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Old 14-04-2012, 04:56 PM
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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
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Old 14-04-2012, 06:34 PM
Ross G
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Looks good Lester.

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

Ross.
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Old 14-04-2012, 07:36 PM
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Thanks Ross, yes the DD stands out.
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Old 15-04-2012, 09:15 AM
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jjjnettie (Jeanette)
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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 )
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Old 15-04-2012, 10:55 AM
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Thanks for your comments JJ, they are greatly appreciated. I will get onto a repro. All the best.
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Old 15-04-2012, 11:36 AM
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strongmanmike (Michael)
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Cool result Lester and some great advice from Jeanette too

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

Mike
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Old 15-04-2012, 01:14 PM
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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
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Old 15-04-2012, 01:56 PM
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I think this one is as good as I can get. Comments welcome.

http://i638.photobucket.com/albums/u...s/e1c40fb3.jpg
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Old 15-04-2012, 02:16 PM
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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.
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Old 15-04-2012, 02:54 PM
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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 04:20 PM.
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Old 15-04-2012, 03:30 PM
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midnight (Darrin)
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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.
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Old 15-04-2012, 04:22 PM
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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
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Old 15-04-2012, 05:23 PM
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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.
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