[MF3D.FORUM:495] Re: Exact fl match for paired lenses.

[Greg Erker <erker@xxxxxxxxxxxxxx>]

>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?

  Read my web page on how I compared the FLs (basically
built a jig with shutter to hold the lenses and then
projected a target onto a large sheet of paper).

  I suspect everyones tolerance for missmatch is
different. For me, how the scene is placed behind
(or cutting) the window is very important to me
(ie I look at the edges of the photo) so unequal
cropping due to size missmatch is a big deal for
me. People who just enjoy the 3d scene without
looking too hard at the edges could tolerate and
enjoy much more missmatch than me.


>      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!

  Shimming one lens out to improve the size match
has the sideeffect of moving the focus point.
So the two lenses are no longer focused at the
same distance. If you like to shoot wide open
or have to shim a lot then this may not work
for you.

  In my case the 4 thou shim I moved makes the
focus points mismatch by 3 (I think) inches at
2m distance. It was barely noticable in my test
shots at f3.5 (newspaper laying on floor shot at
45 degrees) with a 10x loupe. At f8, the widest
I'm likely to shoot for real photos I couldn't
see the difference. And an MF viewer is only about
3x, not 10x.

  But if you have significant size missmatch the
focus shift from shimming may be greater than the
DOF you have at semi-close distances and wider
apertures.

  I could crunch some numbers for you if you get
a measurement for the missmatch (shoot some test
rolls). And tell me what apertures you think you'll
use.

  I don't know how the Mamiya's are constructed but
a camera tech could likely tweak it for you.

  Are these Mamiya TLR's you have or SLRs?

Greg