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Nighttime nature photography is no small task, either on the time required to learn and achieve good results or the necessary equipment. I make no claim at being a master of the field, but here is a little of what I've learned over the years. There is a rule of thumb here, but like many other areas of photography, it should be ignored sometimes :) My basic rule is that you are either shooting to freeze the stars and give the image a natural look, or shoot long enough to get a very surreal feel with long star trails. The next two images were taken with all the same equipment in the same location on the same night, but with camera settings to capture images with a completely different feel. One thing you will always need for night images is either a tripod or solid place to put your camera.
First, a more natural look. Stars at Castle Lake take one.
Nikon D700, Nikkor 20mm 2.8 at 30" F2.8 ISO 6400
The surreal look. Stars at Castle Lake take two.
Nikon D700, Nikkor 20mm 2.8 @ 160' F11 ISO 200
The first natural style is demanding on equipment. Stars tend to blur leaving mini star trails after ten to thirty seconds (depending on your focal length). These little star trails are too short to be interesting and too long to feel normal. So it's necessary to have a camera with high ISO capabilities, a fast lens, or ideally both. This is where you find that kit lenses and most zooms just aren't up to par. F2.8 is only marginally fast enough, and for night shooting it's ideal to have a F1.4 lens if you have the budget. With a 1.4 lens I'd have been able to shoot at either 8" or drop my ISO to 1600. With an F4 lens this shot just wouldn't be happening. In my image you can also see that the stars in the corner are blurred due to coma, a common problem in fast wide lenses. You don't need a remote release for this type of image, but you should set your camera's self timer to a 2" delay so any shake you give it by pressing the shutter is gone by the time the exposure starts.
The best lens I have found for shooting still stars is actually not the most expensive: The Samyang 14mm f/2.8. It has little coma, is ultra-wide and about $1,000 less than the Nikon or Canon versions, which both have excessive coma.
Nikon D700, Samyang 14mm f/2.8 @ 20" f//2.8 ISO 6400
There are a lot of challenges to night time photography, especially in cold weather where batteries suffer diminished life. In cold weather just a few 30" exposures can kill a battery. Getting the second image required a lot more expensive equipment than I normally use: Goal0 Sherpa 120, Sherpa UI, Aputure Timer Remote and the EH-5A AC Adapter.
If you want the starts to be moving in a circular motion, point North if you live North of the Equator, and South if South of the Equator. A wide lens will also give it a more circular look, if a telephoto is used they will generally just be curved lines across the sky. The wider the lens the more you can get away with not being pointed directly North.
Some obvious long exposure issues like hot pixels, but the curved lines idea comes across easily at 500mm
The big question is calculatingg the exposure for a shot like this? I start by taking a 30 second exposure at maximum aperture and as high ISO as need be. This isn't a keeper shot, it is the basis for a little math. My test shot was 30" F2.8, ISO 6400. From there it's simple math, for every step of adjustment to the ISO and aperture, the length of exposure must be adjusted equally. Reducing ISO 6400 to 200 is five stops. So now my exposure time needs to double five times. 30", 1', 2', 4', 8', 16'. Then adjust the aperture; from 2.8, 4, 5.6, 8 , 11: a four stop adjustment. So exposure is lengthened: 16', 32', 64', 128', 256'. My original was brighter than I wanted, so I did some guesswork and dropped the exposure a bit under a stop: from 256 minutes to 160. Now a two and a half hour plus exposure is going to pick up a massive amount of noise and hot pixels, so I split it into ten separate exposures and used the "multiple exposure" feature on the D700, which crapped out of me, forcing me to combine the multiple exposures in photoshop, which is quite easy to do using Dr Browns services.
As a rule of thumb 4-8 minutes is a good exposure length for stacking long star trails. Long enough that you don't end up with a thousand images to process, but short enough to avoid amp noise and hot pixels.
It's worth noting that many newer lenses have rounded aperture blades, which will not give you the star shape seen emanating from the van. Instead it would just be a blob of light. These "sun stars" are an added bonus of the older lenses, particularly those with an odd amount of aperture blades.
Nikon D700, Samyang 14mm f/2.8 @ 60 shots of 5 minutes f4 ISO 200
Nikon D600, Samyang 14mm f/2.8, note the lack of a nice star from the fire that you'd get with an older lens.