Polaroid Alignment Issue.. Forward Focusing?

[mandonbossi]

Hi everyone, This is my first post here although I have followed it for a while for various problems I have had before. I currently have a Chamonix 45 and both the Xenotar 135 3.5 and the 150mm 2.8. I like the "wide open" look that these lenses give and have had success with getting sharp results with both (after I took out the original Chamonix screen and had a Maxwell screen properly installed). I have recently started shooting some Fuji Instant as well as some older Polaroid in both the 54 Fuji Holder as well as the 3.25 x 4.25 Pack size back and am convinced that both of these products are forward focusing from what i have focused on the GroundGlass! I realise that Instant Film is inherently "soft" but i have conducted a number of set shots and there is definitely a sharper point in front of what I had focused on.. This seems to be most prevalent in 3/4 type shots (if you imagine you were shooting a portrait) and less prevalent with extremely close up shots (I took one of newspaper print C/U and this seemed OK but still forward focusing).

When I have actually shot people with it and advised them to stay extremely still, the focus shift seems enough for them to look out of focus (in 3/4 shots) and not so bad when shooting them C/U (as in a head shot)

When I had my GroundGlass installed it was sent to Bill Moretz at ProCamera and he aligned the GG to sit exactly at the film plane. Could this have shifted it out so that it was perfect for film but put instant out? I know Instant is generally used for exposure testing and the like but i do like to use it for "finished" images when shooting people.

If it was actually focusing forward, would that mean I would need to add some to the backs or shim some material away? Either one would be extremely difficult as both are made of plastic but especially if it involved shimming away material...

Anyone else ever experienced this problem? Or am I just expecting too much?

Ok, Thanks so much in advance, any thoughts or advice would be greatly welcomed..

Best Regards Mandon

[mandonbossi]

Anyone at all? Am not sure quite where to go with this problem. Was thinking that I do actually have another back/groundglass combo for this camera (the one that had all the fresnel issues) so maybe I could send that off and that could be shimmed? If focusing forward means that some has to be taken off the back...

Can anyone confirm this? Ok, thanks again, look forward to hearing some responses.

Best Regards Mandon

[John Koehrer]

The term shim usually refers to adding or removing thin washers(shims) or sheets of metal.
It may be easier to experiment with the front standard rather than the rear. The results are the same. You can add paper or cardboard spacers behind the lens to move it forward. to move the lens backward in the front standard you would need to be able to move it into the board with a recess of some sort.
Have you tried simply adjusting the focus by a tad bit? IE:Focus, then move the standard forward and make a test shot if it's worse adjust the standard back & make a test. That would at least tell you which direction to make the adjustment.

Is it possible that you're experiencing focus shift as you stop the lens down? Check this by focusing wide open and watch the GG as you stop the lens down. If this happens, you just adjust final focus with the lens stopped down.