Focus shift - can live view focus stopped down?


WaypointCharlie

Link Posted 25/10/2019 - 15:18
pschlute wrote:
Also get the camera to focus each time from the extremities (infinity or closest distance). It does make a difference.

That's a big factor with some of my lenses. On the screw driven 18-250 I think it makes a difference of as much as 2/3rd depth of field (wide open). It's something I commented on years ago. The SDM driven 18-270mm is a big improvement and there's hardly any difference in acquiring focus from near or infinity.

I know what I'm seeing with the refocussing with changes in aperture. I'm not imagining it and it surprised me. It looks like an attempt to compensate for focus shift, but it's acting in the wrong direction!

WaypointCharlie

Link Posted 27/10/2019 - 16:35
This was from the 18-270mm this morning at 270mm and f/9.0. It's not going to be the finest lens at 270mm, but still useable I think. At this distance it didn't seem to front focus.

Unless you have good light it means using a tripod if you want low ISO (this was 1/4s ISO 80). A tripod rather negates a lot of the convenience of a 'travel zoom' - you might as well carry a better lens!


Lubbyman

Link Posted 27/10/2019 - 17:13
WaypointCharlie wrote:
This was from the 18-270mm this morning at 270mm and f/9.0 ...Unless you have good light it means using a tripod if you want low ISO (this was 1/4s ISO 80). A tripod rather negates a lot of the convenience of a 'travel zoom' - you might as well carry a better lens!

At f/9.0 and ISO 80, any 270mm lens, no matter how 'good', would need the same 1/4 sec exposure for that shot so you'd still need a tripod. Isn't ISO 200, 400 or even 800 OK with your K5iis (can't speak from experience, I jumped from K20D to K3)? And then there's SR. And if you need more stability, try using a handy tree, post, fence (etc.) for support. I've even used a child's shoulder to get a longish exposure!

Steve

Jonathan-Mac

Link Posted 28/10/2019 - 08:28
Focus shift is where the point of focus varies slightly with the aperture used and therefore cannot be avoided by using live-view focusing, unless the lens is actually stopped down to the aperture to be used while it's focusing.
Pentax hybrid user - Digital K3 & K200D, film 645 and 35mm SLR and Pentax (&other) lenses adapted to Fuji X digital
Fan of DA limited and old manual lenses

JAK

Link Posted 28/10/2019 - 17:06
Have you tried another camera yet to eliminate a problem with the one you normally use?
John K
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