Amp Glow

Anand Narwani

Hi Adam,

I have acquired my first set of data and attempting to get a basic understanding of the process using Fasttrack.  I am unable to calibrate out the amp glow in my images.  I am feeling around in the dark here, but here are some of my observations:

1. Amp glow is very obvious in my raw darks, raw lights, and master darks.
2. I do not see it in raw or master dark flats.
3. If I squint hard I can see it in individual calibrated and debayered frames.  Once I star align and integrate it appears in all of its glory.

After reading one of your previous comments, I would expect that amp glow should be visible in my dark flats as if it's electronic signature I should be present regardless of exposure time. Perhaps I need to redo my flats and dark flats? I'd really like to learn how to fish for myself, so if you can point me to some things to look for in my images, I'd appreciated it.  

Anand

BlockHead

Hi Anand,

The ampglow will vary in its brightness with exposure time- but how it varies is the reason why you need to match frames to be calibrated with darks of the same exposure time. Some sensors even switch their mode of operation when the exposure time is less than 2 seconds... making the situation even more confusing.

So for the moment- don't let the matching dark frames for flat fields (flat darks) be an issue.

You can run WBPP without the dark flats or the flat field images. The amp glow should completely go away if the darks are correct. The easier way to test this is with Pixel math- subtracting a the master dark from a light frame. 

However, before I go further- how about you post the screenshots of your WBPP setup?

The Diagnostics button will create them for you (and put them in the logs folder).

-the Blockhead 

Anand Narwani

Adam,

I've re-run WBPP this morning from scratch.  Here's a link to the screen shots, logs, output master files and a sample of raw and calibrated light frames.  I'm going to tinker with pixel math to see if I can understand its odd interface.

Anand

Anand Narwani

I used pixel math to do a subtraction of the master dark from a raw light frame and I think there is still amp glow in the resulting image.  It's really hard to tell because the K values of the pixels in the area are only slightly higher than other dark spots of the image.  I *think* I can see it with my eyes but I can't be sure my brain isn't putting it there.

BlockHead

Hi Anand,

I think you need to make all of the raw data available. 

I was not able to find your raw dark frames. 

Thanks,

-the Blockhead

Anand Narwani

Hi Adam,

I uploaded a Zip file to the link with the raw data.  I'm starting to suspect that I have the gain setting not matched with the darks and lights.  I could not remember what I set it to on the evening I took the lights, so I looked in the Fits header and it said 5.0, so that's what I used for the darks.  Perhaps Indi wrote the wrong value to the fits header? 

Anand

BlockHead

A gain or offset issue will definitely be bad. Please do look into this. The value in the FITs header isn't used for calibration purposes... the main problem would be if he camera was configure for different states (gain/offset settings).

As for believing what it is the FITs header... I never assume things are correct until verified.

-the Blockhead

Anand Narwani

Hi Adam,

Help! I'm stuck. The lights were ostensibly taken at Gain 5 and I have tested with 5, 6 and 9. 5 and 6 do not calibrate out the amp glow.  9 causes large sections in the area to have a K value of 0.  Visually comparing my lights to the master darks created at the different gains, 5 *looks* correct, but what do I know?

I know this is astrophotography, but this part doesn't feel like it should be rocket science.  The darks should calibrate out the amp glow.  I'm at a loss as to why they aren't doing that.  I've read posts that say I should add a pedestal and make sure scaling is turned off.  Do either of these things make sense in my situation?

Anand

BlockHead

You should definitely not be "scaling" (that is dark frame optimization if that is what you mean).

You are right, it shouldn't be hard- BUT you need to be careful and PRECISE. You will likely need to start over and do *everything* just so. The game is to take the lights at exactly the same settings as the darks. And you need to acquire the data with the same software, under the same conditions within the same time period with the sensor at the same temperature, etc etc ... everything needs to  be right.

Basically the idea here isn't to ask the question- "What am I doing wrong?"

Really you want to be so picky that you will list all of the problems you *cannot be having."

It can't be a mismatch in gain you will say. It can't be a configuration error in WBPP you will say (and show the screenshots)... etc etc. This is the best way to approach solving problems quickly! Prove all of the stuff it cannot be- show pictures and screenshots and measured values.

There is an answer- you will eventually find it. The rocket science is finding out what is wrong- not using the software when everything is correct/appropriate.

You gave me an out (I did not continue to follow this since you indicated you might have mismatched the gain)- and I think you need to try again paying very close attention to things and see how it goes. I will happily look at those results if you still have issues!

-the Blockhead