Taken from my Blog:
http://wildaboutlife.net/wp/archives/146
(Formatting is slightly better on the Blog post, doesn't seem to have copied over too well!)
As the winter cold is leaving us behind now is the chance to get some of my favourite type of photos done: Startrails. The end of summer, autumn and spring are some of the best times to do star trails (in the UK), the nights are comparatively warm, the skies less (just) cloudy and the nights just long enough to get some good trails in without having to stay up til stupid times in the morning!
Star Trails?
For those of you that don't know what or how you can get startrails in photography lets go to the basics first. Star Trails are basically long exposures of the stars, and as they move in the sky their tracks are saved in your photo. Obviously the stars don't actually move, it is the earth's rotation changing the location of the stars relative to your position, the same way we get night and day and the moon and sun rise and set. Due to the rotation of the earth on its axis these trails will appear as curves, becoming steeper the closer to the North Star they are (the north star is broadly above the axis of earth and as such doesn't appear to move).
ISO200, f/3.5, 18mm, Fourty five 1 minute exposures
Equipment
So you know how you get star trails and you now want to try it out yourself? Well, as with my
lightning tutorial the equipment you will need is mostly pretty standard stuff, in fact the equipment is remarkably similar and in fact you need less:
Camera with Bulb mode - Most if not all DSLR's will have a Bulb mode, and some Compacts too.
Wide angle lens – Any lens will do but generally you will want a lot of sky and foreground in shot so the wider the better usually, most likely your standard landscape lens (from 10-50mm on a crop sensor) will work just fine, however an ultra wide angle lens would be preferable.
Tripod – A must really, however you could balance the camera on something if you don't have one.
Timer Remote – A bit more specialist, however IMO something that all photographers should have, not essential but highly recommended! However most cameras will need at least a basic remote for starting and stopping exposure in bulb mode.
Heater – Some people find that in some conditions condensation starts to appear on the front element, to remove this risk they buy a heater pad to go round the lens, which usually needs a power source (making them quite HEAVY). I personally have never had a problem with condensation so it's way down my list TBH (See Splogs post below for another take on the matter).
Star map – Again not essential, but it's nice to know what you are shooting some times (and maybe more useful if you can't identify the North star very easily). You can also use it as a time waster.
Torch – Obvious really, but I'll put it in here. Star trails are done at night... usually in the dark... so you'll need a torch... unless you want the fun of stumbling around in the dark with some quite expensive gear...
Startrails.de software – Not essential again, however it's free, easy and light (filesize) so why not? The alternative is to use Photoshop, however that takes longer...
Click Here
Settings
Right, to the nitty gritty, obviously to get trails you need a long exposure, however this is a little more complex than it first appears, firstly due to two techniques you can use to get the trails, the traditional and the "modern" way.
The traditional way, used mostly by film users, is to shoot the trail all in one go, so exposures of one to ten hours can be expected. I guess this can be classed as the "true" star trail, but it has it's pitfalls:
You are relying on one shot for an entire nights work, still a big task for film users as condensation, light or movement of the support could ruin it half way through and ruin an entire nights activity.
With digital (which this guide is aimed at) there are even more pitfalls to this technique. For example unless you hook your camera up to an external power source I don't know of a digital SLR that will expose for more than 2-3 hours, once the battery dies there is no way of knowing if your 2-3 hours of waiting has been worthless due to a corrupt file...
You also have to worry about ambient light, too long an exposure with too much ambient light (this can include the moon!) could leave you with a washed out sky in a matter of minutes. Film users have this issue as well and it's usually solved by going to a desolate place (deserts anyone?) when there is no moon, however that really cuts down how often you can practice it. Film users also have the benefit of Reciprocal failure in film, which basically means the longer the exposure of the film the less sensitive to light it is (I don't really understand it myself, check here if you want to know about it in more detail).
Digital users also have to worry about the sensor heating, causing noise, which can become worse the longer you expose for. You can use either long exposure noise reduction on camera (do you want to wait another three hours in the same place for it to reshoot a dark scene, let alone have the battery power?) or do it in post processing, neither of which are ideal.
The "modern" way of doing star trails reduces or removes entirely the issues with most of the pitfalls in the more traditional way, however it is only feasible for digital users. Instead of taking one long exposure the modern way means taking a number of shorter exposures. This reduces issues such as condensation, dead battery and movement as you can still use the files pre the issue to create a trail, leaving the problem files out. Ambient light and noise are almost completely removed as issues as well, now with shorter exposures your noise levels will go down (although you need to remember long exposure noise reduction is a BIG no-no with this technique, as explained later) and you can adjust your exposure lengths to go with your aperture and ISO, just like shooting in the day, to remove the problem of ambient light. With this technique the moon can be used as a major advantage and even street lights aren't much of a problem!
ISO and Aperture – When using the traditional method of shooting one long exposure the ISO and Aperture will largely be dictated by the length of the exposure you want and the ambient light, however generally you will want to collect as much light as possible to get the most stars in your shot. With this in mind you need to gauge how large an aperture you can get depending on the ambient light and the exposure length.
For the "modern method" you need to be thinking another way. Stars are in fact not very bright so you will generally want, as mentioned before, as much light as you can get onto your sensor (although you may want to vary it a little if you want to manage the "number" of trails in your shot) so you can get as many stars in shot as possible. To do this you want to open your aperture up as much as possible (f/2.8-f/4 is perfect) and up your ISO a little. However, when doing this, you need to remember the depth of field (DoF), usually it's not a problem as you are shooting with a wide angle lens a piece of prominent foreground at basically infinity, with a background definitely at infinity, however if shooting something closer with a longer focal length you may need to think about it. You also need to think about the noise the ISO will create, this will be multiplied anyway due to exposure length so a compromise between sensitivity and noise levels is needed. With both those things in mind I usually shoot something along the lines of f/2.8 or f/4 at ISO200 (on my 400D, with a 5D II or D700 you could probably push it up higher). With these sorts of settings you will probably end up with an exposure length of 2-5 minutes in an out of the way location with the moon up, 30 second exposures can be taken in a very bright location (such as a town). Your ideal exposure lengths should be around the times stated, hopefully at the longer end of the spectrum if possible. When deciding on settings you want work out whether the length and settings expose the foreground scene AND the sky in the right way (star brightness isn't related to exposure length, due to the fact they move (they are affected by ISO and aperture remember) however foreground and sky exposure are).
So to help remember all that (it's not too hard, honest!) I'll condense it into a few short pieces:
Traditional
Very Dark
ISO100
f/8 ish
2-3+ hour exposure
Modern
Very Dark
ISO200
f/2.8-f/4
multiple 5-20 minute exposures
Dark with moon
ISO200
f/2.8-f/4
multiple 2-5 minute exposures
Light (in a town?)
ISO200
f/2.8-f/4
multiple 30 second exposures
ISO200, f/4, 12mm, Eight 5 minute exposures.
Method
With the above settings in mind you should be able to go out and get some good shots but to help I'll go through a bit of the methodology. Most is basic photography and almost identical to shooting at any other time but there are a couple of quirks so it may be worth reading.
Location – First thing is first, where are we going to shoot. Well anywhere really, as long as you can see the sky! Using the traditional method of single exposure you will have a bit less choice as it will generally have to be in the countryside but the modern method can mean anywhere is game. Generally I'll shoot in the countryside, as far away from any streetlights with as little light pollution as possible. Favourite locations include Dartmoor Tors and the coast of Devon/Cornwall.
Scene – This is something you need to think about slightly differently to daytime shooting. You generally want to frame bold structures, you're looking for shape rather than texture in a lot of cases as, unless there is lots of ambient light (such as a full moon), the actual structure will be quite dark, possibly even a silhouette. Good examples of things a lot of people shoot are large structures like Tors, standing stones and isolated buildings like churches and castles. Obviously it's not a hard and fast rule, some of the best photos are those that don't shoot the traditional!
Light – Although it is dark you need to think about the light, both from an exposure point of view and for composition. You have any stray light pollution from nearby towns and villages but also any ambient light from a sunset/sunrise. The most important light compositionally in my opinion is the moon. Think of it like the sun in a daylight shot, except you're not looking for shadow but as a spotlight on interesting features. Generally you will want to keep the moon to your side or behind you, however you can get some good effects by having it in front of you. Unlike the sun the Moon comes up and sets at different times each night so you need to take that into account, you don't want to set up for a shot at 10pm and only then realise the moon comes up at 3am! The other quirk with the moon is that it goes through phases, which also need to be taken into account, if you want to shoot a pitch black night then have a look and see when the next new moon is, or look for a night when the moon comes up at 4am.
So, now you've arrived at the place you want to shoot i'll try and guide you through my method and "checklist" for shooting.
Set up – Set your camera and tripod up, with your chosen lens and compose as best you can (this will be harder said than done as the image through the viewfinder may very well be pitch black and you will almost certainly not see any stars).
Focus – Focussing is the next issue. Some lenses will have a focus ring and allowing you to manually focus to infinity (the ∞ symbol) with ease. Other lenses, including a large number of non "professional" lenses that make up a lot of peoples collections (including kit lenses) don't. The trick to get a good focus with these is to try and focus on something bright at infinity, which can mean the moon if it is out or a streetlamp if you can see it, before you compose. If you can't see a light to focus on then another way of doing it is to see whereabouts your lens focuses at infinity (not normally right at either end) before you head out and then adjusting it when at the shoot site (for example the 18-55 kit lens that came with my 400D would need a 3mm twist from one end to get optimum focus), or you can just do it with trial and error, checking focus using the next technique (or using live view if you have it).
Check – Now you have your kit set up and focus as best you can get you want to check that the photo will come out the way you intend. To do this whack the ISO up as high as possible (don't worry about noise!) and open the aperture as much as possible so you get as much light as possible to the sensor. Once done open the shutter for 30 seconds. Check the resulting image for composition and focus and rerun the 30 second exposure again to check (my motto for star trails is to check, check and CHECK AGAIN! You don't want to have spent 3 hours in the dark and cold only to ruin the photo due to a silly error!). If the 30 second exposure isn't bright enough then expose for a bit longer, maybe a minute of two. This experimental exposure also helps you choose the settings for the main shoot, you can halve the ISO and double the exposure length and get the same overall exposure. Aperture does the same thing:
For example –
ISO1600 and a 30 second exposure = ISO800 and a 60s exposure = ISO400 and 120s exposure = ISO200 and 240s exposure
f/2.8 and a 30s exposure = f/5.6 and a 60s exposure
f/2.8. ISO1600, 30s exposure = f/4, ISO200 and 480s exposure (or an 8 minute exposure)
So that means if your 30s exposure (at ISO1600 and f/2.8) came out perfectly exposed then you don't really want to have any single exposure for more than 8 minutes at a time or you might overexpose your shot.
More detail here.
Expose – So everything is sorted, you've composed and focused properly, worked out the exposure lengths and then checked, checked and CHECKED AGAIN. Now you're ready to shoot (If you are using the traditional method then ignore the rest of this bullet point as well as the next). This is where I get out my Timer Remote and program the exposure length and number of exposures, attach and start it then sit back and relax (or shiver). If you don't have one you will have to concentrate a bit more. Most cameras won't let you expose in bulb mode without even a basic remote so you will need at least one of these. Open the shutter using the remote and then wait until the exposure length is reached (either using the on screen counter if your camera has one or a stopwatch (most phones have them)) and then close the shutter, then open it immediately again (you want the minimum time between exposures as these will leave holes in the trails!), rinse and repeat until you have the time you want, you get bored or the battery runs out... Occasionally, when doing it manually I may flash my torch over the front element between exposures just to check for condensation. You may also want to stick the lens cap over the lens and expose a few more "dark frames" which will be used later to help remove noise (REMEMBER, don't turn on Long Exposure Noise Reduction, also see Splogs post on the matter).
Build – Well that's the end of the in the field work! However if you have done multiple exposures you haven't finished yet. Now is the time to stack them together, here you have two main options, either photoshop or the much easier option (and the way I do it) using the startrails.de software mentioned at the start.
Firstly download the software, extract and run it, no need to install, it will run straight out of that folder.
Use the open button, navigate to the photos you want to merge and select all of them before pressing ok.
Add any dark frames you may have taken using the open button with the black square.
Deselect any images you don't want stacked and press the startrails button.
And you're done. You should have an image almost exactly like you would have done if you did one long "traditional" exposure. You can now go on and process the result if you want (Hint: if you shoot RAW do all the RAW processing first on one photo then save the edited settings and apply them to the rest of the images, that means you won't make one or more images look odd when stacked). Even if you don't like editing images, whether you have used the traditional or modern method you may want to open the image in a photo editing program and remove any aeroplane trails, these will consist of a straight line with dots either side, unlike the stars that will be in a broad ark.
Again, to sum up the methodology, for those that don't want to read the woffle I'll condense the chapter:
Set up your equipment
Compose and Focus
Check by doing a few short exposures (using a high ISO and large aperture)
Work out exposure
Check 1-4, and check again
Expose and shoot your trails
Stack resulting images to get the star trail you want!
Results
So, now you (hopefully) have a brilliant startrail photo and, like me, probably realised that you could do better next time... And then the addiction starts!
If you used the modern method then there is one more thing you can do, using the startrails.de software you can also create a Video, unfortunately the program can only make small ones but they can be quite interesting so it's worth a try! Go through the first 3 steps shown above, but instead of pressing the startrails button, press the button to the right (with the video camera on) and choose the size (I'd leave as is) and framerate (probably around 2-5fps) and save.
I was also shown another website recently, an excellent free program called
Stellarium that shows the night sky and all the stars/constellations at any given date. Perfect for planning a night and just for a bit of fun!
I'm sure it will be appreciated 
In that case it would definately work. Clouds are a pain and that's why I find star trails in the UK can be very difficult, too many clouds, however sometimes they can enhance the photo, rather than detract. 
