Re: [photo-3d] Re: Depth ranges

[Paul Talbot <list_post@xxxxxxxxx>]

abram.klooswyk@xxxxxx wrote:

>              (Dear Paul, your lines are too long...)

Dear Abram, most of the list won't get the dry
humor of your inside joke!  ;-)

> However, John Bercovitz presumes that viewer focal length is
> equal to "working" camera focal length.

He does indeed and while I have pointed that out at
other times, I erred badly when I neglected to do so
in this case.  Thanks for the reminder.

> So be prepared to buy a set of different stereoscopes
> and sort your slides according to focal length.

I wish I fully understood how to modify application of
the formula for when the viewing FL does not match the
taking camera's FL.  Although I don't do stereo base
calculations this way for my shooting, it would be nice
to have a version of the spreadsheet that took both the
shooting and viewing FL values into account.  (Is Tom
listening?)

> A 1:1 magnification means a bellows extension equal to the
> lens focal length, so a "working" focal length of 210 mm.
> According to the Bercovitz doctrine you should buy a
> stereoscope with 210 mm focal length lenses.
> 
> (Sounds strange? I agree.)

For 35mm slide viewing it certainly does!  So I now suggest
that when David does his calculations with the spreadsheet,
he should set the "FL" field set to 35mm so as to retain
the standard 1.2mm MAOFD in the calculations.  And then
hope that someone can explain how the calculation changes
for a shooting lens of longer FL than the viewing lens.
I made an attempt at such an explanation once, but for all
I know it may have been useless (or worse).

BTW, with a FL of 210mm the spreadsheet can produce results
such as the recommended near point being farther away than
the far point.  "Sounds strange? I agree."

Luckily for us all, Dennis Hanser provided an alternate
solution to the problem.  :-)

Paul Talbot


 

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