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Camera technique Questions and advice on how to improve your picture taking can be posted here. This board is discussion beyons the basics, which are catered for in the 'Help and advice for beginners' board.

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Old 18-10-13
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Lightbulb How it was done - Cosmic Dance

Thought a show and tell of how i created Cosmic Dance might be useful.



The image is a composite of about 120 individual frames, blended using a piece of software called Startrails from www.startrails.de

I didn't *need* to use the software as photoshop etc can do the same thing as long as you use lighten as the layer blend mode, but it did mean i could just point the program at the images and let it go

the exposure settings for each photo was determined by 2 things.
1 - the foreground
2 - the star magnitude

we start with star magnitude as more stars makes for a better photo. the limiting factor here is how much light you can get to the sensor and how sensitive the sensor is. the shutter speed makes little difference as the stars will move across the image. the outer stars being the ones that need the 'fast light' grab
i was using a lens of F4, so an ISO setting of ~800 would allow me to get stars down to about 8th or 7th magnitude, so these settings were dialled in and the lens set on widest zoom (10mm), focus changed to manual and set at infinity.
i then set the camera on a tripod, framed the subject and did a test shot, to ensure stuff was still in focus

next i needed to expose for the foreground. this was a simple set the camera into Bulb (B) mode, 'open the shutter for n seconds' and look at the result.
as mentioned in the photo blurb, about 200m away on my right was a power station, and was well lit. i wanted the ruined building in the shot, but knew that the ambient light would mean short exposures.
trial and error showed that a shutter speed of 30s was about right. this also worked out ok for the sky as well, so i had my settings of:
F4, ISO800, 30s

then it was a case of connecting a programmable remote to the camera, setting it to take 180 frames of 30s each, with 1s delay between frames (i'd prefer no pause between frames, but the min was 1s with this particular remote).
note - with the shutter speed being 30s, i could've just set the camera on 30s exposures in high speed shooting mode and left the shutter pressed down.
then it was sit in the car for 90 odd minutes while the camera did what it was told.
after the shots were taken i looked at the lens to see it was covered in dew, and thought that another night had been wasted.
back to the house, download the photos and discover that only the last 60 or so frames were worthless.
next it was off to startrails and let it strut its stuff.
post processing of the combined image was done in lightroom, but to preserve the star colours, white balance was unchanged. the blacks were enhanced as there was a bit of light pollution due to the moon being about 60% lit.



extra stuff....

choice of site - you ideally need somewhere that won't be blighted by stray lights - cars passing, people with head torches etc. and somewhere where you can stay relatively un-noticed. strictly speaking a true dark sky site would be best but there also needs to be some kind of foreground interest. i couldn't find a suitable place for my original choice of foreground subject (not saying what as i intend to find it sometime soon!), so the old farmhouse was used instead of the more usual landscape / treeline.

when - at least 2-3 hrs after sunset and preferably with no moon. winter provides longer nights and darker, clearer skies.

where - to get a circle effect, you need to point the camera due north (or due south in the southern hemisphere) as the celestial sphere rotates around polaris. obviously, you don't need to shoot a circle, but it's always a good starting point.

weather - check the forecast for your shooting location on www.xcweather.co.uk, it is surprisingly accurate. anything other than really small clouds will spoil the shot, so checking www.sat24.com is also worthwhile as you can see what may be heading your way in the imminent future.

how many frames - the earth rotates 360 in about 24hrs, so 1 hr of exposures equates to 15deg of rotation. this is pretty much the minimum and the longer you can leave the camera go, the better the result will usually be. i was aiming for about 23deg, but with dew killing 30% of my shots, i was left with 15 deg. given you know what your shutter speed will be, a simple bit of maths tells you how many frames you need to capture, but just keeping going is king

exposure time - i prefer to shoot long and few rather than short and many. why? it doesn't wear the camera out so much, makes the post processing faster and gives less breaks in the star trails, however as discussed above, exposure times are usually governed by sky conditions and ambient lighting.



hope that's of use?
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Last edited by devilgas; 18-10-13 at 12:03 PM. Reason: speeeeling
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Old 18-10-13
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Re: How it was done - Cosmic Dance

Thanks very much for that information. One of the members at our Photographic Society has used this software, I believe. I will Email him the link.
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Re: How it was done - Cosmic Dance

I sent it to my friend and this was his reply:

"Regarding Startrails, that's an excellent summary of how to do it. There's some useful technical info in there

I've done this using a Canon A460 using CHDK to program the camera to take photos at intervals

To do it on the Fuji S6500 which has continuous shooting mode I used a strong elastic band around the camera plus a little pad of plastic foam to hold the shutter button down"
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Old 19-10-13
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Re: How it was done - Cosmic Dance

Interesting and detailed post of 'how to'
I have copied and saved for a good study later.
Thanks
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Old 21-10-13
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Re: How it was done - Cosmic Dance

I found the startrails software rather unintuitive to be honest. So I used Photoshop to stack the images and used lighten blending.



This is only 35 minutes - next time I will go for a lot longer exposure

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Re: How it was done - Cosmic Dance

i'll admit that the first go with startrails also left me wondering what to click, however, when you realise there are only 3 'action' buttons (foreground average, star trail and make movie), it became quite easy ;-)
it certainly took all of the donkey work out of what would be needed in photoshop - i didn't relish the idea of creating an image with ~130 layers and doing it all manually. sure you can add and flatten as you go, but it would've been quite tedious.
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Re: How it was done - Cosmic Dance

You can select all layers and apply the blend in one go so it is very simple

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