exposure time fluctuates and is a bit longer than the value I set: Canon T4i

[jungshik]

I used BEOS 3.2.2 RC1 (Windows 10) on a Canon T4i to take a few hundred frames of 6 seconds. (I have an alt-az mount and the object is near South so that I couldn't take long subs).  Later, I found that the exposure time/shutter speed didn't remain constant.  Some frames are 6.4" while others are 6.1", 6" and so forth. The camera was  set to M (manual) and B (bulb).  With a release cable with an intervalometer, I never had this kind of shutter speed fluctuation.

Is there anything I can do to keep the frame length constant? 

BTW, I gave  a 2-second pause between frames and chose to save images on the camera only instead of downloading them to the computer. It just occurred to me that I used a 3-second pause instead of 2-second pause between frames when I used my intervalometer + remote shutter release code. I'm speculating that a 3 seconds long pause could have helped, but I'm not sure and still seeking to get others' take on this issue. 

 

Thank you, 

[admin]

All bulb exposures are timed using your computer.  Small fluctuation is caused computer cpu cycle and Windows Timers.

This said, why are you not using TV exposures when imaging < 30 seconds.  It's more precise and TV duration are controlled by the camera, not the computer.

 

 

[jungshik]

Thank you for the reply.

After posting my question, I also thought of using Tv instead of B for the same reason as you wrote.   I'll try that. 

BTW, in your experience, does it matter how long  the pause between frames is ? I want to make it as short as possible to take as many subs as possible.  That's why I chose 'save in the camera' because I found downloading images to computer takes time > 2 seconds. With a long exposure counted in minutes, the pause between exposures makes very little difference, but in my case (short exposures like 6 - 10 seconds), 2-4 seconds pause increase the image acquisition time significantly. 

[admin]

Pause is irrelevant.... it all depends on your computer's ability do to multi-tasking and cpu cycles.  As I said, BULB timing is dependent on your computer.... the bottom line you use bulb for long exposure and a few millisecond variations on 1+ minute is irrelevant.  For less than 30 seconds you use TV and never look back.

[astroman133]

I think that he was asking a second, unrelated question about using Pause in conjunction with Save To Camera.

If I remember, there used to be an issue with older versions of BYE where you needed to give BYE extra time to finalize saving an image to the camera's SD card. However, I believe that in BYE 3.2 that this was fixed. All I can suggest is to try it.