Suggested feature to fix focus shift

Started 5 months ago | Discussions thread
Sittatunga Veteran Member • Posts: 3,660
Re: Suggested feature to fix focus shift

calin wrote:

Sittatunga wrote:

But Canon lens' firmware can be updated, through the camera, in a similar manner to updating the camera firmware.

As PAntunes says, stopped down focussing avoids focus shift if the spherical aberration correction isn't very good. It does slow things up a bit and it's not as precise if the lens doesn't suffer from focus shift. The match-triangles manual focus aid can work stopped down seven stops, depending on the lens, distance and subject contrast, though it can struggle stopped down only four stops with a low contrast subject. That's usually ok though, as the worst case for focus shift is about two stops down; more than that and the depth of field should be big enough to cover the focus shift. Focus shift was less of a problem with classical SLR prime lenses which were usually designed to be focussed at full aperture and stopped down at least a couple of stops.

Agree Sittatunga manual focus is a way around the issue but even with the new R5 focus helpers it's harder to focus especially if you pass the camera to someone else. I'm proposing a way to enable autofocus even throughout the lens range.

Focus shift is not a problem I've noticed with any of my lenses; that could be because most of them are DSLR lenses and my mirrorless lenses are APS-C slow zooms or fast manual primes.  I find the match-triangles manual focus aid of the EOS R quick and magically easy to use, but I've used cross-prism screens or coincident image rangefinders for decades.

I know Sony have avoided the problem by using stopped-down AF. While that simplifies lens design for nice bokeh, it causes problems in very low and bad lighting, unless you are using it at full aperture which eliminates both problems. I can't help feeling that it would be simpler for Canon just to allow AF with the stop-down button pressed.

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