Minimum aperture on adapted lenses for micro 4/3 bodies

msteen1314

Okay, so I finally took the plunge.

I've been very hesitant to digital format in a serious way and micro 4/3 seemed to be the most likely candidate considering the lenses I already own.

Not wanting to spend too much on something I wasn't 100% sure of, I was able to purchase an Olympus EP-1 in a local online classified add for $50.00 Canadian. I figured at 50 bucks I can't let the opportunity pass.

So far the 14mm-42mm has worked well and while I've only had the camera for a week, I'm quite pleased with the find.

One question. While I understand that the focal lengths on adapted lenses will double due to the 2x crop factor, but will the minimum aperture also double?

I never thought that this would be the case however in reading an article online it stated that it would. Any help would be appreciated.

fermy · Joined: 17 Feb 2012 Posts: 2877

You probably mean maximal aperture (smallest f-number). It is a physical property of the lens and therefore is independent of format. What you've heard is the so-called "equivalence theory", according to which a 50mm f1.4 lens on m4/3 behaves like a 100mm f2.8 lens on a full frame camera. This is correct for depth of field calculations, but is incorrect in terms of exposure. If you fix your ISO (say set IS0=100) and set the aperture @ f1.4 in aperture priority, you will get exactly the same shutter speed on full frame and m4/3.

So to summarize, on m4/3 your 50mm f1.4 lens will behave like f1.4 lens in terms of exposure and like 100mm f2.8 in terms of framing and depth of field.

msteen1314 · Posted: Sat Jun 22, 2013 1:05 am Post subject:

Thanks Fermy, it didn't seem correct.

After all having a Voigtlander color skopar 25mm f4 become a 50mm f8 hardly seemed worth all the effort.

I appreciate the detailed and thoughtful explanation.
Martin