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

Started 5 months ago | Discussions
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?

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QuietOC
QuietOC Veteran Member • Posts: 5,327
Re: Suggested feature to fix focus shift for Tamron 24-70 G2

calin wrote:

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.

It more or less effects every lens if you check them carefully. SLRs could've implemented stop down focusing. Nothing necessarily ties it to mirrorless.

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

EF to E-mount adapters with native emulation allow stopped down focusing with EF lenses and would probably work with that Tamron.

Someone could theoretically design a native emulation EF adapter for RF cameras. It would be a lot of work compared to simply passing through the EF support already supplied.

Tamron doesn't seem to have any interest in creating adapters for their lenses--probably since they are a big OEM for other brands.

The Sigma MC-11 adapter for E-mount allows their Art, Sport, and Contemporary lenses to emulate native lenses including stopped down focusing. I am not sure how their MC-21 works for L-mount.

Many Sony A-mount lenses have pretty large focus shifts, but like Canon, Sony only allows those lenses to focus wide-open. Sony SLTs do a form of stopped down focusing for video AF--stopping down lenses to F3.5.

I notice my A7RIV does more wide-open focusing with native lenses than my previous Sony mirrorless cameras. That change may have stemmed from complaints about stopped down AF performance. There are trade-offs for both methods. It would be nice to have user controls for these behaviors. There are settings that effect it on Sony, but they are not obvious.

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

Thank for your feedback QuietOC.

I hope that Tamron has an eye of these threads and thinks about this. If they find a solution to the focus shift they become more competitive that even the Canon/Sony lenses. Currently, unless I manually focus, I can't use my Tamron 24-70 G2 in the F3.2-F8 50-70mm ranges. Also manual focus is complicated by the fact that I have to hold the depth of field preview while focusing to force the stepped down aperture.

Obviously "That change may have stemmed from complaints about stopped down AF performance. There are trade-offs for both methods. It would be nice to have user controls for these behaviors." would be best if the camera is handling it but there is also an opportunity for 3rd party lenses, via firmware, to take the lead.

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Tord S Eriksson
Tord S Eriksson Forum Pro • Posts: 15,490
Re: Suggested feature to fix focus shift for Tamron 24-70 G2

calin wrote:

Thank for your feedback QuietOC.

I hope that Tamron has an eye of these threads and thinks about this. If they find a solution to the focus shift they become more competitive that even the Canon/Sony lenses. Currently, unless I manually focus, I can't use my Tamron 24-70 G2 in the F3.2-F8 50-70mm ranges. Also manual focus is complicated by the fact that I have to hold the depth of field preview while focusing to force the stepped down aperture.

Obviously "That change may have stemmed from complaints about stopped down AF performance. There are trade-offs for both methods. It would be nice to have user controls for these behaviors." would be best if the camera is handling it but there is also an opportunity for 3rd party lenses, via firmware, to take the lead.

Just a thought:

If it would be one of my Sigmas that misbehaves I could use my dock, I believe, as it can be used to reset the focusing of the lens at various distances and focal lengths.
And Tamron has a similar dock?!

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Owner of a handful of Nikon cameras. And a few lenses.
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OP calin Forum Member • Posts: 97
Re: Suggested feature to fix focus shift for Tamron 24-70 G2

Tord S Eriksson wrote:

calin wrote:

Thank for your feedback QuietOC.

I hope that Tamron has an eye of these threads and thinks about this. If they find a solution to the focus shift they become more competitive that even the Canon/Sony lenses. Currently, unless I manually focus, I can't use my Tamron 24-70 G2 in the F3.2-F8 50-70mm ranges. Also manual focus is complicated by the fact that I have to hold the depth of field preview while focusing to force the stepped down aperture.

Obviously "That change may have stemmed from complaints about stopped down AF performance. There are trade-offs for both methods. It would be nice to have user controls for these behaviors." would be best if the camera is handling it but there is also an opportunity for 3rd party lenses, via firmware, to take the lead.

Just a thought:

If it would be one of my Sigmas that misbehaves I could use my dock, I believe, as it can be used to reset the focusing of the lens at various distances and focal lengths.
And Tamron has a similar dock?!

That was the first thing I've done.  However, it had no effect.  I've read later that in mirrorless cameras (Canon at least) Tamron, and maybe other lenses, aren't using the the focus processor hence the Tap-in console (docking for Sigma) adjustments have no effect.

Still trying to fully understand why.  The good thing is that the focus is spot on wide open independently of the focusing values I enter.  Also, in manual mode, when depressing the depth of field preview, the "triangles" focus helpers are also spot on.

This is why I hope that autofocus with step-down aperture will produce a good result.

Note, this is a very different behavior from my Canon 5 Mark iV where the setting have an impact.

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

The camera is Canon R5

The focus distance is at 0.7M

Center crop.

The first row is Tamron 24-70 G2 autofocus

Second Tamron manual focus at F4 then picture taken at different apertures (with the previous manual focus at F4). Note that Tamron when focusing close the real max focal length is 63mm.

Third row is the Canon RF24-105 at 63mm and various apertures starting at 6.3.

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It's really clear that Tamron needs to be manually focused to obtain max sharpness (hence the proposal in the thread)

Surprisingly, Canon is [marginally] sharper at 63mm than even the manually focused Tamron which is a great copy of the lens. Canon did great for that small lens!

 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
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