Suggested feature to fix focus shift for Tamron 24-70 G2

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calin Forum Member • Posts: 97
Suggested feature to fix focus shift for Tamron 24-70 G2

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. In my case, 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.

I really like the lens and want to continue to use it. However, with the current handicap my new Canon RF 24-105mm F4.0-7.1 IS STM is way better unless I manually focus the Tamron @ 50-70mm.

I have a related thread in the Canon EOS R forum, https://www.dpreview.com/forums/thread/4590045#forum-post-65349331, but I think either Canon or Tamron can address the issue independently.

The simplest way for Tamron will be to limit the lens to F4 @ 70mm and F3.2 @50mm using TAP-in utility.

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A more complex solution would be to limit the lens to F4 @ 70mm and @50mm if the depth of field preview button is depressed while the lens is in the 50-70mm range and F larger or equal to 4.

The limitation would be removed if the lens focal selection is below 35 mm.

Usage of the more complex solution:

-Zoom,

-press the depth of field preview button

-Focus

If the focal range is 50-70mm and aperture was set above F4 the camera will think the min aperture is F4 and will focus at F4 addressing the focus shift.

If the aperture was below F4 the camera will focus at f2.8 and the result will be great for 2.8 and ok for 3.2

To put back the aperture to F2.8 for the 50-70mm range temporarily zoom out to 35-24 mm

Any thoughts?

 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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