Quote:
Originally Posted by tlgerdes
The 1000d is still a good camera. I spent 2.5 years playing with mine before i "graduated". On a cold night in the country it performs very well. My issue was heat noise, when ambient temp is above 15deg you can really notice it. Things like dark/heat noise are only an issue when you have clear dark skies where noise is greater than signal. In the city with all the background light we have signal is always greater than noise.
A CLS filter or other light pollution filter will make a difference and if you dont get the EOS Clip variety it could be used on whatever you graduate to as well.
What you really need though is a night in a dark site, once you do this you wont want to do anything else. I used to image from my city back yard, but now I only test there and wait for the next new moon weekend at Wiruna (2.5hrs drive from your place).
If you dont want to drive, I am sure you can hitch a lift with Barry, he is only round the corner from you.
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Thanks Trevor,
Last night out at Linden was a disaster, what with not being able to drift align properly, bugs and leaving my T ring at home, I got very frustrated and decided to stay at home for a while (then it rained for 3 months)....
Next time I get say $200 for an LP filter, I should be also to afford a QHY8L so I think I will save my sanity till then. Keeping in mind the LP from here, I should be right with better spectral response and lower thermal noise. My chip at 18 deg ambient was reporting 25 degrees constantly, although some subs were recorded early in the morning at 13 deg C....
Thanks for the suggestions!
Quote:
Originally Posted by bojan
Chris,
Stacking ALWAYS reduces noise - it is the nature of noise, being a random signal, it averages out over the frame
The wanted signal, on the other hand, is not random - and the stacking process increases this signal.
The end result is increased Signal/Noise ratio, exactly what we want to achieve.
Now, the background illumination (LP) reduces contrast and shifts the colour balance. When you stretch the histogram, the consequence is reduced S/N ratio, plus increased readout and quantisation noise (this is because of limited dynamic range of the camera ADC ).
How to overcome all this?
Dark site, more light frames and adequate numbers of dark frames plus flats plus bias frames (the last two could be done once for the specific camera and lens).
There is no need to spend k$ for a decent result. Of course, if you have plenty of them, no worries.. But even the most expensive camera will have noise, vignetting, readout noise.. the only way to overcome all those limitations is patience and knowhow.
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Sage advice Bojan, a light box or some evening flats are on the to do list. Thanks for explaining the technical aspects, helps to understand why rather than just live with it.
Quote:
Originally Posted by rcheshire
Frankly yes, Chris! They are a waste of time, unless you are guiding and can guarantee at least 6 - 7 minutes with round stars
Alternatively, iso800 and expose for 3 - 3.5 minutes under polluted skies - from Astropix exposure tables. StarTools Wipe will take care of light pollution.
And dither. A prerequisite for DSLR images. Modify your camera.
Have fun!
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Hmmm, OK, so some 120 sec subs at ISO 800 and LOTS of them is a better choice then. Cheers, I might go dig out the 2 min subs and give them a go.
Cheers
Chris