Bent spokes !

"Kim Siddorn" wrote

Nah. Actually very rare, produced for only a few weeks before Tam 'Tipsy' Mc Taggart had to leave his job in the foundry.

Maybe I'm being more dense than usual but I am struggling to see what type of conventional shutter mechanism could produce these results! Clearly, unless you caught the flywheel in your teeth a split second after the shot was taken, it has to be a camera generated aberration - but how!

Mark

A focal-plane horizontally travelling shutter at a high speed (narrow slit traversing the frame) can cause strange effects with a moving object. So can a vertical shutter for that matter, but the travel is less. Be interesting to know what camera was used. Certainly wasn't a leaf shutter.

I think you are right. It appears to be a vertical focal plane shutter, with the slit traveling from top to bottom, if the flywheel is turning clockwise. I have a Ricoh 35mm with such a shutter. Now if we knew the engine RPM, and the flywheel diameter, we could calculate shutter speed....

"Kim Siddorn" wrote

Nah. Actually very rare, produced for only a few weeks before Tam 'Tipsy' Mc Taggart had to leave his job in the foundry.

-- Nick H

So, for the benefit of the ignorant, how many spokes does the flywheel of this engine normally have, and are they straight or curved?

David Mack

Surely a focal plane shutter always travels at the same speed?

Cheers Tim

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"David Mack" wrote

Dunno, but I think they should at least be separated by equal radial intervals!

"David Mack" > So, for the benefit of the ignorant, how many spokes does the flywheel

If it's like all the other Larger Listers, six straight spokes.

Regards, Arthur G

Having mulled it over & taken the foregoing into account, I think the engine fired at the moment of exposure. Although fast, the scanning rate of a digital camera is not instantaneous & the flywheel would accelerate during the scan. The camera's computer would no doubt compensate for the blur of movement and this might result in the bunching and curious curvature of the six spokes.

Finally, all engines on wheeled trollies move to some extent and this would account for the apparent oviality of the flywheel when filtered by the camera's computer.

And rest .........

Regards,

Kim Siddorn

Not if you recently oiled the shutter with 3 in 1 !!!

No. There is acceleration at the start of blind travel and deceleration towards the end. They have a brake mechanism. At slow shutter speeds (=< 1/15 sec or sometimes 1/30) the whole of the film frame is exposed in one go. At faster speeds, a 'slit' travels across the frame, its width varying according to the speed selected, the higher the speed the narrower the slit. This is why focal plane shutters have problems with flash synchronisation. Very few will synchronise at faster than 1/125 sec and they will be vertically travelling metal shutters. Horizontal cloth blinds rarely sync at more than 1/30 sec. If you try higher speeds the flash duration is too short to cover the whole frame. If that picture was taken with a digital camera, it would most likely have been with a digital SLR which has the same mechanical components, shutter wise, as a film camera.

What I meant was that the slit always moves across the frame at the same speed, no matter what the nominal 'shutter speed' may be, so deducing shutter speed from the other data would really be a non-starter.

Cheers Tim

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True, but not consistently at all parts of the frame. It is actually exposing a scene bit by bit. At a slow speed - wide slit or no slit at all, i.e. fully open - you will get overall blurring of a moving object. At a high speed - narrow slit - you get the effect seen in the pics of the flywheel, not much blur but distortion. Given that the speed of the moving spokes is greater at the circumference than at the hub, 'freezing' the motion gives that apparent curvature. It wouldn't happen at a slow shutter speed. I wouldn't attempt to deduce the actual speed though! You can also get falsely elongated or shortened racing cars photographed side on for the same reason.