Piers wrote
>
> That was my first thought, Brian, but after further contemplation, I
> speculate that if the flatness of the back is not matched to the flatness
> of the image produced by the lens, then any chromatic aberrations (there
> must be some) would be exaggerated. In fact, I suspect that a "good" 612
> back does *not* have a perfectly flat film plane, rather one which is
> slightly curved. By how much might be an interesting question.
>
> Piers
>
> -----Original Message-----
> From: Brian Swale [mailto:bj@xxxxxxxxxxxxxxx]
> Sent: 17 August 2010 04:18
> To: olympus@xxxxxxxxxxxxxxxxx
> Subject: Re: [OM] 612 film back advice is needed.
>
> --snip
>
> I have bought a 6 x 12 back for my Linhof Technica ( it came available
> locally) but have not tried it yet.
>
> I fail to imagine how a camera back can yield colour shift.
>
> Can somebody please explain?
I think image 032 shows a need for a circular neutral gradient filter at f/5.6
Alternatively, try exposing at f/16 or f/22.
As for image 031, I'm puzzled. if it is due to the film plane not being in a
(non-flat) plane as (postulated) required by the lens, I'd expect significant
out-of-focus effects - and I could not see any of them clearly.
I suggest trying the 6 x 12 back again with stringent quality controls, such as
...
Maybe a different batch of film, that has been stored refrigerated.
Maybe a type of film that requires a different developing process.
Load the camera in a dark place
Use f/16 or f/22
Unload the camera in a dark place and keep the exposed film well protected
from light until it gets to the photo store or wherever it is processed..
Hope these suggestions are useful.
When I get a chance (won't be until the weekend as tomorrow I am 250 km
away with my partner taking her to hospital for a cataract operation and we
will be away 3 days) I will hold a straight-edge to the film rails of my 6 x
17
and see if that reveals curvature.
Brian Swale.
--
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