[thxbb12]

And you can ride the horse named "equivalence" until it's completely dead

 

Tell me one good reason to erase the difference between two different sensor sizes? Do you think it will be possible one day in future to get an APS-C camera completely equivalent to a FF or even to Medium format DSLR? It's pointless in my eyes, the advantages are so different as they are and will stay that way, not matter of equivalence equations. There are reasons to buy FF and other reasons to go bigger or smaller.

 

'sides, if you don't know about different ways to develop film to different sensitivities, that's alright for me, you're right, the sensors are not films, but 100 ISO gives even in the senor age at the same amount of light the same combination of shutter speed and aperture and that fact doesn't care much about equivalences.

 

Don't you realize we're saying the same? You try to bring in an equivalence to FF format, I say, yes, it's different but nonetheless it is the only fast wide-angle zoom for APS-C and I like to pay respect to Sigma because they just did it? And somebody who needs one for his APS-C cam doesn't have much of a choice, especially because nor Canon neither Nikon have something like that to offer.

 

If somebody's an APS-C shooter with a need for a fast wide angle: Here's one

If somebody's a convinced FF shooter with a fine 24-70 (*overrated* /2.8) lens, great, keep it and shoot happily ever after.

 

Now, the combinations FF/APS-C will weigh

D800+24-70: 1900 grams

D7100+18-35: 1575 grams*

D7100+17-70: 1230 grams

 

* the difference is tiny - but it saves some fast primes which might even not be in the same performance league as this zoom is.

 

Regarding the comparison, you forgot to mention this combo which is much more relevant:

 

D600 + Tamron 28-75 f/2.8: 1268 grams

 

Lighter than the APS-C version while offering much better range.