Canon HF11 + Brevis 35 -- Film Back measurement ?

[Rob O'Day]

I have 0 idea where this thread should go, so here will do for now.

I need to work out the film back measurement for my set up, however I know this is going to be tricky !
I'm told that usually the film back measurement would be 35mm on the brevis, however, since I have to zoom into the ground glass, this changes. Is there some way of me being able to measure what it is ?

(yes this is for matchmoving)

[Bob Hart]

By back measurement do you mean


camcorder >> achromat >> condenser (if fitted) >> groundglass

or

groundglass >> dust excluder glass or condensor (if fitted) >> film camera (Nikon??) lens.


For Nikon F-mount tyle lenses the Nikon flange to focal plane distance in air is 46.5mm. If there is a condensor or thick flat glass in the path, this may be different.


If you are meaning to exactly match the camcorder zoom setting shot for shot, then the only way I can see this happening is to make up a framing chart with the camera hooked up to an underscanning monitor. The best zoom-in position for the groundglass on this camera is established by viewing the image while placing your entire range of lenses on the front mount.

Make sure your widest lenses are not vignetting or suffering from edge or corner brightness falloff problems with that zoom position. Your "apparent" image sharpness or resolution will be better the wider your camera's view of the groundglass is. However, the widest setting that works may not suit all lenses in your kit.

You will have to decide what is best for you. You could make more that one framing chart to give you more than one choice of accurate zoom-in framing tailor made to individual lenses but I would not bother as the differences in apparent resolution or sharpness might be observable from shot to shot.

The outline of the image frame is marked on a blank chart which is mounted to the camera and seen by the camera. Then an accurate outline is marked inside the underscan image frame to accurately represent the camcorder's own viewfinder frame.

The distance from chart to camera and its position relative to the image frame of the camera has to be accurately repeatable, probably a very precise mounting to the tripod baseplate or some sort of jig to relate it accurately to the front of the camera.



Please do not take this reply as having authority. Hopefully Dennis Woods will chime in as he will know his own adaptor best.