[MF3D.FORUM:1182] Re: How much shift can be necessary to set the window?

["Michael K. Davis" <zilch0@xxxxxxxxxxxx>]

Paul,

Thanks for the valuable feedback!  I'm not surprised I overlooked something
- lots to learn here...

Having read your comments about three times and played with the numbers a
bit, I feel dashed at the prospect of settling on 50x50.  Letting go of any
hope of conformity with other peoples' viewers, I suppose I could do 50x63
with a mirrored viewer.  Consider the advantages over 50x50:

50x63 would make an 80mm lens more like a 43mm on 35mm format, vs. 49mm.
50x63 would offer a 13.75% larger diagonal vs. 50x50
50x63 would increase area by 26.0% vs. 50x50 (3150 sq. mm vs. 2500 sq. mm)
50x63 yields the dominant, if not esthetically preferable, 4:5 aspect ratio
50x63 would allow a mix of portrait vs. landscape orientations
50x63 would simply make the best possible use of a 6x7 frame

Thanks for kicking this around with me!

Mike


At 10:15 PM 8/29/00 -0500, you wrote:
>"Michael K. Davis" wrote:
>> 
>> For folks using 6x6 cameras to produce your chips for 50mm x 50mm RMM
>> mounts, for example, do you ever find yourself wishing you had more of a
>> margin horizontally, for setting the window?
>
>The Sputnik produces 55x55mm images, and there is plenty of room
>to set the window in the 50x50mm mounts.
>
>> I'm considering a larger mount, using 6x7 chromes.
>
>Which mount would that be?
>
>> My camera produces a 55x68mm image.  Ignoring
>> any other "gotchas" for the moment, does anyone think a 50x63mm window is
>> too large, horizontally?
>
>Yes, I think it is too wide.
>
>> I know that only leaves 2 mm between images, if
>> centered at 65mm,
>
>I believe you've forgotten to take into account the deviation.
>My guess is you chose 65mm to stay within the constraints of
>a normal parallel viewing viewer.  But 65mm is a reasonable
>figure for maximum *infinity point* spacing.  To allow for up
>to 3mm of on-film deviation, you should plan to space the two
>film chips no more than 62mm apart.
>
>The RMM MF stereo mounts have apertures spaced 62mm apart.
>Coincidence?  Or simply brilliant design?  I say we give
>Joel a little pat on the back.  :-)
>
>> but I'm more interested in getting feedback on whether
>> having only 2.5mm all the way around is enough for setting the window in
>> most circumstances.
>
>It's probably more than enough in most circumstances.
>
>> If not, how much smaller than 63mm would you design it
>> to have enough to handle most situations and still meet the goal of
>> enjoying a larger format than 50x50?  6x6 users don't have much more than
>> 2.5mm all the way around, right?
>
>Sputnik shooters crop 5mm off the vertical and the horizontal;
>of course it is not necessarily 2.5mm from each side.
>
>My investigations of wider apertures has led me to believe that
>57mm is about the largest practical aperture width for mounting
>in the 80x132 King Inn/RMM standard mount dimension of 80x132.
>Of course there is no absolute rule that says you must stick
>with the 80x132 size, but if you go to something larger, most
>other people won't be able to view your work.  I also don't think
>there is much more to be gained.  If you use the 62mm figure above
>for maximum aperture spacing, and allow for a border of, say, 4mm
>between the images (to help create a nice frame, and for the
>structural stability of the mount), you are down to 60mm maximum
>aperture (1/2 the 4mm center border coming from each aperture).
>So you'll have to go to a lot of trouble to obtain an extra 5%
>((60-57)/57) width.  (You could bump that figure up a wee bit
>more some by pushing design to the limit, for example using 66mm
>spacing and 2.5mm maximum deviation, but that's even more potential
>trouble and still gets less than an extra 8% width.)
>
>If you and Bill pool your resources, perhaps you can commission
>a new mount with 57mm wide apertures.  :-)  I'd love to have one
>available.
>
>Paul Talbot
>
>