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 Post subject: first stack with the Sky Watcher 150 (24/05/2012 midnight)
PostPosted: Sat May 26, 2012 10:12 pm 
Hi

This is my first attempt at stacking... nothing but stars.

My first attempt at something that looks like a cluster. Taken with a Sky Watcher 150 reflector on an eq3/2 with dual motors. Shot with a Nikon D7000, no eyepiece.

Stacked two 10s 400iso shots with 1 dark and 1 flat.
Pointing north/east ish from my back yard. No idea what it is. There was sooooo much light polution / haze i'm surprised anything was there.

Image
click image to link to gallary


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 Post subject: Re: first stack with the Sky Watcher 150
PostPosted: Sun May 27, 2012 9:48 am 
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Posts: 1255
Location: Bolton
Well done Mike, and welcome to our growing group of astro-photographers!

Now that you've managed the basics of camera mounting, focussing, etc. next you need master the art of finding your targets, and then capturing more photons - use as long an exposure as you can manage without trailing (or saturating with light-pollution), and then take dozens of exposures (and calibration frames: offsets, darks & flats) for subsequent stacking.

Meanwhile, I've just done a little more work on your image which reveals more stars (but I'm still not sure what it is!):
Attachment:
File comment: Mike's image after some more post-processing (in IRIS)
mh1.jpg
mh1.jpg [ 19.2 KiB | Viewed 5624 times ]


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 Post subject: Re: first stack with the Sky Watcher 150 (24/05/2012 midnigh
PostPosted: Sun May 27, 2012 11:19 am 
Out of curiosity, I stuck it in the Flickr Astrometry group.

http://flic.kr/p/c6bjoq

It's M39 apparently.


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 Post subject: Re: first stack with the Sky Watcher 150 (24/05/2012 midnigh
PostPosted: Sun May 27, 2012 2:37 pm 
Thank you both, that's really helpful.

I've downloaded Iris, but see there's a lot to be learned. I'm shocked that I actually caught a Messier, that's brilliant.

I was wondering how I found what part of the sky i had photographed, so thanks for the Astrometric Flickr group.


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 Post subject: Re: first stack with the Sky Watcher 150 (24/05/2012 midnigh
PostPosted: Sun May 27, 2012 7:47 pm 
I was wondering if you could share what you did with Iris to make such an improvement? How did you remove the bluring of stars around the edges? Is that bluring what a field flattener is used to correct? Thanks. Mike.


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 Post subject: The use of binning to "see the bigger picture"
PostPosted: Mon May 28, 2012 10:35 am 
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Location: Bolton
mhall wrote:
I was wondering if you could share what you did with Iris to make such an improvement? How did you remove the bluring of stars around the edges? Is that bluring what a field flattener is used to correct?

A good question Mike - my guess is that the distortion of your stars is due to a combination of imperfect collimation and "coma"
(see http://starizona.com/acb/basics/equip_optics101_coma.aspx) but I'm not an expert.

But I can certainly explain how I used IRIS to reduce this effect in your image:
  • In the original JPEG which you posted in our Gallery, the resolution of 2048x1356 pixels clearly showed these aberrations, but the image was far too big to fit on my screen, so I first used 2x2 binning to reduce the size of the image to 1024x678 (the binning process condenses each group of four adjacent pixels into a single super-pixel, so the image reduces in area by a factor of four, and becomes 4x brighter too). Thus binning reduces the size of wide-field images, by reducing their resolution (which can actually be an advantage if you suffer from trailling or optical aberrations! 8-) )
  • Then I used the window5 function to select a section of 640x480 pixels around the cluster.
  • I then applied gradient removal to take out the light-pollution from the bottom-left quadrant.
  • Then I fiddled with the white balance and colour stretching and finally the thresholds to get the best contrast.

We'll be looking at processing in IRIS during our tutorial session in July:
http://www.boltonastro.org.uk/activites/tutorials.php


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 Post subject: Re: first stack with the Sky Watcher 150 (24/05/2012 midnigh
PostPosted: Mon May 28, 2012 12:02 pm 
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Joined: Mon Oct 12, 2009 8:27 pm
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Location: Adlington
Mike,
IRIS has more tricks up its sleeve - it can stretch (boost) colour too! Your Nikon has done a good job on recording the red stars.
All will be revealed in the July workshop - well that's the plan.
David
PS north is to the left in your (this) image.


Attachments:
M39.JPG
M39.JPG [ 29.3 KiB | Viewed 5582 times ]
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 Post subject: Re: first stack with the Sky Watcher 150 (24/05/2012 midnigh
PostPosted: Mon May 28, 2012 4:41 pm 
This workshop in July is definatley one to bring a notepad and pen !! ;)


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 Post subject: Re: first stack with the Sky Watcher 150 (24/05/2012 midnigh
PostPosted: Mon May 28, 2012 5:47 pm 
Wow. Are you sure that came from the image I took of a sulphur orange sky?


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 Post subject: Re: first stack with the Sky Watcher 150 (24/05/2012 midnigh
PostPosted: Mon May 28, 2012 8:13 pm 
Like I said ......... Bring a notepad !!.... I certainly will be doing ......


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