Introduction and first newbie-question about BPM

Posted by: SpiritofEden

Hello Mabula and all astrophotographers,

I´m so glad I found this wonderful software which gives us the opportunity of a free trial-period which I'm already in  😉 .

I'm located in germany, am 53 years old and already retired due to health problems. Being a re-beginner in astrophotography, my telescope is a 30 year old Meade 8" SC 2080 and I'm using a Nikon Coolpix P900 mounted piggyback on it. To get the best results being possible with my gear I created a Bad Pixel Map first after having made darks, flats and biases following the tutorial. But my BPM seems to have no bad, hot or cold pixels  🤔 . Can this be possible or am I doing anything wrong? The Coolpix is only about 3 months old. I try to attach a screenshot of the details of my BPM and kindly ask for help.

Thanks in advance to everyone who can help and a happy and lucky day to all.

 

Stefan

 

Hi Stefan, (@spiritofeden)

Thank you for your question and welcome to the APP forum 😉 

Indeed, those zeros are very suspicious, something is not right. So some questions:

1.  Nikon NEF files from coolpix camera's aren't 100% supported in APP (yet). Does your camera give you Nikon NEF files or only TIFF and or JPGs?
2. what file format was the files that you loaded to create the BPM?

Probably, it's best if you send me some of your frames. If they are NEF frames, I can quickly add full support for your camera as well 😉 If the frames are Tiffs or JPG than I will need to see them as well to solve this.

Kind regards,

Mabula

Hi Mabula,

thank you for the warm welcome to the forum ;-).
I know, the Coolpix isn't the holy grail for astrophotography but with it´s 15 sec. exposure time I try to catch as much as I can. Nevertheless I'm looking out for another camera or body. The coolpix only gives me JPGs, I left them untouched to load into APP to create the BPM.

If it´s okay, I´ll send you a dark-, flat-, and biasframe at your support address. Thank you very much for your offer to have a look at them and help.

Stefan

Hi Stefan, @spiritofeden 😉 

Okay, using only JPGs is a bit of a problem. Making a BPM will not work then. Let me try to explain why:

The darks are short exposures (15seconds like you indicate) and so these are almost black. Since the JPG compression works on the original data which is very dark, the result will be that all information on hot pixels is simply lost due to the JPG compression. The fact that the data is very dark makes things even worse. JPG compression on dark areas is very destructive. So the BPM function is not on option for calirbation if you only use JPG data.

For the same reasons, data calibration on JPG data on a pixel basis won't be very effective as well.

Data calibration assumes that data is linear, the JPGs created by your coolpix camera are not linear anymore, so that will reduce the efficiency as well.

So I would suggest to let go of data calibration in this case, since you also use very short exposure times.

The single light frame that you sent me look like this, take note of how the histogram looks:

The histogram peak is still ompletely on the left side, so the amount of signal gathered is also to low to do effective data calibration and/or flat-field correction.

Just try to integrate the lights that you have without calibration and if that shows a nicer image 😉

Cheers,

Mabula

Thank you very much, Mabula, for your quick analysis, explanation and help  👍 .

Seems to me, my Coolpix P900 isn't very useful to do serious astrophotography  😩 .

I will try my wife's camera which is an older Nikon D3000. It gives RAW-files and has a bulb-mode as well. I will start again from the beginning creating a BPM from the D3000´s sensor. There's so much for me to learn. In the future I think there's no way around buying another (maybe used) camera which works better for astrophotography.

Cheers,

Stefan

@spiritofeden,

You're most welcome 😉

Yes, especially using JPGs is a big problem. JPG compression is very destructuve in the low-lights. Using raw NEF files will be much better !

Cheers,

Mabula