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General high-speed discussion / Re: Speed Calculations
« Last post by wally_x on July 18, 2019, 01:14:48 PM »
Awesome! Thanks again for you help!!
Chronos User Discussion / Re: Chronos 1.4 Footage Thread
« Last post by PaulBryanTV on July 18, 2019, 12:41:24 PM »
LONG time since I posted here but I am getting back into my slow mo.
3D printed a ballista to fire and a test cube to hatchet.
Chronos User Discussion / Re: frame straddling
« Last post by foobar on July 17, 2019, 11:50:45 AM »
I'm afraid that this particular pattern of exposure and frame timing will not work. When the camera is operating in gated burst mode the rising edge of the trigger signal starts the exposure for a frame and the falling edge ends the exposure and begins the frame readout. During frame readout, the exposure for the next frame can be started but the exposure must continue for long enough that the falling edge happens after the readout of the first frame completes. A falling edge of the trigger signal while frame readout is in progress will be ignored because the pixel storage nodes on the image sensor are in use and are not able to accept another frame.

Because the image sensor does not have a physical shutter, there is no way to stop or pause the exposure of a frame, the exposure control is actually a signal that just continuously resets the state of the photodiodes to an unexposed state. At the end of exposure, the charge is transferred from the photodiodes into storage capacitors that hold the charge during sampling and readout. Therefore, the end of exposure must be concurrent with the start of the frame readout and only one frame can be held in the storage nodes at a time.
Chronos User Discussion / frame straddling
« Last post by PIVer on July 17, 2019, 10:02:39 AM »

I am trying to set up a Chronos 1.4 for particle image velocimetry (PIV) measurements. Many details about PIV are not important in this context, but two are: 1) images are taken in pairs, and 2) you should have control of the time between frames. The latter is, of course limited by the frame rate, i.e. you can't have a 500us inter-frame time if your recording at 1000 kHz.

One trick to decrease the effective inter-frame time is to use frame straddling, that is, use pulsed illumination at the end of the first image and at the beginning of the second image (see attached figure). While this works very well if you don't have no light apart from your pulsed illumination, the image quality is deteriorated when you have a long exposure time and there is significant ambient light.

To minimize the effect of ambient light, I would like to reduce the exposure using Shutter Gating (as also shown in the figure). By limiting the exposure to only a few microseconds before and after the illumination pulse, the ambient light that makes it to the CMOS would be negligible. My question is: can such a timing sequence be achieved?

Thanks for any help.
Chronos User Discussion / Re: Chronos 1.4 Footage Thread
« Last post by PointyHairedBoss on July 15, 2019, 05:30:21 PM »
Slo mo birds at our feeders. All video recorded at 1057 fps, edited with PowerDirector 16.
General high-speed discussion / Re: Speed Calculations
« Last post by BiduleOhm on July 14, 2019, 07:28:10 PM »
Here you've done time over distance, not distance over time, so that's not good. The speed is actually 400 ft/s (2 / 0.005). Everything else is right ;)
General high-speed discussion / Re: Speed Calculations
« Last post by wally_x on July 14, 2019, 07:08:58 PM »
So basically if my object moves 2 ft on my chart in 10 frames and I was shooting at 2000fps then the math is something like:

10 divided by 2000 = .005 seconds. That divided by 2 gives me .0025 ft/sec, which I can convert to mph or anything else. This sound right?
General high-speed discussion / Re: Speed Calculations
« Last post by BiduleOhm on July 14, 2019, 06:58:57 PM »
The playback speed doesn't matter.

What you want to do is to count the number of frames the object takes to move from the start point to the end point you chose on your speed chart.

Then as you know the framerate of the capture you can know the time (frames number / fps = time in seconds) and you have the distance (let's say it's a foot) so you just have to do distance / time to have the speed in ft/s (or whatever distance you chose on your reference chart, per second) ;)
General high-speed discussion / Speed Calculations
« Last post by wally_x on July 14, 2019, 06:28:39 PM »
Hello, I was wondering if someone could help me with the math on calculating the speed of a moving object that I record with my Chronos.

I've built what I call a "speed chart" (black and whiteboard behind the moving object like on Mythbusters) and I know my capture frame rate and my playback frame rate, but not sure what the equation is. Especially with the capture speed vs the save or "playback speed".

Any help would be much appreciated!

Chronos User Discussion / Re: Corrupted SD card
« Last post by Prehistoricman on July 12, 2019, 11:05:19 AM »
I managed to recover all the files using a tool called PhotoRec. I had previously re-compressed the videos over to my PC so I had all the file names. So it seems that only the file descriptors were corrupted.

I've filled the card and didn't get anything to happen. Perhaps a greater number of files triggers the issue. I'll try copying over all the videos I had and see what happens.

I bought a Samsung Evo Plus 64GB to replace it.
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