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

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

George,

>Message: 8
>   Date: Sat, 28 Apr 2001 12:59:58 -0400
>   From: "Dr. George A. Themelis" <drt-3d@xxxxxxx>
>   Subject: Re: Re: Newbie question-near point distance

[snip]

>>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)?
>
>Me personally? Neither!

OK, Wednesday your advice was to reduce the base when reducing the focal
length.  Friday, you encouraged us to increase the base when reducing the
focal length.  Now, you tell us that it's your personal preference to leave
the base unchanged with changes in focal length.  That pretty much covers
all the possiblities.   Which answer would you give to Clement's question
today -  increase the base, shrink the base, or leave the base alone?  My
guess is you'd have a fourth answer for us if I really pressed you to
answer that question.

>The only stereo camera I use that offers variable
>focal length is an RBT X3 camera with 28-75mm zoom.
>I move from 28 to 75mm without changing the stereo
>base.  I also put 100 and 135mm lenses and I still
>keep the same stereo base.

Is this the same RBT camera you reference below, which doesn't permit you
to change the base?   If so, then you don't really have a choice when you
say you prefer "Neither!" (other than having chosen to use a fixed-base
camera...)

>A few years back I was doing quite a bit of twin SLR
>shooting.  Normally I would have both cameras side-by-
>side on a bar, with 45mm lenses.  The physical size
>of the cameras stopped me from getting them closer
>together.  The only time I changed this was when I 
>used 135mm lenses for close ups of animals, where I 
>increased the camera separation.  The length of my
>twin camera bar now dictated how far I could separate
>them.

So, now you're using a camera that doesn't permit you to change the base
with changes in focal length and that's your preference currently, but when
you shot with twin SLR's, you prefered to increase the base as you
*increased* the focal length.  What camera or cameras were you using the
day you recommended increasing the base with a *decrease* in focal length?

>If the stereo base *needed* to be changed for every
>change of focal length, then RBT would not be making
>twin SLR stereo cameras with zoom lenses.  

Your argument here is that if RBT thought there was any merit in changing
the base with a change in  focal length, they would have incorporated
variable base into their design.  So, not only was their decision to use a
fixed base design not a compromise, you regard (at least at this writing)
their design choice to be proof that there's no need to adjust the base
when focal length is changed.  

>For twin 
>cameras the practical limitations of how close or how 
>far you can separate the two cameras usually dictate 
>the choices.  

But, we should throw away our slide bars and just lock them together, because:

[Repeating from above]

>If the stereo base *needed* to be changed for every
>change of focal length, then RBT would not be making
>twin SLR stereo cameras with zoom lenses.  

Now you're contradicting yourself within a single post.

>I do some amount of single camera work, either hand-held
>or on a slide bar.  Slide bar pictures are all close
>ups.  I don't measure anything in either case.  I
>just shift as much as I think will give a good picture.
>I have never had any real regrets regarding the stereo
>base so I don't see why I should change what I am doing.
>
>I understand that you are trying to point inconsistencies
>in my postings, which should not be very difficult,
>especially since my personal choices are based on 
>photographic intuition and not calculations.  

Is this what you teach in your workshops?  Intuition?

>I am
>sure you agree that there is room for both philosophies
>in photography.  

Thank you! Yes!  There ought to be room for both philosophies!  There
always has been in my mind.  Try and find a thread where I've said anything
against making the choice NOT to use math.  I have only explained my choices.

In this thread, I decided to chase you around the schoolyard when you
contradicted your original answer to Clement's question, after agreeing
with Bruce's rebuttal, but when I tried to isolate your position, you ran
to yet a third possibility: making NO change to the base with a change in
focal length.  

I admit I've been a horrible pest in this thread, but you've set yourself
up the whole way.  I want you to know that I started out only frustrated
that you were sending mixed signals to Clement, but now you've taken that
further still, instead of giving him something he can take into the field.   

If this thread is a model of your "method", then perhaps you should just
answer every technical question with: "Experiment and trust your intuition.
 Go with what looks good to you."  I can vehemently support your choice to
say that, but I find your vascilations to be very annoying, unconstructive
and confusing.

You are, however, quite welcome to use your intuitive approach and even try
to teach it, but am I welcome to use and teach my mathematical approach on
this list?

I don't think so:

>   Date: Wed, 28 Feb 2001 07:26:43 -0500
>   From: "Dr. George A. Themelis" <drt-3d@xxxxxxx>
>   Subject: To math or not to math?
>
>John A. Rupkalvis wrote:
>
>>Years ago, there was a trend to encourage math solutions in conventional
>>flat monoscopic photography.   Photographers were encouraged to carry
>>handbooks in the field.  Some of these, such as Photo Lab Index were over 3
>>inches (75mm) thick, and loaded with formulas.  These were sometimes useful
>>in the lab, rarely in the studio, and never in the field.   I don't ever
>>recall seeing a professional photographer carrying one.  The same thing
>>applies to stereoscopic photography.
>
>John, the thick photo books have been replaced by advanced
>calculators.... Sorry, I cannot resist but quote this message
>that came from the MF list (MF stands for Medium Format, not
>Mathematical Formulas!!!)  I did not write this!!!  Email Paul
>Talbot if you would like to join the MF stereo list.
>
>Here is the quote.... enjoy!!!!  -- George Themelis
>
>excerpt from:
>http://www.pauck.de/archive/mailinglist/mf3d/mhonarc/msg04004.html
>

That was completely unprovoked.   All I did was write an article in MF3D
about how I work, but you saw fit to mock my method.

>I am
>sure you agree that there is room for both philosophies
>in photography.  

Can John Rupkalvis agree?

>   Date: Wed, 28 Feb 2001 11:53:12 -0800
>   From: "John A. Rupkalvis" <stereoscope@xxxxxxxxxxxxx>
>   Subject: Re: To math or not to math?
>
>
>----- Original Message -----
>From: "Dr. George A. Themelis" <drt-3d@xxxxxxx>
>To: <photo-3d@xxxxxxxxxxxxxxx>
>Sent: Wednesday, February 28, 2001 4:26 AM
>Subject: [photo-3d] To math or not to math?
>
[snip]
>
>> Here is the quote.... enjoy!!!!  -- George Themelis
>>
>> excerpt from:
>> http://www.pauck.de/archive/mailinglist/mf3d/mhonarc/msg04004.html
>
>The description referred to above (which I removed, Paul!) is great.  It
>should be framed and hung on the wall in every stereo club.  I wonder if the
>writer has ever done stereo photography of birds or airplanes or sports, and
>if the subject was still around by the time that the calculations were
>completed (even with an advanced calculator)!
>
[snip]
>
>JR

Mike




 

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