PHD2 Bad Pixels/Dark Library seem to make things worse ?

[Spaced Out]

Hi all

Novice alert !

I’ve just bought a 2^nd hand QHY5L-II-C to use for autoguiding with PHD2. I plugged it in today for a quick test and I am little disappointed that it seems to have quite a few hot/stuck pixels.

I thought that the dark library or bad pixel map functions in PHD would solve this problem and clean up the image a bit, but they both seem to make things a lot worse. The results don’t seem at all smooth and they look more like a blizzard of white dots, is that normal ?

I’m a complete beginner with this so I’m sure I’ve probably done something stupid to get these results. I did follow the PHD manual instructions tho (I think).

Any thoughts/advice on where I am going wrong ?

[kens]

I think that would be due to PHD2 autostretching the image. Once the hot pixels are gone it stretches the image more so other noise becomes more evident.

[Spaced Out]

8 minutes ago, kens said:

I think that would be due to PHD2 autostretching the image. Once the hot pixels are gone it stretches the image more so other noise becomes more evident.

Thanks for the reply.

Before this I was using a webcam that had 2 hot pixels, I used the bad pixel map and they vanished leaving a dark sky and the odd star visible. I was quite shocked that when I used the bad pixel map with this camera I got a load of snow ! Is that just normal then ?

Any idea how I can improve this ?  

[SteveA]

Try  using the noise reduction option in PHD2. This can be found on the Advanced Setup/Camera tab. I had good results using this (2x2 mean) on a noisy QHY5-II. Though apparently the 3x3 median is supposed to be effective in dealing with hot pixels.

Steve

[Atreta]

1 hour ago, Spaced Out said:

Thanks for the reply.

Before this I was using a webcam that had 2 hot pixels, I used the bad pixel map and they vanished leaving a dark sky and the odd star visible. I was quite shocked that when I used the bad pixel map with this camera I got a load of snow ! Is that just normal then ?

Any idea how I can improve this ?  

It may sound obvious,  but is the camera in focus?  Maybe it is just a coincidence but with my asi120 i had the same behaviour when it was out of focus  and now i have a nice clear image without using dark library or bad pixel map. 

 

[Spaced Out]

12 hours ago, SteveA said:

Try  using the noise reduction option in PHD2. This can be found on the Advanced Setup/Camera tab. I had good results using this (2x2 mean) on a noisy QHY5-II. Though apparently the 3x3 median is supposed to be effective in dealing with hot pixels.

Steve

Thanks, I already had it set to 2x2 mean for this test and these were the results. When I use no NR I get grey image with vertical banding that changes in brightness from frame to frame, when I use 2x2 mean I get the image above constant dark with the white dots and when I use 3x3 median I get a noisy looking snow storm !

11 hours ago, Atreta said:

It may sound obvious,  but is the camera in focus?  Maybe it is just a coincidence but with my asi120 i had the same behaviour when it was out of focus  and now i have a nice clear image without using dark library or bad pixel map. 

 

I was testing it indoors in the afternoon so camera was on the guide scope with the cap on and covered in a blanket to block out light. I knew it had these white dots from a very quick look the night before, I was just trying to clean them up before a proper test at night. The focus had been left where I had it focussed the night before on a star so I think it was roughly in focus. Did your asi120 show white dots when out of focus then that cleared up when focussed ?

No matter what I do the white dots are consistent and don't move so I'm guessing these are hot/stuck pixels ? I tried using it last night with PHD, didn't use bad pixel map or darks library, I just put up with the static white dots. Didn't get far at all because it kept crashing and saying it couldn't connect to the camera again, another problem to sort out ! 

Perhaps I need to look at the camera settings separately from PHD ? I haven't downloaded the software for that yet, I just chucked it onto the guide scope as it came and was shocked that the two functions that are supposed to improve your guiding image have made it worse.

[SteveA]

It's definitely worth downloading the QHY app called EZPlanetary. As I mentioned I had some very similar issues with a QHY5-II. Okay its a slightly different camera and also only mono, but I struggled with excessive noise for ages. Despite the noise, PHD did work, but was often not guiding particularly well.

Only just this week I had some spare time and set about playing with camera and have resolved my issues. I found some weird stuff in EZP, in my case the camera settings seemed to suggest it was running in colour mode, which for a mono camera is curious. I played around and have eventualy got PHD2 working very well. Noise just about gone and guiding very much improved. Not sure if any of this is applicable to your camera, but I would check it out.

 

[Spaced Out]

5 minutes ago, SteveA said:

It's definitely worth downloading the QHY app called EZPlanetary. As I mentioned I had some very similar issues with a QHY5-II. Okay its a slightly different camera and also only mono, but I struggled with excessive noise for ages. Despite the noise, PHD did work, but was often not guiding particularly well.

Only just this week I had some spare time and set about playing with camera and have resolved my issues. I found some weird stuff in EZP, in my case the camera settings seemed to suggest it was running in colour mode, which for a mono camera is curious. I played around and have eventualy got PHD2 working very well. Noise just about gone and guiding very much improved. Not sure if any of this is applicable to your camera, but I would check it out.

 

Thanks Steve, that looks interesting and certainly worth a try. I will download EZPlanetary and try the settings you suggest to see if I can get similar results.

[Atreta]

2 hours ago, Spaced Out said:

Did your asi120 show white dots when out of focus then that cleared up when focussed ?

I'll try to reproduce the conditions to see if it shows the noise again. 

[StuartJPP]

17 hours ago, kens said:

I think that would be due to PHD2 autostretching the image. Once the hot pixels are gone it stretches the image more so other noise becomes more evident.

This is almost certainly your issue. PHD gains up the image and if there are no bright stars (or in the previous case hot pixels), then everything is gained up to the point that only noise is visible.

What I have done in the past is have a black background on my monitor and only a single lit white pixel and then focused on that.