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A question on optics, macro lenses and crop-sensor cameras

Started Sep 27, 2020 | Questions thread
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Larry Cunningham
Larry Cunningham Senior Member • Posts: 1,228
A question on optics, macro lenses and crop-sensor cameras

As I reported in a post in this forum earlier today, I bought a Venus Optics Laowa 25mm f/2.8 2.5-5X Ultra-Macro lens to use with my Canon EOS M5 mirrorless crop-sensor camera.

The lens is designed for EF (full-frame) Canon cameras and requires a Canon Mount Adapter EF-EOS M to work with the M5.

First, it's my understanding that using the lens with my M5 makes the effective focal length 40mm (25mm x 1.6) (please correct me if I'm wrong). Does using this lens on a crop frame camera change the effective magnification ratios from 2.5-5X to 4-8X?

How does all this affect depth of field at any given aperture? Is the depth of field correspondingly more shallow than when the lens is used with a full-frame camera?

Before buying the lens, I read about diffraction limits when designing ultra macro lenses like this. Does using this with my crop-frame camera make the diffraction worse?

Thanks for any insight!

Larry

 Larry Cunningham's gear list:Larry Cunningham's gear list
Canon EOS M5 Canon EOS M3 Canon EOS M6 II Canon EOS R7 Canon EF 50mm F1.8 II +20 more
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