Suggested feature to fix focus shift

Started 2 months ago | Discussions thread
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calin Forum Member • Posts: 97
Suggested feature to fix focus shift

A reminder that focus shift is an issue specific with certain fast lenses and results in the focus plane not been the same at all apertures.

As cameras are focusing wide open and change the aperture to the specified one when the picture is taken, the lenses suffering from focus shift will not focus well.   There are few Canon and 3rd party lenses that suffer from this issue.

I will follow my findings with my Tamron 24-70mm G2 @ 70mm-50mm focal range.

When focusing closer 0.3-3m with the EOS R5 the focus is acquired at F2.8.   If the picture is taken at F4-5.6 the result is worse than F2.8  and requires manual adjustment of the focus at the new aperture.

With my Canon 5D mark iv Tamron uses it's focusing processor which can be calibrated.  I've calibrated it such that images at 50-70 mm are clear at F4 (loosing the option to have clear F2.8 @ 50-70mm)

However, mounted on a mirrorless camera, the focusing processor is bypassed and the trick above can't be made.

The solution I'm suggesting Canon to add is a feature for focus shift lenses:

- Max affected focal range    xxx

- Min affected focal range   yyy

- Min focusing aperture F zzz

In the Tamron case:  xxx = 70,  yyy = 50 and zzz = F4

How it works:
If the focal range is outside the yyy to xxx

do nothing

else

If the picture aperture F is less (numerical ex 3.2) than F zzz

use the picture aperture

else

use F zzz

-- hide signature --

Having the feature above handled by Canon would help Canon will all its fast lenses.  Otherwise, Tamron and other 3rd party lens manufacturers may release another firmware for their lenses that will put Canon in disadvantage as Canon lenses can't be firmware updated.

 calin's gear list:calin's gear list
Canon EOS 70D Canon EOS 5D Mark IV Canon EOS R5 Canon EF 50mm F1.8 II Canon EF-S 17-55mm f/2.8 IS USM +5 more
Canon EOS R5 Panasonic Lumix DMC-G2
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