Considerations when purchasing a prime lens?

Question

What should I be aware of when buying a prime lens (other than that it will fit my camera)? What specs should I pay close attention to?

Asked by Dan Seaver

Answer

Aside from focal length, the most important thing to consider is the maximum aperture of the lens. That's what people are often looking for when they buy primes. The max aperture is usually part of the lens description such as: 50mm f/1.8 where 50mm is the focal length and f/1.8 is the maximum aperture. The lower that "f/" number is, the better low-light performance the lens will have and the more shallow the depth of field you can get out of the lens.

Other considerations are the same as any other lens: autofocus quality, whether it has IS or can do macro (if you want/need it), if it has a rotating front element (if you plan to use a circular polarizer with it), etc.

Besides those things, there's not much else to look into regarding specs. You can get sharpness test results along with data on distortion, CA, etc on http://photozone.de and search for other reviews on Google. Flickr and it's groups can also help, people often have test data or sample photos you can view large to get an idea of the image quality you can expect -just make sure you get a large sampling of data since poor test conditions or methods can make a lens look worse than it really is.

Answered by Erica Marshall

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