24-105 on FF, or 17-55 on crop?


Aug 13, 2012
I recently stepped up to a fullframe kit, and have been trying out the 24-105 that came in the kit.

I didn't, however, have the extra cash to step up to a full-frame short 2.8 zoom ($2300!!). I previously used a 7D and 17-55 for this.

Question to the great pool of talent here... should I keep my 17-55 for a short 2.8 zoom, or take a hit on low light and use the 24-105?

Seems like the OOF area and IQ differences will sortof balance out (the FF can go a stop faster, same rough IQ, with the same light, but the lens is a stop slower)

However, I'm thinking about keeping the 7D and 17-55 so that I can get better hit on focus in low light (2.8 focus points versus f/4).



I post too Much on Here!!
CR Pro
Jul 21, 2010
I think you've nailed the only difference. The 17-55mm f/2.8 on APS-C has a FF-equivalence of 27-88mm f/4.5, so the 24-105 on FF is wider, longer, and 1/3-stop faster (for DoF with same subject framing). The >1.3-stop ISO boost you get with FF over APS-C more than makes up for the stop of lost shutter speed. So, all you really 'lose' is the ability to activate the high-precision f/2.8 center AF point(s). Honestly, I think a well AFMA'd 24-105mm f/4L on a 5DII using the center AF point, or a 5DIII, will be just fine.

I loved my 17-55mm lens on the 7D, but after getting the 1D X, I sold it (even though I still have the 7D).


Nov 17, 2011
My 2 cents:
If your current camera is 5D III, I would sell 7D, 24-105, and 17-55. Use that money to fund on 24-70 mrk II. This lens is AWESOME. It's sharp end to end at f2.8. AF is very fast.


Aug 13, 2012
Dylan777, it's on my shortlist, however I'm having to juggle some gear to get into the fullframe world. Fiscal responsibility and all that heartbreaking stuff. I was also let down to have to get a 5D2 instead of a 3, but it's a large price jump there too for an enthusiast-level guy.

I've done some preliminary testing, and so far neuroanatomist (love that name/avatar!) is 100% dead on.

Overall it's kind of a wash, which means I'd elect to keep the 24-105 for its' range and better EF compatibility (and red ring woooo haha).

Here's what I found:

1) The 24-105 is indeed wider and longer by a smidge
2) The 24-105 has just slightly better OOF/DOF for portraits wide-open, both quality and quantity.
3) Sharpness is a wash.
4) Camera-wise, the 5D2 has to jump one stop (or maybe a smidge more actually) to match a 7D.
5) Camera-wise, the noise levels at the comparable highish ISOs (7D-1600, 5D2, 3200) produce a comparable IQ/noise level.
6) The 5D2 can exhibit a pretty bad vertical banding if you have to push the levels, but the 7D isn't much good at 1600 (generally messy) in the same vein.
7) The metering is different for each of the cameras, and the color balance (when all set the same in ACR) is visually different... hard to say exactly, but looks like the 17-55 produces a slightly more saturated image with more yellow/green, however I liked the RAW image from the 5D2 better for moving forward with an edit.

The only thing I haven't tested are the center AF points on each in low light... waiting until post-sunset so that I can control the light in my living room. "On paper" they have the same EV working range and sensitivity/type, so you would think the f/2.8 lens would win out, but I'm not sure that I care about focusing in almost full dark with this type lens anyway.

Random Orbits

EOS 5D Mark IV
Mar 14, 2012
I found that the 5D II center point focused better in extreme low light better than the 7D. The 5D III should do better especially when using non-center points.

If you don't need to have 2 lenses on 2 bodies a lot of time, it might make more sense to sell the 17-55. Equivalence would say that the performance between the 24-105 and 17-55 would be similar, but it would be really nice to have that extra stop back.


Aug 13, 2012
I did some quick controlled focus testing, and the 7D performed *slightly* better, but at the breaking point of the 5D's focus (where it hunted more than locked), I would have been underexposed 2 stops at 6400, so I think I'm OK there :D The 7D would have similarly been under by 3 stops at 3200 (the max I would use for that camera).

So, bottom line, I'm going to stick with the 24-105 on the full-frame camera and sell off the 17-55 for other more exciting lenses.

Thanks for the contributions guys!!