CCD cooling

[Uranium235]

I've never tried taking an image with my 460 without parallel darks, maybe I should try it...

One comment to add though, at the moment when I do the dark subtraction of my subs in Maxim, I usually see a noticeable boost in the image, so it looks like they are doing something.

Martin, try this workflow:

(Assuming you have 16+ subs, the more - the merrier!)

1) Drop your subs into DSS, add flats and bias (at least 20 of each, but no more than 40)

2) In DSS, go to the stacking settings, under intermediate files - check the "save calibrated files" box (FITS format). Also check that sigma clipping is being used for flats and bias.

3) Next, you only need to register the images - I use a star detection threshold of 2%, no median filter. Registering the images will spit out calibrated subs into the same directory as your originals - filename extension <filename>.cal.fit. Take a moment to note any subs that have a poor score, often its better to remove those for the sake of noise.

4) Move or copy all the calibrated files to a new directory - just to keep it simple.

5) Open Maxim, drop all of your calibrated subs into it.

6) Under the view menu, select "batch process window", click the record button.

7) Select one of your subs, then go to "Kernel filters" (under the filters menu).

8) Check the hot pixel box, and set a threshold of between 65% and 95%. You can go lower, it depends on how stubborn the hot pixels are - but then you run the risk of messing with your smaller stars. You can preview the result to see the difference, once happy - click ok.

9) Save the image (not save as, just overwrite it)

10) Go back to the batch process window and press stop (you will see it has recorded your actions).

11) Click on the chevron icon, and click "Images", then "select all". Next, run the batch process.... wait a while.... make a cuppa, see the vicar... whatever...lol.

12) All of your subs are now calibrated and with most (if not all) of the hot pixels removed.

13) Stack your calibrated and cleaned subs with whatever software you wish, but ensure that you use sigma clipping. As that will take care of any remaining hot pixels or cosmic ray strikes (which are hard to remove otherwise).

Rinse and repeat for however many channels you are using

ps: It helps if you have a very low noise camera to start off with, it might not work so well on something like the 383L which definitely needs darks.

[Velvet]

H694 here -20 and no darks..... works a treat

velvet

[sloz1664]

Hi Steve,

I set both my SXH9 & QHY8 Pro cameras to -20, no darks but I use the dither function in Maxim.

cheers

Steve

[Komet]

On my IMG2Pro I run at -25 all year round. This is running the TEC unit at ~20% on a hot night and about 8% in winter. I could get down to -30 in the summer and in the winter it can get emabarrassing. The IMG2Pro has great cooling.

[gkec]

I thought I'd read somewhere that it was best to operate your cooler at a maximum of 85%, maybe someone can confirm this - To this end I have -10 degrees below zero for the winter and -5 degrees for the summer (if I'm lucky) if not I have to go for zero degrees. I don't do darks and have just started to dither. This has made a massive difference to the noise levels once stacked. As a result I don't feel at a disadvantage to only being able to cool to relatively warm temperatures for you UK based folks.

It is best not to run at maximum power so the servo has headroom if the ambient temperature changes. That way the temperature can be kept stable.

When I was at the observatory we used liquid nitrogen and ran the chips at around -100 using heaters to control the temperature.

[ollypenrice]

If you are autoguiding you'll have sub pixel accuracy so only polar misalignment will cause your pixels to move relative to the sky. This does seem remarkable but it's true. However, a perfect polar alignment is unlikely to be acheivable without using very complex methods. I tend to think that a slight imperfection works best for me, causing a hint of dither and allowing the Dec corrections to go the same way all the time.

I suspect that dither is more critical in OSC work.

Olly