[MF3D.FORUM:494] Re: Exact fl match for paired lenses.

["Bill Glickman" <bglick@xxxxxxxx>]

Greg

Thank you for the input.  How did you discover the % difference in fl's of
the 5 lenses?   Did you shoot test targets without moving the camera body?
What tolerance would you say would be acceptable after you advise me of how
best to test the lenses?

      If the fl's are off by more than the tolerable %, can I send them off
to a lens shop and have them make the same adjustment you did?  If so, does
anyone know of a lens shop that could accomplish such a task?  I can not get
5 Mamiya lenses to choose from, I would be forced to buy them all then sell
4 of them at a big loss!

Bill





> >I recently bought a second Mamiya 80mm lens. Now I can now shoot with 2
> >bodies side by side with a dual cable release.  I realize that lenses
must
> >be identical fl on each camera for proper stereo viewing.  And the
labeled
> >fl can vary from batch to batch.  These were purchased 2 years apart.
> >
> >1.  What is the best way to determine if this lens matches my other 80mm
> >lens?
> >2.  How close does the match have to be?  +/- 1%
> >3.  What is the effect in the viewer when lenses are not identical, but
are
> >within say 1%?  Is there some break point where things become noticeable,
> >like greater than 2% for example...
>
>   In a window-less stereo system you
> could probably tolerate 3% or more of
> size missmatch if you line up the centers
> of the images. Many people with differing
> eye-glass prescriptions for their two eyes
> have larger image differences for their
> two eyes.
>
>   But when you take your two different
> sized images and mount them in a slide
> mount (with two same sized openings)
> then the image size differences become much
> more visible.
>
>   If you align the bottoms and there
> is no detail at the top (sky for example)
> then the differences are hidden. So 1%
> should be no problem.
>
>   But if there is fine detail at the top
> and bottom then the different cropping
> on L versus R will be very visible.
>
>   When I was building my stereo Ricohmatic
> 225 (SR225) I had 5 sets of lenses to pick
> the best matching pair. The best ones matched
> to 0.35% but I wasn't completely happy* with this
> so I shimmed one lens out a few thou to reduce
> the size difference to 0.13%. Then I was happy.
>
> * the mismatch at the top was visible when
> the bottoms were aligned (test roll shot of
> my brick fireplace).
>
>   Also FYI the RBT 35mm mounts have offset
> adjustments of 0 to 0.4 mm in 0.1mm steps.
> The image height is 20-some mm so the steps
> are less than 0.5%. So RBT thinks aligning
> images to this small amount is worthwhile.
>
>   My SR225 page:
> http://www.angelfire.com/ca/erker/twin225.html
>
> Greg E.
>