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Question....maybe stupid but it's been bugging me lol


Celeste
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Ok, as i'm freezing my wotsits off outside...i'm thinking back on something I pondered about when I started imaging. It may be a stupid question but I am really curious.....the question is....why do we need to do say 20 or more subs of X-secs.....is it not possible to take ONE sub, then duplicate the image so you then have 20x the same sub? I gather there will be reasons why this isn't possible....i'm being dumb with it lol....just curious.......Don't shoot me down in flames for asking a dumb question lol!!


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Some of the light received in each sub may be either: momentarily distorted due to atmosphere, very faint, or not arrive at all. Also the camera will warm up and cause noise the longer you leave it exposed. If you take lots of shorter subs with a cooling gap between each then combine them you'll capture more of the light - but spread in different quantities across each sub.


 


Put the subs all together and you'll have a composite image of all the light that made it through that can be further processed. Bit of a laymans explanation but that's my understanding. I'm sure someone will explain it better. :)


 


When I say shorter subs I still mean long exposures eg 12 x 5mins rather than 1 x 60 mins. 20 x the same sub adds nothing to the total.


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Hi there


simple answer is no you cannot.


If you duplicate the sub you also duplicate all its faults.


By taking lots of subs and stacking them all the best bits are combined to create one super image.


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Yeah I gathered there were reasons for it...I was just wondering lol....typical I just checked 11 of my subs so far and a few have planes going through grrr some look like they have white ghosts spazzing out all over the pane......but some are really nice and crisp and in focus for a change haha.....looks like I may have to do more, without guiding I can't get any decent long subs without some trailing :(


Oh well it's all a learning curve.....start right at the bottom and work your way up :)


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Lol Graham...I am impatient, I want Hubble quality images and NOW hahahaha....at least I am seeing *something* on the screen tonight....i'm not saying it will be any good though! I do try but with a very old CCD and the small chip it has, it's hard. I'm hoping to get an Atik 314l+ after the summer hols.....


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Strangely enough so did I when first starting out.


Then it just becomes an obsession to try and keep improving on your last image.


You think you have cracked it and someone posts up a pic of your best image that makes it look like you took it with a box browny through a tea strainer.


So it starts all over again :lol: :lol: :lol:


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I have an explanation:


 


A finished image can be compared to a jigsaw puzzle.... Light does not reach us all at the same time, so each sub exposure is like putting your hand onto the jigsaw puzzle box and taking a handful of pieces. You won't get all the pieces you need in that one go. Each handful though comes from the same puzzle but a fresh box, so the next hand you grab might have almost all of the same pieces but one or two that you didn't have before. Those that you did already have are now doubled so are more prominent.


 


The aim is to get as many of the pieces as you possibly can to try and complete the picture, and also to make as much of it as prominent as you can. Also as Graham said, any errors you have in one single shot will be magnified if you copy and paste the same shot. You need more shots to get a better signal to noise ratio, meaning the signal is stronger than the noise.


 


I know what you are saying, and I thought the same. I tried it and soon found that it made a bad image. Unfortunately there are no short cuts in astro photography as I am sure everybody who has tried it has soon found out.


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Great explanation Mike :) Yeah I gathered there are reasons or everyone would be doing the *shortcut* haha...I was just curious. Newbies eh....what can ya do! :P


Edited by Celeste
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. Newbies eh....what can ya do! :P

 

Ask questions and learn ;) And if not a newbie, try and help as much as we can :)

 

Remember, there is no such thing as a silly question, and stuff is only simple if you know the answer, never be afraid to ask :)

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"The only silly / stupid question is the one you didn't ask".

Remember, there is no such thing as a silly question

Amen!

Mind you, there are silly answers. :)

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