PHD2+Guide camera - dark frames, bad-pixel map or neither?

[Demonperformer]

I have been reading the PHD2 manual and have noted the statement: "The settings for 'Use Dark Library' and 'Use Bad-pixel Map' are mutually exclusive - you can use one or neither, but not both at the same time".

So, in order not to reinvent the wheel, a question for those of you who use PHD2. Which, if either, do you find works best? Or. if it isn't that simple (and when is it ever?), what are the main things I should consider in making the decision?

Thanks.

[Thalestris24]

Hi

I use bad pixel map but I'd suggest trying both and see which works best for you. It's just a judgement as to which gives you the cleanest image and best s/n. Either is better than neither!

Louise

[Starlight 1]

+1 for bad pixel map .

[Freddie]

Darks for me.

[Davey-T]

Depends how many hot pixels you've got, I've only got 3 so can remember where they are so I use darks.

Dave

[D4N]

I just don't bother, the dark current is highly variable on an uncooled camera and I don't have any bad pixels that show up on such short exposures.

[Demonperformer]

Right, the general concensus would seem to suggest I should at least try the bad-pixel map first. That way I can find out how many bad pixels I have and go on to try a set of darks if the results warrant it (but it is uncooled - I'm going to use my QHY5Lii). Now, where did I put that changing bag?

[Demonperformer]

OK, I have obviously done somthing stupid, but I don't know what. This is my 'bad pixel map' result:

Even pushing the aggressiveness to 95%, I have only managed to find a total of 0 hot and 0 cold pixels! So I took a single 0.01s exposure in the dark and got

which looks an awful lot like a load of bad pixels to me.

Any thoughts/suggestions?

Thanks.

[alexbb]

Never had any issues because the camera is uncooled. In the beginning, I created a dark library which I used ever since. However, I used fast enough optics for guiding: either an 100/500 scope with a 0.5 focal reducer, either a lens 200 f/4. I always had plenty of bright stars to choose from.

This should be helpful for creating a dark library: http://openphdguiding.org/man/Darks_BadPixel_Maps.htm

Alex

[Demonperformer]

Thanks, Alex. Yes that is the document I used, but am very puzzled by the results it produced ...

[alexbb]

Try to reset the dark library (reset master dark frame or so). If I remember well, there are somewhere some options to specify which is the minimum exposure time and the maximum exposure time you use and for which the PHD should take the dark frames for the library. And the number of exposures to be stacked. Try to find that. I'll get to my laptop a little later.

[Demonperformer]

Yes, there is. But this wasn't a "dark library", but a "bad-pixel map", which said there were no bad pixels, but the short exposure suggested otherwise ...

[alexbb]

16 hours ago, moise212 said:

I'll get to my laptop a little later.

Sorry, went home then left again. Did you progress in any way?

[Demonperformer]

I still can't see how PHD2 can describe the image I obtained as having no bad pixels, and until that point is sorted, I cannot see how I will be able to progress.

[Demonperformer]

Seems I'm not the only one with this problem - link - but I don't understand half of what is being said!

[Jokehoba]

On 9/21/2016 at 08:28, Demonperformer said:

Even pushing the aggressiveness to 95%, I have only managed to find a total of 0 hot and 0 cold pixels! So I took a single 0.01s exposure in the dark and got

What does a 15s dark exposure look like?

Just tested creating a BPM on PHD2 using the laptop's webcam and this is what I got:

The values you are getting for mean/median look far too high, like light is getting onto the sensor. So I tried repeating this with the laptop in full sunlight (not perfectly illuminated, unfortunately):

Much higher mean/median values.

Not sure if this helps or adds to the mystery.

[Jokehoba]

Ah, that link... Looks like your camera is producing fully saturated frames...

[alexbb]

Yes, Jokehoba is right. I didn't look careful enough on your screenshot. The mean/median values are at the highest value.

In the link you provided, there's a guy recommending 2.6.1dev9 build. Try a shorter exposure and maybe another version of phd.

[Demonperformer]

I will give that a try this afternoon.

Thanks.

[Demonperformer]

24 minutes ago, Jokehoba said:

 like light is getting onto the sensor.

Well, as the camera does not have a 'cap' to cover the lens, I put it in my old changing bag, that I used to use in my 35mm days (when dinosaurs walked the earth) and (for good measure) folded it up while I was doing it, so I don't see any light having got in. Maybe the prog just does not like long exposures ... I can potentially take them down to 0.01s, but will try a slightly longer exposure first.

Thanks.

[Thalestris24]

Hi

It sounds like you need to rebuild your master dark frame - making sure the guide cam is completely light tight, especially if done during the day. Be aware that some materials allow infra red to pass through and this is of concern if using a mono guide cam. I just rebuilt my master dark and bad pixel map. I use a lens cap plus some aluminium foil to make sure of being being light tight. Don't forget to restart PHD2 after in order to make sure the new bpm is loaded. Don't forget to tick 'use bad pixel map'!

Here is what I just did (in pictures!):

 

15s dark taken with original bpm:

 

Original master dark + bpm:

 

New master dark and bpm: (25 x 15s at 23 deg C ambient)

 

 

2s Dark with new master dark and bpm:

 

 

You expect the frame to appear grey since PHD2 autostretches to the max - it's looking for stars!

Hope this is helpful.

Louise

[Demonperformer]

Right, trying to redo my bad-pixel map using a shorter exposure, but it will not allow me to alter that value on the screen. I did not have this problem when starting from scratch, so how do I delete the previous one, so that I can set up a new one?

Thanks.

[Thalestris24]

42 minutes ago, Demonperformer said:

Right, trying to redo my bad-pixel map using a shorter exposure, but it will not allow me to alter that value on the screen. I did not have this problem when starting from scratch, so how do I delete the previous one, so that I can set up a new one?

Thanks.

Hi

I think you need to rebuild your master dark - say 15s x 25. To do that you tick the box (as above, my 2nd image). Of course you have to have your camera connected  Do read the help info for bad pixel maps and darks (Help -> Contents).

Louise

[Demonperformer]

Yes, that's the screen I have got (with all three boxes ticked). But, as I said, " it will not allow me to alter that value on the screen ".

[Thalestris24]

23 minutes ago, Demonperformer said:

Yes, that's the screen I have got (with all three boxes ticked). But, as I said, " it will not allow me to alter that value on the screen ".

1. run PHD2

2. Connect to camera

3. Menu -> Darks ->Bad Pixel Map

4. Tick Rebuild Master Dark

5. Click on 'Generate'

6. Start

NB max exposure time is 15s

If stuck -> Menu -> Help -> Contents