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ZWO ASI178MC Gain/Offset Combinations

13 Feb, 2018 09:52
Hi @strobin,

I tried my luck at the official ZWO-Forums, but didn't get a response until now, and tonight will be clear skies at my location, so i wonder if here is anybody who can give me an advice about this topic:

After more than half a year using the great ASI178MC with several combinations of Gain/Offset, i thought it would be a good idea to stick to only a few standard combinations. So after reading through many posts in several forums i'd like to discuss if these combinations do make sense or if i need to adjust them (the numbers represent the settings in SharpCap, where Gain=Gain and Offset=Brightness):
  • LOW: G 85 O 75
  • MEDIUM: G 128 O 300
  • HIGH: G 192 O 400
  • ULTRA: G 380 O 400
Any ideas about these settings? Good or bad? Are you using similar settings or are yours completely different?
Thanks in advance for any advice!

Clear Skies,
Edited 13 Feb, 2018 10:08
13 Feb, 2018 20:51
Okay, forget what i've written. These settings don't work :-(
19 Feb, 2018 16:39
I have also been searching for the same information for the ASI178mc and have found very little until recently.  Check this link from the camera manufacturer’s website:

The mini article is about the ASI1600 and ASI071 gain settings however the 3rd question down from a customer (Nicolas) asks about gain settings for the ASI178mc.  ZWO Founder, Sam Wen, says to use the gain settings listed in the ASCOM driver for the ASI178mc.  When I checked the ASCOM settings using SGPro here is what I found:

Unity Gain ==>    Gain: 180   Offset: 25
Highest Dynamic Range ==>   Gain:  0    Offset:  25
Lowest Read Noise ==>   Gain: 270   Offset:  340

I also sought some guidance from the very helpful folks at out of Seattle where I’ve bought most of my telescope equipment and they generally recommended using a gain of around 50-100 for DSO and a higher gain, perhaps ~300+ for brighter planetary targets.Up to this point I have been experimenting with gains in the 250-330 range using short exposures, unguided.  My results are fairly mixed so far.  I live in an area with a lot of light pollution which tends to dominate my photos.  I am awaiting the arrival of a guide camera and scope along with a light pollution filter this week and I intend to try these recommended settings at my first opportunity.
Hope this helps,
Edited 19 Feb, 2018 16:42
19 Feb, 2018 19:12
Hi Joe,

thanks fpr your reply. I played around recently with SharpCap (native drivers, no ASCOM) and the gain/offset settings. Whenever i touch the brightness value (which i believe to be offset)  the images are way too oversaturated - just white. Maybe i am doing something wrong, but at the moment i leave the brightness value at zero.

I am using gains between 64 and 256 depending on the target. I tried short exposures, but then i could not align the images due to too less stars in the field of view. At the moment i try to reduce the differential flexure on my autoguiding setup (see ). When this is fixed i'll come back to the problem with gain/offset combinations.

Nevertheless i am happy for your reply and wish you good luck with your new equipment.

23 Oct, 2018 16:38
Really interested in this. I have an ASI178MC that I am experimenting with. I tried Gain=200 and got what looked like a star shaped light leak in one corner. I assumed it was a problem with my scope, but found its was AMPGLOW, see this ZWO article.

I tried taking 90 second Darks at various levels of Gain and found it diminished until it was virtually invisible at Gain=10 (90 sec Darks).  To see the effect take a Dark into your processing program and stretch it. However I think a gaion of 10 might be too low for DSOs.

ZWOs solution is to control via Darks and disable any dark optimization feature of your calibration program eg DSS.  They say that this effect only occurs in "specialist" sensors and not in those used for DLSRs.  I was staggered, sounds like a design fault to me.

Anyone got any proven settings for this camera.
24 Oct, 2018 08:14
Hey maxchess,

although i switched to a cooled ZWO cam recently, i have made a lot experience with the 178MC.

Ampglow happens to a lot of cams. ZWO seems to have it under better control with their Pro-Series, but the ASI178MC suffers a lot from this problem. You need to use a fast USB3 Port on your laptop, this reduces the problem a bit. But the use of darks is inevitable with this cam. When i'm back home (at work right now) i will check my settings with the ASI178MC and report them here. -> It is important to use a correct combination of gain and offset (well, SharpCap calls it "brightness" ) otherwise you will loose a lot of dynamic range. ZWO provides three standard settings for these parameters in the ASCOM-Driver, which can be read out and used with the native drivers. So you will be sure that you use a combination of these settings which work well.

Greetings, Michael
Edited 24 Oct, 2018 10:40
24 Oct, 2018 14:05
I have been looking at some of the great pics in your gallery you have taken with this camera and notice that you tend to take large numbers of short exposures. E.g. 431x4" (gain: 128.00)  and M27 600x 15 secs, all with lots of calibration frames. When taking images with my DSLR I have always thought that longer exposures gave better results. One of my best images with my Canon 450D was 6min x 10.
Is it different for this type of camera..
24 Oct, 2018 19:56
I have been looking at some of the great pics in your gallery you have taken with this camera

Settings: I can (partly) confirm what Jeziha wrote back in february. ASCOM tells me to use the following settings:
Highest Dynamic Range / Unity: gain 0 offset (brightness) 25
Lowest Read Noise: gain 270 offset (brightness) 340
I suggest you use the first (unity) setting for your first exposures.

Long vs short exposure: From what i have learned, shorter exposures will give you slightly more details in the image but are harder to handle in postprocessing than longer exposures. I experimented a lot with exposure times, but what gives you really a good pictures is the total length of integration time, no matter if you take a lot of short or a few longer exposures (as long as all the other things like autoguiding work). There are some guys here on AstroBin which i would call "Masters of short exposure" like Łukasz Sujka. Just look at his gallery, he also has the 178 in it's cooled and mono version. His images are inspirational and he brings the whole "short exposure thing" to a new level.  But there is no doubt that you can get good results with longer exposures as well.
Edited 24 Oct, 2018 19:56
25 Oct, 2018 17:14
Thanks, I assume you mean:
Unity Gain ==>    Gain: 180   Offset: 25
25 Oct, 2018 19:33
Nope. I wondered also, but the actual drivers for ASCOM shows the same gain/offset for unity and high dynamic range. 0 / 25. Seems odd, but somewhere i read that the 178MC has indeed no REAL unity (or that the theoretical value must be below zero or something). Dont know if this is correct. But Gain 180 / offset 25 sound also not bad. You should try these also.
04 Nov, 2018 13:20
Hi now sorted out gain at 210 and got decently exposed images. Did 300 x 60 secs, whittled down to 240 plus 100 darks on M74. Using ES 102 triplet f7 fl 712mm on HEQ5 pro on pier. However images are very blocky with low detail, indicating under sampling. Skies typical suburban bortle 5.  Looking at Lukas Sujakas recent M74 I am amazed. I see it is 5.5 hrs using mono cooled version, better skies, better mount.
Do you think that if I do more exposures and bump up the hours I can get good results or am I pushing my setup too far?
At 60 sec or smaller exposures, do I need to guide. I seem to get small round stars without at this short exposures.
04 Nov, 2018 15:24
Can you provide a link to a single sub (raw) and maybe the stacked image (also in raw)? I hope i can help better if i see the results.

With your combination (712mm focal length and ASI178MC -> 2.4 um pixel size) you get a resolution of 0.7" per pixel. This is okay and should not lead to under-sampling. But you need to guide carefully, otherwise the image will be blurred. I understand you used 210 gain. Which offset (brightness in SharpCap) did you use?
04 Nov, 2018 18:26
The offset was 10, I use Indi EKOS.

This should link to a zip file containing the DSS output and one sub, both in fts. (please ignore the rest of the site, a thing I started but stopped.

Guiding is the issue, I had hopped the large numbers of very short exposures would avoid/ reduce the need for guiding. At present I cannot get my total RMS reliably below 2, often it shoots up to way above 5.. I am working through the usual steps: Good PA, cables tied, east heavy, flexture, etc. I suspect the issue is backlash in my HEQ5-Pro and in the next few weeks I plan to do the Rowan belt upgrade, however I understand that this will take total RMS just under 1, but this may not be good enough.
04 Nov, 2018 19:38
Okay. The sub seems fine to me which says that the settings are okay. I am not sure why the signal is so faint, but i do not think that this is an effect of wrong settings. You shoot at F/7 which is nearly equal to the F/8 i am using. The signal on my subs is as faint as yours, so no problem here. The single frame is of course noisy (at gain 210 this is okay). BUT: I can see clearly a drift in your stacked image (look at this one: Drift). In the 5 hours of your integration the target moved a little to the right and the bottom, if i am not mistaken. This happens naturally if you image without guiding. But the drift happens canstantly, even within the one minute of each sub. This results in a very tiny elongation of your stars (look here: tiny elongation). The effect is very small, but avoidable when guiding. But this is a very minor problem, the effect is really small. You can try to use even higher gain and take shorter subs or buy a small guiding scope and camera. Then you could easily use less gain which will end in an image with way more dynamic range.

But you can get good results with the technique you are acutally using - without guiding. I took your stacked image and applied very few processes quick and dirty in PI to see if one can get good results with the stack: Quick and dirty edit. If you want i can postprocess the image to the end and send it back to you. But the screenshot looks promising to me  smile
04 Nov, 2018 20:29
Ok,  that's really helpful.
This was my first draft in Startools, very interested to know what you  can do with PI. In my version there is very little detail and its blocky. I s/w binned at 70%
I will try again and see if I can improve.

Do you think it worth shooting another 2 hours worth at the same setting? I can use plate solving to match the frame and the kit has not been moved.
Will lights or bias frames help at all?

I have an Orion SSAG camera with 50mm guidescope and an ST80 for guiding, but guiding is erratic, see earlier comments.
04 Nov, 2018 20:56
I am glad to help.

Regarding guiding: A RMS above 2 is really an issue. Are you using the software that Orion has in stock or are you using PHD2? If PHD, did you try to send your PHD-logs to the guys at PHD-Forum? They helped me there a lot with my guiding issues i had last year with differential flexure (whole story here). I am sure that differential flexure is not your problem, but there must be an issue. The HEQ5 and your guiding-equipment should easily keep RMS under 2!

But back to the image: It is ever worth taking more lights :-) You will improve SNR and reduce noise. Bias may help a tiny bit, but in my experience they dont make a big difference at all. But taking bias is so easy und uncomplicated that you should do that. If you dont take flats, take them! They are making postprocessing way easier by eleminating "donuts" and vignetting. A lot of people use the "T-Shirt-way", but i can recommend the Lacerta FlatField box. Works easy and i need less than 2 minutes to take my flats and flatdarks.
05 Nov, 2018 18:34
After some thinking i would suggest that you try the same target with unity (180/25) settings. Then we can be sure that all settings are correct. It will be easier to sort out the remaining problems then.
05 Nov, 2018 20:14
Ok, will try that, a bit cloudy right now.   However I did get the chance to add 100 each of bias and flats.  I then reprocessed the image and its getting better:
M74 here.    Let me know what you think.

Plus I used the astrobaby guidelines to take a look at my HEQ5 pro mount, I think I have reduced the play in the gears. I have also ordered the Rowan belt upgrade.
So with a bit of luck I will be able to do some accurate guiding and try the new settings in the next week.
Edited 05 Nov, 2018 20:21
06 Nov, 2018 11:14
I can't say if the image is getting better. You processed V2 in a different way than V1 so the images are not directly comparable and i am not an expert in postprocessing :-( But adding bias and flats is the right way. I think you can stretch V2 a bit more, the background is very black.

I wish you a good hand on optimizing your mount! Please report back if you have new findings.
19 Nov, 2018 15:59
ZWO Founder, Sam Wen, says to use the gain settings listed in the ASCOM driver for the ASI178mc.  When I checked the ASCOM settings using SGPro here is what I found:Unity Gain ==>    Gain: 180   Offset: 25
Highest Dynamic Range ==>   Gain:  0    Offset:  25
Lowest Read Noise ==>   Gain: 270   Offset:  340
Sam has said that there is no unity gain for the 178 ( and suggests a setting of 0 / 25 (perhaps the reference Michael above alluded to).  I tested mine recently at different settings and didn't reach any firm conclusions as to what would be best for a given scenario as there was no significant difference when the images were stretched.

So far I'm using gain 200 and brightness 150 in SCP as a middle ground. (I uploaded my first AB image today with those settings.)

Wondering also if anyone has experimented with different USB speeds and even USB 2 vs USB 3 to reduce amp glow and banding. Despite the slower readout speed, I found least glow with my 178 on a USB 2 port when exploring banding issues, though I've not tried a session on USB 2 yet as darks work well to deal with it.
19 Nov, 2018 16:45
Thanks for clarification, nicklin.

Amp glow is an issue with this camera. I got best results on a USB 3 port with the option "High speed USB" enabled in SharpCap. The value was set to 80.

I figured out that when i have high FPS rates in a test szenario with very short exposures the amp glow is reduced when i use similar settings for long exposures. Or in short: The higher the transfer rate, the lower the amp glow.
19 Nov, 2018 17:06
The best gain and exposure will be determined by how dark your skies are.  I've had a the mono version of the asi178 for several months now.  The gain and exposure settings (Gain 70 @ 90s) I had been using was too much, resulting in blown out stars.  I came across this thread on cloudynights:

I live in a heavily light polluted area.  For my latest image, I used a gain of 43, 0 offset, and exposures of 30s.  I may experiment with even lower gain settings.
19 Nov, 2018 17:29
Michael T.
I got best results on a USB 3 port with the option "High speed USB" enabled in SharpCap

Interesting. There's less data transferred with that option on, but I'd not found it made a difference on my setup. Here's a result with USB 3 on the left and USB 2 on the right. Darks work so well at counteracting I don't think it's an issue, but for anyone keen to minimise, USB 2 may be the way to go. These were 2 minutes gain 200 without cooler on.
Edited 19 Nov, 2018 17:34
19 Nov, 2018 17:34
Really interesting. Maybe it depends on the computer? Anyways, i experienced the same as you, nicklin. Darks work really well.
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