Sigma 17-50 f/2.8 os and 1.4X

What are your thoughts about this on a 7d? I know without it, I have a effective range of 28-75 FF equivalent. But sometimes outdoors I would like to have a little more reach. So was considering a 24-105, but got to thinking with a 1.4x converter I would get the extra reach being approx. 45-120 f/4 if my calculations are correct. I think it would be a better combo, rather than lugging around another lens. If I needed wide and fast use the lens normal and when I need that touch more reach, pop on the 1.4x and good to go. I know IQ may suffer some, but will it be that great of a concern that can't be overcome in PP. All your thoughts are appreciated and thanks.

Neither the canon or the sigma teleconverters will mount to the sigma 17-50. A different brand like kenko might mount without an issue but I can not say for sure.

IQ is not the only thing that will suffer. TC's will also slow the auto focus down. TC's are nice for when you need a little bit of extra reach every now and then but I'm not sure it would be a great choice on a lens like the 17-50.

Tcs were designed for long, expensive primes, followed by a few long expensive zooms. Not really meant for WA or normal lenses.

Even if one did fit/work with it, you are 2/3rds the cost on your way to buying a new 85/1.8 that focuses much quicker, be way sharper, and let in over 4 times the light. Plus it's not that big. A lens pouch on your belt and you can easily swap between them.

If you want to keep one lens, you could trade the 17-50 for a 17-70 C and get the reach too and not give up as much aperture as if you changed to a 15-85.

I don't agree on the idea of trading a 17-50 for the 17-70C. I was so unhappy with my 17-70 (earlier version, not C) that I just bought a 17-50 to replace it. The 17-70 was pretty soft below 35mm, IMHO. From reviews I have read, the 17-70C is similar, at least in that respect. I do agree that it would be nice to have the 50 - 70mm reach, but I'd go for better IQ instead.

Perhaps I had a "bad" 17-70, I suppose. I was never crazy about the pictures it took, but always kind of figured it was my fault. Then I recently bought an SL1 plus the 18-55 kit lens just for a lightweight travel setup. I wanted to see how well a kit lens performed, never having had a Canon one. So I tested it against my 17-70. Well, I was shocked to find that the kit lens beat the 17-70 in several tests I did, sharpness-wise, below about 35mm (using f8, which I use often because it is almost always sharp). Since this matched-up with my earlier impressions of the 17-70, I now think it is just kind of a soft lens.

for the price of a TC, you could buy the 55-250IS...at least then you'd get a noticeable difference...the difference between 50mm, and 70mm isn't going to make or break a shot...you could just crop the 50mm