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In a message dated 26/06/2004 09:34:28 GMT Standard Time,
nimbo@xxxxxxxxxxxxxx writes:
With gravity operated shutter the two blinds are accelerating so the effect of I would be very grateful if you could.
The background is that we are setting up a re-enactment of the
Muybridge trotting horse experiment using 12 or more 10x8 cameras. The
retro-invention and consultation elements form an important part of the
exercise. What we have been doing is to simplify the thing as we go along..
Clearly we could use electronic means, or set up systems of levers and stops to
actuate the shutters on the lenses but as the shutters and lenses would not be
the same, it seemed simpler to use a shutter which would be independent of the
camera and the lens.This could be done by placing a gravity actuated guillotine
shutter in front of the lenses which would be set on 'time'.
Taking the analogy of a focal plane shutter and an initial
speed of fall of 32 ft per second, we took , as a starting
point,that a speed of 1/100th of a second could be obtained by using a slot in
the guillotine shutter of 1/100 of 32' feet.
Marty Magid pointed out that as the shutter starts from rest
the average rate of fall is going to be a lot slower (so the slot would need to
be narrower).
I held a 12" ruler at '0', let it go and measured the distance
it fell before I could grab it again. This varied between five inches and nine
inches. I then started and stopped my stop watch to find that the comparable
time for the double reaction was 0.2 of a second this giving me a rate of fall
and distance comparable to those Mike Ware quotes.
Taking these figures into account, I readjusted the
slot in the shutter to 1/4 of an inch. This takes account of other
factors, for example that the rate of fall is non linear ( we have to take
acceleration into account). The width of slot in the first working mock up can
be varied with gaffer tape, the stop on the lens can also be changed. and
the film, itself, will have some latitude. We would use wet collodion if we
could find 12 or more wet collodion cameras to use for the
experiment).
Mike suggests that the varying the width of the slot
will not change the 'speed' of the shutter. We need to 'test' this against
the analogy of the focal plane shutter; we can see what actually is the
case with the first practical experiment with the first working mock
up.
If anyone wants to take part either in the trials or in
the re-enactment, just let me know.
Terry
Terry King
FRPS
RPS Historical Group (Chairman) www.hands-on-pictures.com/ Moderated Discussion Group Post message: artaltphot@xxxxxxxxxxxxxxxxx Subscribe: artaltphot-subscribe@xxxxxxxxxxxxxxxxx Unsubscribe: artaltphot-unsubscribe@xxxxxxxxxxxxxxxxx 1. An excellent thing is as rare as it is difficult.(Spinoza) 2. A man's reach should be beyond his grasp or what's a heaven for.(Browning) 3. Frustra fit per plura quod potest fieri per pauciora.(Occam's razor or 'Keep it simple!'). 4. Nullius in Verba (Horace), 'Take no man's word for it' (motto of the Royal Society). 5. If ignorance is bliss, why are not more people happy ? (anon) |
