Quote:
Originally Posted by alistairsam
Hi Rowland
Are you able to post a dark frame? Surprising that its contributing to noise.
Is read noise a function of exposure time? I thought it was per read event, that is noise generated whilst reading out values, hence longer subs to reduce read events. I could be wrong.
I'm just guessing about the noise issues and need to look at this a little closer. I will happily post my findings once I have assured myself that the problem is not operator generated.
I dont understand how dark sites need longer exposures.
The sky background values are much lower at dark sites and dso's easily pop out of the background whereas from light pollutef sites, you need a number of long exposures to get the dso to reveal any sructure. I would've thought the snr from dark sitss would be higher.
For example, I took a 45 sec test image of m83 from the asv dark site at heathcote and I was surprised to see the amount of detail revealed , whereas the same from the city would be washed out by lp.
The dark site vs light site is counterintuitive - there are a number of discussions about this. I understand the converse to be true.
I know you arrived at the -5c value based on a lit of trial and calculation but looking at graphs showing noise vs temp, -5c and -15c have a marked difference in noise. Ive seen this with my sbig stf8300m. -5c is borderline unusable but -15c is.
Have you tested pushing the cooling to -15 and comparing 5 min darks? Will be worth testing.
-5C is a practical level of cooling, as is 0 and 5C. These presets work within the capability of the design. I have no intention of attempting temperatures below -5.
We may be at risk of making comparisons here. While a cooled CCD has capabilities that exceed a cooled DSLR, fundamentally, they address different needs for the same purpose and therefore demand slightly different strategies in several respects.
And finally, startools does a very good job of controlling and reducing noise when turning tracking off. This produces a smooth image as well. Have a go with the beta release, Ivo mentioned it handles develop and noise better.
I am familiar with ST noise reduction and have used the beta release frequently.
Cheers
Alistair
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I wish I had the time to discuss at more length.
Clearly, testing shows that there are a few issues to be resolved. I suspect these are user generated, rather than the equipment.
Cheers
Rowland.