Reversed wide macro lens performance

Thagomizer · Post by **Thagomizer** » Thu Feb 28, 2019 10:32 am

Would a reversed macro lens (either on the camera or stacked on a longer focal length lens) give better results than a reversed non-macro lens of the same focal length? I'm thinking of focal lengths shorter than 50mm and magnifications greater than 1:1. I've seen Thomas Shahan's results from reversed 28mm lenses and was wondering if a reversed wide-ish macro would perform even better. Just curious.

Lou Jost · Post by **Lou Jost** » Thu Feb 28, 2019 2:50 pm

The macro should give better flatness of field and quality wide open (especially at lower m), but it won't give higher magnification reversed than any other reversed lens of the same format. Might even do worse at high m.

ChrisR · Post by **ChrisR** » Thu Feb 28, 2019 4:39 pm

If you think about the "conjugate distances", ie the image ond object distances it's designed to work at, then a reversed macro lens should have an advantage.
If say your macro lens is optimised for half life size, and you reverse it, you could expect it to be good at twice life size.
However, you're probably only using the middle of its field, so a better optimised lens should beat it.

If it's a wide-angle lens, such as a retrofocus designed 28mm for use on full frame, then the designer had to make compromises for that. Something like the better of the Nikon 28mm lenses (the 8 element one) isn't bad at all reversed.
There are no 28mm macro lenses afaik.

Lou Jost · Post by **Lou Jost** » Thu Feb 28, 2019 5:15 pm

"If you think about the "conjugate distances", ie the image ond object distances it's designed to work at, then a reversed macro lens should have an advantage."

Yes, but that's also why a reversed macro lens may not be as good as a reversed normal lens for high magnifications. A lens optimized for infinity (m=0), when reversed, is optimized for m=1/0 which is a very large number

For small m, the reversed macro lens is best, and for large m, a reversed normal lens could be better, though a microscope objective or stacked lenses would be better still.

ChrisR · Post by **ChrisR** » Thu Feb 28, 2019 5:52 pm

Sure, that's why I wrote "twice life size", Lou. Even a fairly close-focusing normal lens would have to be at a very high magnification when reversed, for the conjugate distances to be right.
And as you say they don't work very well like that.

Thagomizer · Post by **Thagomizer** » Fri Mar 01, 2019 11:47 pm

ChrisR wrote: If it's a wide-angle lens, such as a retrofocus designed 28mm for use on full frame, then the designer had to make compromises for that. Something like the better of the Nikon 28mm lenses (the 8 element one) isn't bad at all reversed.
There are no 28mm macro lenses afaik.

I was thinking of the Pentax 35mm f2.8 macro, which I hope to add to my roster at some point. Not really "wide" on APS-C, but wider than the 50 or 70mm Sigma macros I've got. I know that reversed it would give greater magnification than a 50mm, but was curious about how it would compare with a normal 35mm. Sounds like not necessarily better, from what I'm hearing here. I was hoping someone might have tried these out and made the comparison themselves. I'll have to play with my Sigma 50mm macro and compare it to my SMC Takumar 50mm f4 macro (which is 1:2) and non-macro 50s. I've already got a number of ways to get 1:1, but more ways to go beyond 1:1 are always welcome. Microscope objectives are a definite wish list item, too.

Lou Jost · Post by **Lou Jost** » Sat Mar 02, 2019 5:07 am

You haven't mentioned what magnification you are seeking. If you are seeking 2x or 3x, that Pentax lens might be very good. The lenses you already have would work well at those mags, with more extension (which is cheaper than buying a lens). A very good economic lens option at 3x is the Lomo 3.7x objective. Go to Robert's website (www.closeuphotography.com) for extensive tests of many options, which usually mention"best value" options as well as high-end winners.

Thagomizer · Post by **Thagomizer** » Sat Mar 16, 2019 9:34 pm

I guess I don't have a specific magnification in mind, I mostly just mess around with whatever I happen to have. I should really sit down and test & try the various combinations of reversal, extension and stacking with the lenses I've got to find out what works best for what. Just doing that would keep me busy for quite some time!

Both the Lomo you mention here and the Amscope 4x that Robert mentions as a good bargain objective are contenders for my first microscope objective. Either one looks to be a winner.