Received my Tamron 17-70mm today...

Dennis wrote:

Lettermanian wrote:

BeatX wrote:

Uhh.. That Tamron 17-70/2.8 is big! I mean it looks like similar size to any 24-105/4 FF zoom lenses (?)

A 2.8 lens is still a 2.8 lens in terms of light gathering, so there's not a direct comparison to a 24-105 f4.

You've been around here a long time (long enough to have read plenty about equivalence) you can't really believe that ?

In a nutshell: whatever your reasons might be for choosing an f/2.8 zoom over an f/4 zoom on APS-C, someone can accomplish those same goals with an f/4 zoom on FF.

There's no ff lens in any current system that gives 450mm-equiv non-cropped images at the size and weight of Fuji's 70-300.

Yeah, that's where I kind of get stuck, too. I don't mind having a bigger lens at home for running outside for opportunistic wildlife photographs. But I really like the idea of a small, light kit I can travel around with and have up to 300mm APS-C equivalent. My Sigma 100-400 isn't all that big, but considerably bigger than the Fuji 70-300. If Nikon came out with a killer 70-300 lens for Z I could contemplate cropping but then I'd need a pricey Z7 II for the resolution and the lens would have to be very sharp to compete with the Fuji after cropping down to APS-C size.

So even though a lens like the 17-70/2.8 (or the 16-55/2.8) makes me question whether it's not just better to go FF with an f/4 zoom (same argument to be made for f/1.4 primes versus f/1.8 for FF), I can see an easy case for it when it's just one big, equivalent lens and the rest of the kit is smaller.

- Dennis
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Gallery at http://kingofthebeasts.smugmug.com

I don't know if this helps, but I went from m4/3 to FF, shooting Sony and Fuji simultaneously right now.  I miss the m4/3 lens size and love the FF low light. FF lenses are all big. I'm by no means a pro, so APS-C to me is the right compromise for me.  The A7iii isn't a big camera, but the lenses are definitely bigger and heavier than APS-C.