EF 50MM F/1.8 STM LENS

[peterl]

Considering purchasing this lens to start a Prime collection, it seems very cheap, what will all the ramifications of using this lens on my 70D EF-s camera be?

[kvbarkley]

I think of focal length and aperture, though it does appear that others use focal ratio.

[ebiggs1]

"That's low *aperture ratio*, not focal ratio."

The 'speed' of a lens is found by dividing the focal length by the aperture. This 'aperture ratio' is normally refered to as focal rario.

[kvbarkley]

I wouldn't say "normally". it seems to be more of an astronomy term. It seems pretty rare in photography literature.

[ebiggs1]

"I wouldn't say "normally"."

Must be the circles we run in.  I bet I haven't heard aperture ratio used in describing the f-ratio of a lens twice. 

[RobertTheFat]

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@ebiggs1wrote:

"I wouldn't say "normally"."

Must be the circles we run in.  I bet I haven't heard aperture ratio used in describing the f-ratio of a lens twice. 

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Maybe just a regional difference in terminology. Where I grew up, we called a creek a "bayou". Here we call it a "brook".

[TCampbell]

The "ratio" being discussed is the "focal length" to "aperture" ratio.  

Usually I hear this called the "focal ratio" and only occasionally do I hear someone say "aperture ratio" (it really is both ... if you wanted to be really specific then you'd use the term "focal length to apeture ratio" and that would eliminate all ambiguitity.   But people like to shorten things.

Either term is correct (or at least correct enough that everyone else should know what you mean.)