Re: Pinhole and SLR

[Edward Meyers <aghalide@xxxxxxxxx>]

On Fri, 30 May 1997, Joe Berenbaum wrote:

> At 18:44 30/05/97 GMT, you wrote:
> >| ... making a pinhole that
> >|could come quite close to the film plane- much closer than a pinhole >|mounted
> >|on an SLR body cap could. It would be on bellows and so in theory I'd >|have a
> >|zoom pinhole. Then I could check the coveage indoors with some high
> >|intensity lights and calibrate it so I have an idea what it covers at >|what
> >|bellows extension, and then just use a separate viewfinder of some sort >|for
> >|framing the picture in normal light levels. Well it's an idea...
> >
> >If you used a Speed Graphic and mounted the pinhole diaphragm on a
> >regular Graphic lens mounting board, the sports finder should show you
> >what it will include, no?
> 
> I may be totally mistaken, but I thought that the pinhole's effective focal
> length varied with distance from the film plane. If so, the bellows would
> give quite a variety of focal lengths from the one pinhole simply by
> altering the bellows extension -efffectively a zoom. Thus a way to assess
> the angle of view other than a single fixed finder (and other than by
> looking at the extremely dark ground glass), would be useful.
> 
> >Sounds intriguing.  Maybe I'll drag the Speed Graphic out of mothballs
> >for the first time in years...
> >Bob Long
> >(boblong@xxxxxxxxxxx)
> 
> Well if you do, let me know if it zooms!
> 
> 
> Joe B.
> 
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Although moving the pinhole farther from the film plane
in effect produces a more magnified image and moving it
closer to the film plane produces a more wide angle
effect...Each pinhole size is optimized for one particular
focal length. At that focal length or distance from the
film plane it produces the sharpest image. Ed Meyers
 

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