topic Re: Why are 45mm and 50mm appearing so different? in EF & RF Lenses

Why are 45mm and 50mm appearing so different?

bigbrother — Tue, 15 Dec 2020 22:41:00 GMT

Hey all. I've got an M50 and have observed something quite strange.

I've only got two lenses- the 15-45 kit and a nifty fifty.

I've noticed that at full zoom, the 15-45 still has a noticeably wider field of view than my fifty. Why is this? I get that the printed focal lengths might not always be right on, but this seems like a difference of at *least* 10mm. Seems strange. Thoughts?

Thanks!

Re: Why are 45mm and 50mm appearing so different?

Waddizzle — Wed, 16 Dec 2020 00:42:32 GMT

Yeah, that can happen with kit lenses.

Re: Why are 45mm and 50mm appearing so different?

MikeSowsun — Wed, 16 Dec 2020 04:05:25 GMT

Popular Photography always includes the "tested" focal length in their reviews.

EF 50mm f/1.8 STM SPECIFICATIONS 50mm (51.39mm tested),

There is also "focus breathing" with most lenses where the focal length changes a bit depending on how far away it is focused.

Re: Why are 45mm and 50mm appearing so different?

kvbarkley — Wed, 16 Dec 2020 14:43:13 GMT

You can measure it for yourself

http://www.bobatkins.com/photography/technical/measuring_focal_length.html

Re: Why are 45mm and 50mm appearing so different?

ebiggs1 — Thu, 17 Dec 2020 15:15:07 GMT

"I've noticed that at full zoom, the 15-45 still has a noticeably wider field of view than my fifty. Why is this?"

It is wider because 45mm has a larger AOV than 50mm. Why do you think this is odd. It is normal and expected.

On my 1DX the AOV is 50mm = 46.8°; while 45mm = 51.4°.

Re: Why are 45mm and 50mm appearing so different?

ebiggs1 — Wed, 30 Dec 2020 15:36:08 GMT

"... the actual focal length of the lens is unchanged, as is its aperture."

The aperture doesn't, can't, change. The FL also doesn't, can't, change. It is the apparent FL or equivalent FL that appears to change. This is due to the smaller sensor of the camera and has nothing to do with the lens. The lens is what it is at manufacture.