# Focal plane distortion

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• 03-20-2012, 02:42 AM
Leigh B
Quote:

Originally Posted by RalphLambrecht
i thought, yhis image was an example of horizontal shutter distortion with fast-moving subjects, which is different to focal-plane distortion.

Nope. Horizontal distortion stretches the subject width without distorting vertical lines.

Think of a narrow slit moving across the film. Lines parallel to the slit will not be distorted.
Lines perpendicular to the slit will exhibit distortion, the specifics of which depend on the direction of subject and shutter movement.

As a shutter slit moves across the film, different areas of the film capture different points in time,
i.e. the 1/500th sec at the top of the film is not the same time as the 1/500th sec at the bottom.

- Leigh
• 03-20-2012, 04:21 AM
Ian Grant
Quote:

Originally Posted by RalphLambrecht
i thought, yhis image was an example of horizontal shutter distortion with fast-moving subjects, which is different to focal-plane distortion.

It depends on what you mean by Horizontal and vertical. These older Focal plane shutters tended to have blinds that had a horizontal slit that moved vertically for the exposure, like modern Seiko SLRshutters. Older SLR's tended to use cloth shutters with a vertical slit that moved horizontally.

When governed by tension and slit width like on a 5x4 Speed Graphic a horizontal edge of the shutter curtain slit takes just over 1/10th of a second to cross the film plane at the minimum tension #1, yet with the narrowest slit width this gives a shutter speed of 1/350th. So there's a time lag of 1/10th between the exposure at the top and at the botton, slightly longer if a wider slit is used.

Even at the top speed of 1/1000 which is at the maximum tension #6 there's a lag of 1/35th of a second.

Ian
• 03-20-2012, 04:26 AM
Schlapp
http://www.flickr.com/photos/schlapp/2833892718/

Using a auxiliary shutter [slot in cardboard in front of lens]. My partner walking .
• 03-20-2012, 07:28 PM
Newt_on_Swings
Moving roll film would work as well. I asked about this a bit back as well. I'll post the link for the old post when I can find it later.
• 03-20-2012, 07:48 PM
Leigh B
Quote:

Originally Posted by Sirius Glass
I tried 1/30s, 1/25s, 1/20s, 1/15s, and 1/10s multiple times slowly panning cars move 50mph perpendicular to me

Hi Sirius,

Like I said... Your shutter speeds are too slow.

To get the "sliding" effect you need a narrow slit moving across the film.

At the speeds you listed I believe the SG focal plane shutter is completely open, which will not deliver the desired result.

- Leigh
• 03-20-2012, 10:14 PM
Newt_on_Swings
http://www.apug.org/forums/forum42/8...an-camera.html

I will have to revisit it again soon as the weather is nice now, I never really got the chance to do it, and when I did set it up, I didn't have a target I could get to easily to experiment with. Plus I think a motor for rewinding would provide a better/steadier flow than hand winding.
• 03-22-2012, 08:28 PM
jnanian
Quote:

Originally Posted by Sirius Glass
Thanks, I will try it again with a smaller slit. I guess that I had bad advice before.

i did mine at 1/15 of a second .. (the one posted) ..
i have done more than once ...
perhaps both advisements are correct ... ?
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