The Katz Eye is an independently manufactured manual focus replacement screen for many different makes and models of auto focus cameras, including the Nikon D-200. From several independent testimonials, it seems as though it does not affect auto focusing of the camera with AF lenses, nor does it affect metering. From Fox O'Rian on flickr:
"I'm impressed with how well centered the prism is relative to the AF points (though it took some careful placement to get it that way.) The AF and metering aren't affected at all by this screen, and I dare say the center AF point is performing better than usual.Copied from the Katz Eye website:
Most importantly, the prism and microcollar actually works correctly. When shooting with AF, I can now easily tell if the AF is focusing correctly and if I need to quickly make any minor adjustments in case it was off. This should really help me get more sharp shots more often. It's invaluable with lenses like my 85mm prime."
"The Katz Eye™ focusing screen for the Nikon D200 has NO effect on existing viewfinder information. All viewfinder markings, including focusing points and on-demand gridlines will still function normally. The Katz Eye™ focusing screen for the Nikon D200 shows only a very minimal effect on light metering. In our testing, the Katz Eye™ screen tested within factory tolerance in nearly all situations. The only exception is when using spot metering mode with lenses having a maximum aperture slower than f3.5 (higher numerical f-stop). With lenses slower than f3.5, it is advisable to use either centerweighted average metering or matrix metering to preserve accurate meter response. In the event that spot metering mode must be used with a slow lens, it is advisable to set an appropriate exposure compensation by reading the histogram of a test shot.For many photographers who grew up using manual focus cameras and who still possess a collection of very nice and familiar manual focus glass, a split prism surrounded by a microprism in the viewfinder has an importance that is not entirely related to familiarity. Much of my past photography relied on a shallow depth of field with fast prime lenses.
A few days ago I received an auto focus 50mm ƒ1.8 lens that I won on ebay. My 85mm ƒ1.8 lens is also a fast prime. Essentially, all my manual focus lenses except for the 300mm ƒ4.5 light pipe have been replaced by an equivalent either in a prime lens or through a zoom lens. At 300mm (actually 450mm on a DX camera) the focus assist of the Katz Eye would almost certainly black out. I would gain an extra f-stop by using my manual 50mm ƒ1.4 and 35mm ƒ2.8 Ai-S lenses, but the ISO capability of the D-200 compensates admirably for the loss of one f-stop.
The Katz Eye manual focus screen is $105 without the OptiBrite treatment, $160 with it. There is presently a 10% off Spring special happening. The Katz Eye would have been good to know about when I first purchased the D-200. I had a collection of Ai-S lenses at hand, but I am not sure whether or not I would benefit from such an addition to my camera now. I suspect I would, as I find myself shooting in low light with fast primes frequently. The real question though, is how fast and how accurately the auto focus system works in such an environment. Only time can tell me that.
Independent review of the Katz Eye split prism screen on a Nikon D-200
Katz Eye Installation instructions for the Nikon D-200 (pdf file)