The old Motor Sport car "Leaning Forward" effect

[Sirius Glass]

It was caused by the focal plane shutters in Speed Graphics. Due to the travel of the shutter, the top of the car would get a slightly earlier exposure than the bottom, resulting in the leaning effect.

Yes, except you need to multiply what you said by -1. The bottom of the image is exposed first, then the top providing the forward lean as in the top is further forward than the bottom. To confuse things, this means that the focal plane slot goes from top to bottom - remember that the image is inverted in the camera.

Stev

[polyglot]

What matters is the relationship between the speed of the shutter curtains and the rate at which the subject is moving across the film plane. Motion blur will also occur, the amount of which will increase with slit width and subject velocity.

So to get the nice distorted effect, you want to have a very narrow, slowish-moving slit and fast-moving subject. In terms of an SLR, you can tell how fast the slit moves by looking at its flash x-sync speed, since that is the shortest shutter wherein both curtains are open concurrently. Say you have an x-sync of 1/160s, that means it takes about 1/160 for one curtain to open and 1/160 for the other to close and the width of the slit is 1/160 of a second. Run that shutter at 1/1600 and the slit will be about 1/10 of the frame wide and at 1/8000 it will be 1/50th of a frame wide. If you can find a subject that moves appreciably in 1/160 of a second (the total exposure duration), then the distortion will be visible.

If you want to cause the distortion, look for a camera with a really slow - like 1/50s - x-sync speed: at that speed, it takes each curtain 1/50s to traverse the frame. So to get the distortion without too much motion blur, you need a shutter speed of about 1/2500 and a subject that can move an appreciable distance across the frame in 1/50s.

If you want extreme, go buy a (sorry it's not analogue) scanning back In fact, you could think of the slitted-cloth shutter on the 4x5 as a kind of scanning back... same goes for clockwork pano cameras that expose using a slit.

[Francis in VT]

I think I understand most of the replies to this post.
I also remember one of the photo magazines years ago doing a story on this subject. They used a camera with a cloth curtain, probably a Leica but they did a series with the camera in different positions to change the curtain direction. The wheel image changed from forward to reverse to no direction at all.
Hopefully someone else will have a better memory of the article.

Francis in VT

[polyglot]

If the bottom of the image (top of the film plane, considering it's inverted) is exposed first, the wheel will lean forwards. Conversely to get it to lean backwards. If the shutter travels in the same direction as the wheel, it will not be sheared but it will be either stretched or compressed, depending on which way the shutter is travelling.

[lxdude]

BTW, that's a picture of the first car and driver that won the first Indy 500.