Hi,
I am working with a ZWO ASI174MM for some 16bit solar imaging. I'm trying to understand the timestamps as provided in the SER file, in particular as they compare to the info in the CameraSettings.txt file.
What I'm wondering about is whether or not the "exposure" listed is really the interval between frames and if the shutter time would be something different? The interval between the SER file timestamps matches the set and stated "exposure." But I would imagine that it actually takes a bit of additional time between frames being recorded.
I saw an example of output from FireCapture where someone had a "shutter" of 1ms but the timestamps showed an interval of a few ms.
Is there a way to interpret the info so I know what corresponds to the exposure/shutter interval and what corresponds to the time the exposure began/ended? I've tried Google but my search skills seem to fail me. And I apologize if I should have posted this in a different topic area.
Thanks in advance,
mconsidine
Shutter time vs exposure interval?
-
admin
- Site Admin
- Posts: 13287
- Joined: Sat Feb 11, 2017 3:52 pm
- Location: Vale of the White Horse, UK
- Contact:
Re: Shutter time vs exposure interval?
Hi,
there are two limitations on the frame rate (or the interval between successive frames if you want to look at it that way round).
1) The length of the exposure you are taking
2) The time taken to transfer the image from the camer to the PC
For longer exposures, the frame rate/exposure interval will be limited by the exposure length - at 100ms exposure you will get a frame every ~0.1s and ~10fps. For shorter exposures, you are limited by the time taken to transfer to the PC - at 1ms exposure with your 174MM, you might get up to about 165fps, so you can see that the camera will spend about 1ms exposing, then about 5ms transferring the data before starting the next 1ms exposure.
In general, the time between exposures is pretty small when the camera is in video mode and the transfer rate is not limiting you - probably well under 1ms gap. I have certainly seen frame rates of >2000fps on the 174 model cameras with a small ROI.
The timestamps in the SER file for this camera will be the timestamps from the computer clock at the point that SharpCap received the frame data from the ZWO software. That is some point after the end of the exposure time of the frame, but the actual offset is unknown (depends on the time to transfer the data to the PC and the amount of time the ZWO software spent handling the data before giving it to SharpCap).
Hope this helps,
Robin
there are two limitations on the frame rate (or the interval between successive frames if you want to look at it that way round).
1) The length of the exposure you are taking
2) The time taken to transfer the image from the camer to the PC
For longer exposures, the frame rate/exposure interval will be limited by the exposure length - at 100ms exposure you will get a frame every ~0.1s and ~10fps. For shorter exposures, you are limited by the time taken to transfer to the PC - at 1ms exposure with your 174MM, you might get up to about 165fps, so you can see that the camera will spend about 1ms exposing, then about 5ms transferring the data before starting the next 1ms exposure.
In general, the time between exposures is pretty small when the camera is in video mode and the transfer rate is not limiting you - probably well under 1ms gap. I have certainly seen frame rates of >2000fps on the 174 model cameras with a small ROI.
The timestamps in the SER file for this camera will be the timestamps from the computer clock at the point that SharpCap received the frame data from the ZWO software. That is some point after the end of the exposure time of the frame, but the actual offset is unknown (depends on the time to transfer the data to the PC and the amount of time the ZWO software spent handling the data before giving it to SharpCap).
Hope this helps,
Robin