50 vs 85 1.8

Started 2 months ago | Discussions thread
Dem Bell Regular Member • Posts: 187
Re: 50 vs 85 1.8

Tom Axford wrote:

Dem Bell wrote:

Tom Axford wrote:

So the 85mm lens gives the same depth of field, but much more background blur.

To clarify, for the same framing, the 85 mm gives the same relative amount of blur but magnifies the background more and shows less of it.

If you look at the background blur produced by the 50 mm and the 85 mm, they will have the same appearance except everything in the 85 mm shot will be 85/50=1.7 times bigger.

Correct, everything in the background at infinity is magnified 1.7 times (relative to the background in the 50mm shot), but the subject is the same size of course, so the background blur is 1.7 times greater relative to the subject.

(See my previous post for the mathematical formula)

Sure. I just wanted to emphasise to other people reading this that because both the amount of blur and the magnification change by the same factor, the background does not look more or less blurry when we use a longer lens and step back to maintain the same framing on the subject.

Say, we can barely make out the letters on a shop far behind the subject when using the 50mm lens. The letters will still be legible if we use the 85 mm lens at the same framing. To blur the letters (so you can no longer read them) one needs a tighter framing, not a longer lens.

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