Using ISO-800 and above on the newer breed of cameras, such as the 40D and above, and ISO-1600 on the 5D Mark II, may be all well and good. Having done my fair share of imaging using the 300D and the 350D (Duncan's 400D isn't too far removed from the 350D), I know that ISO-800 makes for grainy images (especially, when printed). I'm a fan of printing so I have a bit of a bias there.
I'm not sure if you saw my earlier work, but the large majority of it, wasn't under 2 hours in total exposure. The trick is to take plenty of light frames and to take a fair quantity of dark frames. When I was using my 350D, I'd take at the bare minimum, an hour's worth of darks. I'm not the best imager out there, (though, my aim is to try to be the best with what I own), my ISO-400 images look quite nice (at least I think so!) and print rather well.
Horses for courses. If Duncan owned a 40D, I'd be suggesting trying between ISO-400 and ISO-800.
When I finally get the chance to put my 5D Mark II towards reflection nebulae and clusters, and my modified 40D for everything else, I'll still be sticking to ISO-400 for that smooth, clean look.
Using ISO-800 and above on the newer breed of cameras, such as the 40D and above, and ISO-1600 on the 5D Mark II, may be all well and good. Having done my fair share of imaging using the 300D and the 350D (Duncan's 400D isn't too far removed from the 350D), I know that ISO-800 makes for grainy images (especially, when printed). I'm a fan of printing so I have a bit of a bias there.
I'm not sure if you saw my earlier work, but the large majority of it, wasn't under 2 hours in total exposure. The trick is to take plenty of light frames and to take a fair quantity of dark frames. When I was using my 350D, I'd take at the bare minimum, an hour's worth of darks. I'm not the best imager out there, (though, my aim is to try to be the best with what I own), my ISO-400 images look quite nice (at least I think so!) and print rather well.
Horses for courses. If Duncan owned a 40D, I'd be suggesting trying between ISO-400 and ISO-800.
When I finally get the chance to put my 5D Mark II towards reflection nebulae and clusters, and my modified 40D for everything else, I'll still be sticking to ISO-400 for that smooth, clean look.
Regards,
Humayun
The way I read this and I may well be wrong is , "you own a 40D and it's diferent." If this is the case I can assure you all my earlier work was done exclusively with a 350D at ISO 800. ISO 800 was selected after quite a bit of testing which indicated exactly what was mentioned earlier. Reduced exposure time = reduced heat = reduced Dark noise.
Naturally the whole requirement is to lift the signal level above the noise to give enough data to smooth out the processing. There will always be a point in every camera where gain/ISO will produce diminished returns on S/N but at 800 ISO and subs below 10minutes this is not the case. The 350D did suffer quite a bit from an amp glow problem but either a great arrray of darks or a minor adjustment in framing and a small crop usually fixed this problem.
At Duncans stage of imaging he needs as much good Signal as he can get to allow his processing skills to climb the tall ladder you and I know exists. That being the case I would strongly urge him to stick with ISO 800, keep his exposure times down around 5 to seven minutes and take lots and lots of them and do like wise with darks, flats and bias frames and he, and we will see a marked improvement in his skills.
Thanks for info guys, so what exposure what you recommend before noise becomes an issue? at either ISO400 or 800
I supopse you would need a summer max exposure, and a winter one
My recommendation ISO 800, keep exposure times to 5 or 7 minutes Max and take manual darks and in all cases take lots of them. Take at least as many darks as lights and aim for between 10 and 20 of each. Also worth allowing 30 seconds between frames to allow the CCD to come to thermal equalibrium or as close as you can. This delay between shots makes a diference also.
It will make imaging and processing sessions longer but the results will be stunning.
maybe i could just spend a night inside, making a library of darks, so i dont have to do them all the time?
I mean, i know they have to be at the same temps roughly, to if i take some 5 min flats, dump the first one, and just keep a batch of them in a folder, then i should be able to use them as required?
What format are you saving out of DSS, I find the default 16bit format gives washed out images like yours. I manually save to 32bit Rational TIFF.
I have attached the same picture saved as 16bit TIFF and 32bit TIFF from DSS. I have then used PS to only down size and convert to JPEG. Look at the image information difference. For DSS I used MEDIAN as the stacking process. I have tried all variations with the same raw data and I cannot notice any real improvement with the data I use.
These pictures also started life as Canon Raw from a 1000d.
Heres the image, if doing this is wrong ie changing the white balance please chime in and let me know but it seems to work for me. I'm at work atm moment so normally I'd spend a bit more time with it....If you click on the button that says Tune that will bring up the colour palate.
How do you save them as 32bit tiffs I cant find the setting anywhere.
Thanks
Sandy
Quote:
Originally Posted by tlgerdes
Hi Duncan,
What format are you saving out of DSS, I find the default 16bit format gives washed out images like yours. I manually save to 32bit Rational TIFF.
I have attached the same picture saved as 16bit TIFF and 32bit TIFF from DSS. I have then used PS to only down size and convert to JPEG. Look at the image information difference. For DSS I used MEDIAN as the stacking process. I have tried all variations with the same raw data and I cannot notice any real improvement with the data I use.
These pictures also started life as Canon Raw from a 1000d.
I'll probably get shot down for this, but, I'd advise against going down the path of creating a library of darks -- the dynamics of your sensor vary depending on a number of variables (temperature/humidity, et. al.) and no matter what you do, you won't be able to recreate the same characteristics, weather-wise, as when you were out imaging. You will inevitably gain hot/dead/stuck pixels over time. If you owned a good quality CCD, it's a different story, you could probably get away with a library of darks with controlled temperature.
Of course, this all hinges on how accurate you want to be and how much effort you want to put into your images (do you want to be able to print them and hang them on the wall?). I don't necessarily agree with the whole starting-out-so-take-it-easy approach. My personal way of doing things is to do them properly (or to the best of my ability) the first time. Throw yourself in the deep end and learn how to swim. I get a lot more out of it this way. I know it's different for everyone.
Imaging is like climbing a mountain, it's not easy.
I'll probably get shot down for this, but, I'd advise against going down the path of creating a library of darks -- the dynamics of your sensor vary depending on a number of variables (temperature/humidity, et. al.) and no matter what you do, you won't be able to recreate the same characteristics, weather-wise, as when you were out imaging. You will inevitably gain hot/dead/stuck pixels over time. If you owned a good quality CCD, it's a different story, you could probably get away with a library of darks with controlled temperature.
Of course, this all hinges on how accurate you want to be and how much effort you want to put into your images (do you want to be able to print them and hang them on the wall?). I don't necessarily agree with the whole starting-out-so-take-it-easy approach. My personal way of doing things is to do them properly (or to the best of my ability) the first time. Throw yourself in the deep end and learn how to swim. I get a lot more out of it this way. I know it's different for everyone.
Imaging is like climbing a mountain, it's not easy.
My $0.02 AUD, only.
Regards,
Humayun
no mate, i can see your reasoning, thats some good advice.
How do you save them as 32bit tiffs I cant find the setting anywhere.
Thanks
Sandy
Yes as Dunc said, once you have stacked the final image, by default it creates AUTOSAVEXXX.TIF. This is saved as a 16bit TIFF file, if you then hit the "Save Picture to File" link in the Processing menu frame you can save the file as a new name and select a different format to save in. Photoshop prefers 32bit Rational TIFF, if you select Integer it will not read.
