[photo-3d] Re: Newbie question-near point distance

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

Hi George!

Here's an excerpt from a post you made on Wednesday...

>Message: 10
>   Date: Wed, 25 Apr 2001 13:29:43 -0500
>   From: "Dr. George A. Themelis" <drt-3d@xxxxxxx>
>   Subject: Re: Newbie question-near point distance
>
>> Please someone tell me if the 1/30 rule is still appropriate when 
>> using 35mm lenses instead or normal 50mm or 55mm. 
>
[snip]
>
>I like the way David Lee deals with MOF. His practical
>treatment is somewhere in Steve Berezin's site and has been
>presented in the Stereogram 5.6 Tutorial (Single Camera
>Stereos, Part II - deals with "how much to shift") 

[snip]

I think this is the page you referenced:

   http://www.berezin.com/3d/Tech/lens_separation_in_stereo_photog.htm


Here's an excerpt from a post you made on Friday...

>Message: 1
>   Date: Fri, 27 Apr 2001 10:30:33 -0500
>   From: "Dr. George A. Themelis" <drt-3d@xxxxxxx>
>   Subject: Re: Re: Newbie question-near point distance
>
>Bruce Springsteen writes:
>
>> Both are recommendations to reduce base when increasing focal length, or
>> add base when subtracting focal length.  This is just the opposite of the
>> old PePax rule of increasing (or decreasing) base and focal length
>> together.  

[snip]

>OK, here is my response:

[snip]

>It so happens that McKay's PePax rule (of increasing
>base and focal length together) works very well in
>most practical situations.  And the results are very
>ortho-like, despite the fallacy of ortho-stereo as you
>say.
>
>What bothers me with the "maximum on-film-deviation"
>approach is that it is "artificial".  There is no physical
>reason why the on-film-deviation has to be constant
>or maximum or even be a serious consideration in a
>photographic situation.  On the other hand, McKay's
>PePax rule has an explanation (as you said, serves the
>"useful purpose of counteracting unpleasant 'stretch' 
>and 'squeeze' effects).
>
>The PePax rule really deals with increasing the focal
>length.  What happens at the other extreme, i.e. very
>wide lenses?  You will notice that in these situations
>people tend to come very close to the near object
>so usually they do not have to either increase or
>decrease the stereo base.  For example, quite a few
>people are experimenting with the RBT SLR type
>cameras and super wide lenses with good results, 
>while fitting 200mm lenses on an RBT camera will 
>lead to disappointments.  
>
>George Themelis

As Bruce Sprintsteen pointed out, the recommendation you made on Wednesday
(like mine) says "to reduce base when increasing focal length, or add base
when subtracting focal length."  Two days later, you wrote: "McKay's PePax
rule (of increasing base and focal length together) works very well in most
practical situations."  And: "There is no physical reason why the
on-film-deviation has to be constant or maximum or even be a serious
consideration in a photographic situation."  

So which do you prefer for dealing with a change in focal length?  David
Lee's method or McKay's PePax rule (Wednesday or Friday)?

Mike


 

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