QHY5-II / PHD2 - Noise and horizontal banding...resolved!

[SteveA]

I’ve been using the QHY5-II for quite a while and although guiding with PHD has occasionally been  acceptable, quite a lot of the time it isn’t. I’ve played around with the camera on numerous occasions  but have always been plagued with a very noisy output and truly atrocious horizontal banding that quite often exhibits s a weird flashing and scrolling image with each exposure in PHD2.  Although I’m not sure of it, I suspect this noisy output has been affecting the performance of PHD2.  Most of my attempts to resolve the problem have taken place on the job so to speak whilst trying to image and inevitably ends up with me giving up and just getting stuck into the imaging, irrespective of the quality of guiding. I know….not great is it, but with clear nights being rare, I quite often try and ignore problems  in the vain hope that the imaging results will be okay when I come to process the data. Rarely is this the case of course and  I was  almost at the stage of giving up on the QHY5-II. In fact I had started looking around for a replacement.  As you know the QHY5-II is a fairly inexpensive camera, but  I was slightly shocked at what I might need to spend in order to get something better. Deciding that maybe I couldn’t afford anything at the moment, I thought I had better spend some time trying to get to grips with the issues and sorting them out. With a quiet time at work at present, I brought my imaging laptop and cameras into work and spent some time with them on my desk. I have to say this definitely beats trying to figure stuff out whilst sitting in the dark and cold!

I started with downloading the latest release of PHD2, mainly in the hope that there might be an updated driver included…there wasn’t! I then popped over to the QHY site to see what there maybe there, again hoping for a new driver, disappointed again , but I did  come across a forum post regarding the horizontal banding and thought I had struck gold. The symptoms described in this post were fairly similar to what I was seeing and I thought it worth looking into.

http://qhyccd.com/bbs/index.php?topic=3490.0

The post suggests using  EZPlanetary, which tbh I hadn’t looked at since the day I unboxed the QHY5-II. On opening up the camera settings the first thing I found was that the camera was set to work in RG/Colour mode rather than RAW, which was interesting to say the least. I followed the post and played with the RGGB offset until I got what looked like a good result (pure guess work tbh). After closing EZP I then fired up PHD and was immediately disappointed that nothing seemed to have changed. Back to EZP and played randomly hoping for more success, still no joy. I then turned my attention to the new version of PHD2 and created a new profile and let the application build a dark library. Now I have to admit to having never used darks in PHD2, I suspect that was probably a significant error on my part because after the library was built and I started looping in PHD2 (even with the gain set at 95%) the output was unbelievably better. Nearly all the noise had disappeared and I was left with static horizontal bands. Feeling somewhat elated I then started playing in PHD and turned on the 2x2 noise reduction…BINGO! Horizontal bands gone and no noise. I really couldn’t quite believe it …why hadn’t I tried this before?

Anyway, I wasn’t quite ready to celebrate as I wanted to try the QHY5-II guiding for real first. Last night was a lovely clear night and with a full moon it was an ideal time to play without feeling guilty about  not collecting any images. I have to say I was blown away…..The guiding I got was the best I have ever had. I then tried out the new guiding assistant in PHD2 to help set some of the guiding parameters….unbelievable! Guiding  improved even further.  For the first time ever, I have perfectly round stars when tested on 10 minute exposures and a much calmer guiding graph.

So I changed a lot of things, a new version of PHD, camera settings changed, used darks and also tidied up a bunch of hanging cables on the telescope. I guess all these contributed to the performance gain…feeling pleased with myself now.

[jbrazio]

I find that PHD2 does some background automation for you in order to be "Push Here Dummy", one of this automatic adjustments is camera gain. I've found out by experience that when PHD is unable to detect a star in the image it will start increasing some sort of gain (can't tell if it is native camera gain or post-process since you can set the camera gain on the brain dialog box to a fixed value) until you just see noise, like the picture on the top left corner of your image. As soon as it detect a start the overall image noise will decrease and you get a decent uniform background.

At least this is how PHD2 behaves with my ASI120.

[SteveA]

On 10 May 2017 at 13:09, 0x0539 said:

I find that PHD2 does some background automation for you in order to be "Push Here Dummy", one of this automatic adjustments is camera gain. I've found out by experience that when PHD is unable to detect a star in the image it will start increasing some sort of gain (can't tell if it is native camera gain or post-process since you can set the camera gain on the brain dialog box to a fixed value) until you just see noise, like the picture on the top left corner of your image. As soon as it detect a start the overall image noise will decrease and you get a decent uniform background.

At least this is how PHD2 behaves with my ASI120.

I seem to remember reading somewhere (not sure where or when) that this camera needs to run with the gain set really high. Sounds a bit daft I know, but I've never tried setting it up with anything but around 90% gain. I was always rather surprised however that when running EZP, even with the camera capped, I see no noise what so ever, which suggests that the gain stayed low, though maybe the ASCOM driver behaves differently?

[tooth_dr]

@Spaced Out