tamron 200-500mm f5/6.3 @ 400mm?

[maisatomai]

Anyone has any idea how do we calculate the aperture f-stop @ 400mm for this lens? For example, at 500mm, we get f6.3. What about at 400mm? Because I was thinking of either buying this or canon 400mm f5.6 which cost a lot more (dunno why? Guess is the brand?)

 

[PrimePhotog]

Anyone has any idea how do we calculate the aperture f-stop @ 400mm for this lens? For example, at 500mm, we get f6.3. What about at 400mm? Because I was thinking of either buying this or canon 400mm f5.6 which cost a lot more (dunno why? Guess is the brand?)

Not sure about max aperture at 400mm because it depends on which lens.

Anyways, the 400L is much more expensive as it is a white tele prime (IQ is top-notch) and is by Canon.The build quality is also much better than the Tamron. If you can afford it, by all means go for the 400L