View Full Version : Bendy Puma Blades!!
Blind
22nd Sep 2005, 11:57
Any ideas on what is going on in these pics? I use an SLR film camera and understand the concept that fast shutter speeds will freeze the blades and slow shutter speeds will show the blades as a disc. These were given to me by someone who used a digital camera and I am a bit intruiged as to what is going on.
To prevent sarcy comments about CHC having dodgy choppers I will point out that the white Radome is a Bristow paint scheme.
http://www.helicopterservice.com.au/photos/pprune/Puma%201.jpg http://www.helicopterservice.com.au/photos/pprune/Puma%203.jpg http://www.helicopterservice.com.au/photos/pprune/Puma%202.jpg
Cheers.
NickLappos
22nd Sep 2005, 12:14
Those pictures were taken by a camera with a focal plane shutter, which uses a pair of black screens that slide across the film and sequentially expose the film to the picture from right to left. Since the right edge of the picture is exposed first, it catches the blade at an earlier part of its revolution. As the shutter screen sweeps across the film, the rotor is turning, so the center and left edge of the film catches parts of the blade that have rotated significantly.
This is a photographer's mistake, having selected a shutter speed that is close to the rotor frequency.
Modern cameras do not use focal plane shutters, they use a fast moving iris mechanism that moves radially, and produces fewer such artifacts.
Hi Blind
The shutter on a SLR camera is made up of a pair of screens (or blinds) that move very rapidly across in front of the film. When the exposure time is less than about 1/60th of a second then the two screens form a slot moving across the film. Each section of film is exposed for the selected time, however during the time the 'slot' moves across the film, the blades will move.
Does that make sense?:confused:
TeeS
wg13_dummy
22nd Sep 2005, 13:31
Whats the reason for the apparent 'floating' tail rotor blade in pic one? Ive seen a similar effect as the banana blades but never seen a blade appear detatched.
Jetboxer
22nd Sep 2005, 16:36
Looks like you need a new camera!!!!
OR
You've been sneaking a few bottles of the 'hard stuff' offshore!
Blind
22nd Sep 2005, 16:47
Nah, there's nothing wrong with the camera just need to adjust the shutter speed settings.
I do know which member of the deck crew took the photo though and I am sure he'd never sneek a coke can injected with Bacardi to work with him!! :\
Thanks for the techie answers, much happier now I know what was going on.:
Matthew Parsons
22nd Sep 2005, 16:51
Much like the mechanical blinds mentioned, many digital cameras will scan top to bottom. The rotor blades caught in the horizontal looking unaffected is evidence that this camera scanned top to bottom.
The floating tail rotor is just the tip that is passing down through the image faster than the camera is scanning.
Matthew.
My guess, main rotor blade.
The 'slot' didn't catch up with the blade early enough for the rest of the blade to appear at the top of the picture. (I think!!!:ugh: )
TeeS
(Or of course the engineer didn't bolt the tail rotor blade on tight enough!!!!)