Re: Lens matching & Mamiya TLR Q

[erker@xxxxxxxxxxxxxx (Greg Erker)]

>Not really, but if I didn't have to take much apart, I
>could borrow a camera from a friend or a store and slap
>it on the bench for a quick test.

  Good point. Are their any other Dia's in MN?  Or do
you have them all :)

>That would work.  My vision was to ship only this little
>bench projector set-up with instructions on exactly where
>to place it relative to the screen.  This could very well
>be too inacurate for these tests.
>
>Maybe we could scale the system down and project onto a
>reasonably-sized ground glass (4"x5"?).  Then we could
>build and ship the whole contraption along with tracings
>of each lens test on the ground glass.
>
>>   One thing I'm not sure about, regarding this

>I don't know either...

  We'll ask Sam when he returns. I'm pretty sure
he was doing this with his Stereo pro. In fact he
started out with 3 element lenses and upgraded
to 4's since the threading on the Yashikas is
consistent.

---

  My plan B is to use the camera body as a projector.
If I put my test grid slide at the focal plane and
blast some light through the back (for a short while
with the shutter open on B) I can project on the wall
by playing with the focus.  Ideally I want the test
points to be more than 200mm apart on the wall. That
way a measurement error of 1/2 mm causes me an error
of only 0.25%.

  But what I'd like is for the camera body to be
focused at infinity. But then my slide won't be
in focus (at least not closer than 50 feet).

  But if I use a piece of glass as a spacer (1/8"
or 1/4" stuff) the image will be in focus at a
reasonable distance and a reasonable size that I
can mark it on a big sheet of paper.

  Swap the body, focus at infinity and repeat.
Then send the spacer and test slide to you. I could
send the marked up paper also if necessary in
a poster tube.

  I tried a bit of this by replacing the normal
bulb in my luxo lamp with a halogen 60W spot
light. Aim it at the camera back, have a diffuser
between the light and slide. Used a thin glass
as a spacer (blank 2.5x2.5 hologram). Seemed
to work though I wasn't seeing the whole slide
at once. Not enough diffusion I think, and not
enough light control (the halogen light was
illuminating the wall also).

  I think it's workable.

  If only the Dia/225 opened like the Ricohflex's.
Then the tripod screw would still be usable
when the backs open.

Greg

  BTW I asked a question about whether Mamiya
matched the TLR lenses on rec.photo.mf.  It's
phrased so 2ders can understand.

Text follows:
  I have heard that the taking and viewfinder
lenses are the same (and thus interchangable)
on these cameras. True?  (I'm primarily interested
in the 80mm f2.8 black ones.)

  If you repair your viewfinder glass by replacing
it with glass from a second lens/shutter will
your focusing be off?  To phrase it another way
did Mamiya match the focal length of the taking
and VF glass, or is their normal manufacturing
tolerance close enough it doesn't cause problems?

  It seems to me if the FL's were mismatched by
5% (say 80mm and 84mm) and they were calibrated
to both focus at infinity. But when you focus
in, say at 3 ft, the focus point of the VF will
be quite a bit different than the taking lens.
Thus it would seem they would need to match the lenses
in manufacture.

  Thus^2 you might run into trouble if you mix
glass from two different lens/shutters together.

Thanks - Greg E.

---end---