Valid short exposure times

bulrichl

Hi,

I use an ASI294MC Pro since January 2018. I've got some questions about the valid values for exposure times using this camera. My questions concern especially short exposures, far below 1 s. I use Sequence Generator Pro (SGP) as capturing software and the ASCOM camera driver.

1) Is the ASI294MC similar to DSLR cameras, i.e. the exposure are "quantized" (e.g. 1/1000, 1/2000, 1/4000 s, but nothing in between)?

2) If the answer to 1) is yes: Is there a list of valid exposure times for this camera?

3) What is the shortest exposure that is supported?

4) What happens when an exposure time of 0 s is set?

5) Have I to use different software than SGP in order to get full access to very short exposure times?

I would appreciate a detailed reply to my questions very much, thank you.

Bernd

Sam@ZWO

1.no

the shortest exposure is 32us or 64us and this is the smallest unit of exposure

when you set 0, it will set to shortest exposure, 32us or 64us depends on your USB Bandwidth setting

you can use ASICAP to do short exposure

bulrichl

Thank you for your detailed answer, very much appreciated.

Bernd

Support@ZWO

You are welcome.

f23ljup2

@Sam@ZWO#18052 Is the exposure time always a multiple of 32us? For example, if an exposure time of 1ms is requested, is the exposure time rounded to 992us (31 x 32us)? What is the expected repeatability of the very short exposure times?

Tech@ZWO

f23ljup2 Nope, 1ms is 1ms.
I am not sure about the repeatability you said, could you tell us more specifically?

f23ljup2

I am trying to image bright stars so I am using short exposures, specifically 0.001 seconds. This would seem to be well within the camera's capability, but the variation from exposure to exposure is much higher than expected, considering the readout noise, dark current, sky noise, and the signal from the star. I suspect that the exposure time varies from exposure to exposure. This is why I am asking about the repeatability that I should expect for such short exposures.

My camera is an ASI290MM. My telescope is a WO RedCat 71, and I am using Johnson B and V filters. My target is Vega (alf Lyr), which is magnitude 0.03 (very bright).

Thank you for your help.

John

w7ay

f23ljup2 the variation from exposure to exposure is much higher than expected,

John,

Can you add a neutral density (ND) filter to the stack? An ND3.0 should give you a factor of 1000, which turns microseconds time scale to milliseconds.

Baader sells ND filters with factors of 0.6, 0.9, 1.8 and 3.0.

The 1.8 one will give a factor of 64 (i.e., transmission of 10^-x ), which might already give you the measurement constancy that you need. (The longer exposures reduce "seeing" dependencies too, that you would otherwise may need to make multiple shorter exposures, anyway.)

Chen

Tech@ZWO

f23ljup2
Don't have an accurate value, but several years should be ok.