Logitech C920 Manual Exposure Weirdness

[electronsandstuff]

Has anybody had success using manual exposure on a Logitech C920 webcam in labview?

I have a working VI which grabs images.  Everything works except that when I went to do manual exposure I can set the "exposure mode" attribute to manual and then change the the exposure values to something in the allowed range it sometimes changes it back.  That is I'll set it, and when I take the image about half of the time it is with the exposure I set and half the time it has changed it to correctly expose the image and I can read back the new value.  The camera still says it is in manual exposure mode though.

I've also been able to replicate this in the measurement and automation explorer.  That is, I set exposure to manual mode and then drag the slider to some random exposure value, but the camera will change it back while staying in manual mode.  It really doesn't make sense and I thought I'd check if anyone has experience with this.

[Bob_Schor]

Offhand, it sounds like the Logitech camera is not "taking" the "Manual Exposure" setting.  It could be something you are doing (which we can't evaluate because, as so often happens in the Forums, you failed to post your code, so even if we had the identical camera, we wouldn't be able to see if we could duplicate your finding), or it could be the camera (in which case you need to contact Logitech).

For further help, post (all of) your code!  Do not post "pictures" of code, post the actual VIs.

Bob Schor

[electronsandstuff · Accepted solution]

Solved it!

For anybody coming across this post, the issue was that for this particular camera "IMAQdx Start Acquisition" will helpfully try to autoexpose and autofocus the camera before you acquire the image.  The camera does this even when in manual exposure mode.  This was fighting with me trying to change exposure myself.  I was able to fix it by breaking out the IMAQdx Grab VI into it's components and dropping my exposure setting code in between.

[Wattorama]

Out of curiosity, is there a way to (in the files that the camera uses) manually set manual focus, zoom and focal length?

I am apparently unable to have any settings survive restart. 

[matan0200]

Actually, using q4vl2 on linux, I'm getting the exposure take immediate effect on the camera stream as I use its exposure time slider. With what I'm pretty sure is a logitech C920 from comparing the looks of it to online images. And it clearly sticks at the exposure level that I set it in real time. So it's likely not a limitation of the hardware IMHO. Unless they had multiple firmware versions for this model.