[MF3D.FORUM:1538] Re: Mike's method (was Re: folio comments...)

["Bill Glickman" <bglick@xxxxxxxx>]

> I thought I'd jump in to answer your questions about how I'm choosing
> on-film deviation and discuss the rest of my method.

      That was your cue Mike, thanks for jumping in!

> I'm sure Bill would agree that what he was saying here is this:
>
> "I think specifying a value of 50% in the %MAOFD variable Mike Davis's
> formula uses will correct the problems I had when shooting at 100% MAOFD."

           Yes, thanks for the clarification for others, I should have been
more clear.

> Yes.  More precisely, the 50% figure Bill proposed would cut the on-film
> deviation from 100% of MAOFD to 50% of MAOFD, where MAOFD is FL/30.  So,
> yes, for an 80mm lens, 50% MAOFD would be 1.3mm vs. 2.7mm for 100% MAOFD.
>
> >Would it be equivalent
> >to changing the usual "7 ft to infinity" guideline for a normal stereo
> >base camera to "14 ft to infinity?"
>
> Yes, exactly.

        Where the near is too close, I will have to live with greater
greater sepeation, i.e.  a wider base...but Mikes slides looked great at 80%
he showed me, but I am glad I had the opportunity to see other slides in the
expo which seemed to have offered even easier fusing...   Hence my desire to
cut the base down as much as poosible, so in the future, I will probably
float between 50 % and 70% factor which Mike discusses above.   Paul T once
said, that 65mm is all our eyes ever have, and we perceive 3d well in the
real world, and this is very true, but when looking through a 3d viewer, it
is not always apparent how far away a subject is, in which case I like the
capability to provide more depth than  we would have perceived if looking at
the real world scene.   Conversley, I am also starting to appreciate the
great benefits of the fixed stereo cameras small interocular spacing, mainly
when things are very close in the scene.  But one can only carry so much
gear in the field!

> >> I have viewed some of
> >> Mikes shots, and he used even less correction and his fused very
well... so
> >> I am convinced this is the problem....

> I can't remember the context of this quote, but as it reads here, Bill
> sounds like he's suggesting I had used bases which produced less than 50%
> MAOFD.  That's not the case.

        Sorry, what I meant here was Mike shoots less than 100% and
everything fused well, hence my move to be safe and use 70% as my max.
And when in doubt, I will go down to 50% of max.   My reasoning is simple,
the wider the bases the more potential for problems..... I much rather have
a great shot with a tad less stereo effect vs. a ruined shot that every one
struggles to fuse, sees minature effect, retinal rivalry caused by different
vantage points of the cameras, etc.


> In the interest of making the medium of this art less prominent, so that
> the content can be appreciated without having to compete with the "special
> effects", I have for the moment, settled on a deviation equal to 70%
MAOFD.

       I really think this is a good move... if one uses this as their
ceiling they will most likely never ruin a shot...


.  On aesthetics alone, I don't
> really feel moved to cut this down to 60%, but this is especially
> undesirable since that would push my Nears further away from the camera
still.

       Yes, this is the price we would have to pay to be safe, that is why
it is a judgement call...

> It's impossible for me to obtain bases less than 165mm with my equipment,
> so at 70% MAOFD, again compensating for viewerFL/cameraFL mismatch, I can
> not shoot subjects closer than 19.5 feet, when the Far point is at
> Infinity.   If I allowed the deviation to increase to 100% MAOFD, my
> minimum base of 165mm would permit Nears as close as 13.6 feet, with my
> equipment.

       This is why the high tripod is such a great concept...but Mike, not
all of us are willing to carry a step ladder into the field :-)    You gotta
love this guys tennacity to do whatever it takes to get the shot!!!

  After focusing on that target, with both lenses, I restore
> the intended composition.  (My thanks go to Bill Glickman for this tip!)

       My pleasure !  :-)

> To meter, I use a Pentax Spotmeter V to place the highlight detail at 2.5
> stops above 18% grey (placement at Zone 7.5), then check the shadow detail
> to see if it's more than 5 EV below the highlight.  If it is, I elevate
the
> shadows by pre-exposure using a home-made diffuser (two layers of white
> plexi from a 5000k light box, measuring 6 inches square, separated by a
> frame of 1/4-inch balsa wood. Nothing can bond acrylic to balsa better
than
> SuperGlue, by the way.)
>
> Having determined the main exposure (using the calcuated f-stop at
whatever
> shutterspeed will place the highlight at Zone 7.5 and freeze subject
motion
> hopefully), I stop down either 2, 2.5 or 3 stops for the pre-exposure on
> each camera (M7 II's permit multiple exposures.)  I just hold the
diffusion
> panel flat to the front of the lens and fire the shutter, first on one
> camera, then the other - they don't have to be sync'd.  :-)   A -2 stop
> pre-exposure will lift Zone 0 nearly 3 EV's but this is about the
brightest
> pre-exposure you can make without elevating the midtones a wee bit too and
> running the risk of large areas of shadow appearing "milky."  The -2.5
stop
> pre-exposure is nearly always safe, elevating Zone 0 about 2.5 EV's.  A -3
> stop pre-exposure is guaranteed to be "undetectable" even with large areas
> of shadow - it will elevate Zone 0 only about 2 EV's.  The neat thing
about
> pre-exposure is that the higher the original luminance of a given subject,
> the less it will be affected by pre-exposure.  Your darkest shadows get
> lifted more than the higher zones.  At -2.5 and -3, midtones and,
obviously
> the highlights, are completely unaffected.  The main exposure (made after
> the pre-exposure) is done at the calculated settings, as if the
> pre-exposure was not applied.

         This is one of Mikes greatest little photo inventions - it works
great!!!...Who would have ever thought a $5 gadget could save so many shots!
For stereo it is so important to open up those shadows to prevent black
holes in our images!  I also use this little trick in 4x5 and 8x10 chromes
when the exposure range is too high for the film....

Bill G