Author Topic: M81/M101 now I've got guiding working again.  (Read 3604 times)

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RobertM

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Re: M81/M101 now I've got guiding working again.
« Reply #30 on: Apr 11, 2008, 17:58:26 »
Thanks for the advice, I certainly know who to come to next time  :)

RobertM

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Re: M81/M101 now I've got guiding working again.
« Reply #31 on: Apr 29, 2008, 10:12:47 »
Sorry, got bored with the clouds so I reprocessed this for some more detail in the core.  Unfortunately a few of the stars have suffered but overall I think it's better.  I'm starting to think that post processing is the tricky bit, and thats just monochrome :(

http://gallery.orpington-astronomy.org.uk/albums/userpics/10031/Messier81-final.jpg

JohnP

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Re: M81/M101 now I've got guiding working again.
« Reply #32 on: Apr 29, 2008, 10:23:33 »
Interesting Robert.. I re-processed mine also yesterday... :-)

http://homepage.ntlworld.com/john.punnett/graphics/2008/m81-feb08.html

Looks like you have held back the core well during in processing - you can see details all the way in unlike mine which is horribly burnt out. How did you do that - did you use mask layering or something?

I agree processing is the tricky part - if all your equipment is working getting the subs is easy.. :-)

John


RobertM

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Re: M81/M101 now I've got guiding working again.
« Reply #33 on: Apr 29, 2008, 10:59:29 »
Hi John,

I used two main techniques.

1) DDP stretch in Maxim - if you look at your image histogram it only covers part of the range (it was approx 6000 on mine).  I then adjusted the stretch so the original 6000 was about 50, maxim then stretches the image to the fill 16 bits.  This can be done multiple times to stretch the dynamic range out and in doing so bring out more detail but in doing so I did burn out the core a tad. 

2) Process the result as two images the merge in PS.  The first to emphasise the faint spiral arms and the second for the detail (oversharpened).

There was an awful lot of fiddle faffing about and I couldn't reproduce all the exact steps but I think the above roughly summarises the steps.  I believe your image has more potential as you have much less noise and have much more detail in the faint outer arms because of it.

The ADU count in the core before processing was about 63000 - a bit close to the well depth and saturated a few of the brighter stars but I don't think I really had much choice given the conditions.

Robert

JohnP

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Re: M81/M101 now I've got guiding working again.
« Reply #34 on: Apr 29, 2008, 11:08:34 »
maybe I should email you my fits & see what you can make of it... :-)

I've just checked raws & Min to Max is 688 to 47,000 (brightest star) - The galaxy core is approx 42000 ADU. This was for 240secs subs - I should have probably done longer...

Cheers,  John

RobertM

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Re: M81/M101 now I've got guiding working again.
« Reply #35 on: Apr 29, 2008, 11:59:24 »
Crypes ! if your background is at 688 then you must have had an incredibly dark sky.  You might even have captured some of the intergalaxy debris visible on some ultra long exposures I've seen.

I don't know what improvements I could make but if you want to email the combined fits image then I'll look forward to giving you my interpretation :)


JohnP

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Re: M81/M101 now I've got guiding working again.
« Reply #36 on: Apr 29, 2008, 14:05:50 »
Robert I've sent you a pm. John