Ever wanted to photograph star trails? ....well it may be a whole lot easier than you think!
This image posed a little difficulty in the fact that it is not simply a star trail on it's own. It contains foreground elements that needed to be considered on their own in terms of exposure.
The shed was shot first with a 30 second exposure, using two consecutive flashes (different angles) and red foreground glow provided by a red LED head lamp.
A second image was shot for the stars, using a known exposure rating of 25 mins f5.0 ISO100.
The two images where then combined in Photoshop. This two frame technique allowed me to experiment with the shed lighting and get instant feedback (yes I was shooting digital).
The star trail exposure was a given (I had previously ran some tests and determined that 100ISO f4.5-5.0 would expose the stars correctly) and to shoot the foreground lighting within the start trail exposure, ran the risk of wasting a 25min exposure if I stuffed up the shed part.
With limited battery power on hand and the weather changing rapidly (fog rolled in at the tail of this exposure) the two shot method was considered the safest option.
It should be noted that you can leave the shutter open for any length of time to get the length of trail required, BUT you need to consider the noise generated with long exposures and also the camera battery life. In my case I found that 25-30 minute exposures are still very clean with my camera and this time also provided enough star movement for me.... while also allowing safe battery for the exposure and the following 25-30 minute noise reduction exposure that follows.
If you're shooting film, it's no different except that you will be able to comfortably shoot longer exposures, as film "grain" remains a constant unlike digital "noise" that increases with the exposure length.
The stars are moving in a circle because "Celestial South" was an important inclusion in this composition. To find celestial south in the night sky, first find the Southern Cross and then extend the long arm about 4.5 times.... that's it... simple huh! ;-)
What's that... you're in the northern hemisphere and want to know how to find Celestial North? Well you guys are lucky and have a northern star marking the point, but sorry, I can't see it from here. :-( I am sure that a quick Google (or a chat to 3 wise men) will find the answer that you are looking for though. ;-)
Cheers
Rusty
Australian Digital Photo Of The Day: http://www.potd.com.au
Photography help for beginners - Film & Digital Camera Techniques - Post Processing - Photography tips and tricks - Star Trails
thanks for sharing your experiences in photography! i appreciate it! (:
ReplyDeleteAfter you've taken the 25 min exposure, you need to wait for a further 25 mins for the camera to process the image. Should you leave the camera on the tripod untouched until its finished processing or can you move it?
ReplyDeleteGabby you can move the camera during this period, as the "dark frame" used for noise reduction is actually taken with the shutter closed.
ReplyDeleteSo you can move on to setting up your next shot if you wish, but make sure that you don't do anything that will cause the dark frame to be aborted.
Also you will need to stay in the same environment. Sensor noise is a variable and effected by temp, so if you were to move back into a warm room/car for example, the noise generated during the dark frame would not match the original exposure and therefore become useless for noise reduction.