Global Reset Shutter, with external mechanical shutter

[Scipione205]

Hi,

from an old post of a1ex :

There seems to be a global shutter for starting the exposure, but a rolling one for stopping it. It's visible on the motion blur shape from the full-res silent pictures, which matches the graphs from the other thread.

It's called 'Global Reset' and is available on scientific CMOS sensors. I was wondering if it was possible to do it, and sending a signal outside the camera for each RESET (and also the time of the shutter selected in Exposure Override), while shooting movies (either in H264, either in RAW).

WIth an external shutter it would be possible to caputre action scenes (fast moving cars, trains, chasing, rapid camera movements), flashes and gunshots' muzzle flashes, etc. I feel the camera with the rolling shutter an extreme stop to my creativity.

The ARRI Alexa Studio M works in this way: it has a regular rotary disc shutter (so it has got a conventional loupe, also).

In another thread I asked if it was possible to synch the camera's shutter with an external one, and you guys told me it was possible using the led. However I thought it was useless, because the sensor need to be reset on all lines as soon as the shutter will open (and the it doesn't matter how much time is needed to scan all the lines in rolling mode, but at least before the next global reset.).

Hope it would be possible.

[CITY-U1001]

rolling shutter - LCD shutter experiment

[Greg]

Wow, it looks great. 
This can be used with full res silent pic.

If this is to go to 1000MHz. We can go x-sync 1/1000s

[Scipione205]

Ok how to implement that on EOSs ? I am very disappointed by the RS on the cameras we have acces to here (600D, 6D, 5D MkII/MkIII, BMCC 2.5K ) because I can't let the steadycam operator to do slap pans, we can't record muzzle flashes and I can't implement 'broken' flickering neons in the scene.

[ItsMeLenny]

Very cool.

@CITY how did you sync it?

[Scipione205]

not only how did he synced the LCD shuttr, but also did he performed a Global Reset?

[ItsMeLenny]

not only how did he synced the LCD shuttr, but also did he performed a Global Reset?

I believe that is the point of the LCD shutter. The sensor already starts with a global start (and the LCD shutter open), but then when the first line finishes its capture it closes the LCD shutter, resulting in the rest of the lines capturing black (nothing) for the rest of their exposure.

[CITY-U1001]

ItsMeLenny its not my video 

[Scipione205]

he's Italian, like me, today I will try to call him

[a1ex]

The sensor already starts with a global start

This only happens in photo mode. In LiveView, it uses rolling shutter for both start and end.

I don't know how to switch between the two modes yet.

[Levas]

Now if he or someone else can make this LCD shutter fit into a box that fits inside the camera like those AA filters from Mosaic Engineering...

[Scipione205]

This only happens in photo mode. In LiveView, it uses rolling shutter for both start and end.

I don't know how to switch between the two modes yet.

I downloaded the original video and examinated it frame by frame; I don't think he just synchronized the LCD Shutter with the Sensor's readout (First Line reset = Ex. Shutter Opened, Last line readout = EX Shutter closed), because in this case the effect would be like when you are filming in video mode, in a complete dark room, an a flash flashes.

The only way to overcome the Rolling Shutter readout without using Global Shutter Circuits (on all the scentific literature I studied, the Global Shutter is always connected in a loss of DR performance), is to perform a Global Reset on all the lines, keep opened the external shutter for the exposure time selected, and then read the lines in the classic rolling way after the external shutter is closed.

I don't know how he did this, I'm still struggling to contact him, today I will try to do a series of phone calls to find him.

@a1ex:

I was thinking that since in silent picture mode you saw that blur effect (I assumed that it is a Global Reset readout, but without the camera's mirror shutter operating, so you see that effect) maybe it would be possible to do that when shooting RAW?

I don't remember how the RAW Video trick works; I recall that we just grab the data from the buffer or VRAM, but maybe in LiveView mode it is still impossible because since the Mirror Shutter is locked in the open positions, the camera does perform Rolling SHutter Readout to allow you see in the LCD.

I will find him today and ask, that's a promise.

[dmilligan]

(First Line reset = Ex. Shutter Opened, Last line readout = EX Shutter closed)

Why wouldn't you do: last line reset = shutter open, first line readout = shutter closed? You would just need to use a shutter speed in camera that's as close to the frame rate as possible (as soon as you readout a line you turn it back on).

If you think about it, it makes no difference if you can do a global reset or not, as long as you turn each line back on right after reading it out, all of the lines will be back on by the time you open your external shutter (it makes no difference if they come on early).

I was thinking that since in silent picture mode you saw that blur effect (I assumed that it is a Global Reset readout, but without the camera's mirror shutter operating, so you see that effect) maybe it would be possible to do that when shooting RAW?

The silent picture mode that a1ex is talking about is a "photo" mode. It does not use LV (you use it "from" LV so that the shutter/mirror mechanism is open, but during this time, LV itself is actually disabled). In LV, only rolling shutter is possible (for now).

[Scipione205]

Why wouldn't you do: last line reset = shutter open, first line readout = shutter closed? You would just need to use a shutter speed in camera that's as close to the frame rate as possible (as soon as you readout a line you turn it back on).

If you think about it, it makes no difference if you can do a global reset or not, as long as you turn each line back on right after reading it out, all of the lines will be back on by the time you open your external shutter (it makes no difference if they come on early).
The silent picture mode that a1ex is talking about is a "photo" mode. It does not use LV (you use it "from" LV so that the shutter/mirror mechanism is open, but during this time, LV itself is actually disabled). In LV, only rolling shutter is possible (for now).

Maybe I understood what you mean...