Focus_Stacking.pdf

Are manual focus lenses Telecentric? Probably not, but you can get decent results anyway.

\$\endgroup\$
5
  • 2
    \$\begingroup\$ ...object space telecentricity is quite different from ordinary macro ... \$\endgroup\$ Commented May 6, 2019 at 0:21
  • \$\begingroup\$ Hi, welcome to Photo-SE. While your answer is interesting, it doesn't seem to address the question, which is primarily about the telecentricity of a reversed MFT lens. \$\endgroup\$
    – scottbb
    Commented May 6, 2019 at 1:25
  • \$\begingroup\$ To explain: an object space telecentric lens cannot image anything larger than its front element (or very far away), and behaves somewhat similar to a lens of infinite focal length. \$\endgroup\$ Commented May 6, 2019 at 7:45
  • \$\begingroup\$ Sorry, this is where I thought you were going, from Wikipedia: "Many lenses that have been specially optimized for digital SLR cameras are nearly [image-space] telecentric on the image side, to avoid the vignetting and color crosstalk that occur in color filter array-based digital image sensors with oblique incident rays. The Four Thirds System uses this approach." \$\endgroup\$
    – Mattman944
    Commented May 6, 2019 at 10:15
  • \$\begingroup\$ Yep. Now the core question is, does a reversed image-space telecentric lens become object space telecentric? I might have started confusion with the word "macro", I admit - but them, an object space telecentric lens with usable infinity focus seems to be physically impossible :) \$\endgroup\$ Commented Jun 5, 2019 at 9:44
-1
\$\begingroup\$

The typical camera lens is optimized to image objects at different distances and project images onto flat film or image sensor. A macro lens, on the other hand, is optimized to work flat subjects. Also, be aware that most macro subjects are flat like postage stamps or objects with limited thickness (contour). By inverting a “standard” lens, the rear elements, optimized work a flat, yield improved resolution when tasked to work in close.

Additionally, the object distance measurement is subject to forward nodal point. Whereas the focal length is a measurement taken rear nodal to image plane. These two cardinal points likely do not fall at the center of the lens barrel. In fact, they are likely spaced apart and they can even be flipped placing the rear nodal closer to the subject. Thus, inverting the lens improves resolution and likely grants a little additional magnification.

These improvements are likely to subtle meaning, don’t expect magic. In other words a true macro is your best bet.

\$\endgroup\$
1
  • \$\begingroup\$ My question was not about some resolution improvement, but about telecentric perspective (as in, get it to image isometrically) like some machine vision lenses have.... \$\endgroup\$ Commented Sep 13, 2021 at 16:34

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.