OT

Mark · 12 March 2006, 04:12 PM

I'm trying to find the answer to a question and wondered if someone here might know the answer-

When a spinning propeller is photographed, often one of the blades will appear curved or scimitar shaped. Especially a 4 bladed prop will usually have one that is curved.

Is there a name for this phenomena and how is it caused, does anyone know?

Thanks!

Mark

Dan_San_Abbott · 12 March 2006, 04:47 PM

Mark:
It means camera speed of the camera is slower than the rpms of the propeller. If the camera speed and the rpm were exactly the same the camera would photograph a stopped propeller. synchronized or dissynchronized??
Blue skies,
Dan-San

Greybeard · 13 March 2006, 08:24 AM

Depends also on type of shutter, if central (diaphragm) or lateral moving. This latter gets that optical phenomenon since film isn't all exposed at same time.

S!
GB

Mark · 13 March 2006, 05:08 PM

Thank you Greybeard!

I was asked this question and could not figure out why it was.

Mark

Cigogne · 17 March 2006, 10:05 AM

I also noted that in vintage racing photos where the race cars are slanted forward.

GrzeM · 17 March 2006, 11:29 AM

It's very simple: the photographed object moved during the film exposition to light. And the end of the propeller moves faster than the part close to axle.
So diring the exposition time end of the propeller was "photographed" in fact in all the locations in which it was diring the exposition, creating continuous picture, wider than the original propeller blade.

With the car it is exactly the opposite. In order to not have the photo moved, photographer was following the car with his camera (panning) as fast as the car was moving. But if he panned the camera little faster (nobody's perfect) than the car was moving, the car came out slanted forward. If he moved the camera too slow, effect would be the opposite.

Cheers!
G.