For most of your pictures, you will be using your telephoto, however you will find a use for a wide-angle because the birds can get very, very close.
Because the light can be very contrasty you may want to try using some fill-in flash – either from the camera's integral flash unit or from a more powerful on-camera unit.
For trips where you'll have the opportunity to capture other birds as well as a few landscape shots consider taking a light-weight support such as the Befree tripod
Where To Find Them
Head to Seahouses and catch one of the many boats that go to the Inner Farne island and you'll find these birds in their numbers nesting on or very near the boardwalks that are the pathways around the island. Guide ropes keep you to the boardwalks and can also take you round nests if birds are actually on the boardwalk.
The terns 'attack' you as you walk close by their nests. A hat is definitely highly recommended – and one that has some give is a good idea too. The terns are defending their territory so this is normal behaviour and try to peck the highest point – the top of your head – until you move away from their nest. Their beaks are very sharp so can draw blood, hence the need for a hat. It is like running the gauntlet as you leave one tern's territory and enter another's but just keep your head down and walk quickly past.
You do need to try different techniques to see what you get – and you may have to lend the camera a helping hand. You also need to set up the camera before you get to a bird's territory rather than fiddle around once you are under attack.
If you want to try to quickly grab a few pictures as you walk past them, obviously without upsetting the birds or lingering around too long, you won't want to be messing around with buttons and dials.
Also, once you are past the terns, try turning around and photographing fellow visitors as they deal with the terns. You can get some good candids this way.
Obviously, do consider the birds' welfare and fellow visitors too who may not share your passion for photographing arctic terns.
Your camera's autofocus system may work perfectly well with this challenging subject, but equally it may not. The terns are flying so the distance is constantly changing and with something like a sky as a background, the AF sensors can struggle to keep up and the system may 'hunt'. If you find this to be the case, try manual focusing. If that is too difficult, just preset a distance and shoot when the bird gets within range – you might be surprised how good you are at gauging distance after a little practice. It is obviously a hit-and-miss technique but you are shooting digitally so there is no cost.
Automatic exposure modes might not cope brilliantly if the lighting is very contrasty so you might be best to use manual metering and take a reading from the ground. That way, you are at least exposing for the underside of the birds. The best thing is to try that reading for a couple of shots, and if the images are coming out too light, then quickly stop-down.
The question of exposure is made more complicated if you use flash. If it is bright, you may not be able to set a fast enough shutter speed to allow correct flash sync as well as get the right exposure. If you camera synchronises with flash at a modest 1/200sec and it a bright day, you will find that you run out of apertures and low ISO settings to enable you to use that shutter speed for correct ambient light exposure. If you have one handy, a polariser or a neutral density filter can be used on the lens to cut down the amount of light reaching the sensor.