Need for f/2.8 lens on 5D Mark III?

I'm going from a 60D with a Canon 17-55 f/2.8 lens as my "walk around" lens to a 5D Mark III.

With the improved handling of higher ISOs, if I shoot the same type of work, can I correctly assume that my 24-105 f/4 L Canon lens will suffice and that I don't need to scrape up more cash for a faster f/2.8 lens for a while. I normally try to stay at ISO400 or so with the 60D and figure that ISO800 on the 5D Mark III at f/4 would be equivalent to ISO400 on the 60D with the f/2.8 lens.

Is this a fair assumption?

Thanks,

John
--
Enjoying God and His Creation.

John Vant Land said:

Is this a fair assumption?

Click to expand...

Noise-wise - yep. DOF-wise - no.

But probably going from a 1.6X crop to FF, the f/4 on the FF won't be much difference in DOF than the f/2.8 on the crop. But, yes, I was thinking noise-wise.

schmegg said:

John Vant Land said:

Is this a fair assumption?

Click to expand...

Noise-wise - yep. DOF-wise - no.

Click to expand...

--
Enjoying God and His Creation.

The EF 24-105 f4.0 IS is a little soft compared to the EF 24-70 f2.8. I do use the 24-105 as my walk around and I'll use it for semi-casual groups,

When you move up your ISO 800 is more like ISO 2000-3200 on the 5D MKIII. I sell the heck out of ISO 4000 images off a 5DMKII. Another reference point would be Gene Higa who shoots weddings at 1600 on 5D MKII.

My point is when you move up run the ISO way up for a few days (when you can) to learn where your new boundary.
--
Phil Agur

5DMKII - 7D Dual Body Bag - Go 'L' and don't look back!

Got 7D? See http://www.usa.canon.com/dlc/controller?act=GetArticleAct&articleID=3167

John Vant Land said:

But probably going from a 1.6X crop to FF, the f/4 on the FF won't be much difference in DOF than the f/2.8 on the crop.

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Yep - pretty close actually - for the same composition (FOV and subject distance).

Wide open at the short end the crop will have a bit narrower DOF with the 17-55 than the FF will have with the 24-105 though.

Phil said:

My point is when you move up run the ISO way up for a few days (when you can) to learn where your new boundary.

Click to expand...

+1.

Thanks for the good suggestion.

Phil214757 said:

My point is when you move up run the ISO way up for a few days (when you can) to learn where your new boundary.

Click to expand...

--
Enjoying God and His Creation.

I just moved from a 7D/17-55 IS f/2.8 combo to a 5D Mark III/24-105 IS L f/4 and I am frankly thrilled with this. I was at first worried since the 17-55 was magnificent and I took a lot of indoor shots without flash. Well, my worries were baseless. The handheld interior shots of the 5D3 and 24-105 are great to my eyes -- so much cleaner even at ISO 6400 with better colors. I do not miss my old set up at all.