The fallacy of 35mm "equivalent focal lengths"

Started 3 months ago | Discussions thread
OP Tony Beach Forum Pro • Posts: 11,934
Re: Even though you're right, you're actually wrong

Lee Jay wrote:

Tony Beach wrote:

Lee Jay wrote:

Tony Beach wrote:

Lee Jay wrote:

Tony Beach wrote:

Lee Jay wrote:

When I crop, my 35mm-equivalent FOV

Even a lens used on 35mm format can have its equivalent FOV changed. The issue then becomes how much latitude you have in doing that. Compared to my S95, my 50mm f/1.8D lens just became a 50mm-150mm equivalent lens.

No way.

This is the previously shown crop from the S95 taken at 22.5mm ("105mm focal length equivalent") next to a crop from the the NIKKOR 50/1.8D using my D800; both at 100%.

You've done something wrong. You've got 4.6MP vs 12MP and they are the same size. Can't be.

You missed the relationship between pixel density and focal length. The S95 has 2.4x as much pixel density as the D800, so 22.5mm on the S95 will result in a 100% crop equal to a 100% crop from a D800 using a 54mm lens.

No, what I missed was that the S95 was 105mm equivalent and 10MP instead of 120mm equivalent and 12MP like the S110 and S120.

Okay. In my OP I actually resized the 35mm focal length shot taken with the D800 and NIKKOR combo to match the 100% crop from the S95. In the above example the 50mm lens is resolving much better than the fully zoomed S95 lens, so a longer focal length and/or more pixel density might change the equation some, but my point was relative to the S95 my NIKKOR 50/1.8D on my D800 is now a "50-150mm focal length equivalent." Relative to a different DSLR and lens, and/or a different compact camera (such as the one I will be taking possession of this week), those "equivalent focal lengths" are subject to change and are only relevant in describing the maximum AOV of the lens.

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