Photographers that worked with the older EOS-1D Mark III aren't in for a shock in terms of design and handling because the EOS-1D Mark IV is nearly a carbon copy; the body is built from magnesium alloy and is carefully sealed to protect from environmental damage. Thankfully, weight hasn't increased at all so, as before, the Mark IV with its battery weighs in at 1.4kg. The camera is very easy to get comfortable with and is fully customisable, so you can set it up to your preferred style of shooting.
In terms of photo quality the Mark IV is spectacular. The photos we captured over our two week test period were absolutely brilliant; we observed fantastic colour and an incredible amount of detail whether we shot in JPEG format or RAW. This Canon's a fast worker too, we were able to take advantage of its capabilities and shoot 121 JPEG shots in quick succession before the camera needed to empty its buffer. If you prefer shooting in RAW the Mark IV is equally impressive, here it grabbed 28 shots before needing to clear its buffer and write to our CF card.
The Canon EOS-1D Mark IV blows its predecessor out of the water when it comes to ISO performance. Whereas the Mark III struggled to maintain detail and quality at an ISO setting of 6400, the Mark IV returned professionally-useable photographs at the very high setting of 25,600. Beyond this we noticed quality degradation, with the top most settings being completely useless.
Beyond grabbing still images the Mark IV can capture movies. Unfortunately the shooting experience here lags behind what the camera delivers when shooting in still image mode. The first problem we have is that the body while great for grabbing still images through its viewfinder, is clumsy and awkward to work with when shooting movies. This is a bit of a shame because it actually sports some powerful features. The second issue is that these features, while great, feel a little too tacked on, rather than integrated. Still, if you can work around these hurdles the EOS-1D Mark IV captures excellent video footage at Full HD resolution.