[MF3D.FORUM:742] Re: I need a MF 3D Dr.

[Paul Talbot <ptww@xxxxxxxxx>]

Richard Twichell wrote:

> The closest object in each shot is 10 feet away?  and the base ranges
> from 6.5 inches to 17.3 inches?  If I'm reading this right, you have
> what Ferwerda calls "close-up misery" in each case.  The good old
> 1-in-30 rule is violated - if the nearest object is 10 feet, the base
> should not exceed 4 inches.

With some help from DrT, I checked the numbers with the image
non-overlap formula George recently posted here.

> The amount of the "unrelated" scene
> is equal to the deviation between near point *and infinity*
> or, in my terminology FB/I (F: Focal length, B: Stereo Base, I:
> distance of near point).  As you come closer (I increases) then
> the unrelated scene increases.  Large focal lengths and stereo
> bases work against you too.
 
Applying the formula to Bill's shooting parameters I get:

 I     Base  FL(80mm)  "non-stereo"
120     2.5   3.15        .066
120     6.5   3.15        .170
120     7.1   3.15        .186
120     8.0   3.15        .210
120     9.7   3.15        .255
120    14.0   3.15        .368
120    17.3   3.15        .454

All values in inches.

So in the worst of his examples, he'll have .454 inches (11.5mm)
of non-overlap image area on each film chip.  Taking 11.5mm from
70mm leaves him 58.5mm to work with.  That is plenty for good
mounting in the RMM mounts (the Sputnik has only 55mm wide image
to start with), provided he makes sure he uses a "center crop." 
If he trys any left-right unbalanced crop, he'll probably end up
with mounting problems.  Moving back up the chart to some of the
more moderate stereo base situations, the problem becomes less
severe.

So I think that with Bill's wide film format and the data he
came up with, he is probably avoiding close-up misery--at least
for now.

Paul Talbot

Paul