I bought a Nikon D3300 with an 18-55 mm kit lens, and now I’m considering additional lenses, especially a telephoto zoom. While reviewing the options on a retailer’s website, I noticed that some are designated as FX while others are DX. What’s the difference and which type should I buy?
This is a question that comes up quite often with various brands of cameras and lenses, Tamara. The key is to understand the difference in the two types that are available. Some lenses are large “multi-platform” types, designated as FX, EF, DG, DA, Di, etc., depending on the brand. These are perfect for the full-frame digital SLRs with a 24 x 36 mm sensor and also suitable for the majority of other DSLRs (like your D3300) that employ a smaller sensor. On the other hand, most current lenses are the smaller type, designated as DX, EF-S, DT, DC, Di II, etc., and are made for cameras that do not employ the huge sensor.
I have previously discussed the issue of sensor size in Should I buy a full-frame DSLR?, so you might want to read that Q&A item as well. The smaller format lenses can project only the smaller image circle required by a DSLR with a smaller sensor so they’re not suitable for full-frame cameras such as the Nikon D800 or D610, Canon EOS 6D or 5D Mk III, or the Sony a99. Since you, like the vast majority of photo enthusiasts, own a camera with the more typical smaller sensor, you can safely choose either the DX or FX lens.
Some lenses—such as pro-grade models and the 70-300 mm zooms, 300 mm f/4 primes and macro lenses longer than 60 mm—are available only in the multi-format type (FX in Nikon). On the other hand, the 55-200 mm, 55-300 mm and similar zooms are made only in the smaller format (DX in Nikon). This also applies to the most suitable ultra-wide angle zooms such as the 10-24 mm and other models like it. The primary benefit of a smaller format lens is reduced size and weight for greater portability and, usually, a lower price.
If you believe that you’ll want to upgrade to a full-frame camera at some time, buy a multi-format lens if it’s available in the focal length(s) that you’re currently considering. It will be fine for your D3300, but it will also be suitable in the future for a DSLR with the 24 x 36 mm sensor. Since you won’t need to buy a new lens for that future camera, your budget will definitely benefit.