Super Grainy images - any tips for processing

[Kerberus]

Hi All.

I've been using DSS to stack my exposures, and subtract dark frames but for some reason, all of my images come out looking monochrome, and grainy... is this just the nature of my setup, or my crappy old camera?

I'm shooting Afocally with an older Olympus Camedia 4040-Z. Its only 4mp but its got a F/1.8 lens. and its directly coupled to my telescope, so no extra light gets in...

This is an image from last night, its 9 x 16 second frames. Does anyone have any suggestions for how i can get smother, cleaner looking images? or maybe some sort of camera hack to allow me to take exposures longer than 16 seconds...

any help or suggestions would be greatly appreciated...



thanks in advance,
Kerberus

[mplanet62]

Hi All.

I've been using DSS to stack my exposures, and subtract dark frames but for some reason, all of my images come out looking monochrome, and grainy... is this just the nature of my setup, or my crappy old camera?

I'm shooting Afocally with an older Olympus Camedia 4040-Z. Its only 4mp but its got a F/1.8 lens. and its directly coupled to my telescope, so no extra light gets in...

This is an image from last night, its 9 x 16 second frames. Does anyone have any suggestions for how i can get smother, cleaner looking images? or maybe some sort of camera hack to allow me to take exposures longer than 16 seconds...

any help or suggestions would be greatly appreciated...



thanks in advance,
Kerberus

First, It's a very good image. I doubt it may be much better with Camedia 4040. But, to have less grain, you need to go with lower ISOs - which makes it hard with exposures. To my best knowledge, there's no simple hack to this camera. Things to try:
1. Interpolated mode that makes 7Mp pictures may lower the noise a bit - need to try.
2. Take TIFFs instead of JPGs and process them. They're much easier to fix.
Clear skies,
Michael

[Kerberus]

Thanks for the advice. I'll lower the ISO for my next round... I was shooting at 400 (max for this camera) and i am shooting in TIFF, DSS gives me errors about darkframes and .jpgs...

I thought that the interpolated mode would be bad for image quality since its not actual data...? But, I'll give it a shot it can't hurt.

[psonice]

Does the camera have built-in dark frame subtraction? If it does and you use dark frames, you'll be subtracting them twice, which would make it like this perhaps (normal camera noise is additive which looks like speckles on the image, if you're subtracting twice it's subtractive noise which looks grainy). You can usually tell if it does, because it'll take 16s to take the photo, then another 16 seconds before it's ready to shoot again. Check that, or just try stacking without dark frames, see what happens.

If you drop the ISO down, you'll get less light.. I don't know if this will help, because you'll need much longer exposures to get the same image. I'd say keep the ISO high and use more frames, because more frames will help reduce the noise levels anyway.

Also try 'dithering' - moving the camera slightly after each shot. That means the image is in a different place in each frame, which helps smooth out sensor noise.

[kwalker]

I'm not sure about the camera capabilities but I agree with keeping the ISO at 400.
Try taking more subs and dark frames
even though Andromeda is a bright target 20 or 30 subs will bring out more detail with less effort in processing keeping the image cleaner.
If your light pollution is low try keeping the white balance at daylight and if your cameras capable try taking the shots in raw format
other than that the image is pretty good