ICEINSPACE
Most Read Articles
Moon Phase
CURRENT MOON Waning Crescent
35.8%
The Sun Now
Time Zones
Sydney
11:32 pm
Perth
9:32 pm
Auckland
1:32 am
New York*
9:32 am
Paris*
3:32 pm
GMT
1:32 pm




Go Back   IceInSpace > Images > Deep Space

Reply
 
Thread Tools Rate Thread
  #1  
Old 14-04-2012, 05:56 PM
Lester's Avatar
Lester
Registered User

Lester is offline
 
Join Date: Jan 2006
Location: E.P. S.A.
Posts: 4,954
Crux with 85mm f2 lens and 20Da

Hi all, this is 34x2 minute exposures with 20Da at ISO 800, using 85mm f1.2 lens at f2.

http://i638.photobucket.com/albums/u...s/aa436797.jpg
Reply With Quote
  #2  
Old 14-04-2012, 07:34 PM
Ross G
Registered User

Ross G is offline
 
Join Date: Apr 2007
Location: Cherrybrook, NSW
Posts: 4,043
Looks good Lester.

So many stars and so much detail. I can see the Dark Doodad in the bottom right corner.

Ross.
Reply With Quote
  #3  
Old 14-04-2012, 08:36 PM
Lester's Avatar
Lester
Registered User

Lester is offline
 
Join Date: Jan 2006
Location: E.P. S.A.
Posts: 4,954
Thanks Ross, yes the DD stands out.
Reply With Quote
  #4  
Old 15-04-2012, 10:15 AM
jjjnettie's Avatar
jjjnettie (Jeanette)
Apollo Legend

jjjnettie is offline
 
Join Date: Feb 2005
Location: Far Far Away
Posts: 16,481
The data looks quite good.
May I give some critique though....
During processing, you clipped the black point of the image. Making the brighter stars quite blobby and the dark dusty bits too dark.
There is also a blue cast over the image.
I had a play with the image in CS3 and managed to tone it down by adjust the blue channel in curves.
I could tone down the clipping in curves as well, but you will be able to do a proper job of that by doing a full repro.
You did really well on the Doodad Keeping the little Globular Cluster under control.
If you do a repro, keep an eye on that open cluster at the centre top. If it starts getting blown out, back off a bit.
Next time you image this region, try knocking the f stop up to F4 and the ISO down to ISO400. You'll achieve tighter stars and more subtle detail to the image. (yes, you'll have to take more subs, but it's really worth it )
Reply With Quote
  #5  
Old 15-04-2012, 11:55 AM
Lester's Avatar
Lester
Registered User

Lester is offline
 
Join Date: Jan 2006
Location: E.P. S.A.
Posts: 4,954
Thanks for your comments JJ, they are greatly appreciated. I will get onto a repro. All the best.
Reply With Quote
  #6  
Old 15-04-2012, 12:36 PM
strongmanmike's Avatar
strongmanmike (Michael)
Woohoo it's clear

strongmanmike is offline
 
Join Date: May 2006
Location: Canberra
Posts: 9,521
Cool result Lester and some great advice from Jeanette too

See the running chicken in all her flapping glory at the top there?

Mike
Reply With Quote
  #7  
Old 15-04-2012, 02:14 PM
Lester's Avatar
Lester
Registered User

Lester is offline
 
Join Date: Jan 2006
Location: E.P. S.A.
Posts: 4,954
Thanks Mike as always. Well 3 repros later here is the best I came up with so far. No doubt there is still some improvements to be made. Thanks again JJ.

http://i638.photobucket.com/albums/u...s/48a8f0d7.jpg
Reply With Quote
  #8  
Old 15-04-2012, 02:56 PM
Lester's Avatar
Lester
Registered User

Lester is offline
 
Join Date: Jan 2006
Location: E.P. S.A.
Posts: 4,954
I think this one is as good as I can get. Comments welcome.

http://i638.photobucket.com/albums/u...s/e1c40fb3.jpg
Reply With Quote
  #9  
Old 15-04-2012, 03:16 PM
gregbradley's Avatar
gregbradley
Registered User

gregbradley is offline
 
Join Date: Feb 2006
Location: Sydney
Posts: 10,115
I played around with this one myself yesterday. You got some nice data there.

Despite your $2000+ Canon lens being L glass it is showing terrible chromatic aberration. I guess this is the price you pay for F1.2.
I see similar type of stars with my $250 Pentax 67 lenses although not quite as magenta as these.

So we see how much Canon is getting away with here on what is no doubt a superb lens in normal daytime photography. Its the same with Nikon. I have seen Nikon 85mm F1.4 lenses give terrible chromatic aberration which is being shown up with these new 36mp D800 cameras. Awful, yet its an expensive lens. F1.8 lenses will be cheaper and perform better. 50mm F1.8 is hard to beat, super cheap and super high quality with little distortion and little chromatc aberration. Hence the nickname "nifty fifty".

The easiest way to handle this is to use the selective colours tool in Photoshop. Select magenta and pull down sliders and up cyan and then select blues and pull down magenta and up cyan. You will be able to get it looking more bluish which would the actual colour of the stars.

I'd run HLVG which is a free green noise Photoshop plug in from Rogelio Andrea to reduce the excessive green in the image.

Then you will be left with more natural colours that you can then enhance as you will without pushing the colour bias even more.

If you black clipped the data early on then youd have to go back and start again and keep an eye on the histogram.

Hope this helps.

Greg.
Reply With Quote
  #10  
Old 15-04-2012, 03:54 PM
Lester's Avatar
Lester
Registered User

Lester is offline
 
Join Date: Jan 2006
Location: E.P. S.A.
Posts: 4,954
Thanks for your reply Greg, I appreciate all your advice. Strange bit is I used the same settings and set-up to shoot the Antares region and the colours just seem to fall into place without much altering. This area seems a lot more difficult. I will give the selective colours a go in Photoshop.

All the best.

Last edited by Lester; 15-04-2012 at 05:20 PM.
Reply With Quote
  #11  
Old 15-04-2012, 04:30 PM
midnight's Avatar
midnight (Darrin)
Always on the road

midnight is offline
 
Join Date: Aug 2010
Location: Australind, WA
Posts: 891
The dark lanes certainly stand out there Lester which gives it some nice contrast.

Give Jjj's advice a go. I find F4 a nice stop on my 50mm.

Crux is certainly one of those southern gems!

Darrin...

PS Greg, would stopping a F1.2 lense down to say F4 help resolve the magenta problem or this a characteristic of a very fast lense that stopping down can't really resolve to a great extent (at least in relation to Lester's image)? Just out of interest.
Reply With Quote
  #12  
Old 15-04-2012, 05:22 PM
Lester's Avatar
Lester
Registered User

Lester is offline
 
Join Date: Jan 2006
Location: E.P. S.A.
Posts: 4,954
Thanks Darrin for your comments. I should rename this thread the "Never ending story"; here is my 4th attempt with Greg's advice added. It altered the colours nicely IMO.

http://i638.photobucket.com/albums/u...s/881253fa.jpg
Reply With Quote
  #13  
Old 15-04-2012, 06:23 PM
gregbradley's Avatar
gregbradley
Registered User

gregbradley is offline
 
Join Date: Feb 2006
Location: Sydney
Posts: 10,115
Quote:
Originally Posted by midnight View Post
The dark lanes certainly stand out there Lester which gives it some nice contrast.

Give Jjj's advice a go. I find F4 a nice stop on my 50mm.

Crux is certainly one of those southern gems!

Darrin...

PS Greg, would stopping a F1.2 lense down to say F4 help resolve the magenta problem or this a characteristic of a very fast lense that stopping down can't really resolve to a great extent (at least in relation to Lester's image)? Just out of interest.

It may help for sure. Those Photozone lens reviews often comment about sharpness of lenses and very few lenses are sharp to the corners wide open in full frame cameras. Same with chromatic aberration.

How much better is a matter of trial and error though. I have noticed though that the longer the focal length of the lens the less this seems to be an issue.

It certainly reduces other aberrations like coma which is often seen at fast f-ratios.

If you work your way through your lenses you'll find the sweet spot for each. Fortunately the magenta star issue corrects quite well in Photoshop.

Greg.
Reply With Quote
Reply

Bookmarks

Thread Tools
Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +10. The time is now 11:32 PM.

Powered by vBulletin Version 3.8.7 | Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Advertisement
Astronomy Alive
Advertisement
OzScopes Authorised Dealer
Advertisement
AS&T October 2014
Advertisement
FLI Cameras and Imaging Accessories
Advertisement
ZWO Cameras at Optics Central
Advertisement
Bintel
Advertisement
Astronomy and Electronics Centre
Advertisement
Advertisement
10x IceInSpace Stickers