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PostPosted: Sat Jan 03, 2009 11:38 pm 
Hi, had another go at some star trails tonight, as i got my new cable release today :D , it was difficult this evening, because the moon was very bright, so a little to much light, but i still managed to resurect the image in LR!
Its a 3861 Sec (about 64 mins) exposure at f/6.3, ISO 400, at 17mm!
Tips for the next one will be appreaciated, and next time maybe i will, get some more stuff in the foreground, etc, and finally get the WB just right :wink: :lol:


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PostPosted: Sun Jan 04, 2009 4:22 am 
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Nice shot Ed... but how long an exposure do you dare?! Or how about stacking a few 1 hour shots to get larger arcs...

Of course you can see the effect more so by zooming-in, but you may not have as many interesting (or bright) stars in the field.

An interesting astro-photography technqie for better seeing the colour of a star is to slightly defocus the lens at regault intervals - say every five minutes over a half hour exposure. Those trails will turn into cones and give you a good idea of the star colour. Well, it's a bit of fun anyway! If you're worried about wobbling the lens while you turn the focusing ring, just temporarily cover the lens with a black cloth or a hat!


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PostPosted: Sun Jan 04, 2009 1:21 pm 
Thanks, well i would stack images, but i dont have any software to stack them, and am rather short on money at the moment! Also i was surprised how well this shot came out because there was a rather bright moon out, which made my picture, look completely white, on the cameras screen, although i managed to rectify it in LR! Although the colours of he stars, was not helped by my heavy editing, and then trying to adjust the WB, i found it very difficult to get the WB even vaguely right, that is why the image has a blue tint!


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PostPosted: Sun Jan 04, 2009 1:33 pm 
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I found this from Digz using it, but there is free trail stacking software at http://www.startrails.de/

The way it seems to work is to essentially take the lightest of all frames, so it doesn't add light pollution of the shorter exposures. So you can optimise the shorter exposures to a suitable level of light pollution and get more star brightness. Can also subtract dark frames to help noise or bright spots.

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PostPosted: Sun Jan 04, 2009 2:06 pm 
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Thats a pretty good attempt there. I can see a dust spot though on the lower left quarter of the image ;-)

I use the startrails software as it is free and automated. You can achieve the exact same effect in Photoshop by adding all the layers in one file and changing each layer to 'multiply' or 'overlay' I think, although some may correct me on this. This can be time consuming at first but I think there are some downloadable actions if you do a google search. I just found THIS one. You could make your own action as well. The only issue with this is that the camera must not move during the individual frames otherwise you will have to manual align (or register) the stars manually. Something that stairtrail softwar will do automatically for you.

With foreground interest you can use multiple shots and with the last one paint your foreground subject with a torch. I did this with THIS shot and painted the tree with a torch on the final frame then added all frames in the Startrails software.

In addition THIS site has some interesting reading that may help.

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PostPosted: Sun Jan 04, 2009 2:54 pm 
Ok thanks, digz, i might well give that a go!


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PostPosted: Tue Jan 06, 2009 4:01 am 
Hey Ed, how long does your 40D take to process the image? and does anyone know what would happen if your battery died during the shot?
if were you pop in a fresh battery would your camera continue to pp the shot or would the shot be lost?


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PostPosted: Tue Jan 06, 2009 11:14 am 
Hi tomis, my 40D took about 40-50 mins to process the image, i am sure if i had shot in Jpeg, it would have been ALOT quicker, i would doubt the exposure would work when the battery went flat, because the camera would probably know when the battery goes flat to shut the shutter and save the image! Or i could be wrong, anyone else got any comments about this?


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PostPosted: Tue Jan 06, 2009 1:10 pm 
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When you say "process" the image what do you mean? Is that built in long duration noise reduction after the shot is taken? If so, you might find it better to turn that off and remove hot pixels afterwards in PP.

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PostPosted: Tue Jan 06, 2009 5:33 pm 
I mean save the image to the memory card, and i might well try and turn NR off next time i do it, and see if it speeds it up!


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PostPosted: Tue Jan 06, 2009 5:51 pm 
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Ok, that does sound like the long duration noise removal working. Turning it off will save all that waiting, but you'll likely have lots of hot pixels. If you use the multiple short exposure stacking method, then a single dark frame taken manually can be subtracted from all of them and save lots of time.

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PostPosted: Tue Jan 06, 2009 5:52 pm 
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Turning off NR will speed up the process. With NR the camera will automatically 'take' a dark frame (for want of a better word) and then apply this to the image. It is the same process you would do manually, that is take your exposure, then take a dark frame (of equal length exposure to your light frame) and use PS or similar to remove hot pixels from the shot.

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PostPosted: Tue Jan 06, 2009 11:19 pm 
Ok, my next attempt, this time i stacked 109 images (30 sec each), with the software you guys mentioned, i used ISO 400! Although i turned NR off, and it makes a big difference in Noise quantity, although it does not show up so much in this shot, but others i took, had far more noise than usual!

Image




Next time i am planning to stack more images, oh and yes i know about the cloud, i did try removing the shots with the cloud in when i stacked the images, although, the gaps looked worse than having the cloud there!
Let me know what you think!


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PostPosted: Wed Jan 07, 2009 12:07 am 
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Looks good. I like that you can see the star colours quite clearly and how it shows Polaris isn't quite on the spot.

You might also want to play with the animation option in the software :)

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Canon DSLRs: 7D, 5D2, 1D, 600D, 450D full spectrum, 300D IR mod
Lenses: EF 35/2, 50/1.8, 85/1.8, 135/2+SF, 28-80 V, 70-300L, 100-400L, TS-E 24/3.5L, MP-E 65, EF-S 15-85 IS
3rd party: Zeiss 2/50 makro, Samyang 8mm fisheye, Sigma 150 macro, 120-300 f/2.8 OS, Celestron 1325/13
Tinies: Sony HX9V.


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PostPosted: Wed Jan 07, 2009 12:12 am 
What does the animation bit do? Hoping to do another one soon, when theres another clear night, starting to enjoy this photography more and more :wink:


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