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Why are 45mm and 50mm appearing so different?

bigbrother
Frequent Contributor

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!

5 REPLIES 5

Waddizzle
VIP

Yeah, that can happen with kit lenses.

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"Doctor told me to get out and walk, so I bought a Canon."

MikeSowsun
Respected Contributor

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. 

Mike Sowsun
80D, 5D Mk III

kvbarkley
Honored Contributor

ebiggs1
Forum Elite

"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°.

EB
EOS 1DX and 1D Mk IV and several lenses!

"... 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.

EB
EOS 1DX and 1D Mk IV and several lenses!