Yes I have read most of the previous threads on mirror and shutter shake with the P67 and have really improved my knowledge of Newtonian physics. One thing still puzzles me. The biggest problem with "Big bertha" is said, by consensus, to be shutter speeds between 1/30 and 1/2, particularly 1/15 and 1/8. It is possible to work around this with coice of film speed, ND filters etc. However, I just can't logically follow why a vibration, which would be at it's maximum when the shutter opens and then gradually decay, should not be present during a longer shutter opening i.e. 1 second and longer. Unless we are talking about lighting so low that the lens can be capped until the first vibration dies away.

-- Nigel Craig (ncraig@globalnet.co.uk), August 07, 2000

Answers

I too have wondered about this. If one assumes that the vibrations start immediately after the shutter opens and dies down with time then the longer the exposure the more "recording" occurs when the vibration dies down and hence a sharper picture for a longer exposure. Here is my reasoning for the contradiction (pure speculation). When it comes to shutter vibration most of the vibration occurs when the shutter is stopped (as opposed to when it is released and when it is traveling). When the shutter is stopped, the energy must be dissipated by a dampening system or this energy will be transmitted onto the camera body where it may cause vibration (when the shutter is released the only vibration would come from the release mechanism and this would be insignificant relative to stopping the shutter). So if we assume that the bulk of the vibration occurs when the shutter is stopped then at high shutter speeds with slit exposure only the last slit will be affected by this vibration and hence most of the image will be sharper. During exposures of 1/30 or longer there is no slit exposure and hence the whole picture "receives" the "shutter stopping" vibration effect.

-- Milton Barrocas (mbarroca@americasm01.nt.com), August 07, 2000.

During very long exposures the camera stops shaking before a large percentage of the total exposure is made. If the majority of energy striking the film does so after the vibration damps out the shake will have little impact on the image.

-- Chuck Bernards (chuckb@hevanet.com), August 07, 2000.

Milton and Chuck; thanks for your responses. Only thing i'm still wondering about on this whole issue of shutter shake is how much it is a vibration, in which case the cure should be to damp it out, or, an opposing movement of the camera body (Newton's ?rd Law of Motion) in which case the answer should be to stop it twisting or moving. I was speculating who might have the resources to create test conditions to answer these questions....my feeling is Pentax!

Au revoir

-- Nigel Craig (ncraig@globalnet.co.uk), August 10, 2000.

I posted vibration measurements as related to tripod head choices in an earlier thread. It's still on the board somewhere. The measurements aren't difficult.

As far as shake and vibration, they are the same thing. It can be damped out. Some people lay a sandbag over the camera. It probably works fairly well. You'd definetely want a sandbag that didn't leak. Maybe I'll take some measurements this winter when the weather gets bad and I get bored.

-- Chuck Bernards (chuckb@hevanet.com), August 10, 2000.