Focus Trim on Phase One XF

[Bill Caulfeild-Browne]

Having just installed Update #4, I'm now re-doing the focus trim for all my lenses. I'd be interested in any views on the focal length I should use for the SK40-80 zoom.

One logic says that trimming at the longest focal length (80) is best because any slight shifts with zooming would be covered by the extra DOF at wider angles. Another says to use 60mm, right in the middle of the range, as the best compromise.

There are some great techies on this forum so I seek your better educated advice!

Thanks
Bill

 

[DrakeJ]

This is not a techie advice, but my philosophy was/is, trim at the focal length you use the most.

 

[Steve Hendrix]

Having just installed Update #4, I'm now re-doing the focus trim for all my lenses. I'd be interested in any views on the focal length I should use for the SK40-80 zoom.

One logic says that trimming at the longest focal length (80) is best because any slight shifts with zooming would be covered by the extra DOF at wider angles. Another says to use 60mm, right in the middle of the range, as the best compromise.

There are some great techies on this forum so I seek your better educated advice!

Thanks
Bill

Our XF Expert (I call him the XFpert) Brad Kaye recommends trimming the zoom at the long end. In our experience, having trimmed hundreds of lenses, we have not see focus shift when zooming from 40mm - 80mm (and vice versa). As a result, using the largest magnification for viewing will produce a more accurate focus trim.

This was covered in great detail on our recent XF Advanced Training Tour:

https://captureintegration.com/the-xf-xpert/
https://captureintegration.com/capture-integration-xf-road-tour/
https://captureintegration.com/advanced-phase-one-xf-camera-gallery-tour-wrap-up/



Steve Hendrix/CI

 

[med]

Is the 40-80 truly parfocal, in that you can zoom in, focus, and that the lens maintains that focus point throughout the zoom range? If so I would probably stick with your first option and do the offset for 80mm. But I also like the idea of doing the focal length you use the most.

 

[ejpeiker]

Unless you only use the lens at a single focal length, it is usually best to do the calibration at the longest focal length. As for the other comment on the parfocal nature of the lens, it is very close to parfocal but not perfectly so. If you focus on your subject and then zoom out, you will typically easily be covered within the DOF range at 40mm even with the lens wide open but if you focus at 40mm and then zoom to 80 mm, focus will be slightly off but not by much. The 75-150 is nearly perfectly parfocal though.