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Old 28-02-2011, 09:39 PM
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Screwdriverone (Chris)
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DSLR Sub length and ISO question on guided exposures

Hi All,

What settings should I use for subs when using my Canon 1000D (CMOS) DSLR?

I have been trying 5 mins @ ISO 400 (looks washed out), 60 secs @ IS0 800 and 1600 etc and I am not sure what works best.

I know the brightness of the target comes into the equation (and probably skyglow is my issue), but I am after some guidance on a happy medium to get me started now that I have my guiding working so that the image subs arent too grainy which makes me think they are wrong and I throw them away.

Or do I simply process them properly and the washed out look goes away when using flats/darks in the right way?

Any help here would be appreciated so I start on the right track. ie for Eta C, try 20 subs at 5 mins @ ISO 100 for example.....


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Old 28-02-2011, 09:58 PM
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Merlin66 (Ken)
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ie for Eta C, try 20 subs at 5 mins @ ISO 100 for example

IMHO ISO200 will give you as good a result as anything else..the gain in the camera is kept under control and you can stretch in your imaging program.
The more subs the better the signal to noise; the longer the subs the better the build up of photons....so, more, longer subs.
Light pollution is probably the real limiting factor.
Just my 2c
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Old 28-02-2011, 10:06 PM
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Screwdriverone (Chris)
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Hi Merlin,

Was that a good guess or just a fluke?

So, as long as I can at lowish ISO - say 200 and then take HEAPS of them to build up the SNR. Good darks and flats and then get the encyclopaedia of Photoshop for the final mile.....


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Old 28-02-2011, 11:17 PM
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[1ponders] (Paul)
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Chris, I can't add much more than what Merlin's said, longer and more is the rule of thumb.

I'm a 5 min ISO800 sort of person, but then that's just me. One thing to remember though is that long subs will tend to wash out any star colour, so its a balancing act.

Some will swear at ISO 400 and it obviously works for them. Others ISO200. In the end its a personal choice. The lower the ISO the longer the exposure to get the same or similar result with high ISO. The trade off is more noise at higher ISO and to a certain degree (just my experience) lower native colour intensity/richness.
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Old 01-03-2011, 12:42 AM
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jones (Salvatore)
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I found that the best compromise between gain and noise, with my camera (unmodded Canon 450D) is at ISO400.
For the length, if you're under light polluted sky, then I guess the best you can do is expose as much as you can while keeping the peak of the histogram at around 75% of the window. Just make sure the right tail doesn't get cut by the right border (in that case you'd be losing information).

So expose as long as you can, as many times as you can. During summer I wouldn't do ISO800 as the noise would be really high.
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Old 01-03-2011, 01:03 AM
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Octane (Humayun)
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ISO-400 worked the best for me, between 5 minutes and 10 minute exposures. That was with the 300D and the 350D.

When I got the 40D, I took a walk on the wild side just before I got rid of it and started shooting at ISO-800 with 10-minute exposures and was able to get this type of image with it: http://members.optusnet.com.au/mrozy..._NGC_4945.html

With the 5D Mark II, ISO-1600 was my default.

Dark skies help.

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