ZWO - Camera & ASIAir settings

[CheshireChris]

In the absence of any clear sky in NW England l have several questions about what settings to use and perhaps equally important when.

Setup is ZWO based : ASIAir/AM3+TC40/ASI533MC Pro/ASI120mm mini+ZWO Mini Guide Scope/Samyang 135mm - only filter is a ZWO IR Cut filter (which l haven't captured an image with - yet) I've not even managed to get the guide scope focussed.

I get the fact that no single set of parameters can be universally applied and conditions will vary over several nights imaging sessions: if l ever get several any clear nights.....

1. How do l decide what gain and exposure times to use for a given subject? The two images l have managed so far (NGC7000 & M31) look great - to me - for first images and were shot at the default gain of the ASI533MC Pro.

2. BIN Settings - when might l need to change them? I get the impression that anything other than BIN1 isn't much required but do wonder why it's there?

3. Temperature - so far just used -10deg. Do l really need to use any other value?

4. Calibration frames - l have shot a lot of dark frames at various gains/exposure times but so far have not shot any flat/bias frames...yet - indeed some astroimagers (mainly on youtube) seem not to bother with them for dedicated astrocameras (DSLR's are a different matter). A bit unclear on that one.

5. Best dither settings (assuming l get the guide scope set up correctly!) for the Samyang 135mm.

I have watched lots of YouTube videos - probably too many - but l enjoy watching those by Trevor Jones (AstroBackyard) & Peter Zelinka: far more interesting than anything on TV.

Thanks

Chris

 

[Tony Acorn]

Excelent set of questions Chris and I will be interested to see what the learned body of SG reply as it will be informative for my bundle too - even if that has an ASi533MC-Pro rather than my ASi585MC (not pro) camera.

Thanks for asking and hope we both get some more frequent clear sky nights!

Tony

[Elp]

1. On a per target basis based on the signal being emitted and your local LP level. Only you can really determine that. There is a standard factor to use so that signal swamps any other noise, though I don't really use it. As long as per sub exposure looks good, guiding is good I use that, typically 60-120s, but your LP mustn't take over, hence why you need to determine it.

Default gain? Do you mean unity gain when the camera High Gain Conversion kicks in, this is 100 on the 533mc.

For gain you decide if you want low gain = higher dynamic range/higher read noise, or high gain = lower dynamic range/lower read noise. CMOS sensors generally have quite low read noise so gain setting I find isn't much significant unless you compare two extremes.

 

2. Use bin1, you can always downsample post process but can't go the other way (technically there is an option). Binning combines pixels and respective pixel signal to effectively make your signal "brighter" at the loss of resolution.

 

3. Temp, use whatever works based on your environment. I find there's little gain beyond 0 Deg C camera temperature but usually use minus 10. You can save power if using batteries and less cooling demand.

 

4. Flats are usually essential, don't know where you've seen it isn't. Bias aren't essential as people image darks (dark flats (darks for your flats)) at the same duration and temp of your flats. Flats remove any dust motes and vignetting, if your optical setup doesn't change (filters being removed and reinstalled, focus position, optical train) you can usually reuse flats, as I setup and breakdown every time I need to make new flats every session.

 

5. I usually dither the max 30 pixels every ten minutes of imaging or so, as long as it's often enough (and not like every 30-60 minutes) you'll be fine, can also get away with smaller pixel movement.

 

[saac]

This is a little bit like asking for the secret chord David played   My honest and best advice would be try different settings and see what shakes out as best.  If you get good results with the default gain then use it, perhaps try increasing it to do a comparison on the same subject. A higher gain would generally be required for the more fainter subjects but it comes of course with the penalty of briming more noise , but don't be afraid to play around with it.  Temperature - 10 oC  is a typical default with cooled cameras and again is fine - stick with it  there are plenty of other things to concentrate on at the movement. Your best Bin setting is, for optimal performance,  determined by your chip size and telescope focal length and seeing  - it affects over/undersampling.  You can use the the calculator (provided under the menu tab Resources) to have a look at the effects of binning and how well your current setup is matched .  Calibration frames - there is a lot of differing opinion out there regarding use of bias with CMOS cameras - I still do it together with flats and darks - the ASiAir makes the task of acquiring calibration an easy task so it's no real hassle. Dithering, I use when I remember to set it, a dither every 2 or 3 subs, if you set it at a higher frequency you will quickly prolong your imaging session at risk of running into clouds or bed time or even worst time to get up time!  

Ok, so joking aside I do think we can get too focused on getting the perfect optimised setting. Sometimes we forget to "get the images in" . There is a saying in aviation "fly the aircraft" and I think that translates well to astro imaging!  Maybe you could take one or two of the variables above and play around at changing them one at a time to see what effect they have then take it from there. Have fun.

CCD calculator https://astronomy.tools/calculators/ccd_suitability

Now I've heard there was a secret chord
That David played, and it pleased the Lord
But you don't really care for music, do you?
It goes like this, the fourth, the fifth
The minor falls, the major lifts
The baffled king composing Hallelujah

Jim 

Edited August 28 by saac

[CheshireChris]

14 minutes ago, saac said:

This is a little bit like asking for the secret chord David played   My honest and best advice would be try different settings and see what shakes out as best.

 

Jim 

Thanks Jim,

 

Yes, couldn't agree more about trying various settings out - problem is clear nights have been so few and far between in NW England this year (and this my 1st year of imaging): it's a trade off between trying various settings and as you say... 'get the images in'.

 

Chris

 

Edited August 28 by CheshireChris
Clarity & Typo

[saac]

5 minutes ago, CheshireChris said:

Thanks Jim,

 

Yes, couldn't agree more about trying various settings out - problem is good, clear nights seem far between in NW England this year (and this my 1st year of imaging): it's a trade off between trying various settings and as you say... 'get the images in'.

 

Chris

 

I totally agree, and we all feel that pressure, the last thing we want to do is ruin a potential and rare imaging session because of an incorrect setting on our equipment. I would start off with the default settings and get things like your guiding going reliable. And then of course there is the other massive learning curve the post processing. My biggest challenge is skill fade as I tend to forget what worked well and how I did things from one year end to another.  

Jim

Edited August 28 by saac

[CheshireChris]

13 minutes ago, Elp said:

2. Use bin1, you can always downsample post process but can't go the other way (technically there is an option). Binning combines pixels and respective pixel signal to effectively make your signal "brighter" at the loss of resolution.

Yeah, l think l can safely ignore (i.e leave at BIN1) for anything I'm doing in the forseeable future. I'm one of those who wants to know what every setting is for and the ZWO manuals are , quite frankly, dreadful and tell you nothing.

 

Chris

 

[Fegato]

here's my two pennyworth, mostly repeating and agreeing with Elp above...

1. Gain - certainly for starters I would recommend using the 100 Gain (where High Conversion Gain kicks in).  No point going higher really - you don't gain much in read noise, and you lose dynamic range. Gain 0 is the other obvious option, particularly  if you have dark skies and don't mind longer exposures (I do have dark skies, but still shoot at the HCG point....).  

Exposures - I have calculated the minimum ADU to ensure read noise is swamped for my cameras, but only use that for reference. That gives a minimum exposure length - with a fast system, I'm normally way above that, and I guess you will be too with an F/2 Samyang. As you go longer - keep an eye on saturated pixel counts to make sure you're not blowing out too many stars. The other factor here is LP - as that rises, you get less benefit from longer exposures. Obviously filters also play a part here once you use them. There is no perfect answer - you can get similarly great results with different approaches to exposure length - key thing is that you're happy with your results!

2. You tend to use Bin 2 or more when you are over-sampled. With your setup you will be under-sampled, so no need to do anything other than Bin 1.

3. As already said, -10 is fine, as long as (a) you can keep it that low in warm weather (probably OK in the UK!), and you have the power. I use -10 too, but agree it could be a bit warmer without noticeable penalty.

4. Agree with Elp - Flats are the most important. I use a flat panel, which makes this straightforward (but costs money obviously!). You need the bias to calibrate the Flats. I believe bias will work with this camera (although you might want to double check that) - in which case you don't need to use Flat Darks - these are a pain as you have to shoot them every time you redo flats. 

5. I believe the general recommendation for dithering is to aim for 10 pixels (in your imaging system). You need to work out the resolution of both your main and guide system to work out how many pixels to set for dithering in the guiding system - this tool helps: https://astronomy.tools/calculators/guidescope_suitability . Think yours works out at 9.

[daz]

I run my 533 at a gain of 76 - I can't remember how I got to that number now, but I just leave it at that and vary exposure times according to target/conditions.

If you change the gain, you need to shoot matching calibration frames, so I find it easier it not having to do that!!

 

As others have said, flats are a must. I do use darks, I have a library of different exposure lengths - all at -10. Libraries are fine on the CMOS chips now as they are pretty "well behaved" in terms of their read noise.

And flat darks - or dark flats - are just dark frames, but at the same exposure length as the flats. Flats are likely to be very short, so you could get away with bias frames (0 length exposures) but if you use a flat panel on a dim setting and increase the exposure time, I would recommend shooting matching darks. (Bias frames are really used to optimise the darks where they are a different exposure length than the lights. WBPP in Pixinsight makes it all very easy, but shooting matching darks is pretty easy - especially with our cloudy skies )

 

 

[CheshireChris]

3 hours ago, Fegato said:

5. I believe the general recommendation for dithering is to aim for 10 pixels (in your imaging system). You need to work out the resolution of both your main and guide system to work out how many pixels to set for dithering in the guiding system - this tool helps: https://astronomy.tools/calculators/guidescope_suitability . Think yours works out at 9.

Thanks Robin

I have noticed that the ASIAir works out the focal length of the Samyang to be 129mm rather than 135mm - why does that happen? I put the numbers in to the astronomy.tools calculator you linked and got these results:

 

Chris

 

[Fegato]

3 minutes ago, CheshireChris said:

Thanks Robin

I have noticed that the ASIAir works out the focal length of the Samyang to be 129mm rather than 135mm - why does that happen? I put the numbers in to the astronomy.tools calculator you linked and got these results:

 

Focal length is measured from the primary lens / mirror to the point of focus. So I guess this just means that's not quite as specified - could be the scope, or the backspacing / focus more likely I guess. 

With 1 / 1.07 - if you divide 10 pixels by 1.07 you get 9.34 - so 9 pixels would be the amount to specify for the guide system to dither in order for the imaging system to dither c 10 pixels. A small difference in focal length won't make any difference to this calculation. The exact amount you dither isn't vital either - I guess too low, and you lose the benefit, and too high, and you will need to crop too much around the edges of your image.

 

[CheshireChris]

Thanks everyone for all the replies so far. Complicated? Yes - to me; it's all so new. Interesting? Oh yes - l love this. Frustrating? Totally; clear nights seem to be at a premium. My other half, bless her, is very patient but has observed that the opportunities to use some rather expensive equipment are few and far between 🤣 She is also dropping some hints about a telescope she can 'look through'.........more money <sigh>.

Chris

 

Edited August 28 by CheshireChris
Clarity

[wesdon1]

7 hours ago, CheshireChris said:

In the absence of any clear sky in NW England l have several questions about what settings to use and perhaps equally important when.

Setup is ZWO based : ASIAir/AM3+TC40/ASI533MC Pro/ASI120mm mini+ZWO Mini Guide Scope/Samyang 135mm - only filter is a ZWO IR Cut filter (which l haven't captured an image with - yet) I've not even managed to get the guide scope focussed.

I get the fact that no single set of parameters can be universally applied and conditions will vary over several nights imaging sessions: if l ever get several any clear nights.....

1. How do l decide what gain and exposure times to use for a given subject? The two images l have managed so far (NGC7000 & M31) look great - to me - for first images and were shot at the default gain of the ASI533MC Pro.

2. BIN Settings - when might l need to change them? I get the impression that anything other than BIN1 isn't much required but do wonder why it's there?

3. Temperature - so far just used -10deg. Do l really need to use any other value?

4. Calibration frames - l have shot a lot of dark frames at various gains/exposure times but so far have not shot any flat/bias frames...yet - indeed some astroimagers (mainly on youtube) seem not to bother with them for dedicated astrocameras (DSLR's are a different matter). A bit unclear on that one.

5. Best dither settings (assuming l get the guide scope set up correctly!) for the Samyang 135mm.

I have watched lots of YouTube videos - probably too many - but l enjoy watching those by Trevor Jones (AstroBackyard) & Peter Zelinka: far more interesting than anything on TV.

Thanks

Chris

 

@CheshireChris Chris I reside not far from you in Liverpool, and in all my years doing visual then imaging astro, I cannot remember a worse time weather wise! Just this year alone, I've counted only 5 cloudless nights! The only caveat to that staement is last year around June, we got 5-6 totally cloud free nights, and I remember feeling like I'd won the lottery! LOL. 

What I'm hoping is generally speaking, mother nature likes balance, so hopefully us NW England folk are due some seriously good cloudless night skies very soon! 

( I cannot help with your questions because much more experienced SGL members have already given you awesome tips and advice! )

Clear Skies, Wes.

[Swoop1]

I can't help with a lot of the questions re binning, gain and dither as I use the default for bin and gain on my ASIAIR PLUS/ 533MC PRO combo and haven't tried guiding yet (new to ASIAIR use- received mine a few days ago).

I do use flats (have to) darks and bias. I expose my darks at the same settings as my lights (exposure length/ gain) and let the ASIAIR decide the rest when I set up an autorun sequenece for the flats and biases.

I use an LED tracing panel on top of a double layer of white cloth for my flats and used to expose at around 0.1sec but, saw somewhere that exposures of 1sec+ are better so last time I just used the back of the panel for the light source as opposed to the brighter front. I think it timed each flat at about 2 secs or so.

[wesdon1]

16 hours ago, Swoop1 said:

I can't help with a lot of the questions re binning, gain and dither as I use the default for bin and gain on my ASIAIR PLUS/ 533MC PRO combo and haven't tried guiding yet (new to ASIAIR use- received mine a few days ago).

I do use flats (have to) darks and bias. I expose my darks at the same settings as my lights (exposure length/ gain) and let the ASIAIR decide the rest when I set up an autorun sequenece for the flats and biases.

I use an LED tracing panel on top of a double layer of white cloth for my flats and used to expose at around 0.1sec but, saw somewhere that exposures of 1sec+ are better so last time I just used the back of the panel for the light source as opposed to the brighter front. I think it timed each flat at about 2 secs or so.

@swoop. @CheshireChris If I could just add to what you mentioned about flats, I've found that if I'm using a strong light pollution filter, like my 7nm/7nm L-Extreme, then I have to expose flats for longer than say, when I'm doing flats for a "lite" light pollution filter like the L-Pro. I would go with around 8 seconds and 2-3 seconds respectively. ( actually struggled getting my flats done properly for my personal setup and gear but after lots of experimenting I've now found a sweet spot, so to speak )

Please note that I'm only an advanced beginner so my advice could be way off what seasoned pro's would advise! 

Best of luck my friend!

Wes.