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PostPosted: Fri Jan 18, 2008 1:22 pm 
Hi Bob,

Thanks for the link. I'll keep that in mind next time I attempt this.

This is turning out to be more complicated than I thought lol.


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PostPosted: Mon Feb 04, 2008 1:37 pm 
Amazing shot Gordon. Will try it when the skies clear up. cheers


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 Post subject:
PostPosted: Wed Feb 06, 2008 3:07 pm 
The sky was clear tonight and so I was able to successfully get a shot of the stars for the first time! :D Nothing spectacular and definitely nowhere in the league of the some of the other shots I've seen in this section(Bob's, Gordon's and Cybermystic's come to mind) but I'm really pleased that I was finally able to get stars.

Image
2.5s at F2.0, ISO 800

I messed around with the levels, lowered the luminance in the red channel and lowered saturation in the blue and purple channel in an attempt to get rid of the noise.

Here's the original image if anyone wants to see:

Image


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 Post subject:
PostPosted: Wed Feb 06, 2008 5:00 pm 
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Hi Graham,

Congratulations. Just goes to show that you don't need tracking mounts etc. to capture the stars. Interesting how the processing appears to have highlighted the vignetting. Looking forward to more shots as and when you can. 8)

Bob.

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Olympus OM-D E-M1 + M.Zuiko Digital ED 12-40mm f/2.8, Lumix 7-14mm f/4, Leica DG Summilux 15mm f/1.7 ASPH, M.Zuiko Digital 45mm 1:1.8, M.Zuiko Digital ED 75mm 1:1.8.
Leica D Vario-Elmar 14mm-150mm f/3.5 - f/5.6 ASPH.
OM-D E-M5, H-PS14042E, Gitzo GT1541T, Arca-Swiss Z1 DP ball-head.
Astrophotography: TEC 140 'scope, FLI ML16803 camera, ASA DDM60 Pro mount.


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PostPosted: Wed Feb 06, 2008 9:54 pm 
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Hi Graham, good shot! If the sky's dark enough though, try a longer exposure...

If you're using an 18mm lens on a typical DSLR, you should be able to get away with 20 seconds (maybe 30 nearer the pole) without showing star trails.

Hmmm, f2.0? Sounds more like a 50mm though, which would be acting like 75mm ish on a typical DSLR - even then you should be able to do 5-10 seconds without trailing.

It's all about experimenting! Good luck and let us know how you get on!


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PostPosted: Thu Feb 07, 2008 12:36 am 
Thanks Bob and Gordon.

Bob, I was concentrating on bringing out the stars and getting rid of the red colour and didn't realise that I had worsened the vignetting so thanks for pointing out.

Gordon, I assumed that I would need all the fastest lens possible so I never even considered the 18-135. I'll try that next time there's a clear sky!


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PostPosted: Thu Feb 07, 2008 1:40 am 
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Hi Graham, well it's all about weighing up your options... An 18mm may allow you to use longer exposures, than, say a 50mm, before you'll see star trails, BUT at 3.5, it will capture four times LESS light than a lens at f1.8.

So yes, your f2.0 lens will still probably be better overall, even if it's a 50mm. And even then I reckon you could get away with 10 second exposures...


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PostPosted: Sat Feb 09, 2008 1:40 pm 
Had a second go today using your advice Gordon. I made sure there was no vignetting this time.

18mm, f/3.5, 20s, ISO400

Image


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PostPosted: Sat Feb 09, 2008 1:45 pm 
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Nice one Graham. That 18mm lens sure pulls in a lot of sky. 8)

Bob.

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Olympus OM-D E-M1 + M.Zuiko Digital ED 12-40mm f/2.8, Lumix 7-14mm f/4, Leica DG Summilux 15mm f/1.7 ASPH, M.Zuiko Digital 45mm 1:1.8, M.Zuiko Digital ED 75mm 1:1.8.
Leica D Vario-Elmar 14mm-150mm f/3.5 - f/5.6 ASPH.
OM-D E-M5, H-PS14042E, Gitzo GT1541T, Arca-Swiss Z1 DP ball-head.
Astrophotography: TEC 140 'scope, FLI ML16803 camera, ASA DDM60 Pro mount.


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PostPosted: Sat Feb 09, 2008 1:55 pm 
Thanks. It pulled in some of my roof as well, which explains the crop. :D


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 Post subject:
PostPosted: Sat Feb 09, 2008 3:02 pm 
grahamnp wrote:
Had a second go today using your advice Gordon. I made sure there was no vignetting this time.

18mm, f/3.5, 20s, ISO400

Image


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PostPosted: Sat Feb 09, 2008 11:00 pm 
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Hi Graham, good work, and the Orion nebula is already visible there...

Since the sky looks quite dark there, why not also try increasing the ISO sensitivity to 800 or 1600. It'll get noisy, but you'll also get more stars...


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PostPosted: Sun Feb 10, 2008 12:26 am 
When I tried ISO 800 the sky started to come out grey. Is it still possible to "extract" the stars when the sky colour is similar to the stars themselves?


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PostPosted: Sun Feb 10, 2008 12:49 am 
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grahamnp wrote:
When I tried ISO 800 the sky started to come out grey. Is it still possible to "extract" the stars when the sky colour is similar to the stars themselves?

Yes. The simplest way would be to adjust Levels in a photo-editor. If you are up for a slightly steeper learning curve then IRIS (free from http://www.astrosurf.com/buil/us/iris/iris.htm) is worth a look. You may have to experiment to see if it understands your RAW files but it can certainly work with JPEGs or TIFF files as input.

A little overexposure of the sky isn't necessarily bad as programs like IRIS can not only subtract a constant signal but they can also calculate and subtract a gradient. With your 18mm lens that will be very usefuul as the amount of background light pollution present will almost certainly vary across the frame (areas of the frame closer to the horizon have worse light pollution issues). In your case as the camera is unguided you may run into a constraint of star trails becoming an issue before the background gets too bright.

By the way, are you using that trick I mentioned to overcome the Nikon long exposure noise reduction?

Bob.

_________________
Olympus OM-D E-M1 + M.Zuiko Digital ED 12-40mm f/2.8, Lumix 7-14mm f/4, Leica DG Summilux 15mm f/1.7 ASPH, M.Zuiko Digital 45mm 1:1.8, M.Zuiko Digital ED 75mm 1:1.8.
Leica D Vario-Elmar 14mm-150mm f/3.5 - f/5.6 ASPH.
OM-D E-M5, H-PS14042E, Gitzo GT1541T, Arca-Swiss Z1 DP ball-head.
Astrophotography: TEC 140 'scope, FLI ML16803 camera, ASA DDM60 Pro mount.


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 Post subject:
PostPosted: Sun Feb 10, 2008 12:59 am 
Um no. I was under the impression that it only affects files taken at ISO800 and above? I thought that ISO400 would be an easy way to avoid all of that. :? Was I wrong?


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