Lense options for full frame?

I have the T3i and have been waiting around for something new to come out that is actually worth the upgrade. The 6D looks like it is the answer, I am preparing to get this camera in January, after the December release. With my T3i I've been using the Sigma 17-70 f/2.8-4 OS lense, which was a perfect zoom range for me.

With a crop body I assume the 17mm would be extremely wide angle?
what is a lense that gives me similar zoom range on the crop body?

I'd preferably want a lense with a lower aperature like a set f/2.8.

Any suggestions?

I was thinking about Sigma 24-70 f/2.8
Canon lenses are a bit pricey for me at the moment to justify paying those prices.

Canon 24-105 f/4 seems nice but aperature is not low enough as I was hoping.


I also shoot video so a lower aperature is pretty important.
I had a Canon 17-85 f/4 before and the F/4 aperature was not that great in low light in night.

I recommend primes, but that's my personal preference. I like bokeh, so for FF I would suggest a 50 1.4 to start, a 135 2.0 next, and then a 24 or 14, depending on how crazy you want to get with the wide angle. One of my favorite lenses is the 200 2.8 II, which is a steal and crazy sharp.

The 28-135mm IS USM or the 24-105L are the closest zoom ranges to the 17-70mm equivilent. it's about 27-112mm on a FF body. 24mm is pretty freaking wide on FF and it is awesome. With modern bodies, 5D2 and up, the high ISO control is very good and if you are worried about f/4 being to slow, you shouldn't be. Especially because the lenses you'll be looking at will have IS. Unless you NEED f/2.8 for background blur or faster shutter to stop action, don't worry about it.

17mm is about 28mm on a FF body.

So the 24-105 is wider, and almost as long, and 'faster' by any real usable measure (on FF).

If you must have f2.8, then pick up one of the 24-70s. The new Canon Mark II is coming out, so you might find a good deal on a used 24-70/2.8L "Mark I", which is still a very good lens.

Keep in mind that you'll likely find at least one stop higher usable ISO with the 6D, compared to your T3i. (No one has hands on with 6D yet to speak of, but if it's at least as good as 5DII or III, you should expect a stop higher ISO will be usable... maybe more.) That might make up for an f4 lens.

An inexpensive lens choice that might make a useful walkaround lens would be the 28-135 IS. It sells for around $450 new, but you can find lightly used ones for around $250 pretty easily, so many have been sold in kit with 40D and 50D, in particular. It's much better than most "kit" lenses.

Of course, if shallow depth of field is your goal, there's no substitute for f2.8.

Frankly, I don't consider f2.8 all that big an aperture for low light shooting. For that I look to reasonably affordable primes such as 28/1.8, 50/1.4, 85/1.8 (all three of which can be bought for about the price of a new 24-70/2.8L "Mark I"). Primes aren't as convenient, though.

The 24-105L works deceptively well in low light.

The math is the same- just reverse it for full frame to crop. The 24-105 represents a 15-65 range. The 24-70 represents an even narrower range- 15-44 on a crop. The 24-105 works surprisingly well for a f/4 lens. The real problem is- if you need f/2.8 because of low light- you probably need to add light anyways- or go to a faster prime to make a real difference.

Out of curiousity- what are you shooting that makes you think the 6D is the worthwhile upgrade ? What are you shooting ? OK- personally, some of the specs on the 6D is both troubling and well, I think it blows.