Erratic Exposure with Canon EOS R5 + Canon RF 15-35mm f/2.8L — Lens Fails to Stop Down 

2021-11-11 • SEND FEEDBACK |
Related: Canon, Canon EOS R, Canon EOS R5, Canon Lenses, Canon mirrorless, Canon RF, Canon RF 15-35mm f/2.8L IS USM, exposure

This bug is a disaster when shooting a group of related images, such as an aperture series, focus bracketing, focus stacking, panorama, etc.

Canon EOS R5: Erratic Exposure Due to Failure of Lens to Stop Down

An apertures is shown with perfect matching exposures at f/2.8, f/5.6, f/8, f/11, but an f/4 which is wrong.

I have a tentative diagnosis—it appears that it is a failure of the lens to stop down. What I am as yet unsure of is whether it is lens specific (model, sample), or whether it is a firmware glitch in the Canon EOS R5. But I saw a similar bug back in 2008, so it appears that the bad/buggy code may have carried over into Canon mirrorless.

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Erratic exposure with Canon EOS R5 — lens fails to stop down fully

f2.8 @ 1/100 sec, ISO 100; 2021-11-05 16:27:10
Canon EOS R5 + Canon RF 15-35mm f/2.8L IS USM @ 15mm

[low-res image for bot]