Flat frames are not calibrated

[Altayer]

I'm having an issue with my L and blue frames. they refuse to be calibrated with flat frames.

 

I have used for processing Pixinsinght, DSS and MaximDL for processing with Dark, Bias and Flats. Flats were captured at 30,000 ADU or later with 37,200 ADU (QSI advised this value for high gain).

 

It appeares that the flat frames are biting the L frames with the dust particles instead of removing them. or somtimes the ripples caused by dust is still in the image even with the

image is calibrated with flat frames.

 

I tried stacking the calibration frames with different settings, mean, average , sigma-clipping with no progress.

 

I opened the camera and cleaned the filters. also cleaned the ota.

 

even vignetting is not removed with L frames but they are removed with Red, green and blue frames.

 

I tried many objects: M1,sculptor galaxy, flame nebula, M81 and many more with the same results.

 

could it be that I'm exposing the flats for the Luminus to much?! I also se vertical stripes on Blue frames all the time.

 

 

my equipments:

 

Astro-Tech 8"RC

QSI 683 wsg w/ Astrodon LRGB gen2

Spika-a flat fielder EL panel

 
 

[Earl_UK]

i use a 683 and astrodons and aim for 24000-25000 adu with my flats

that is with a fsq 106 at f3.6 though.

[Altayer]

hi Earl,

is your camera set at High gain (1.1) or low gain (0.5)?


your answer would really help a lot.

because either way I will change the way I acquire flat frames.


thanks

[Earl_UK]

er... good question where do i check, I was plugged into nebuloisty with standard settings

[Altayer]

in nebulosity on the right, under the Duration you will find gain control as I remember.

I use sequence generator for acquiring images and the gain setting is easy to find.


here is the link for advised flat exposures from QSI:

http://store.qsimaging.com/kb_results.asp?ID=28



high gain (0.5) is usually used with binning 1X1 and low gain (1.1) used with binning higher than 1X1.

I will try your ADU value tonight

[Earl_UK]

My nebuloisty is set to 0 gain

[Altayer]

I did 300sX15 only L for M74 and calibrate it with 25,000 ADU flats and here is the result in the attachment 

the frame in the right is not calibrated with flat frames and the one on the left is.


calibration done with MaximDL and DSS with the same results?!

 

[gvanhau]

Hello

I had some simmilar problems.
This is likely caused by light incoming into the telescope from different angles than when taking the flats, or by light being reflected inside the telescope. It can also be that you are working outside the linear part of the sensor.

Finally I decided to capture my flats in same condidions as the light frames:
I pointed my telescope to the sky at night, and took several 30s frames moving the telescope between each frame and then took corresponding 30s flat-darks and used this set as flats.

Regards
Geert

[jkmorse]

Altayer,

Just out of curiosity, how many subs are you shooting for each of your masters and are you shooting different flat subs for each filter.  Reason I ask is that, while your flat master looks good, your dark and bias look very noisy, suggesting they don't include many subframes.  I typically shoot 25 or 36 flats subs for each filter, 100 dark subs and 400 bias subs to build my masters.  Also, are you using scaled darks or ones that match your integrations.  Finally, how are you processing your master flats, with a master dark or with a bias or both?

Best,

Jim

[Altayer]

Hello

I had some simmilar problems.
This is likely caused by light incoming into the telescope from different angles than when taking the flats, or by light being reflected inside the telescope. It can also be that you are working outside the linear part of the sensor.

Finally I decided to capture my flats in same condidions as the light frames:
I pointed my telescope to the sky at night, and took several 30s frames moving the telescope between each frame and then took corresponding 30s flat-darks and used this set as flats.

Regards
Geert

hi Geert,


looks interesting to use the dark-flats. I will do it when the weather gets clear.

it could be the flat panel issue.


will post any update

[Altayer]

Altayer,

Just out of curiosity, how many subs are you shooting for each of your masters and are you shooting different flat subs for each filter.  Reason I ask is that, while your flat master looks good, your dark and bias look very noisy, suggesting they don't include many subframes.  I typically shoot 25 or 36 flats subs for each filter, 100 dark subs and 400 bias subs to build my masters.  Also, are you using scaled darks or ones that match your integrations.  Finally, how are you processing your master flats, with a master dark or with a bias or both?

Best,

Jim

wow. that's a lot of subs.

taking that much bias is easy, but darks are a bit harder to shot that many if your exposure are shot at 5m. you mentioned rescaling my darks? how?

[jkmorse]

Altayer,

The theory of scaling darks is that you take darks that are longer than your lights (some say as long as 5 times longer), then subtract the bias (because you need to remove the bias to get the darks to scale properly).  Now you can use one set of darks for images of different iteration lengths.  PI does a lot of this automatically if you include both a master dark and master bias frame in imagecalibration and checking the optimize and calibrate boxes under the Master Dark setting. 

Personally, I like shooting darks that match my light times since it avoids the long darks and doesn't need the bias subtraction, but you are right, its still a lot of calibration subframes.  I shoot those about once every six months at home and while they take a couple of days, who cares when its cloudy out or your working anyway.

Hope that helps,

Jim