I'm not sure the 75-300 is even sellable... Like Brightcolours, I would probably recommend to use Tamron 70-300 VC, as it's better than the Canon 70-300 (and naturally the 75-300) mechanically, and surely optically as well.
The Sigma 8-16 may not work at all... I tried a 10-20/4-5.6 on my APS-H bodies during a recent trip, and not only it had black corners at 10mm, but also strong vignetting everywhere else, even at 20mm (and that on 1.3x crop, mind you!) If the 8-16 uses the same principle, it may not be work at any focal length on FF. But I've never handled that lens, so it's just a guess.
24-70 macro... funny, I've seen a guy using one on a 6D at the Venice's Biennale in early August.
Though there aren't many tests of this lens around, it'll probably be okay'ish in the center, with pretty blurry corners. Here's one review, so you know what to expect:
http://www.the-digital-picture.com/Revie...eview.aspx
The Sigma 8-16 may not work at all... I tried a 10-20/4-5.6 on my APS-H bodies during a recent trip, and not only it had black corners at 10mm, but also strong vignetting everywhere else, even at 20mm (and that on 1.3x crop, mind you!) If the 8-16 uses the same principle, it may not be work at any focal length on FF. But I've never handled that lens, so it's just a guess.
24-70 macro... funny, I've seen a guy using one on a 6D at the Venice's Biennale in early August.
Though there aren't many tests of this lens around, it'll probably be okay'ish in the center, with pretty blurry corners. Here's one review, so you know what to expect:http://www.the-digital-picture.com/Revie...eview.aspx
Quote:Usually you can apply the crop factor to determine what will be the usable range on FF, with these UWA APS-C lenses. So in case of this Sigma, that would mean 8 x 1.5 (it is fine on 1.5x crop factor APS-C) = 12mm to 16mm on FF. You sure can use it at 16mm anyway, so even if my rule of thumb would not go for this particular design, you can still use it as a 16mm UWA "prime".
This lens will work better on the 6D even, so no problems there. Nice cheap normal lens to have on APS-C.
This never was a super lens, but will perform adequate anyway on the 6D. So, untill you run into performance limitations, you will not have to get a different standard zoom for FF.
All the 75-300mm Canon lenses were ok-ish to rather disappointing (image quality wise, especially at 300mm). So this lens would be the 1st on the list to be replaced, in my opinion. On a budget, look at the Canon EF 70-300mm f4-5.6 IS USM or the Tamron 70-300mm f4-5.6 USD VC. Both have rather good optics over the entire range, good IS. The Tamron will perform a tad quicker/better when AF tracking in AI-Servo mode, and has no rotating front element, handy for when you want to use a pol. filter. Also, the Tamron has the sun hood (great impact protection) included, with the Canon you have to buy it separately, adding a bit to the price.