Friday, 30 July 2010

Lens coverage

I often get friends asking me what type of lens to buy after they have bought a new shiny digital SLR. A lot of them have switched over from an old analogue model to a new digital body.

A friend asked me last week to recommend a lens for her. She found that the wideangle lens which came bundled with her EOS 550d wasn't wide enough.

"Would you recommend that I get myself a 24mm?" she asked

I knew then that she had probably previously owned an analogue SLR.

"A 24 mm lens on your camera would be equivalent to a 38mm on your old SLR" I told her.

"How is that?" she asked.

Well to cut a long story short. I explained to her about the coverage provided by the APS-c sensor in her camera compared to the sensor in my camera (an EOS 5d)

"Your camera's sensor magnifies the centre part of the picture by 1.6, where as mine uses all of the picture."

I showed her this little chart that I put together. The pictures were taken one after the other using the same lenses my EOS 5d and my new 7d. The figures in brackets refer to the magnification factor from the 7d, so for example, the 300mm on a 7d body is "equivalent" to a 480mm lens on my 5d.


This simple chart explains more than reading about it on the 'net.

She is now looking for a 16mm Sigma lens which will be equivalent to a 25mm wideangle.

When I bought my first digital EOS (a 20d), the widest lens in my arsenal was a 24mm. For someone doing architecture, this was useless, giving the coverage equal to a 38mm. I forked out for a 20mm but this was also too limiting, being equal to a 32mm. So I sold that lens and bought the very lovely Canon EF 17 - 40L. I also bought a full frame body to be able to use it effectively as the widest setting was only like using a 27mm!

This means that my lens collection now goes from a 16mm to a 300mm, but when I use both bodies, taking into account, the magnification factor, the focal length of the longest lens is increased to 480mm

I've written a little bit more about it on my website and you'll find the exact page here.

Well. It's now nearly the weekend. Time to charge up your batteries and take some photos. As usual I welcome your comments and emails.

Have yourselves a great weekend.

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