Different lenses, same focal length / aperture = same brightness?

[sabee]

Hi guys, just wish to ask a general question.

Given any 2 lens on the market, if I set them to the same focal length and aperture, for example my Tamron 17-50 @ F2.8 and Canon EF 50mm @ F2.8 should I expect the same level of exposure at the same shutter speed? Does the size of the lens play a part too? What other factors are there? Please enlighten me, thanks.

Basic assumptions like same kinda filter, same subject etc applies.

 

[Burnings]

It should be different as the lens consists of different number of glasses.

 

[karnage]

Possibly same, but don't be surprised if it's different. As mentioned, amount of glass, type of glass, coatings, flare control etc all play a part...

 

[jaRv1s]

and rounding of focal length...

 

[sabee]

and rounding of focal length...

Please elaborate, what do you mean?