Viewfinder / Autofocus
On paper, the Mark IV appears to feature the same large viewfinder as the 1DS series - the specifications are all the same. However, because it has a smaller sensor than the 1DS III, the view through the viewfinder is also smaller (the edges are effectively masked off).
In the diagram below you can see the AF ellipse and 45 focus points, plus the center metering spot. The AF points, with cross-type sensors marked in black and horizontally sensitive ones in light gray, are not lit in the viewfinder unless they are selected, at which point they light up red (depending on AF area mode). The buffer space indicator adjusts its estimate of space available depending on the selected ISO sensitivity.
|1||FE lock||11||Shots remaining
|2||Metering mode (Evaluative, Partial, Spot, Center Weighted)||12||Highlight Tone Priority indicator|
|3||Manual Exposure||13||ISO speed|
|5||Flash ready||15||Exposure compensation
Exposure meter (manual mode)
|6||High-Speed sync||16||Flash exposure level|
AF point selection
|17||Maximum burst in continuous mode
AF point selection
Memory card number
Flash exposure compensation
|10||White balance correction||20||Battery Level
In automatic AF point selection mode the camera will highlight (glowing red) the AF points which were used to measure AF distance (you can turn them off using C.Fn III-13). On the right side of the viewfinder is the eyepiece shutter lever (not visible above), this allows you to blackout the viewfinder eyepiece to prevent stray light entering the camera during long or remotely triggered exposures.
Default display is indicated in bold.
Diagram reproduced from the EOS-1Ds Mark IV manual with permission.
One figure hidden away in every SLR's spec is the size of the viewfinder (often in a format that makes comparison between competing models difficult). The size of the viewfinder is a key factor in the usability of an SLR - the bigger it is, the easier it is to frame and focus your shots, and the more enjoyable and involving a process it is.
Because of the way viewfinders are measured (using a fixed lens, rather than a lens of equivalent magnification), you also need to take the sensor size into account, so the numbers in the diagram below are the manufacturer's specified magnifications divided by the respective 'crop factors'.
|Although the EOS-1D Mark IV has the same 0.76x magnification finder as the 1Ds Mark III, its smaller sensor means it ends up only offering 0.58x magnification once this is taken into account (making it a fraction smaller than the EOS 7D)|
The 1D Mark IV shows approximately 100% frame coverage in both the viewfinder, and the LCD screen in Live View mode. Because of the smaller tolerances necessary in creating 100% viewfinders, they are typically only found in high-end DSLRs, where a price premium is already expected.
|The EOS-1D Mark IV offers 100% frame coverage|
Lens mount / Mirror / Shutter
The EOS-1D Mark IV has the EF lens mount (identical to previous 1D and 1DS models) and therefore supports all Canon EF type lenses. As is usual for the 1D series, the 1D Mark IV has the unusual APS-H (27.9x18.6 mm) sensor size. This is smaller than full-frame (36x24mm) but larger than APS-C (~24x16mm), giving rise to an effective 1.3x 'crop factor'. As such the EF 16-35mm lens gives you the same field-of-view as a 21-45mm lens mounted on a full-frame camera. You cannot use EF-S lenses designed for APS-C DSLRs though, since they will foul the mirror (and are fitted with a guard to stop you from mounting them and damaging anything).
| C.Fn III-17 enables 'Mirror lockup' mode, in this mode the first press of the shutter release locks the mirror up, the second press opens and closes the shutter curtain (and thus takes the shot). This mode is especially useful for shooting long exposures or high magnification macros. New for the Mark III is the option to cancel the Mirror Lockup using the set button.|