5DMIII vs 7D for birding

[sparda79]

Hi...

I'm currently using a 70-200MII + 2xIII for birding and I'm wondering how bad will I miss my 7D by upgrading to 5DMIII? 
A super-tele is definitely a big NO for me.

I know that by going from crop to FF, I'll lose the extra reach. The subject will be smaller in the viewfinder and the extra 4mp of the 5DMIII will not be much of a help.

However, I've seen in another thread here in CR discussing the comparison in DPReview between 5DMIII and D800 by enlarging the 5DMIII image with a slight quality loss on the Canon side.

So, back to my question, how much can we enlarge 5DMIII images until the quality degrades to a level comparable to a 7D image?

[neuroanatomist]

Enlarging an image in postprocessing rarely gives completely satisfactory results.  It really depends on what your final use for the image is.  If a 9 MP image will be sufficient, then you can crop the shot from the 5DIII. if you need more megapixels for cropping or printing large, then that might not be the best way to go.  The 7D is, in effect, an optically perfect 1.6x teleconverter.

Personally, I am getting a 1D X. It will replace my 5DII, but I'm keeping my 7D for birds and wildlife (with the 100-400mm).

[smirkypants]

Maybe it's something you could pull off with the D800. Its 36MP translates to 14MP at a 1.6 crop. That's a good bit of information to work with. A 5D3 has 8.6MP in the same framing as the 18MP you get with the 7D. Also, unless you have an f4 lens, the 1.4x teleconverter won't work with your 5D3 without some tinkering, and unless it's 2.8 it won't work with a 2.0x. Stick with the 7D.

[TexPhoto]

For the past 2 years, I've had a 5DII and a 7D because they are each so great in their area.  The 5DIII definitely makes up some ground, but assuming you have a lot of light,  the 7D is still the better camera for birding because of the higher pixel density, and faster frame rate.