[MF3D.FORUM:370] Re: 1/fl

[Tloc54452@xxxxxxx]

In a message dated 2000/03/29 18:54:49, tmd@xxxxxxxxxxx writes:
>>Also, I find it's been so long (relative to the length of my
>>memory) since I've done MAOFD, that it's a bit vague now.
>>Can someone explain the 1 over focal length argument to
>>me or cite me on the subject?  Sure would appreciate it.
>
>Heck, I cite you all the time, John.
>
>http://www.werple.net.au/~kiewavly/bases.html is a beautiful thing.

Thanks for the reference, Tom.

I didn't study it really closely, but I didn't see 1/fl right off in there.
However, Oleg came over Friday to take pictures of the hills behind
my house and he uses a different cheat sheet for each focal length.
Then it dawned on me that he's keeping the on-film deviation constant
at something like 1.2 mm regardless of focal length.  And that's what
generates the 1/fl rule.  That's the rule that old what's-'is-name
used to use, I'll never forget his name.  Since I've not experimented 
with viewing from other than the center of perspective, I can't comment.
However, it does seem logical in a way.  

On the other hand, if you are shooting for projection, you are planning
on a longer distance from observer to screen so you should use a longer
focal length and can use more on-screen deviation than if your viewing 
distance were for 50 mm or 35 mm lenses   On the other other hand, I
think Oleg said he shoots for the hand viewer, and slide competition
is incidental to his main aim (correct me if I'm wrong).  In this case,
going with the 1.2 mm limitation sounds right, though I've not tested it.
I know what's-'is-name would agree, and he does 3D for a living.

So it looks like we have three rules going:
1) Constant maximum on-film deviation regardless of focal length 
(but dependent on format: 1.2 for 35 mm format, 2.7 for MF, etc)  
2) base = near point/30 regardless of focal length  
3) on film deviation = focal length/30

#1 I attribute to what's-'is... Aha!  Good old Bob Mannle!
#2 is the common rule from Ferwerda, for example
#3 is Spicer's and my rule which can be back-derived from
   Ferwerda and Waack, at least their advanced sections

John B