asi1600mm pro settings newbie question

[Wirral man]

Hi all just wanted to know about the asi1600mm pro settings ie unity gain, hdr ect... the other night i had it set at unity gain think it was 139 gain by 29 offset and exposure was 120seconds in a bortal sky of 6 but read a few articles saying that it is too high and will be noisy ?

this is all new to me can anyone give a brief oversight on what is what with this camera please? thanks in advance John 

[kens]

There’s no hard and fast rules. Unity gain is fine for LRGB but I and others prefer 76 or so. For narrowband I use gain 200. If you are not sure about which offset to use for gains that are not preset just use the one for the next highest preset. I just use 50 always as it has negligible impact on dynamic range at lower gains, and it’s one less thing that could go wrong.

The general thinking is that lower gain means more dynamic range - less saturation of bright objects. Higher gain means less read noise so shorter exposures are possible. It’s always a trade off. 

If you expose to a level where read noise is not dominant, regardless of gain, you are fairly optimal noise wise. Then the noise is just a matter of how much integration time, ie number of subs, you are able to fit in.

[Wirral man]

3 hours ago, kens said:

There’s no hard and fast rules. Unity gain is fine for LRGB but I and others prefer 76 or so. For narrowband I use gain 200. If you are not sure about which offset to use for gains that are not preset just use the one for the next highest preset. I just use 50 always as it has negligible impact on dynamic range at lower gains, and it’s one less thing that could go wrong.

The general thinking is that lower gain means more dynamic range - less saturation of bright objects. Higher gain means less read noise so shorter exposures are possible. It’s always a trade off. 

If you expose to a level where read noise is not dominant, regardless of gain, you are fairly optimal noise wise. Then the noise is just a matter of how much integration time, ie number of subs, you are able to fit in.

i thought gain is like iso the higher the gain the more noisy the image??

[LightBucket]

3 minutes ago, Wirral man said:

i thought gain is like iso the higher the gain the more noisy the image??

In a nutshell, that is correct...

[kens]

34 minutes ago, Wirral man said:

i thought gain is like iso the higher the gain the more noisy the image??

ISO and gain are equivalent but that does not necessarily make high gain more noisy. It all depends on what tradeoffs you make. At low gain you have higher read noise and higher quantization noise. And if you expose longer to overcome the read noise you can get glows, and noise from dark current. At high gain the main problem is dynamic range. Increasing gain is akin to stretching contrast in post processing.The brighter pixels hit a maximum level. Saturation or clipping is itself is a form of noise. With high gain, small variations in brightness are amplified so noise can be accentuated but in relation to non-saturated signal it is not noisier per se.

[GraemeH]

1 hour ago, LightBucket said:

In a nutshell, that is correct...

I'm not sure I agree with this - there are many people much more knowledgeable in this field than me who argue that the higher noise sometimes seen isn't actually due to the increase in ISO (or gain) but rather it's because of the shortened exposure to achieve the same image brightness which results in a decrease in SNR.  This article http://www.lonelyspeck.com/how-to-find-the-best-iso-for-astrophotography-dynamic-range-and-noise/ presents some interesting arguments about why the high ISO/high noise belief isn't necessarily true, and again demonstrates that there are always competing effects which mean that no matter what settings are chosen, they are always a compromise.  The article is specifically written about DSLRs, but I don't think there's any reason to believe that the same principles don't apply to astro cameras, especially CMOS cameras like the ASI1600.

[LightBucket]

50 minutes ago, GraemeH said:

I'm not sure I agree with this - there are many people much more knowledgeable in this field than me who argue that the higher noise sometimes seen isn't actually due to the increase in ISO (or gain) but rather it's because of the shortened exposure to achieve the same image brightness which results in a decrease in SNR.  This article http://www.lonelyspeck.com/how-to-find-the-best-iso-for-astrophotography-dynamic-range-and-noise/ presents some interesting arguments about why the high ISO/high noise belief isn't necessarily true, and again demonstrates that there are always competing effects which mean that no matter what settings are chosen, they are always a compromise.  The article is specifically written about DSLRs, but I don't think there's any reason to believe that the same principles don't apply to astro cameras, especially CMOS cameras like the ASI1600.

I was just saying in a nutshell it is correct, as ISO and gain are pretty much the same thing, I made no comment on where noise fits into the equation...

[vlaiv]

10 hours ago, Wirral man said:

Hi all just wanted to know about the asi1600mm pro settings ie unity gain, hdr ect... the other night i had it set at unity gain think it was 139 gain by 29 offset and exposure was 120seconds in a bortal sky of 6 but read a few articles saying that it is too high and will be noisy ?

this is all new to me can anyone give a brief oversight on what is what with this camera please? thanks in advance John 

There is two approaches to answering your question

First would be: use unity gain (139), set offset to anything between 40 and 50 (you might as well set it to 50 because it is default in latest drivers), shoot at least 1 minute subs (2 if you are at dark site) for LRGB and 4 minutes for NB and you will be fine.

Second would involve quite a bit of explaining and understanding how things work so we eventually arrive to the above conclusion. We can do that as well if you like, but it has been done several times before in these forums, and you might want to do some searching and researching on your own about this topic first (if not, just give us a shout, we can do explaining).

[groberts]

A picture's worth...see graphs below, this is from ZWO + summarised in this table + USB settings I use:

GAIN	OFFSET
0	10
75	12
139*	21
200	30
300**	50
*USB	40
**USB	60
ADU 25,000

 

 

 

 

[GraemeH]

2 hours ago, LightBucket said:

I was just saying in a nutshell it is correct, as ISO and gain are pretty much the same thing, I made no comment on where noise fits into the equation...

Fair enough.  I misunderstood the intent of your comment and thought you were agreeing that higher ISO or gain automatically meant higher noise.

[Wirral man]

ok guys will play around and see what works and doesn't work.. i do have a issue on colour dont know if it is me but the other night i took 10 luminance shots at 120sec and just one 240 sec on each colour r g b just so i could have a little play around the subject was m51.

i stacked each channel separately and followed the guide in the book "make every photon count" and done everything correct so i ended up with a lrgb image in tiff format but when trying to pull any colour out its still in mono black and white ....is this because i dont have enough colour data ? you can clearly see m51 but mono...i didnt have time to make any calibration files ie dark flat etc. it was just purly so i could just have a little mess around

i use dss and cs2 but is cs2 good for lrgb work?

[happy-kat]

Did you buy the book Dark Art or Magic Bullet? Goes into greater depth on processing. I don't think you've had enough time yet to exhaust the software you already use.

[Wirral man]

4 minutes ago, happy-kat said:

Did you buy the book Dark Art or Magic Bullet? Goes into greater depth on processing. I don't think you've had enough time yet to exhaust the software you already use.

yes i have both and followed the guide step by step several times and still grey?? hope it is just something simple to fix this..... i only mentioned about cs2 as just wondered if there is anything easier to use 

[happy-kat]

Time makes things easier to use. Colour is probably due to lack of data.