PDA

View Full Version : Dmk21618 usb



fast Freddie
July 13, 2012, 23:51:00
If I set a frame rate of 60 and 1/30 second exposure I only get about 24fps as shown on the live view. If I drop the frame rate to 30fps I actually get 30fps as shown in live view as I would expect for 1/30 sec exposure. Why is the actual fps lower when set to 60fps? Am using 2.2.345.1235.
Thanks

fast Freddie
July 19, 2012, 20:38:27
Anyone any ideas?

Stefan Geissler
July 20, 2012, 09:23:13
Hi Freddie,

I am very sorry, but I lost your question from my focus.

The question is very common.

If the camera runs with exposure times longer than the frame rate's time interval allows, then the camera changes the internal working mode. There are two of them:
1. ) exposure time shorter than frame rate:
exposure and image delivery to computer is done in parallel, that means, delivery time is frame rate time.
2.) exposure time longer than frame rate:
exposure and image delivery is done in sequence, that means, delivery time is exposure time + frame rate time.

Therefore, the frame rate is below the exposure time.

fast Freddie
February 27, 2013, 10:03:43
Hi Stefan, I usually use 1/30 -1/60 exposure and have used the information you gave about the camera working mode to deliver the maximum frames to my computer and this works as expected and described in your reply. However, I have just found that at 1/13 exposure, the maximum frame rate is achieved when the frame rate is set to 60. In live view, I get 11pfs when set to 60, 10fps when set to 30, 7fps when set to 15 and 8fps when set to 7.5. This doesn't follow the camera operating mode you have described. any thoughts?
Thanks
Freddie

Stefan Geissler
February 27, 2013, 11:28:09
Hi Freddie,

I do not know the exact timing of the USB controller. I only know , USB 2.0 is a little bit faster (480mBit/s) as FireWire (400mBit/s). Maybe this makes the difference.

In order to clarify your question completely, I would have to setup a lab with measurement equipment. It would take several hours to do this for me. Is this question essential for you?

The exposure times are as correct as possible, this was verified by measurement directly on the camera sensor.

fast Freddie
February 27, 2013, 12:19:35
Hi Stefan, thanks for getting back to me. I wouldn't say that this is essential but it would be very interesting as it appears that the the camera mode operation you described does not apply at long exposures of 1/13 or slower. At 1/15 and shorter the camera mode rule you described applies exactly as you have stated but at 1/13 I get more fps showing on live view when the cam is set at 60fps than I do at lower fps settings. This therefore does not comply with the rules you have described and I just found that interetsing and wondered why. Maybe if you get some spare time you could look to see why your rule does not apply at 1/13 sec or slower exposures.
Thanks
Freddie