Re: Medium Format Training

[T3D john bercovitz <bercov@xxxxxxxxxxx>]

It sounds like you're going to be doing product shots which are 
static.  This is excellent because it gives you a great advantage 
which is that you can use a slide bar for perfect control of the 
situation.  If you have people in your product shots, it's going 
to be tougher because they move between shots.  Although I have 
seen good slide bars of people who are able to "freeze", I 
wouldn't count on it.

First thing you asked was what spacing you want for your shots.  
Generally it's going to be 65 mm so that the recreated scene will 
be life-size.  If you want to play around and make it appear like 
a table top shot of miniatures instead instead of a full size 
shot, then you need to increase your stereobase significantly.  If 
you have a problem with too much depth in the scene, you will have 
to decrease your stereobase to reduce the total parallax or 
decrease the amount of depth in your scene to reduce the total 
parallax.  A significant reduction in stereobase will make the 
scene look larger than life.

Excess parallax is only a problem if you have too much depth in 
the scene.  That is, if you have very near objects and very far 
objects in the same scene you may have a problem.  It's surprising 
how many times you think you have a problem if you use the 1 in 30 
rule but you find you actually don't have a problem if you use the 
more correct maximum allowable on film deviation rule.  
Fortunately it is easy to find out if you have too much parallax.  
Download the maofd spreadsheet from bobcat using your web browser.  
It's an Excel spreadsheet.  The web (or ftp for that matter) 
address is:

ftp://bobcat.etsu.edu/pub/photo/photo-3d/technical/maofd/

The spreadsheet appears in several formats.  PCmaofd.XLS.uue, 
PCmaofd.XLS, and Macmaofd.bin seem to work fine but Macmaofd.hqx 
seems to have a problem of some sort.  They're all the same so if 
you can get one of them to work, you're in.  If you don't have 
Excel, I can translate the spreadsheet into some other format with 
some effort.  You will also need maofd.txt if you'd like some 
theory and you'll need maofd.instrs to easily learn how to run the 
spreadsheet.  Just plug in the distances from the camera lens to 
the nearest and farthest objects in your shot along with a few 
other parameters, and the spreadsheet will give you the maximum 
amount of stereobase you can tolerate.  This doesn't mean you have 
to use the maximum.  If it says you're allowed up to 12000 mm of 
stereobase, I'd still hold it down to 65 mm.  8-)

You asked if there was anything more complicated about medium 
format as compared to miniature format.  Just remember to stop 
down one extra stop and use a film speed twice as fast.  8-)

Then you asked how to scale down your views when reproducing them 
for the viewer.  The first thing you need to know is the focal 
length of the viewer.  If you are going to be viewing with a red 
button, then the viewer focal length is about 44 mm.  If you are 
going to be viewing with a Star (Brumberger?) then the focal 
length is about 50 mm.  Same for a toy V-M: 50 mm.  Now let's say 
you took your shots with an 80 mm lens on the MF camera.  Then you 
need to scale down to about 1/2 size (actually 44/80 size) for the 
red button or 5/8 size for the Star D.  Either way, you'll have 
plenty of film left to trim off so you can set the window 
distance.

If you want to play games and stretch the shot, say you're taking 
a nose-on shot of a car and you want it to look really long, then 
you want to do more demagnification of the transparency when you 
print the final transparencies.  For instance, instead of making 
the finals 1/2 size, you could make them 1/3 size for a subtle 
increase in car length.  This game only affects the depth 
dimension.  This contrasts with changing the stereobase which 
changes all three dimensions in exact proportion causing a 
miniature or gigantic scene in perfect scale.  If you want to 
squash the third dimension, then you need less demagnification, 
say a reduction to 2/3 size, for a subtle effect or just leave 
them 1:1 for a not-so-subtle effect.

Stretch and squash are a little tricky.  Some people will spot 
them right off.  Some people can't see them until it's very large.  
Some people still won't see them but they'll know something is 
"wrong".  And some people are stereoblind.

Don't make the mistake of thinking you're trying to fit the 
aperture of the stereo format.  If you reduce the medium format 
transparency to 1/5 size to make it fit in a toy V-M viewer, 
you'll get a tremendous amount of stretch of the third dimension 
(unless you were taking with a 250 mm lens).  I seriously doubt 
you'll enjoy the effect of a 3X stretch.

John B


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