3 ms·

As of today it should be easy to do a relatively cheap rapatronic-like camera with LCD film. The basic principle is more or less the same: two linearly (?) pol

As of today it should be easy to do a relatively cheap rapatronic-like camera with LCD film. The basic principle is more or less the same: two linearly (?) polarized sheets at 90° that block all the light going through, and a sheet/material in the middle that rotates 90° the light polarization when an electric current is applied. Some of those glass windows that can obscure instantly work with this technology. https://en.m.wikipedia.org/wiki/Liquid-crystal_display https://en.m.wikipedia.org/wiki/Liquid-crystal_display What I don't know is the speed of polarization rotation for liquid crystals (compared to a Kerr cell) that would define the minimum "obturation" speed available.

adg001 4y ago
A back of envelope calculation for the shutter speed of a Pimoroni LCD shutter [1] suggests 1/15s is the fastest speed available. [2] [1] Pimoroni LCD shutter [Not available any longer ] https://shop.pimoroni.com/products/lcd-shutter https://shop.pimoroni.com/products/lcd-shutter [2] Testing the amazing Pimoroni LCD shutter https://youtu.be/i3GCfAtdZYI https://youtu.be/i3GCfAtdZYI
- tecleandor 4y ago
  I've never researched much about this, but this company claims that TN shutters can do up to 100hz and "liquid crystal pi cells" can do 1000hz. http://www.liquidcrystaltechnologies.com/products/lcdshutters.htm http://www.liquidcrystaltechnologies.com/products/lcdshutter... This is interesting, I might expend the afternoon reading about it Edit: Related 6 years old EE Stack Exchange post: https://electronics.stackexchange.com/questions/276014/characteristics-of-tn-lcd-shutters-light-valves https://electronics.stackexchange.com/questions/276014/chara... Also this company sells a pi-cell shutter with "50 microsecond rise time 1.3 millisecond fall time" for ~$200USD. I have to calculate the refresh for that : https://boldervision.com/liquid-crystals/pi-cell-shutter/ https://boldervision.com/liquid-crystals/pi-cell-shutter/
LightRailTycoon 4y ago
Auto-darkening welding helmets claim 40 microseconds.
- tecleandor 4y ago
  That seems to match with a shutter vendor that says "50 microsecond rise time 1.3 millisecond fall time". So I guess 'rising' is going dark, and 'falling' is going clear. Or 'rising' means changing the natural state of the crystal (thus rotating 90° the polarization), and 'falling'... well, falling back to the natural resting state. It makes some sense that falling back when unenergized is slower than rising. Now it'd be interesting to know what happens during rise and fall time. Progressive linear polarization? Waiting time until the crystal reacts?
dekhn 4y ago
See https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=8166 https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=81... for examples of modern LCD shutters. They have closing times that are in the hundreds of microseconds, so they are not really replacements for ultra-short exposures. But they are "cheap".

adg001 4y ago

A back of envelope calculation for the shutter speed of a Pimoroni LCD shutter [1] suggests 1/15s is the fastest speed available. [2] [1] Pimoroni LCD shutter [Not available any longer ] https://shop.pimoroni.com/products/lcd-shutter https://shop.pimoroni.com/products/lcd-shutter [2] Testing the amazing Pimoroni LCD shutter https://youtu.be/i3GCfAtdZYI https://youtu.be/i3GCfAtdZYI

tecleandor 4y ago
I've never researched much about this, but this company claims that TN shutters can do up to 100hz and "liquid crystal pi cells" can do 1000hz. http://www.liquidcrystaltechnologies.com/products/lcdshutters.htm http://www.liquidcrystaltechnologies.com/products/lcdshutter... This is interesting, I might expend the afternoon reading about it Edit: Related 6 years old EE Stack Exchange post: https://electronics.stackexchange.com/questions/276014/characteristics-of-tn-lcd-shutters-light-valves https://electronics.stackexchange.com/questions/276014/chara... Also this company sells a pi-cell shutter with "50 microsecond rise time 1.3 millisecond fall time" for ~$200USD. I have to calculate the refresh for that : https://boldervision.com/liquid-crystals/pi-cell-shutter/ https://boldervision.com/liquid-crystals/pi-cell-shutter/

LightRailTycoon 4y ago

Auto-darkening welding helmets claim 40 microseconds.

tecleandor 4y ago
That seems to match with a shutter vendor that says "50 microsecond rise time 1.3 millisecond fall time". So I guess 'rising' is going dark, and 'falling' is going clear. Or 'rising' means changing the natural state of the crystal (thus rotating 90° the polarization), and 'falling'... well, falling back to the natural resting state. It makes some sense that falling back when unenergized is slower than rising. Now it'd be interesting to know what happens during rise and fall time. Progressive linear polarization? Waiting time until the crystal reacts?

dekhn 4y ago

See https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=8166 https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=81... for examples of modern LCD shutters. They have closing times that are in the hundreds of microseconds, so they are not really replacements for ultra-short exposures. But they are "cheap".