Most wildlife photographers, be they professional or amateur, will have a telephoto or zoom lens in their camera bag; there are so many occasions when you need to be able to bring your subject closer but you can’t get yourself physically closer.
Unfortunately good telephoto lenses longer than 300mm are seriously expensive – thousands of pounds/dollars – so it is not really possible to just go out and buy yourself a bigger lens.
Teleconverter / Extender
Luckily there is a cheaper option; you can buy a teleconverter/extender. (Nikon call them teleconverters, Canon call them extenders).
A teleconverter is a device that fits in between your camera and your lens that has the effect of multiplying your lens’ focal length by anything from x1.4 to x2; potentially making a 200mm lens into a 400mm lens.
The question is; are teleconverters worth using?
Let’s take a quick look at the pros and cons.
Pros:
- They will increase the effective focal length of your lens.
- A x2 teleconverter will turn a 300mm lens into a 600mm lens. That will allow you to get much tighter on small subjects like birds or bring distant subjects much closer.
- Teleconverters don’t weigh much. A 600mm lens is a heavy and expensive beast. A x2 teleconverter weighs very little.
- A teleconverter won’t affect your lens’ minimum focussing distance.
Cons:
- The biggest disadvantage is loss of speed. Because less light is able to pass through the lens to your camera’s sensor the maximum aperture you can use is reduced. A x2 teleconverter will cost you 2 f-stops. A x1.4 teleconveter will lose you 1 f-stop.
- No one teleconverter will work with all your lenses. Even though they may all share the same mount, not all lenses and teleconverters are compatible. Before buying a teleconverter you need to check carefully that it will be compatible with your camera. In particular make sure that you will retain full auto-focus functions. Some DSLRs struggle to focus when using a teleconverter.
- The increase in focal length will cause any vibration or camera shake to be magnified.
- Teleconverters work best with the best quality lenses. This is because they magnify any imperfections the lens may have. This can result in a loss of sharpness and/or contrast.
Conclusion:
If you only need a really long lens occasionally then a teleconverter costing a couple of hundred pounds makes far more sense than a long lens costing in excess of £5,000.
Even if you plan to use it a lot, many people happily continue using teleconverters for years rather than splashing out thousands on a big lens.
Prevailing wisdom says that you should always buy the best lens you can afford, so a really good 200mm lens with a x2 teleconverter will almost certainly give better results than a poorer quality 400mm lens.
Crop Frame (APS-C)
If you are using a DSLR with an APS-C sensor (often called a crop frame DSLR) you may already be getting a significantly increased focal length. Using lenses designed for Full Frame DSLRs on crop frame DSLRs will give a magnification of x1.6 on Canon and x1.5 on Nikon. So your 300mm lens may already be equivalent to a 480mm or 450mm lens.
If you add a x2 teleconverter to this you will then have a very long lens indeed, 900mm.