Topic: Testing a focal plane shutter

[original_ann]

Anyone ever hear of doing this?
http://rick_oleson.tripod.com/index-135.html

[Skorj]

Makes good sense, as a TV screen is essentially a 50 or 60Hz strobe, depending on if you're PAL or NTSC... Skj.

[Francois]

This trick's been around for ages. For slower shutter speed, you can use a turn table with a piece of tape stuck to the disk.

But there's also some plans to make an electronic one on a French site
Mesure Vitesse

It uses a phototransistor and a few components to hook it to an old PC COM port... ingenious.

[Pete_R]

Anyone ever hear of doing this?
http://rick_oleson.tripod.com/index-135.html

Only works with CRT screens though, not flat screens.

[Francois]

Yes, that's true. LCD's don't scan like CRT's which use persistence of vision quite a bit in order to display anything.

[Pete_R]

But there's also some plans to make an electronic one on a French site

The phototransistor way, whether you plug it into a computer or use dedicated electronics, is OK for slower shutter speeds but it becomes increasingly inaccurate as the slit width of the shutter gets closer to the beam width. I can get reasonably accuracy with mine up to about 1/500th by using a laser fired through a pinhole to reduce the beam width to a fraction of a millimeter. Just using a sensor with a light shone through the lens probably won't be accurate much above the flash sync speed of the shutter.

[Francois]

True... but I was thinking on improving on the idea using the phototransistor from an old (OK, neolithic would be more accurate) 5 1/4 disk drive. I have a few which came with a plastic slit on a cover... might make it more accurate (a bit).

Though these things require often quite a bit of light to let power through...