Vibration App, etc

[Jac@stafford.net]

Got an iPhone and the 'Vibration' app to muck about with because vibration has long been a concern with some shutters. (I gave up on Sinar shutters years ago.) Will report outcomes if you like. The tripod is an old monster, a converted wooden surveyor's item.

I'll start with a 240mm Sironar-N, Copal 3 on a Deardorff V8, then on a Century 1 8x10, and on a Calumet C1, all at 1/15th.

Because none of the cameras are in the house right now, I tried it on a Leica M9 triggered by self-timer @ 1/15th which I thought would be very still. There was a significant reading. Perhaps I've much to learn of the app and to distinguish resonance from movement - or does it matter? Resonance == Vibration?

[jp]

Resonance == vibration, but vibration != resonance, unless you're hitting a resonant frequency.

I'd want to know where on the X scale the film/sensor actual receive light. Some camera like my speed graphic get pretty wild, but it doesn't seem to be during exposure, but more at the stopping of the focal plane shutter travel, when it doesn't matter.

[Jac@stafford.net]

Resonance == vibration, but vibration != resonance, unless you're hitting a resonant frequency.

Excellent point. Thank you. I have data for frequency, too. Much to learn.

[Struan Gray]

You need to mount the iPhone firmly to the camera, so that there is no wobble or oscillation in the mount - basically, you want the iPhone to follow the camera's movement, not just flap about in its own good time as a result of an impulse from the camera.

For the LF cameras there is a problem that the iPhone will only measure movement at its mounting point, but the image is affected by relative movements of the lensboard and filmholder. You might need more iPhones :-)

It would also be worth finding a way to tell at what point during the vibration measurement the shutter opens. A lot of the Sinar shutter crash-bang supposedly occurs after it is closed.

[Jac@stafford.net]

Struan, would it be adequate to measure movement at the lens? Any movement there translates to film-plane consequences

[Struan Gray]

Some information is always better than no information.

The problem is that different forms of motion have different degrees of severity in terms of blurring the image. A uniform translation of the camera has little effect on distant scenes, more on closeups, and is almost always beaten by a rotation of the whole camera, or relative movement/rotation of the front and rear standards.

You can extrapolate from the measured vibration at a single point, but it's worth keeping in mind the gotchas.

The 'best' way would be to put a quadrant photodiode at the focal plane and measure the movement of a focussed light spot. With a modern iPhone and slo-mo filming you could probably get useful information at LF-relevant shutter speeds. Focus on a distant light bulb and film a close up of the focussed light.

[Jac@stafford.net]

The 'best' way would be to put a quadrant photodiode at the focal plane and measure the movement of a focussed light spot. With a modern iPhone and slo-mo filming you could probably get useful information at LF-relevant shutter speeds. Focus on a distant light bulb and film a close up of the focussed light.

In that case, focusing the video camera on the aerial image might be best.
.