Re: Slit-apertures ?

Let me see if a can think of an answer as I write it, here it goes

> Has anyone ever tried slits ?

I haven't unfortunately, therefore all my opinions are just academic ones.

> I've read in the "E.Renner-Bible", that you have to cross two slits for
> getting a disorted image.
> But there's no info about how far the slits have to be away from eatch
> other;

Sorry, can't help you with this one.

I would assume it becomes a decision based on aesthetics, in other words how
you like the results of the differerent settings. Now, once you decide how
far from the film plane and each other you want them, it all becomes very
simple.

> what slit-diameters are the best etc.

The "slit-diameter" (actually, the width of it) depends on the distance you
have decided to install them away from the film plane. To find out that
width or "diameter" as you call it, just use the same formula you use to
calculate your round pinhole diameter. You can clearly see that the front
slit will be wider that the slit closer to the film plane.

> Does anyone have some formulas e.g. ?

Here are some:

Let be: F = distance film to front slit (slit "f")
             R = distance film to rear slit (slit "r")
Remember that distances F and R are for you to decide, beforehand.
             Df = width of slit "f" (front)
             Dr = width of slit "r" (rear)
             Lf = length of slit "f" (front)
             Lr = length of slit "r" (rear)
             S = short side of the film (4" for 4x5 film format, for
instance)
              L = long side of the film (36mm or 1.417" for 35mm format
film, for instance)
              C = diagonal of the film
              SQR stands for Square Root
             All the above distances measured in inches when calulating Df
and Dr
Let's also assume you always install the slit "r" (rear slit) along the long
side of the film.

Lf = S * ( (F/R) - 1 )

Lr = L * ( 1 - (R/F) )

The formula I use for "round" pinhole diameters is:

  diameter = 0.0073 * SQR(focal length in inches)

Using the above formula:

Df = 0.0073 * SQR( F ) inches

Dr = 0.0073 * SQR( R ) inches

No wonder slit photography is not that popular!!

Well, I hope this answer some of your questions.

Corrections or additions to the above are welcome.

Guillermo
Received on Thu Aug 31 19:48:24 2000