PHD2 problem with hot pixels!

[UlteriorModem]

Recently I started imaging with a narrow band filter. Now all of a sudden occasionally the guider will sometimes lock onto a hot pixel because of the diminished signal level of the stars.

No problem you say? Just create a dark library, or a bad pixel map.

Thing is that with the Starlight Express guide camera when you go to shoot the bad pixel map frames the image is swamped by noise and you cannot see the bad pixels. The Starlight Express is kind of odd in that if there is no signal or stars in the field it just kind of fills with white noise. Only when it 'sees' an actual star does the background turn black?

I made a new dark library last night and used that but one bad pixel in particular is still there. One time while doing a drift alignment I thought I had nailed it! Near perfect guiding.... oh that's a hot pixel!

Anyhow anyone have experience with this issue? Any hints or tips I might try?

My thanks in advance.

[SKEtrip]

Trying to remember from the tutorial I've watched - isn't there a way to exclude a pixel?
If I catch a break I'll look for it. Then again, maybe you shouldn't listen to someone who
manages to have PHD correct in the wrong direction & hasn't figured it out yet....

[UlteriorModem]

There is a way to 'manually' add a hot pixel to the map. That's the problem, the image is so washed out you cant see any of the hot pixels to add them.

[yobbo89]

Have you tried changing the star search size, I cannot remember the settings name sorry, there's a value you can change that helps phd From locking onto dead pixels. I'm in the same boat actually trying to tune this out.sgp and phd keep failing because it's locking onto dead pixels, I'll fire my laptop up tomorrow and show you the value I'm changing, I've also ditch the ascom driver and gone back to the native which shows less noise with the dark library

[yobbo89]

Only when it 'sees' an actual star does the background turn black?



My thanks in advance.

I get this too, it's like the dark frame doesn't get applied until phd detects enough signal.

[UlteriorModem]

Well I 'think' I found a work around.

If you run the bad pixel map without the camera looping it leaves the background dark and pops up little red dots if show bad pixels is selected. I guess to manually add a hot pixel it will have to be looping and actually have some stars in the background. Otherwise no matter the settings you just get a screen full of white noise.

I ran it and it found 57 hot pixels and 0 cold. I may need to back down the tolerance some but for now I am going with the bad pixel map as it is.

[shadowoo2]

The general recommendation of the guider focus is to be slightly out of sharp focus so your stars are slightly bloated to allow for an easier lock and tracking. By doing this you should be able to tell what is a star and whats a dead pixel. You should be able to tell if you are on a dead pixel fairly easily if you have minimal RA and DEC movement. Taking Dark's as recommended will help

[JimMinCT]

Question:
Why can't you run the bad pixel map using the L, or no filter?
does the number and/or position of them change when switching filters? I would think not.
So, a map can be made using no filter, matching the exposure duration and it should come out OK, No?
just a thought...

[UlteriorModem]

The bad pixel map is shot just like dark calibration frames, with the cameral or tube covered.

The last one I shot by running the BPM app in PHD2 without the camera looping seems to be working okay. Havent had a hot pixel lock since then.

What we are talking about is the ability to manually add a hot pixel to the already generated bad pixel map. The problem is that if the Starlight Express does not have any signal (stars) all you get is a screen full of white noise. It of course is impossible to see any hot pixels amongst all that noise. But once it picks up a star poof the background turns to dark and smooth. With some signal and a 'good' background I just pan around a little and the hot pixels should be obvious since they dont move. I did that last time out and saw no obvious hot pixels so the BPM must have worked.

It is just an oddity with some guide cameras.

[seigell]

Are you certain that your "Swamped with Noise" issue isn't simply a case of your interpretation of PHD2's Auto Screen Stretch?? PHD2 applies a Screen Stretch to the Displayed Image, factored to the Brightness required to get Stars to Show for Display. And with a Covered Scope, no Stars / No Light equals Extreme Stretching...
You should be able to let PHD2 product the BPM for you. Else Capture an Image to File, and then open that TIF / JPG to identify your Hot Pixels.

[UlteriorModem]

I am certain. It matters not where you set the stretch to. It only changes the 'level' of the noise. Like I said as soon as an actual signal is captured the noise goes away and gives a 'normal' display.