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  #21  
Old 27-03-2012, 06:56 PM
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tlgerdes (Trevor)
Love the moonless nights!

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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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  #22  
Old 27-03-2012, 07:08 PM
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Screwdriverone (Chris)
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Quote:
Originally Posted by tlgerdes View Post
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.
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 View Post
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.
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 View Post
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!
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
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  #23  
Old 27-03-2012, 07:46 PM
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bojan
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20 light frames is enough. Additional 100 more will do not much to the end result (1dB ? ). I am using usually 12 or 16.
Followed by the same number of darks.
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  #24  
Old 27-03-2012, 08:54 PM
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Screwdriverone (Chris)
I have detailed files....

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Good to know, I will limit myself to 20 x say 2 min subs, at ISO 800....with corresponding darks and sooner rather than later, some flats.

Might have to go digging up on how to take the proper flats with the T shirt method, I vaguely recall something about 2/3 of the histogram and fastest shutter speed, or is that bias?

Thanks for your help Bojan

Cheers

Chris
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  #25  
Old 27-03-2012, 09:26 PM
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rcheshire (Rowland)
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Quote:
Hmmm, OK, so some 120 sec subs at ISO 800 and LOTS of them is a betterchoicethen.Cheers, I might go dig out the 2 min subs and give them a go.
It still depends on the sky condition.These articles are very good and speak to some of your questions.
http://www.pbase.com/samirkharusi/beginners
http://www.iceinspace.com.au/forum/s...00&postcount=1

http://www.samirkharusi.net/filters.html

Last edited by rcheshire; 28-03-2012 at 02:08 AM.
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  #26  
Old 28-03-2012, 02:30 AM
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Tandum (Robin)
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Chris,
I built my light box out of foam board from office works, hot glue, spit and solder, but I saw one of Exfso's boxes at pmrid's and it's built way better than anything I could ever knock up.

When shooting flats, I normally aim for the center of the hystogram bell curve to be around 20,000. As the maximum is 64K, 20K is close to 1/3. Some of us with slow shutters have problems getting the light dim enough to achieve this as we need to expose for 4 seconds at least to avoid shutter artifacts in the flats. Introduce mono cameras and binning and the problem gets worse. But with a one shot colour it shouldn't be an issue.

Here's a flat from the other night plus the image I used it on, rotated 90degrees CCW, I've been chasing eggy stars The black bit to the left of the flat is the prism from the off axis guider sticking too far into the light path and yes it needs a clean but they flatten out the image a lot

Also, if you are going to get an LP filter, get an Hutech IDAS filter not a CLS. The CLS will throw a colour cast over the image which I found near impossible to correct at the time, the IDAS does not do that but it costs more.
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Last edited by Tandum; 28-03-2012 at 03:06 AM.
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  #27  
Old 28-03-2012, 10:11 PM
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Screwdriverone (Chris)
I have detailed files....

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Update:

I surrender........for now

I have been stacking every which way from Sunday till now, using different bayer method options and tiff conversions, even reverting to stacking JPG to try and get something out of the data I captured and I have had enough of looking at my pc grinding its progress bar up and up.....

I just dont seem to be able to get any colour out of these shots. The RAW files have heat noise and LP all over them but I can still see colour in the stars in the straight RAW shots.

No matter what I try, once I stack, its all washed out. With OR without darks. (no bias or flats taken)

So, with this in mind, I have decided to bin this lot (pun intended) and give it a rest for a while, wait until I can capture some better data at higher altitude and hopefully less LP, and start fresh with fresh eyes and hopefully a better result.

Having said that, I will post this short stack of M104 (6 minutes - 3 x 2 min subs at ISO 400) just because I havent captured a galaxy yet, or posted one....

Its really quite crap, but hey, why not. As you can see, the three stars on the right (which are quite yellow in real life) look white and the galaxy itself is almost monochrome.....but hey, I can recognise it at least.

Nothing done to it (because I dont know how to anymore) in any processing, this is simply DSS result converted to JPG and sized to 1024 x 700 something to get under 200kb. - EDIT - I think I may have played with the curves slightly in Startools and used the gradient function...I cant really remember now, Ive done it so many times Ive lost count....

Ive posted M104 as a direct comparison to Robin's version to highlight what I mean. I have also posted a JPG version of one of the RAW subs showing how much colour there really is, BEFORE I start stacking....?

Hope you arent sick when you look at it, apologies if you are

Thanks to those who offered advice and encouragement while I banged my head on the desk and had a tantrum.
Cheers

Chris

p.s. I have decided to pursue a proper cooled CCD in another thread I've posted, just need to scrounge up the cash and leave this cruddy data be.
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Last edited by Screwdriverone; 28-03-2012 at 10:21 PM.
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