A short wide field astrophotography primer

This is a subject that have spoken about on a number of occasions at my local camera club and to others that see my images.
There are very few things I enjoy more than standing under a dark sky photographing the stars.
For many people the ability to see stars and indeed more so the milky way is hampered by light pollution, getting outside a town or city to be able to view and photography the milky way can be a really breath taking experience for those who have never been able to see it.

The best times to do this in the uk are at the end of summer and during the winter. to get a nice dark sky and sea the stars at their best we are also going to be looking to do this on a night where the moon has either not up or already set. There are number of apps and website that you are able to get this information from.

Wide field astrophotography is something that can be by pretty much anyone with only a few bits of essential equipment needed.
The basic equipment needed includes the following:

Camera – 90% of all modern DSLR’s and Mirror less cameras are capable. A full frame camera really comes into its own and would be something I would recommend long term for anyone looking to do this on a regular occasion however can be done very well with smaller sensors with the way a lot of modern cameras hand high ISO.

Lens – This very much depends on what you are looking to photograph. If you are starting out I would aim for the widest and fastest lens you have, this is not essential but will make life a lot easier to get started. I have personal experience of using the Samsung 14mm f/2.8 on full frame cameras and the samyang 12mm f/2 on mirror-less APSC cameras. Both are fantastic and relatively cheap lenses which give superior performance when compared to more expensive alternatives.
If using an APS-C sensor then aim for something between 10-16mm if at all possible to start with, like wise if using a full frame sensor then look for something between 14 – 18mm. An Ideal lens is the fastest lens you can get. Any lens that is f/4 or below will be good to get you started but anything f/2.8 or below is what I would recommend.

Tripod and Cable release – A tripod is a essential peace of kit due to the long exposure times required. A good quality tripod will last for years but can be picked up these days for very little money. Again due to to the long exposure times a good quality tripod will help prevent camera shake from wind.
A Cable release is something that I would recommend but no essential to get started with most modern cameras. The ability to trigger the camera without having to touch it again will help to prevent camera shake but can be minimised without using other techniques which I will explain soon.

Flask and warm clothes – This really should be at the top of the list for anyone wishing to do this type of photography.
Dark nights and a clear sky normally will mean that its gets cold, standing in middle of nowhere with only the slightest wind can make it also feel a lot colder than it is. Even during the end of summer here in the uk it can reach less than 5C during the night and I have personal experience of standing out in remote locations during winter months (when we get the most clear nights) when I have seen temperatures of -15C.

The first thing we are going to want to do is set the camera up on the tripod and get your composition and the focus set.
The important thing to note here is that its going to be dark, you can try and focus on a bright star but if that fails then you are going to have to learn how to manually focus your lens (something I will not go into here). At this point I would also recommend you disable any kind of stabilisation that you may have on the camera or lens, not only is it not needed but it can actually make things worse.
This is also where a wide angle lens will come into its own, being able to get some decent foreground and a plenty of sky is the here, try putting the camera into portrait mode to get more of the milky way in the shot.

Once you have got the focus and composition set then we are going to need to actually get the camera setup for the shot, this is where most people struggle. To start will set you ISO at anything between 1600 – 6400. Once you have you ISO set you are going to want to set your aperture. This will depend very much on the lens but I would go as fast as possible, I regularly shoot at between f/2 and f/2.8 but anything below f/4 is good to get started.

Now is one of the most import things the shutter speed. The idea here is to get a shutter speed that is long enough to get enough light but not so long as to get trailing in the stars to their movement (no they do not stay in the same place).
Your shutter speed is also dependant on the focal length of the lens. the wider the lens the longer you can expose for without seeing any trailing.

This is very much a topic of discussion but there a few simple ways to work out your maximum shutter speed.
I would start by using the 500x rule, and then try using the 400x rule for images that are going to be view larger or printed larger.
What you want to do it take your lens focal length and decide it by either 500 or 400, this will give you the theoretical maximum shutter speed that you can acheieve without getting trailing. this will vary slightly and if you are looking close or intend printing large then I would use the latter and be a little more conservative.

For example a 18mm lens would be 500/18 = 27.7 seconds. In this case I would try to start at 25 seconds and see how you get on.

The other thing to remember here is if you are using an APS-C sensor then you are going to have to take into account the crop factor of the sensor when working out the lens focal lenth.

A Nikon / Fuji APS-C sensor has a crop factor of 1.5
An 18mm Lens then has the effective focal length or FOV of 27mm, this you need to take into account when working out your shutter speed.

For example the maximum using the same 18mm Lens on a Nikon / Fuji APS-C Camera would then work out at 500/27 = 18.5

I tend to use the 400x rule now and find I get better results.

So now you have set your shutter speed (either using manual mode, timer mode or bulb mode) then you can start taking your first image.
At this point check the image and you should find that you have nice sharp stars.

DSCF5898

A few tips I can give you regarding this also include doing this without a shutter release cable. you should enable mirror lock-up if using a DSLR and also enable shutter delay so that you can press the shutter and allow a short delay before its start taking the exposure.
If you are shooting near water you may notice that the stars in the sky are sharp but there may be trailing in the water, this is normal. any water movement due to wind or the flow will course you to get trailing in the reflections.

I hope you find this helpful in getting started and demystifying some of the issues that many people face when doing this for the first time.
If there is anything you feel I have missed or could explain better then please feel free to get in contact with me.