Added ZWO settings dialog?


I see:

“Added ZWO settings dialog”

in the release notes for, but I don’t know what that means or where to find it.

The ASCOM settings for my ZWO camera look the same.

Please advise.

Auto Exposure

It’s in the native implementation for ZWO, not the ASCOM driver. Camera device is “ZWO Camera”.



Here is a screenshot of it. Pretty simple:



OK thanks.

Any reason to prefer that to the ASCOM driver (which has more settings and info)?

I’m not having any issues with the ASCOM.


With the native you can set gan and offset per event within SGP. With ascom
you cannot. Essentially just more control over the gain and offset with the
native. But if ascom is working just fine then no real reason to change


Jared Wellman
– Co-Founder and Developer



I use the ASCOM drivers for ASI camera and have been using the set gain and offset by event and it works.


The gain should work but the offset won’t work with the ASCOM driver.


Jared Wellman
– Co-Founder and Developer


Just to be clear, you’re using the ASCOM driver and setting both gain and offset?

What are the chances of adding this for QHY cameras?


We cannot set offset through ASCOM. So you won’t get offset values set. Only gain.

Good if I can get a cmos loaner from them (@bmorrelltx) . My Qhy11 had to take an unexpected trip back to China. Hope to have it back soon.



Jared the ascom driver sets the gain and offset. So I’m not sure what’s
going on… Bruce


Correct. You can set these in the ascom driver but we can’t set them in SGP due to the fact that ascom doesn’t expose offset. We added native support for ZWO so that isers can set gain and offset per event. We’d like to do the same for QHY.



If users are changing gain or offset per event, they Will also need
calibration frames for each… on surface it does not sound like a good
idea? … Bruce


I would think it essential to have separate calibration frames for each combination of gain and offset. Bias and darks at least. Flat fields could be common but it would be worth checking that.

Also the offset must be set so there is still a small ADC value in the bias frames.

Thinking about it, if the gan is changed then flat frames will also be needed for each gain. The flat frames compensate for changes in sensitivity and the gan changes the sensitivity.


This is exactly why we NEED the ability to change gain AND offset per event. Many people have a gain/offset setting for LRGB and a separate gain/offset setting for narrowband. As it is right now, only gain can be set per event, meaning that we can only take LRGB OR narrowband during a night’s imaging session (unless of course we manually pause the sequence and change the offset). Adding the ability to change offset would allow us to mix and match LRGB and narrowband on the same night.

I’ve gotten around this by having the same offset for both LRGB and narrowband, but I think it would be better to be able to have a lower offset for LRGB and higher for narrowband.


If you set the offset so that you can’t see the black point then you can’t calibrate. There’s no point is setting the offset any higher than that.


I don’t quite follow Chris. Are you saying: there’s no point in setting the offset any higher [than where I can see black space on the left side of the histogram]?

If so, I get that. Offset isn’t super critical and as long as the black point isn’t clipped that’s all that’s necessary. Still, I’ve found that for narrowband if the offset is higher then it makes processing a bit easier to avoid clipping. But yeah, the offset isn’t critical.


There are several LONG threads about proper exposure of asi1600 on cloudynights, and a lot with math I don’t follow, but multiple people have come out with recommendations similar to this chart:

“Median ADU shown in SGP:
Gain 0 Offset 10: 400 ADU
Gain 75 Offset 12: 550 ADU
Gain 139 Offset 21: 850 ADU
Gain 200 Offset 50: 1690 ADU
Gain 300 Offset 50 : 2650 ADU”

You would use the lowest gain/offset combo that gave you a reasonable number of subs to stack, over your planned integration time.

Probably Gain 0 for LRGB or OSC and maybe gain 139 or 200 for NB.

I shoot for a medium ADU above the targets in the chart, but with stars not clipping.

FYI there’s another set of charts (also for asi1600) that predicts exposure time, given f ratio, light pollution and moon age, for LRGB and NB. In those the target parameter is “expected ADU above bias”.

The ultimate results are said to be similar, however for the 2nd set of charts it didn’t seem to map to the broadband exposure I ended up with (at my f ratio and sky).


I think that’s what I mean, the dark or bias frame will show a peak on the left hand side which corresponds to the range of zero values for the different pixels in the image. You should be able to see almost all of the peak.

As for gain AIUI what you need to look at is the ADU units as electrons per ADU. Once you have one ADU per electron additional gain will give no improvement.

Where you need reduced gain is if the total number of electrons in each pixel - the well depth - is greater than the number of ADC levels.


In all this discussion of gain for this camera, I not sure that everyone realizes that as you increase gain you are losing dynamic range. At zero gain you are starting with about 12 bits of resolution and 300 gain you are down to 8 or 9 bits. When you stretch an astronomy image as much as is needed, the lower resolution results in a blocky looking image. If you are shooting nothing but stars, the lower resolution might work. But if you are shooting a galaxy or nebula, you need the extra resolution to get good detail. For me, I shoot every thing at zero gain because I want the details.
Here is the graphs for the camera: Look at the DR (Dynamic range) graph. Every f stop is a loss of one bit of resolution.


But like all things in Astroimaging, it is a trade off.

You may need a higher gain so your NB sub exposure isn’t longer than your ability to guide.

Short exposures (if guiding or seeing is the limiting factor) could yield more detail than longer “blurred” exposures. That’s the cooled cmos short exposure theory anyway.