Recently I’ve been in the market for a new lens for my Canon XT. I want something to replace the kit lens that came with the camera and I wanted something that would do the same and more (in terms of magnification). And so I’ve been reading and researching and a lot of the forum posts i’ve come across start with someone asking how to convert “zoom” (i.e. 12x) to mm (i.e 250mm), and the next several posts are generally along the lines of “zoom” is a verb, you can’t convert the zoom factor to a focal length” by people with an over-inflated sense of self because they are forum admins (thus the reason i hate forums).

It seems that it comes down to a couple of simple things.

  • First the answer most folks are looking for is this: a normal field of view is (generally accepted on the internet as) 50mm, thus a lens with a focal length of 250mm will have a magnification rate of 5 times (250/50 = 5).
  • Second lenses that are generally labeled in terms of mm of focal length are often advertised as having a zoom ratio (i.e 12x) which is not the same as a magnification ratio.  So a lens that is labeled as 18 to 250mm will magnify at 5x but may be advertised as as having 13.8x zoom ( thats 250/18 = 13.9).

All of that being said, I’ve procured a new Sigma 18-250mm f/3.5-6.3 DC OS HSM IF Lens, It’s not actually in my hands as of yet but I’m quite excited to give it a try as it will have me a lot more reach and flexibility than the kit lens, some of the reviews on Amazon also said it was sharper between 18 and 55 which is all the kit lens allows.

Here are some photos I’ve taken recently:

  • Nemo


  • Train by night

    Whitefish train station, 2009

  • Patriotic Fly Over


  • A dog named Grizzly

    A dog named Grizzly

  • The Light

    The light