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Is it me or is this noisy...


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Hi,

So, I've finally got around to taking some images with my Atik 414ex mono. These are single frames (a 30s and 60s unguided). Is it me or do they seem particularly noisy for a camera with 5e- read out noise?

I have no idea what i should be expecting? They were from 2 different nights. 

Maybe i just need to stack lots of them together.

Joe

30s: get.jpg

60s: get.jpg

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Atik say darks are not needed

On my Atik, you do want them for good results. Dark current isn't part of the readout noise spec, its charge that accumulates over time and the rate varies quite a bit between pixels.

You also want to tell DSS (or whatever you use) to remove any remaining hot pixels, 'cause it seems astro cameras are pretty dumb and don't make any effort to correct for variation/brokeness of pixels like a DSLR would. Probably so more powerful and efficient stuff can be done by processing on your PC across many frames.

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Hi,

So, I've finally got around to taking some images with my Atik 414ex mono. These are single frames (a 30s and 60s unguided). Is it me or do they seem particularly noisy for a camera with 5e- read out noise?

I have no idea what i should be expecting? They were from 2 different nights. 

Maybe i just need to stack lots of them together.

Joe

30s: get.jpg

60s: get.jpg

Hi

Yeah, you want to be stacking these (DSS - DeepSkyStacker) - maybe 20 or so @ 60s. More the merrier, generally. Longer exposures are also good :)

Louise

Louise

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I took 50 :grin: can't stack them as about 95 % are covered in cloud. The night was crystal when i set up. Had a brew, came back and bam cloud everywhere. I will be going for longer exposures when i get PHD set up, so much to do!

I was just asking as to whether the level of noise in a single frame is due to the camera or something else. I'm new to CCD imaging, but my £200 Canon seems less noisy than this!

Joe

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Atik say darks are not needed

 I know that some manufacturers say this, especially with the Sony Chips..... but I have done both, with and without darks on a Sony chip and the difference was noticeable. Now I would always use darks regardless of the specs and USP's of these Sony chipped camera's.

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I use a master bias every session that is about 6 months old!

Don't forget with setpoint cooling you can make a darks library - I have one set for my NB at 1800s and one set for luminance at 600s. They're about 6 months old too!!

Edited by swag72
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Thanks. How many are in your dark library? Do you combine them to make a master dark each time then?

My delta is -30 so I've been taking lights at -20.

If I get started with a dark library at -20 that should get me going.

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always use darks, superbias and flats. once they are done it makes a huge improvement, cosmetic correction is also worth using. dither while guiding too. all helps get better snr and simple to do.

Edited by Earl
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There's a fabulous video from Craig Stark (author of PHD) on sources of noise and how to avoid it. It is quite long but well worth watching from beginning to end, grab the popcorn.

Edited by wuthton
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Hi,

So, I've finally got around to taking some images with my Atik 414ex mono. These are single frames (a 30s and 60s unguided). Is it me or do they seem particularly noisy for a camera with 5e- read out noise?

I have no idea what i should be expecting? They were from 2 different nights. 

Maybe i just need to stack lots of them together.

Joe

30s: get.jpg

60s: get.jpg

There is noise but relatively for a single frame these are quite clean. Try stacking 16~20 of these and noise level will be dramatically reduced. Try dithering your subs in the capture software for further reduction of noise and if you apply Sigma Clipping during stacking the hot pixels will be taken care of too. Application of Dark Frames may help but since the 414 is quite a clean sensor the mileage you get may vary somewhat.

A.G

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Remember the Universe is inherently noisy! You will always get noise from the background sky, at a level of the sqrt(number of photons) - this is totally independent of any camera noise.

NigelM

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I also have the 414 and in practice I have found I get negligible results using darks, so I do not bother with them any more. Bias and flats, with dithering between subs and the noise comes out in the stacking. I also use the batch pre-processing script, but will often do integration separately rather than use the results from the script.

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Ah ok. No dark library for me then.

I'm looking at dithering. Need to get PHD stable first though. Graph is bouncing all over the place.

I would only make that decision after seeing the result of using darks as all cameras are unique. even if the same model.

Making the best out of the pre processing options makes everything else after easier.

Some people find Darks make things worse for them with there cameras.

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Ah ok. No dark library for me then.

I'm looking at dithering. Need to get PHD stable first though. Graph is bouncing all over the place.

Hi Joe,

 First of all you have one of the best and quitest modern sensors in your camera that is commercially available. Second, you also have set point cooling. Your sensor is quiet and clean as your post has shown. Sony ICX sensors generally do not need Darks certainly not at any sub length below 300C. I have not used Darks with either my 428 EXC or 314L+. They work at between -10C~ -15C. I don't use Darks even with my 383L+ which is a lot noisier than the ICX ones. I just set it to -20C. You do not need a Dark library for sure. A Dark library maybe useful for DSLR imagers since they do not have set point cooling or often any cooling,  therefore for any length of exposure they need a set of Darks thinking that after a exposure of 120s~180s the sensor temperature stabilises which does not. I have posted links to various research and articles stating that unless the temperature of the sensor could be very closely matched Darks taken at one session are not of any use to another, yes you can match the exposure length but not the exact temperature sensor as this has to be within a couple of degrees of C. A camera without active set point cooling can start imaging with the ambient temp @ 5C and end the session when the ambient temp at -3C for example, this often happens during the long winter nights. A temp difference of 8C will render  the Darks useless but not with a camera with set point cooling since once set to lets say -15C it will stay @ -15C no matter what the out side temp. What you have to do to is reduce the noise in the stack. Firstly use a lot of subs with dithering and then you get rid of the noise in the low signal areas post process. Regarding calibration frames, the more you take the better. I have master Bias made out of at least100 Bias frames and master Flats made out of 55 Flats. This is so that the master calibration frames would be as clean as possible and not induce any more of their own noise into the process or in another word these master Calibration frames are neutral as far as noise is concerned. If you must use Darks then I suggest that you take 25 @ 300s, 25 @ 600s and 25 @ 900s exposure time all @ - 15C and then use them if you must. You can then compare the result to the one without Darks and judge for your self.

Regards,

A.G

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