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Which lens should I get? Canon 24mm 2.8 IS USM vs Canon 28mm 2.8 IS USM

Started May 19, 2016 | Questions thread
Steve Balcombe Forum Pro • Posts: 15,582
Re: Maybe this will help

Rainbow21 wrote:

I would go wider. You cannot shoot a 28 lens at 24, but you can shoot a 24 at 28. You do this in post processing by enlarging or cropping the image. So if you stood in one spot and took a photo with each lens and then zoomed in "4 mm" by cropping, the images would have the exact same perspective and you likely cannot tell them apart. If you have a zoom, you can try this to convince yourself.

This is certainly a way to solve the dilemma, but the difference in field of view between 24 mm and 28 mm is more than you might think. As a diagonal FoV, 24 mm (on full frame) is 84 deg and 28 mm is 75.4 deg.

Another way to express this is the loss of resolution if you crop as suggested. A 20 MP image would be reduced to 20 x 24^2/28^2 = 14.7 MP - i.e. you would lose more than 1/4 of your resolution.

On the other hand, for close subjects where it is practical to use 'sneaker zoom', stepping forward from 14 feet with a 28 mm lens to 12 feet with a 24 mm lens will frame the subject exactly the same. The perspective will change of course, and that may or may not be acceptable. And you can't normally do this for landscapes!

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