Backfoucs

[DP Marcus Larsson SE]

Hello witch is the best way to check the back focus on the Raven? i don't have the Focus hook.

Best Marcus

 

[ericyoung]

The procedure to adjust Flange Focal Distance (FFD) is basically the same with any camera.

Although you don't have the focus hook, there are body markings to indicate the sensor plane (looks like a circle with a line through it). Use that as your focus distance measuring reference.

If you don't have a dedicated FFD calibration tool, you should use your widest lens on the widest setting with an aperture closed down a couple of stops from wide open (to maximise centre sharpness). Put a focus target like a Siemens Star (one printed A4 or bigger from the internet works fine), filling as much of the frame as possible at a known distance from the sensor plane eg 5 or 6 feet, and check that the lens is in sharp focus at that distance when the focus ring is aligned to that distance. If not, adjust the FFD following the procedure in the camera's operation manual.

Also a good idea to check at other distances where the lens has a marked distance. It may be that you have to compromise between getting two or more distance markings slightly less sharp over a single marking being perfectly sharp.

This does assume that your lens has accurate calibrated lens focus distance markings and that the lens itself has a correct FFD. If you have more than one lens, there's no guarantee they will all have exactly matching FFDs, but it's best practice to get the widest angle one correct first, as the shortest focal lengths are more sensitive to incorrect FFD than more telephoto ones which have more leeway.

With a zoom lens, especially stills lenses, the lens should be made simultaneously sharp at the fully telephoto and fully wide focal lengths (may have to go around the FFD adjustment at both ends a few times to find the best compromise), but expect that it will go out of focus zooming in between (ie not parfocal).