I've been thinking about picking one up to use with my manual focus glass.
How much darker is it in low light situations? Does it effect auto-focusing in low light?
Is it tough to install? Is it worth it? Does the D700 and D3 use the same screen? It looks like there isn't a microprism ring on the D700 screen as there are on the other ones either.
The KatzEye screen has no effect whatsoever on autofocus, because the screen isn’t in the light path for the autofocus module.
It supposedly affects metering slightly, at least with centre spot metering, but to be honest I didn’t notice much difference. Any camera’s meter is often a stop or more off my desired exposure anyway, so worrying about 1/3-stop differences in metering is futile, in my opinion.
I found the screen acceptably bright with all my lenses, the slowest of which is f/3.5. With the slower lenses it was clearly dimmer than brighter ones, but brightness is pretty good with an f/2.8 or better lens.
I view the lack of microprism collar on the D700 as a benefit, since it provides more room for viewing the subject or focusing on the matte screen. It’s less cluttered. I’ve had KatzEye screens in both the D300 and D700, and preferred the D700 screen for its lack of microprism collar and smaller split-prism area. In addition, since the D700 has a greater effective magnification (at 0.72 ×, it’s even better than current FX Nikons) it’s easier to really nail the focus with this camera and the KatzEye.
Since KatzEye Optics doesn’t sell screens for the D3 or D3S, I presume those cameras use a different screen than the D700. They do have different viewfinder optics.
As for installation, it’s not exactly difficult but it is nerve-racking. It would be very easy to slip while unclipping the wire bend holding the focusing screen in place, and a slip would surely destroy the focusing screen. Dropping the screen into the mirror box is another risk. There’s also the near inevitability of dust entering the camera at some point in the process (I place the camera on a damp towel while working on it to minimise dust). Have a look at the instructions (PDF).
One thing to keep in mind is that the precise focus enabled by the KatzEye screen might reveal inaccurate alignment between the focusing screen and sensor of your camera. This would require shims to correct, part numbers (for the D700) as follows:
I understand Nikon’s new spare-parts policy in the USA might make getting these difficult there, but perhaps you can find them somewhere else if you know the part numbers.
You can calculate the approximate shim thickness you need by following Toothwalker’s instructions here.
Is a KatzEye screen worth it? For the D700, that’s a resounding ‘yes’. I’d recommend it to anyone.
For a D300-class camera I wouldn’t so enthusiastically recommend the KatzEye screen to others, although I’m personally pleased with it too. With the D300 there are greater tradeoffs in brightness and viewfinder clutter, and focusing is still not super-easy in the smaller and darker viewfinder, despite the KatzEye screen (though it is very much easier than with the factory screen).
I find the Katzeye pretty useless whenever you don't have straight lines in the scene you shoot. The mattness surrounding the split prism is not matte enough to use for focusing, so you also have to focus and recompose, which isn't always a good idea.
Right now I have the Canon EG-S which has no focusing aid at all, but it gives me more keepers than the Katzeye. This screen makes me have to exposure compensate a lot though, so it's not perfect.
