Will a new D800/600/D4 improve my work?

I've been using a D700 for he past 3 years and now also a D800.

My short answer to your question is "No", a newer body will not give you better results - unless you work harder at getting better results.

I find the D800 to be more challenging than the D700 to get good results, especially accurate focussing. The D800 (or D600) will give you more latitude to crop and better dynamic range, but the rest is up to you.

The one thing that the D800 pointed out to me is just how good the D700 actually is !

Currently I am the weak link in the photographer/D800 chain and I'm sure with more practice the D800 will wow me more - but at the moment I'm sure glad that I kept my D700 !

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Jacques
Apple & Eve website and blog : apple-and-eve.com