Re: 6x6 and lenses shoter than 80 mms

[P3D Greg Erker <erker@xxxxxxxxxxxxxx>]

I think John B wrote this:

>>If you use a lens shorter than 80 mm in
>>the 6x6 format, you'll have no end of trouble finding something with
>>which to view a transparency.  Either the coverage will be inadequate
>>or the aberrations will be insufferable or the price will be out of
>>anyone's range because you'll need custom designed and built optics.

Dale Walsh responded:

>What exactly do you mean by this?  Why would prints be easier to
>view that transparencies?  I have a 65 mm lens for a Mamiya C330 so I
>am interested in knowing why a regular 6x6 transparency viewer
>would not work.


  John B is known as orthoman, so he was talking about the
ortho case (where you view the transparancy with the same
FL lens as the cameras taking lens). Thus a shorter FL camera
lens requires a shorter FL viewer lens. An 80 mm FL by 35 to
40 mm dia achromat can be found for between $15 and $80.
And it will work well as a viewer lens.  A 65 mm FL achromat
of sufficient diameter will be more expensive and probably
have more distortion, or won't cover the corners of your
6x6.

  If you are willing to view with a longer FL and live with
the stretch in the depth, they you can shoot with a wide
angle camera lens.

  On to prints: Suppose you view your 2x2" transparancy with
an 80 mm lens to get an ortho view.  If you make a print from
it that is 4x4" the proper viewing lens is now 160 mm FL.
This is a lower power lens and should be cheaper. In fact, a
single element lens may have low enough distortion that you
no longer require an achromat. In this case the cost would
be much lower.

  One problem with viewing a pair of 4x4" prints is that
the infinity points will be separated by about 4" whereas
your eyes are only separated by say 2.5". You either have
to diverge your eyes or view through the lenses offcenter
like in a old stereoscope.

  So using 4x4 prints makes the ortho lens easier to build
but causes a new problem.

Hope this helps - Greg E.



------------------------------