[MF3D.FORUM:176] Re: Welcome new MF3D'ers

[Greg Erker <erker@xxxxxxxxxxxxxx>]

>The ETRS is a 645 format while the Rollei is 6x6.  The "normal" lens for
>both is 75mm.  Since the 645 is basically just a cropped 6x6, would
>these two images be close enough for a twinned rig if I trim off the 6x6
>print?  Or is the 75mm different for each format?  Am I missing
>something?

  It might work, but likely not very well. They
are both nominally 75mm FL but might actually be 72mm
or 78mm say. The old JCII allowed +/- 5% tolerance
on the FL from the nominal AFAIR. (JCII was the Japan
Camera Inspection Institue that put those stickers
on cameras and lenses that many people never
remove).

  Another potential problem is distortion. One
lens might have 1 or 2% of barrel distortion
and the other could have 2% of pincushion
distortion. Would make for an image that is
hard to fuse. But if you are lucky they will
be similar.

  So I'd suggest trying it. The next time you
have slide film in both cameras aim them both
in the same direction and take a shot. You can
either try to make a stereo pair and then view
it to see how well it works. Or take an infinity
shot with lots of edges in it (eg. a city skyline).
Then overlap the two images and see how much
the magnifications differ.

  An ideal shot might have a row of buildings
running thru the center line of the image and
a fence running across the bottom. Use the buildings
to judge the percentage difference in the two
lens FLs and use the fence edge along the bottom
to compare the lens distortions.

  BTW it helps (with slide film) to overexpose
the shots 1/2 or 1 stop if you plan to overlay
them for measurements. Otherwise the sandwich
gets so dark you can't see where the building
edges line up etc. (With neg film underexpose
if you plan to overlay the negs).


Happy shooting - Greg E.