Buying lenses can lead some to a phenomena known in many crafts as GAS, or Gear Acquisition Syndrome. In photography it refers to the compulsive need to buy more and more equipment, in particular, lenses.

How do you know if you have GAS? Well perhaps you have a bunch of lenses with overlapping focal lengths? Or a really expensive lens, such as an uber-fast f/1.2 lens that has sat on a shelf since the day you bought it? Do you have a tilt-shift or fish-eye lens that you used once or twice? Do you collect lenses from particular manufacturers just because you like things in sets? Then it’s likely that you are afflicted. This affliction may be worse if you have half a dozen camera bodies.

It occurs because new lenses keep appearing, ones with new features, or just some sort of novelty (go on you really need that circular fish-eye, don’t you?). A lens that is just that little bit sharper, or even newer. Manufacturers often rely on lens GAS, because few people splurge out on a new camera body every year, but lenses, well that’s another matter altogether.

So how to decide when you need a lens? Here are some questions to ask yourself:

• Do your current lenses inhibit your ability to be creative?
• Is there a genre of photography you want to try which requires a new lens?
• Will the lens be used more than once?
• Is the lens affordable? (and is there more than one option)?

If you said yes to all the above, then it can probably be justified. Having said that, sometimes you just want a new lens, and there is certainly nothing wrong with that.