ZWO ASI178MC Gain/Offset Combinations

Okay, forget what i've written. These settings don't work :-(

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 https://www.astrobin.com/333878/?nc=user ). 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.

Cheers,
Michael

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

I have been looking at some of the great pics in your gallery you have taken with this camera

Thanks!

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.

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.

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?

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  8)

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.

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.

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 (https://bbs.astronomy-imaging-camera.com/viewtopic.php?f=21&t=6792&p=12206&hilit=178+unity#p12206) 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.

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:

https://www.cloudynights.com/topic/633664-suggested-sub-exposures-for-zwo-asi178mm-cooled/

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.