Cost -- you can have a modest 200 - 500 mm f/2.8 for $24,499 give or take. So when are you going to buy one? And that is a Sigma, i believe. lol or maybe a 70 - 200, f/2.8 for a litle under 800.00.

Canon has L series fixed F4 zooms. They are lighter than their F2.8 counterparts but fairly expensive. Nikon kept all their non pro zooms as variable aperture probably for marketing reasons.

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I've looked around for a couple of all-in-one zoom lenses, and my question is: Why no zoom lenses with f-stop ratings in the 1.4 area across the entire zoom range?

I see lenses that are 70-300mm w/3.5-5.6 f-stop rating and such. Would the lense end up being so large that it wouldn't be use-able? Or would it be the cost?