ccd imaging at -15 instead of -5

[iwols]

what are the advantages of imaging at -15 compared to -5 cheers with a ccd

[don4l]

I've got a fairly noisy, but sensitive camera(STL6303).  It's also 10 years old and has obvious damage (caused by cosmic ray hits - I believe).

As I go down in temperature, the improvement in noise is obvious.  The dark frames also appear to act in a more consistent manner.

In the summer I image at -20, but at this time of year I usually image at -35.

 

I've also got an Atik 16HR, which has a Sony CCD.  Low temperatures are far less important with this camera and the dark frames are much easier to work with, in that they produce consistent results.

 

To explain what I mean -  Tonight I was processing some images that were taken at -20.  When I used the correct darks, I was left with some black patches.  I ended up using shorter exposure darks, but I then had to remove some hot pixels.

 

 

[iwols]

does it improve graininess

[RayD]

It largely depends on your camera/sensor.  With no cooling my KAF 16200 sensor has visible artefacts, which I guess you could call 'noise' but at -15 this is all under control.  I have cooled lower as it will allow -50, but didn't see any significant difference so I stick with this temperature all year round, which I Spain is still pushing it in the height of Summer.

My Sony sensor cameras, on the other hand, seem to need somewhat less cooling, or at least are less noisy to start with, and still work well at less (-5) on occasions where the ambient is particularly high.

[don4l]

RayD has summed up exactly what I have seen. 

However, I am seeing even bigger differences because the  KAF sensor in the  STL6303 has not aged as well as the Sony sensor in the Atik.

In fact, my old 16HR isn't cooled at all, and it isn't a big issue.  With the 6303, every 5 degrees makes a very noticeable difference.

 

However, other factors are also important.  The 6303 chip size is about 5 times the size of the 16HR chip.  The 6303 is also very sensitive to Ha which makes a big difference as I live in a very light polluted area.

If I were to buy a new camera today, it would be 16200 based.  If Sony made a similar CCD, then I would probaly go for one of those.

I wouldn't describe the effect as "graininess", but the impact is quite similar.  More data, and dithering, combats it in the same way.

[iwols]

im using the atik 414 ex ccd

[RayD]

8 minutes ago, iwols said:

im using the atik 414 ex ccd

That is a good camera and uses the Sony ICX 825, which is also very good.  I think it cools to a Delta T of -30 which for most of the year will let you (in the UK) image at -15, but in the summer you may struggle.  That isn't a problem as they do perform well at higher temperatures and, as I did with my 460 you may want to have a Winter and Summer threshold, which just means Winter and Summer calibration frames.

[iwols]

am i ok to integrate images that have different cooling temps

[RayD]

40 minutes ago, iwols said:

am i ok to integrate images that have different cooling temps

Yes, so long as they are calibrated with the appropriate calibration frames first.

[don4l]

2 hours ago, iwols said:

am i ok to integrate images that have different cooling temps

 

It is best to use the correct dark frames, but IMO, not very important with the Ex-Had chips.

 

When I was using the 16HR, I had no choice as it didn't have a cooler at all!  It wasn't an issue that had any noticeable impact on my images.