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Second M31 - Andromeda


moondog
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Thanks for the comments.

Steve, I did the stacking and processing with Images Plus and this is only my second go with using it. It only came on Monday. My first go was with the M42 I posted last night.

Far better than any of my attempts with Registax or Deepsky Stacker with PhotoShop Elements.

Noise - this is a difficult one with M31. I produced an image with far less noise but didn't like the look of it, so I backed off.

It's personal taste.

Thanks for the play, the noise has gone down but I'm afraid you've lost the subtle colouring of M31. The core was supposed to be yellowish and the surrounding area is pinkish.

8)

MD

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Great image MD. Much better than anything I have achieved so far.

ImagesPlus is wonderful. It has some fantastic smoothing and sharpening tools. Have you looked at the video tutorials yet. M31 is used as an example for some of the tools. Have a look at the tutorials on rank adaptive filters, edge sharpening, image math and mask tools. Lots there to play with!

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MD - fab image matey! Gotta love that Canon :D

Steve - yes is the answer. Dark frame correction would remove a lot of the noise. Ideally you need the same number of subs at the same duration, ISO and temperature. Registax has an option to create a master dark, deep sky stacker does it automatically when you tell it which are the dark frames.

And, if you use a 'proper' ccd camera, you can create a library of master darks. With DSLR's and webcams, you need to capture the darks at the same time as the light.

:D

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Steve

I didn't take any darks, flats or bias shots.

I will be doing so now. Image Plus has some great routines, but I'm on a steep learning curve !

I am posting below an edited image of M31 with background noise removed

Martin

Only done the videos on the first install disk - not looked at the other 5 - it's a great learning tool

Daz

Yes the Canon is a nice camera, very low noise - and it will be even lower now the cold weather is here.

8)

MD

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CC

Yes it does and it's not too bad - problem is each 45 sec shot becomes 90 secs with auto dark frame substraction.

With creating dark frames to process later, you can shoot all your lights first , i.e. before the clouds roll over and all the darks afterwards.

The bias and flat frames can be taken at other times. I understand you also get much better results subtracting the darks outside of the camera.

8)

MD

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I've read of people putting their DSLT in the fridge to get the temp down. Not sure I fancy doing that to mine......!

Nice re-edit there MD! Much cleaner :D

Also heard of people putting freezer packs on the back and leaving the camera to cool between shots. Apparently the sensor heats up during the shooting sequence and can get warmer than ambient with continued shooting.

Captain Chaos

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Noise comes from the camera in the form of thermal radiation. You can see this when it gets to be a real problem as things start to glow if they get hot enough. Room temperature stuff also glows but it is so dim as to be invisible, but not dim enough to be not there. Cooling stuff down helps reduce the thermal noise that the sensor picks up hence CCD imagers generally have cooling systems to keep the insides as cold as possible.

Captain Chaos

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SR

It depends on your camera really.

With my DSLR for the moon, as it's so bright I use 200 ISO

For DSO's, I try for 800 ISO, but some faint ones need 1600 ISO.

Planets usually need the highest ISO rating, 1600 for my Canon, but other models have up to 3200 ISO

Most DSLR's have a native ISO rating which is usually 100 or 200 ISO. A formula is applied to all ISO settings above this native ISO rating to increase the sensitivity. This creates extra noise in these images.

The Canon EOS 350D is quite a low noise camera so isn't too bad at high ISO settings.

If the only way to get even a faint image is to use a higher ISO setting that's what you do.

8)

MD

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Hi MD. Cheers for that. Have been looking at non SLR digital cameras too - more out of interest than anything as yet. A lot of them suffer badly from noise at high ISO levels, even the more expensive (respected badge) ones. The DSLR cams look be the job for the astro photographers not using webcams - do you think ANY of the non SLR digital models under say £200 be a serious option? Any more than that and it'd be worth saving up the rest for a DSLR. Haven't trawled through the forum yet but will do at sometime. Am sure there'll be SOMETHING in here.

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WRT ISO in digital cameras, all the software does is bitshift the data so that each step doubles the effect that the light has on the recorded image.

Imaging a single pixel gets enough light to give a histogram level of 1 (binary 00000001) at ISO 200, then you try again with ISO 400 which is twice as sensitive. This causes the camera to interpret the binary 00000001 reading that it gets off the same pixel as 00000010, or in normal numbers a level of 2. Next you go to ISO 800 and the camera gets the same information off the sensor and outputs 00000100 etc.

When the camera is interpreting each pixel to write to the memory card, all it does is move the number left a space and adds a zero on the right for each step up in ISO that you set, the left hand bit is ignored.

As all the information is bitshifted, the lowest noisy pixel at ISO 1600 gets turned into 00001000, or a histogram level of 8 so the noise is magnified.

There is a little bit more to it than that in modern DSLRs, but that's the principle that they work on.

Due to the very low levels of light getting onto the camera sensor for astrophotography any noise at all is significant and this can come from heat, cosmic rays, electrons leaking within the sensor from one pixel to another or just stray light reflecting off the supposedly blackened interior of the camera.

Captain Chaos

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MD I'm not convinced that noise is related to dark current. It looks more like bias noise. to eliminate that you just need some bias frames which are short dark exposures with no need to keep repeating them. all explained in the ImagesPlus tutorials.

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