The Digital SLR (Single Lens Reflex) camera is ideal for airshow photography as it allows you to fit a wide range of quality lenses from wide-angle for static display aircraft up to long telephoto lenses for aircraft in the air. This type of camera also has a bright TTL (Through The Lens) viewfinder, no noticeable shutter lag, and many operating features and modes for taking quality photographs. You can also find more information on using a digital SLR at Airshows on this website.
When buying a Digital SLR camera then take a look at the specifications for the sensor size. A Full Frame Digital SLR would give you the same field-of-view as a standard 35mm SLR camera although many popular Digital SLR's have a smaller cropped sensor which give you a smaller field-of-view (See photo below).
A Digital SLR Camera with a cropped sensor has some advantages but also some disadvantages for airshow photography. The advantage is when using a long lens for aircraft in the air then it appears to magnify the lens even more, however the lens magnification stays the same, and it just reduces your field-of-view. A disadvantage is when you require a wide-angled lens to photograph an aircraft in the static display, you would then need a wider-angled lens (usually more expensive) when using a camera with a cropped sensor.
When using a Digital SLR camera which has a sensor with a 1.6x crop factor then a 300mm telephoto lens will have the effective field-of-view of a 480mm lens (300X1.6=480), and a 15mm lens will have an effective field-of-view of a 24mm lens (15X1.6=24). If you are using a camera with a 1.6x crop sensor then a wide-angled lens of about 17mm will be useful for static aircraft & museum aircraft and a telephoto lens of 300mm-500mm will be useful for taking photos of aircraft in the air.
A Digital Camera's resolution is measured in megapixels and a megapixel is equal to one million pixels. Generally it is preferable to have a camera with more megapixels as it is useful when you need to crop an image and you still have plenty of resolution to play with, or you may want to make very large prints. However, probably more important then the number of megapixels a camera has is the sensor size, low-light performance, frames per second, dynamic range etc.
Batteries and Memory Cards:
When using a Digital SLR at an airshow all day then it is wise to bring a few more spare batteries along. The camera manufacturer batteries tend to be fairly expensive but you can get reliable third-party batteries for your camera which work well. A battery grip makes a decent addition to your camera, making it easier to grip, as well as holding two batteries which will last twice as long as a single battery.
Many cameras now use an SDHC (Secure Digital High Capacity) memory card and some older cameras used a Compact Flash memory card. Obviously, a higher capacity memory card will hold more images but you should also consider the performance or speed of the card. A faster memory card which has a fast write-speed will not affect the captured image but it is useful when you are taking photos of an aircraft in the air and you use 'Continuous Shooting' mode where images need to be quickly saved to the memory card. As with batteries it is a good idea to bring some spare memory cards with you when attending an airshow.
Early Digital SLR Cameras used to suffer badly with a dirty sensor after being used just a few times. Modern DSLR Cameras usually have built-in auto sensor cleaning which shakes the loose dust of the sensor every time the camera is switched on or off. This works very well but over a period of heavy use then you may find that the sensor needs a more thorough clean.
For general photography you will probably not notice any dust spots on your images but when photographing aircraft against a bright sky then they sometimes show up and can spoil your shot. You can of course clone out the dust spots using software such as Photoshop but having to do this with hundreds of photos can be very time consuming.
You can check how dirty your sensor is by taking a photograph of a clear blue sky using 'Aperture mode' and setting the Aperture to f/22, and then view the image on your computer using graphics software such as 'Photoshop' or 'Paint Shop Pro'. Using the software then select 'Equalize' which will help to show up any dust spots in the image.
If the sensor is particularly dirty then you can either take your camera to a reputable camera dealer and let them clean it, or you can clean the sensor yourself. If you tackle the job yourself then you will need a proper sensor cleaning kit which includes a blower brush, Eclipse fluid, and sensor swabs which can be bought from Wex Photographic.
There are plenty of tutorials on the internet for cleaning camera sensors which can be found by typing 'How to clean your camera sensor' into Google.