Well, it's now been a little over three months that I've shot with the EOS 5D and its accessory dual battery grip. I've used the 24-105mm f/4 L zoom, the EF 50/1.4, the EF 85/1.8,and the EF 135/2 L-series on the 5D, as well as Nikon's 105mm Defocus Control lens and a few other Nikkors. Now that I've shot a few thousand frames with the 5D, I'm familiar with the kind of results it can produce. Overall, I think the 5D is a fine camera, but one which could benefit from a better body with a little bit better feature set and design. Specifically, the 5D DOES allow a TON of crap to make its way inside the viewfinder system--it's the worst SLR design I have ever shot with in terms of allowing dust to enter the viewscreen/pentaprism areas. The EOS 5D could use a pop-up flash in a major way. And a couple more control buttons. Yet still, the 5D has proven itself to be a practical, easy-to-use, versatile camera, with a great mix of value, image quality, and simplicity in use.
One of the 5D's biggest operational problems is the ultra-soft touch ON/OFF switch on the accessory battery grip. Normal use and handling of the camera can turn the ON/OFF switch slightly forward, away from the ON position by a millimeter or two, rendering the grip's shutter release inoperational. The control has far,far too light of a touch,and has an almost non-existent detent at either ON or OFF. Numerous times, I've found that the vertical grip's trigger is dead, even though I NEVER turn the grip's trigger OFF. The switch is large,and has no safety lock...it's free to move toward OFF at any time, with almost no pressure. A crappy design,really. One must constantly make sure the trigger on the grip STAYS where it was put, since it wanders to OFF of its own accord quite often.
Lens-wise, the 85mm f/1.8 Canon EF lens is a tremendous value for the money spent. The 135mm f/2 L is a good telephoto lens, on par with Nikon's 135 f/2 Defocus Control lens,with maybe a bit higher image contrast being shown by the Canon lens.
Canon's 50mm f/1.4 EF is amply sharp and contrasty ,and it focuses very quickly, but the 50/1.4 EF has had some very,very odd failures to initiate autofocus over the last few weeks. While all three of these prime lenses appear well-made and feel solid and they handle and shoot very nicely, I must confess that the operational failures I've had with the $345 50mm lens are kind of pissing me off as of late. The 50's failure to initiate AF has been when the lens got confused and went wayyyy out of focus, and would simply NOT make an effort to seek focus until manually shifted out of AF and into to Manual focus,and the lens ring had to be turned and turned and turned by hand. Perhaps this 50 is a clunker--I've had this odd AF failure happen three times,and three times it has cost me the shot. I've never had a similar experience before or since with any other lenses of any brand.
I've only recently, this week in fact, purchased the 70-200 f/2.8 IS L-series zoom and the 135mm f/2.8 Soft Focus lenses, and have only shot those two lenses a little bit, and only on informal stuff. All of the Canon EF lenses I've used have been good to excellent performers, and the camera's AF performance has been MOSTLY very good, with a few occasional failures to acquire focus where more-sophisticated AF systems (like the one in the D2x) can be utilized for surer performance. But on MOST subjects I've used it for, the EOS 5D's AF system has been pretty good with the lenses I own. One thing is also clear: top-quality Nikkor lenses like the 85mm f/1.4, 105mm f/2 DC, 135mm f/2 DC, and 300mm f/4 AF-S and 300mm f/2.8 AFS-II are superb optical performers on the 5D's excellent sensor.
ISO flexibility is one area where the 5D does well; its performance at elevated ISO settings like 500,640,and 800, is noticeably better than what the D2x can do at those ISO settings. AND, and this is a big and, the 5D's sensor is more sensitive than the meter indicates in most real-world scenes I've run into. The 5D is an excellent low-light d-slr.Better than anything I've yet shot.
Keep in mind that since the 5D's design, Canon has cribbed/stolen/copycatted Nikon's "AF ON" button,and has added the AF ON button to their new pro sports/action EOS 1D Mark III and to the upcoming EOS 40D semi-pro camera. While it's a crude system compared to the two-button,user-customizable AF-AE buttons Nikon's D1 and D2 series have always offered, Canon's copycat move to add a single "AF ON" button is an excellent ergonomics example of where NIKON has long been a leader, and Canon's body ergonomics are and have been seriously lacking. Canon is adding an AF ON button, but is not adding the AE or light meter button Nikon has in its pro bodies. However, Canon engineers are willing to copycat half of Nikon's engineering and ergonomics leadership position and with the adoption of an AF ON button, Canon has finally recognized that a human's right thumb can actually serve a purpose in the control of the camera; in camera control ergonomics, Canon still lags behind Nikon in designing useful,logical camera control systems. In terms of control buttons, the EOS 5D lags behind most Nikon body designs. The 5D is a very simplified body.
Autofocus on the 5D is a mixed bag. Usually the 5D delivers very good AF, but occasionally,it stumbled and provides just the dumbest, crappiest AF performance you can imagine. Weird. I do not think that the user can assign AF points very intuitively with Canon's body controls, and I think that the tiny multi-controller "button" Canon uses is a joke. Better than nothing, but a laughable piece of crap compared with the large, positive, foolproof 4-way-controller Nikon has used for years. Again, imitation may be a sincere form of flattery, but the diminutive Canon multicontroller is VERY difficult to use when one wishes to assign AF to the two points just inside the outermost AF brackets, on either side of the viewfinder screen. Canon's multicontroller does a horrible job when trying to assign AF to any of those four total outer AF brackets,and it represents the same engineering failure on the 5D as on the 20D. If memory serves, the 20D was the first Canon to use the multi-controller "nipple",and the 5D is not far removed from the 20D,engineering-wise. Like I said earlier, while the 5D normally has excellent AF performance, at times it seems very,very "stupid" when using some pretty good Canon lenses--not slow consumer zooms, but the "good stuff". On a scale of 1-10, the 5D gets an overall AF score of 8.75 in my book.
In terms of image quality, the 5D delivers excellent image quality at all normal ISO settings. The camera is not too large or bulky,nor is it overly heavy. I like the "look" of full-frame digital captures very much. The 12.8 megapixel image sensor delivers clean,noise-free images under even poor lighting conditions. The files offer excellent workability in Photoshop. While the body controls and autofocus systems both are somewhat "simplified" and "middle of the road" compared to pro-level cameras, the price is nowhere near as high as the pro-level bodies from either Nikon or Canon. The EOS 5D offers a lot of bang for the dollar spent,and the files it produces are excellent. it is not a perfect camera, nor is it a particularly fast-handling nor a fast-reacting camera; it feels quite slow,mechanically and in terms of overall responsiveness, compared to the Nikon D1 and D2 series bodies I am used to. The EOS 5D is basically a superb image sensor enveloped in a mid-level camera body. The viewfinder information is very difficult to see in bright light. The viewfinder information is exceedingly skimpy. The body controls are rather primitive. But the pictures.....ah...the pictures; the image quality is where the 5D truly delivers.