shooting 8x10 provia in available light

[Angi Welsch]

i have a question - i am shooting a series of portraits on 8x10 provia with only available light - i've been running into some trouble because the film is 100 iso and my exposure is usually f5.6 and 40 or f5.6 and 60 because i like to shoot in even light and because the exposure is slow(er) when i load the slide into the camera, there is a slight shift of focus. is there any way of avoiding this loss of focus? without having to bring in artificial lighting.

[David de Gruyl]

Is the film plane accurate for other films? I don't see how available light has anything to do with focus. What I mean is: can you shoot at 5.6 and check in brighter light / faster film? I suspect there might be an issue with the location of the glass wrt film holder.

Some shims might help (or removing shims).