ASI174MM exposure issue

[janek950]

Hi,
when using ASI174MM camera and exposure times shorter then 500ms, everything is OK. However when I enter exposure time 500ms or more, there is (on average) 222ms dead time between exposures. No preprocessing, I've been playing with USB setting etc - no way. The same on two different computers. Both running W10 with latest updates, last camera driver 3.0.0.6 and last SharpCap. Is this a bug or some mystery setting can help ?
Thanks ...

[admin]

Hi,

For exposures below 500 ms the program runs the ZWO cameras in video mode – basically the camera is continually taking images. For longer exposures the program runs the cameras in a still camera mode where it requests each image to be captured separately. I'm sure that this is what is leading to the delay between exposures. Still camera mode is required for longer exposures as it is more robust when doing things like cancelling an exposure part way through in order to change the length of the next exposure.

Hope this helps, Robin

[janek950]

Hi,

this explanation clears situation - thanks. However as one of the purposes of the camera (for me) is timing occultations, such dead time is really unwanted. It's a pity but I have to use for camera control in those rare cases where >=0.5 second exposure time is needed, some other SW handling this in better way.

BTW - is this situation common also for other ASI cameras - like ASI1600 MM etc. ?

Many thanks, Jan

[admin]

Hi,

This is common to all ZWO cameras. There is no particular reason for the cut off point to be 0.5 seconds – I wouldn't be averse to increasing it to perhaps two seconds, although higher than that would probably start to be a problem with responsiveness when you change the exposure control. Would a two second exposure be sufficient?

Thanks, Robin

[janek950]

Hi,

yes, I think 2 seconds will be enough. That would be great !

jan

[Bob_CA]

Robin,

I'm also an occultation observer, though I'm using smaller-chip rolling shutter cameras (ASI462MM and ASI290MM) and am seeing a similar big jump in dead time, though for me it's for exposures >= 1 second. Given that for exposures shorter than 1 sec there seems to be essentially no dead time, I'm assuming the cause is the same as with the ASI174.

Was this changed to 2 seconds, or only 1 second?

I also see similar behavior with a Player One Mars-M camera (also IMX-290M sensor).

There are very few circumstances where one would want to use 2 or more second exposures for occultations, but occasionally 1<T<2 is helpful for very faint target stars, and longer events like TNOs. Any chance we could get that 1-2 sec exposure window without a big jump in dead time?

Thanks,
Bob

[admin]

Hi Bob,

the changeover between video mode and still mode for ZWO cameras is currently set at 2s - that is, if the exposure is 2s or above you will be in still mode with the potential for dead time, at less than 2s you will be in video mode with (theoretically) no/minimal dead time.

There is no such changeover in the SharpCap code for PlayerOne cameras - SharpCap operates them in video mode for all exposures unless you switch the whole of SharpCap from live mode to still mode.

I guess I should point out that what I'm describing above is just covering how the issue is handled in the SharpCap code - I can't be sure of how this is handled internally by the ZWO SDK or the PlayerOne SDK... Perhaps those change behaviour as the exposure time increases leadng to dead time even with the camera in video mode?

Unfortunately I can't see anything in either camera SDK that would give more control over this

cheers,

Robin

[Bob_CA]

Okay, Thanks. Naturally I have no way to know what's going on in the camera drivers either. I thought it worth checking to see if SC had anything to do with it, particularly after seeing Jan's message.

Bob