CCD cooling

[kirkster501]

What temp do you guys cool your CCD down to please? And do you always dial in the the same temp summer or winter? And this is a relative thing right wrt the ambient temperature? So when people talk about -20 they mean 20 degrees less than the ambient temperature and not a true -20C below freezing?

Basic stuff i know but just sanity checking!

[Martin-Devon]

I always set mine for -20 degrees (true value, so 20 degrees below zero). In the summer months, this can be a little difficult sometimes if the ambient temperature is high in the evenings, and I settle for the maximum that the Atik460 can draw, this can be -18 on a warm evening. It doesn't make a lot of difference, but means that I need a different set of darks also taken at -18 to get the frequency & position of hot pixels to match up - incidentally there are remarkably few hot pixels with the 460 chip.

Martin

[Gina]

I use -15C true value. I have a few more hot pixels on my 460 compared with either 314L+. Something ten or a dozen on the 460 and about half that on the 314s

[kirkster501]

Gee whiz thats incredible! -15 to -20C !!! I knew they were "cooled" but no idea they went that low! So if its a typical night at say 6C its easy to get down to that kind of temp?

[Gina]

Yes. As I recall, the 314L+ can do 28 C below ambient and the 460EX 27 below. The Peltier cooling I had on my 1100D DSLR could also do 28 below ambient. At one time a while back in the hot weather (can't remember when that was now! ) the ambient was +14C and I had the sensor temperature at -14C. Mostly I used -10C on the DSLR though - I didn't seem to get much benefit in noise level below that.

[ollypenrice]

We default to -20C here (real minus 20, not 20 below ambient) but on very hot summer nights we can't get there and have to settle for -15 and do new darks. I've never invoked the water cooling on the Atiks, though. Bit scary pumping water through your £4K cameras... I suppose I ought to try it some time. I guess you need some kind of aquarium pump and a picnic box of water with ice in it. Nah, don't fancy it!!

Olly

[swag72]

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.

[kirkster501]

Its a rare night indeed in the UK to get above 16C and the vast majority of astronomy nights are between 4 - 8 C in my diary. That would imply -15C is not even breaking into a sweat for the camera and that -20C is fine most of the time.

I think Gina's -15C is the best of all worlds, and can be reached pretty much constantly in the UK thus facilitating one set of darks.

Is there no concept of ISO on CCD cameras?

EDIT: Or of course keep two sets of darks, one at -15C and the other at -20C and select accordingly - which woudl be -20 most of the time in the UK

[Uranium235]

I think Gina's -15C is the best of all worlds, and can be reached pretty much constantly in the UK thus facilitating one set of darks.

Depends on the camera being used. I found that the 314 has no need of darks.

In fact, they degrade your imges if used, so bias and flats are all thats needed.

[Freddie]

-15 and no darks for me.

[Gina]

That's right - I've never used darks with the 314L+ and I think the same applies to the 460EX.

[Martin-Devon]

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.

[swag72]

If you have Maxim Martin, have you tried dithering?

[Martin-Devon]

No I've not tried dithering yet, but I will give it a try - I did a search earlier today of posts for dithering and it looks like Maxim will do this, so next time out I'll have a go at it.

[swag72]

Maxim does it very effectively - Using it will totally negate your need for darks I reckon.

[ncjunk]

I use darks for getting rid of the hot pixels and then dithering to ensure none of those fall in the same spot in every image.

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[kirkster501]

So the conversation moves to dithering

So surely when tracking the sky the same pixel is not seeing *exactly* the same piece of sky, sub after sub? I mean, they are infinitesimally small so to get an exact match like that? And yet people do dithering for this reasons since it is real?

I have PhD and will get the Artemis software that does not support dithering. Anyone used APT with a CCD?

And my question about ISO with a CCD? IS there such a concept?

Sorry this thread heading all over the place!

[swag72]

Apologies for contributing to the thread drift Steve - It's all useful information!!

There's no ISO on a CCD.

[kirkster501]

Apologies for contributing to the thread drift Steve - It's all useful information!!

Absolutely fine!!!!! The more subjects the better Sara !

And thanks about the ISO. Thought as much but nice to put that question to bed.

[swag72]

When you are framing and want a little more sensitivity you can bin, but generally for capture people use 1x1 bin. You may see that some use 1x1 bin for their luminance data and 2x2 bin for RGB. There's pros and cons for that, I'm sure there's threads about it.

[ncjunk]

If you have a hot pixel and are guiding it can fall in the same part of the picture in each sub.

When you combine it a higher percentage of those subs end up with the pixel in the same spot and it shows up on the combined image (this does depend on which processing methods you prefer as some remove them better than others)

In something like the mesu mount its worse as it tracks so darn well.

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[johnrt]

Set to -25 and no darks with my Atik314l+

The pixel rejection routines in pixinsight do a very good job at removing hot pixels.

[kirkster501]

Set to -25 and no darks with my Atik314l+

The pixel rejection routines in pixinsight do a very good job at removing hot pixels.

Great to know John. Thanks.

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[IanL]

I've never invoked the water cooling on the Atiks, though. Bit scary pumping water through your £4K cameras... I suppose I ought to try it some time. I guess you need some kind of aquarium pump and a picnic box of water with ice in it. Nah, don't fancy it!!

If you were going to go down that route you'd want to be using non-conductive fluid designed for PC water-cooling. Here is a review of some of the products (a bit out of date but there are plenty on the market):

http://www.bit-tech.net/modding/2008/02/16/watercooling_fluid_shootout/

Provided the fluid is kept free of contaminants (dirt, dust and metals from the kit) it will be non-conducting and won't damage the electronics in case of a leak. On the other hand I imagine some (or all) of them might have a detrimental effect on scope optics, optical windows, etc. in case of a big leak. Distilled water would actually be the safest choice as it is non-conducting and contaminant free, but unfortunately it does not stay that way for very long since it is such a good solvent and you'd need to purge and re-charge the system frequently.

As far as pumps, tubing and cooling loops, you'd want to look at the PC overclocking/watercooling scene as that is where you could source almost anything you require for the job.

[DrRobin]

I was advised to use dithering on a Canon. I changed a few things between the non-dithered run and the dithered run so it's difficult to know, but the run with dithering was definitely better. APT handles the dithering very well and also supports CCDs, I hooked my Atik up to it one night, but the weather was against me, so didn't do any images. It did however, take photos with just the same efficiency as the Atik app.

Robin