2016-04-01, 22:15
Yes this is true, we hear this marketing stuff all the time about screen refresh rate 120Hz, 240Hz and Epson talking abut "Bright 3D Drive Technology doubles the image refresh rate from 240 Hz to 480 Hz". It is very impressive but how it does really work and what the true frequency of the glasses is compared to fancy panel drive speed?
I had a chance to test Samsung TV with 3D active glasses one of the top models at the store with their demo disk. The display had this out of sync. jitter effect with active galsses. I wasn't quite sure if the settings were correct for this TV or this was limitation of the 3D active glasses.
Right now with the testing on my Epson projector I am convinced that all 3D active glasses for TVs and projectors are operating at 60Hz. This is independent from manufacture and design features brand names or not. If you put 3D RF glasses on and turn away from the projector or TV screen and look at the window day light. Move you head and eyes around or your hand against the window. You will see strong flicker a lot slower then 240Hz or even 120Hz. Human eye can notice flicker up to around 75Hz. The flicker of the glasses (try one eye only) does look like a flicker from old 60Hz CRT type of displays.
The image from couto27 probably some marketing material from Epson confirms that glasses are operating at 60Hz.
For simplicity we pick upper line 240Hz Drive. Please look at the starting upper point of the bright pink field marked as 1 Right. This will be the first time when the right eye gets the light. Shutter stays fully open for 1/240sec as per diagram and closes for phase change (right to left) another 1/240sec and then stays closed for 2 more cycles when the left eye gets the light and phase change again. By the time we get back to right eye fully open it will take four cycles of 1/240s. The complete cycle for one eye is 4 times longer then then the panel drive. 4 times of 1/240sec is 1/60sec equals 60Hz! Lens on one eye stays closed for 3 cycles of 1/240sec and open for 1/240sec (3 times longer closed then open). That makes those glasses very dark when activated.
When looking at 24fps video (North American movies) with the example above we will have 10 identical snapshots displayed by the screen using 240Hz panel drive and glasses showing 3 snapshots of identical frame and 2 snapshots of the next frame. Pushing the panel drive timing to 480Hz shortens the time when both eyes are blocked for left/right phase change but the cycle of glasses from right eye fully open to the next time right eye is fully open takes 8 cycles of 1/480sec! This is back to 60Hz per eye again!
The gasses operate opposite from left to right. 2 and 3 shots of consecutive frames are not at the same time for both eyes. This is probably more like 1 to 2 shots of the same frame per eye since the glasses are open for short period of time.
It's not as bad as it sounds. Most people don't see this as a problem. The reality is that activating good frame interpolation on the TV or projector removes 2:3 pull down effect generated by the glasses. Additional frames from electronic interpolation will be in sync. with the glasses.
The rating of the glasses up to 240Hz is probably referred as the ability of glasses to switch from fully open to fully closed. The faster the glasses the shorter the time of switching from fully open to fully closed eliminating ghosting etc. but the drive frequency for the for full cycle per eye would be still 60Hz.
Please correct me here if I'm wrong and provide some data.
I didn't take picture from my tachometer set up but if you guys insist I'll set it up again and post it here.
Tachometer is used for measuring of linear and rotary speeds. It also has optical sensor and reflective tape for measuring speed of rotating disks in RPM. I had this idea to point the sensor through one lens of 3D glasses with the reflecting tape on the other side. When glasses were active and synchronized with projector I got 3600 RPM as pulses per minute. This is 60 complete on/off cycles per second = 60Hz with slight variation for 23.976 fps.
I had a chance to test Samsung TV with 3D active glasses one of the top models at the store with their demo disk. The display had this out of sync. jitter effect with active galsses. I wasn't quite sure if the settings were correct for this TV or this was limitation of the 3D active glasses.
Right now with the testing on my Epson projector I am convinced that all 3D active glasses for TVs and projectors are operating at 60Hz. This is independent from manufacture and design features brand names or not. If you put 3D RF glasses on and turn away from the projector or TV screen and look at the window day light. Move you head and eyes around or your hand against the window. You will see strong flicker a lot slower then 240Hz or even 120Hz. Human eye can notice flicker up to around 75Hz. The flicker of the glasses (try one eye only) does look like a flicker from old 60Hz CRT type of displays.
The image from couto27 probably some marketing material from Epson confirms that glasses are operating at 60Hz.
For simplicity we pick upper line 240Hz Drive. Please look at the starting upper point of the bright pink field marked as 1 Right. This will be the first time when the right eye gets the light. Shutter stays fully open for 1/240sec as per diagram and closes for phase change (right to left) another 1/240sec and then stays closed for 2 more cycles when the left eye gets the light and phase change again. By the time we get back to right eye fully open it will take four cycles of 1/240s. The complete cycle for one eye is 4 times longer then then the panel drive. 4 times of 1/240sec is 1/60sec equals 60Hz! Lens on one eye stays closed for 3 cycles of 1/240sec and open for 1/240sec (3 times longer closed then open). That makes those glasses very dark when activated.
When looking at 24fps video (North American movies) with the example above we will have 10 identical snapshots displayed by the screen using 240Hz panel drive and glasses showing 3 snapshots of identical frame and 2 snapshots of the next frame. Pushing the panel drive timing to 480Hz shortens the time when both eyes are blocked for left/right phase change but the cycle of glasses from right eye fully open to the next time right eye is fully open takes 8 cycles of 1/480sec! This is back to 60Hz per eye again!
The gasses operate opposite from left to right. 2 and 3 shots of consecutive frames are not at the same time for both eyes. This is probably more like 1 to 2 shots of the same frame per eye since the glasses are open for short period of time.
It's not as bad as it sounds. Most people don't see this as a problem. The reality is that activating good frame interpolation on the TV or projector removes 2:3 pull down effect generated by the glasses. Additional frames from electronic interpolation will be in sync. with the glasses.
The rating of the glasses up to 240Hz is probably referred as the ability of glasses to switch from fully open to fully closed. The faster the glasses the shorter the time of switching from fully open to fully closed eliminating ghosting etc. but the drive frequency for the for full cycle per eye would be still 60Hz.
Please correct me here if I'm wrong and provide some data.
I didn't take picture from my tachometer set up but if you guys insist I'll set it up again and post it here.
Tachometer is used for measuring of linear and rotary speeds. It also has optical sensor and reflective tape for measuring speed of rotating disks in RPM. I had this idea to point the sensor through one lens of 3D glasses with the reflecting tape on the other side. When glasses were active and synchronized with projector I got 3600 RPM as pulses per minute. This is 60 complete on/off cycles per second = 60Hz with slight variation for 23.976 fps.
