Am I the only one who feels like Canon is hindering the practicality of upgrading?

I've been considering selling my 7D and moving to the 5D3, primarily for the improved ISO performance, among some other less significant reasons. If I were to do this, I would sell the 7D, the 17-55, and maybe even the 28mm. Problem is, I feel limited as far as lens selection, in a such a way that I'm wondering if I'm actually better off with my current setup.

The main issue is trying to replace the 17-55 with an equivalent. Would be nice to have the 24-105 for the versatile range, but the f/4 obviously isn't f/2.8. The only other alternative is the 24-70 f/2.8, but at $2000+, not having IS seems absurd to me.

Therefore, if I upgrade my camera body, it's as if I'm being forced to downgrade my lens.

f4 on a FF body is easily equivalent to f2.8 on a crop. In terms of DOF and light gathering ability (when you take into account the larger sensor) the 24-105 is better than the 17-55 and has more range, is better built too.

What RobDickenson said is correct. The 24-105L on a 5D3 will be like having an EF-S 15-65 f/2.5 on the 7D in terms of range, DOF and low light capability.

JeffreyG wrote in post #14909940
What RobDickenson said is correct. The 24-105L on a 5D3 will be like having an EF-S 15-65 f/2.5 on the 7D in terms of range, DOF and low light capability.

Interesting....So just to clarify, are we saying that the full-frame sensor itself is gathering more light at any given aperture for the same scene (framed identically)? Or are we saying that the superior low-light capability is due to the full-frame sensor producing less noise at higher ISOs?

Less noise at higher ISO due to the 2.5 times larger sensor.
So for shutter speed f2.8 vs f4 you just bump the ISO a stop.

Ok, so lets say you have the following settings:

7D f2.8 ISO 100
5D3 f4 ISO 100

My understanding is that I'd get a shutter speed of x seconds for the 7D, and 2x seconds for the 5D3. Correct? If so, then this would place the 17-55 ahead of the 24-105 in regards to low-light performance in terms of shutter speed. Of course the 5D3 is going to have less noise even at ISO 100, but to me the 7D noise at ISO100 is essentially negligible anyways.

Yes, the 5d3 will be 1 stop slower shutter speed, but just bump the ISO to 200 and its all even and the 5d3 will produce as nice an image as the 7d at ISO 100.

So technically, the size of the sensor has nothing to do with the amount of light it gathers per sq. mm of the sensors surface area. The better low light performance is solely related to the ability to use higher ISOs with less noise in comparison to a crop sensor at the same ISO.

But if I could toss that 17-55, with it's IS, on the 5D3....now that would be something.

You would have to double its size so it made a big enough image circle then re engineer it so it doesnt use the short back focus ability. Think 16-35L with 20mm more range and an extra step up in size for the IS system...

You could look into the Tamron 24-70 f/2.8 VC. It would fill the 17-55-on-crop's shoes.. very well.

I've sworn off Tamron for the time being...had some very poor experiences.

The 24-105 is simply a great lens

I don't know why people moan about the lack of IS on the 24-70. I use this lens as my walkaround on a 5DII and not once have I ever thought that IS would be nice, or the lack of it caused me a problem.

Hmm non of the lenses I own now have IS lol. They dont even all have autofocus.

Sorarse wrote in post #14910123
I don't know why people moan about the lack of IS on the 24-70. I use this lens as my walkaround on a 5DII and not once have I ever thought that IS would be nice, or the lack of it caused me a problem.

For me, I tend to use the IS quite a bit when out and about in a downtown/city setting at night. It's very rare that I want to tote around a tripod or even another prime lens when I'm out.