From: shoppa@erin.caltech.edu (TIM SHOPPA)
Subject: Re: Astro-(disposable)-cam
News-Software: VAX/VMS VNEWS 1.41    
Organization: California Institute of Technology
Date: Sat, 12 Sep 1992 18:23:00 GMT

In article <1992Sep12.063202.7343@hpcvaac.cv.hp.com>, billn@hpcvaac.cv.hp.com (bill nelson) writes...
>shoppa@erin.caltech.edu (TIM SHOPPA) writes:
>: 
>: My current plan is to attach some sort of spring or battery-powered mechanism
>: to the takeup spool, then clamp the shutter button down.  As the film
>: is dragged across the little sprocket, the shutter will fire once each frame.
>: As has been pointed out, the film will continue to move while the shutter
>: is open, adding some blur to the picture.  If this is severe enough, I suppose
>: I'll figure out how to stop the film while the shutter is open.  I'm not
> 
>Use some sort of reciprocating lever/cam to wind the film. Have the cam
>trip the shutter when it reaches the end of a stroke. That way, the film
>will not be moving.
> 
>I guarantee that you do not want any film motion - it is far worse than
>camera motion.
>
Hmm.  More complex than what I had originally envisioned.  I'm a nuclear
theorist, not a mechanical engineer (to mangle Dr. McCoy's famous line from Star
Trek) so I'll try it the simple way first.  If you can come up
with some definite plans for such a mechanism, let me know, and I'll try
to make it with my admittedly limited machine shop skills.  (The
experimentalists in the building occasionally let me go into their shop
and make a fool of myself.)

With a mechanism like this, we would have a mini disposable movie camera, if
we had enough film and advanced it across quickly enough!

Actually, there is a little bit of hesitation in the cam right before
the shutter fires.  I doubt this will stop the motion of film, though.

Let's do a little calculation and see how bad this is.  The shutter is,
I believe, 1/250th a second.  There is about 1.5 inches of film per frame.
If I do 1 frame a second, the
film speed will be about 1.5 inches a second.  Thus the image will move about
1/160th an inch on the film.  Now when I print I enlarge by a factor
of 4 (i.e. to about 4" x 6" from the original negative).  This 1/160th
an inch enlarges into 1/40th an inch.  Yep, that is some quite visible blur,
but I'll live with it for now.

Going to the original speed of 2 frames per second that I had thought about
using, the blur is about 1/20th an inch.  That's a little too much for me!

> 
>: sure, but I believe the original packaging that came with my disposables
>: said the shutter speed was 1/250th, but I'm not absolutely sure about this
>: figure.  Of course, the slower the shutter speed, the less motion blur you'll
>: get in the picture, whether from rocket movement or film movement.
> 
>Wrong - the faster the shutter speed, the less the blur. 
> 
>Bill
> 
Yes! You're right, I meant "shorter", not "slower".  (Not only do I
mix up similar sounding words in speech, but also in typing!  At least
I don't stutter at the keyboard as well!)

Looking at the mechanism, it looks like
you could increase the shutter speed by putting a stiffer spring in.  But
then the cocking action would also take more force, and the plastic parts
in the camera may not be able to take this force!

					Tim (Shoppa@erin.caltech.edu)

Newsgroups: rec.models.rockets