Hi Stan

I'm still evaluating the CCD stack software and appear to be having trouble with calibrating my images.

When I apply the calibrated flat frame to any of my images the imperfections such as dust donuts do not disappear.
The imperfections actually look intensified.
I can calibrate my frames successfully in Maxim DL with good results.

I followed the tutorial both PDF and online.
The steps I'm going through are as follows

1)create master bias using 50
2)create master flat frame subtracting the bas from the flat
3) Calibrate the image by subtracting the master flat only.

I'm using a QHY8 CCD and do not use darks.
I'd really like to use CCD stack if I can get this worked out.

Thanks
Troy

Flatting is sensitive to bias levels, so it is important to know your camera bias and to keep track of the bias during processing (e.g. it is removed via dark subtraction).

"Enhanced" donuts are usually due to removing too much bias from the flat or not removing bias from the image (e.g. neglecting to dark subtract). It may be that you dark (or bias) subtracted the flats and then subtracted a pedestal or bias again during the calibration. Your description is confusing (e.g. you say you subtracted the flat, but that should never be done). Also, you are not dark subtracting the image, which messes up flatting.

Now that you have a master bias, use it in the calibration form to dark subtract the image and use it to subtract the flat (enter it in both boxes). Do not pre-subtract the flats, unless you are combining them via data rejection, in which case, do not bias subtract the master flat in the calibration form. That should do it (though there are other ways).

FYI - Measure the avg ADU in a bias frame – that is the camera’s “bias level / pedestal”.

Stan

Hi Stan

Calibration works great now.

Next hiccup I've come across is trying to open debayered colored images.35mb for each one

I cannot open more than 14 because of an error message "the number of images exceeds maximum allowable"
Searched the forum and found a suggestion to clear the registry however this does not fix the problem.
It breaks my install and I have to run a repair.
tried increasing the CCD large stack settings with no luck.

Ideally I'd like to be able to stack 20-30 debayered images.

Any suggestions?

Thanks
Troy

The limits are in "Settings" (Edit main menu). The defaults are for normal computers with 32 bit OS (XP-32 or Vista 32), but some 32 bit computers can tolerate higher limits. However, it is likely that you will encounter "out of memory" errors or erratic performance when the VM exceeds 900 megabytes (VM is displayed on the left bottom in parenthesis). Bayer deca-mega-pixel images consume very large amounts of memory and require batch processing when using 32 bit OS; see other msgs about this topic in the forum.

If you are using 64 bit OS then turn off caching and limit notification. 64 bit OS can handle huge numbers of images, though it will be sluggish after VM exceeds the physical RAM.

Stan

Hi Stan, you say: "Do not pre-subtract the flats, unless you are combining them via data rejection, in which case, do not bias subtract the master flat in the calibration form."

I combine my 40 flats (with bayer matrix) with sigma reject Mean, normalise:none (I use an EL sheet), sigma multiplier:2 iterations limit:1 but I don't bias subtract. I do that when calibrating with the master.

Does sigma reject mean effects the bayer matrix in the raw flat subs? Have I been doing it wrong all this time? Thanks.

It is unnecessary to normalize the flats because your light source is constant (unlike twilight flats). Using sigma reject on flats that contain bias throws-off the sigma calculation because the bias is counted as "signal". So bias-subtraction is recommended when using sigma-reject.

However, there is no reason to use rejection for artificially illuminated flats, as they will not contain significant outliers. Such flats are too short to accumulate cosmic rays and they are usually bright and numerous enough to overpower an improbable stray ray. And obviously stars are not a problem (as they can be in late twilight flats). Thus is it likely that there is no significant difference in the Master flat you would get from “simple mean” vs. “sigma reject”.

Calibration procedures are basically unaffected by Bayer matrix because CCDStack operates separately on each Bayer-pixel position (e.g. flat fielding is independently done four times, one for each Bayer position). And pixel rejection is done per pixel position, so Bayer has no effect.

Stan

Cool - thanks for clearing that up.