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M31 Widefield 2 nights data :(

Keiran

By Keiran
in Imaging - Deep Sky

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Keiran

Keiran

Posted
Posted

Hi all,

I have been taking some subs of M31 over the last 2 nights... 26 x 100 sec on saturday and lastnight 16 x 150 sec, I have now combined the two bits of data.... i didnt have much luck with the first as my battery ran out on the camera, so i couldnt get asmych data/darks as i wanted :)

I have combined the two, but it still seems very noisy... I have taken 10 darks for the second set, and aboutn 3 to the first...

Is it because i have not got enough darks or is it beacuse ISO800 on my camera is toooo n oisy?

I would like abit of guidance to the percentage of darks to lights, and whether you need bias... and how critical are flat?

Thanks all for looking

Keiran

I have taken the advice onboard, and came up with this.... so thanks

bulldog_keiran-albums-dso-picture7304-m31-16-17-10-10-data.jpg

bulldog_keiran-albums-dso-picture7282-m31-16-17-10-10-data-16-x-150-sec-subs-10-x-darks-26-x-100-sec-subs-iso800.jpg

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Demonperformer

Demonperformer

Posted
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Keiran

I have read somewhere that about 20 darks gives the best result/number. Apparently fewer than that will increase the noise and more than that is a case of diminishing returns.

I'm sure I've seen the maths on a thread a while back, but can't track it down on the spur of the moment.

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Shibby

Shibby

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I have taken 10 darks for the second set, and aboutn 3 to the first...

This will certainly be a factor. In fact, 3 darks will add around 15% extra noise to your image. It might be worth re-stacking all your frames without darks.

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Keiran

Keiran

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This will certainly be a factor. In fact, 3 darks will add around 15% extra noise to your image. It might be worth re-stacking all your frames without darks.

I though darks were there to reduce noise???

Thanks anyway to the both of you... Im glad to see abit more structure, but annoyed it looks sooooo shocking :)

Never mind, there is alway next time.... Such a learning curve :)

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Psychobilly

Psychobilly

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Have a look at them and see what they are like... Generally higher temps generate more noise... Thats why i am hoping for another very cold clear winter...

People should always check out their own particular camera before making their mind up what they can get away with...

I find that the hot and cold pixel removal in DSS is normally enough (in the cosmetic tab)...

"dedicated" CCD users often get confused by the way DSS does things .....

Peter...

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Psychobilly

Psychobilly

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The 500D is very low noise compared with the 1000D which itself isnt too bad...

I have given up on the 500D as a terestrial cam havent got the glss to get the best from it..

So I will try and get the cash together for a Nikon 7000 or 700 and the 500D will go under the knife after Wales rally GB...

Peter...

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dph1nm

dph1nm

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I though darks were there to reduce noise???
Darks reduce fixed pattern noise from hot pixels, and will remove the *average* level of any amp glow or dark current. However, they will always add some random noise. So whether they help or hinder depends on the relative levels of these effects.

NigelM

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Cloudwatcher

Cloudwatcher

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Hi Keiran,

Is this the M31 image you mention in your PM?

If so,then,to be honest, I don't think theres much wrong with it as it is.

If you want to add a bit of glamour,isolate the core and outer regions and overlay with colour filters to taste,blur the edges and use the dodge tool to darken the 'lanes' a tad.

Heres a quick cropped example to give you an Idea of what I mean.

post-13495-133877494229_thumb.jpg

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MartinB

MartinB

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DSLR - just let DSS take care of it .. give it whatever you have and it sorts it out .. although there anre a number of combos that will will give correctly calibrated images...

DSS does things differently...

But there is little point in collecting a load of bias frames if you are also using darks and not using flats. Surely it helps to have a basic understanding of what's going on.

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jgs001

jgs001

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When you are combining data from multiple nights, don't just stick them all in the same tab on DSS... When you add images to DSS, if you look at the bottom, you'll see you're adding them to the Master Group, and that Group 1 will appear. The Master group is for data/adjustment frames (dark/bias/flats) that will be applied to all the data in the sets. Files in group 1 will only be applied to group 1 etc... So add a file to the Master group, group 1 will be created, remove the file from the master group... You can leave the Master Group blank. Then add each nights data to a new group. This will ensure that any flats etc from each night are only applied to that nights data... It's less of an issue with darks, although they should really be matched, but very very important with flats.

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Cloudwatcher

Cloudwatcher

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As promised here is a rough and ready 'flow chart' hopefully showing how to isolate and colour sections of your image...... read left to right, top to bottom.

This gives a guide only and the use of other tool in Photoshop will be employed to brighten/darken,sharpen/blur,saturate etc. as one sees fit......... all good fun! :)

post-13495-133877494439_thumb.jpg

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Psychobilly

Psychobilly

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But there is little point in collecting a load of bias frames if you are also using darks and not using flats. Surely it helps to have a basic understanding of what's going on.

Im not going to bother digging out the info again... :)

There are essentailly 3 recommended calibration methods depending on which of the various calibration files that you have available...

Only one of these doesnt require bias frames but is only valid if you Have Darks, Flats, and Dark Flats instead...

DSS often causes confusion... its all covered in the online help files...

Peter...

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