Katz Eye focusing screen
I now have a Katz Eye focusing screen in my Pentax K10D and I'm very happy with it.
When I got my first DSLR in 2006 (the Pentax K100D) I was pleased to see that the optical finder was so much brighter than the digital finder in my previous compact camera, the Canon PowerShot S3 IS. But I was disappointed that the K100D lacked a split-prism focusing screen like my old Nikon N65 film SLR and most of the 35mm film SLRs I've used in the past. Although the optical finder is bright and clear, it is of course quite small, and as a result manual focusing is very difficult. The image is in focus when it looks like it's in focus. But you're making this assessment looking with one eye at an image that's smaller than a postage stamp.
The Katz Eye focusing screen from Katz Eye Optics provides a split-prism focusing screen that you can install in your own camera. I heard nothing but good reports from other photographers who had installed the Katz Eye screen in their cameras, but I hesitated for a long time because I was worried about the installation process. Finally I decided to write to the proprietor, Rachel Katz, and ask her how difficult it was. She briefly explained the process to me and I was convinced I could do it, so I placed my order in early 2008.
Installation is in fact quite straightforward. The instructions that come with the screen are clear and easy to follow. If you are doing it yourself for the first time, you might find it helpful as I did to have a small, bright flashlight that you can hold in your mouth, to shine into the camera while you are working. But the installation is easy for anybody who can follow instructions and who can use a small screwdriver and a pair of tweezers without injuring themselves. I have installed RAM inside computers dozens of times and this is an easier operation than that. Nevertheless, some people are simply terrified by the idea of opening up their camera and poking inside it and I understand that. So I am not recommending it to anybody and certainly am not promising that you will not hurt your camera if you try this. But if you are reasonably careful and coordinated, it's a piece of cake.
And the results? Very good. With the Katz Eye screen installed, it's much easier to focus manually. The Katz Eye screen works much like the split-prism screens I remember from the old days of film SLRs: the central part of the image seems to be blurred and broken in two when it's out of focus, and as you improve the focus, the central area comes into sharp focus and the two halves of the image come together. It's especially easy to focus if you've got a straight edge in the the photo to look at. With the Katz Eye, I can usually go right to a sharp focus without having to overshoot it and come back, as I so often had to do before. My one small complaint about the Katz Eye is that I would prefer that the split be diagonal rather than horizontal.
The Katz Eye focusing screen is said to have a number of small disadvantages. These are listed on the Katz Eye Optics web site, to which I linked above. I must confess that, after using the screen for a week, I am not experiencing any significant problems as a result of the Katz Eye.
The one thing that I can see is that the Katz Eye screen makes a measurable but small difference to the way my camera meters the scene. If you are looking at the camera's meter to tell you what's a correct exposure, with the Katz Eye installed, the camera will have a slight tendency to overexpose the photo. I gather that this happens because the Katz Eye screen itself blocks a bit of the light coming to the sensor while you are focusing, composing and metering the shot. See photos 5, 6 and 7 in my test gallery, here. From what I read prior to buying the Katz Eye, I had gotten the impression that with the Katz Eye screen installed, I would not be able to use center-spot metering. I may change my mind in the future, but at the moment, that does not seem to be the case. I just need to be aware that using center-spot or center-weighted metering, the camera will tend to overexpose slightly. Since I almost always shoot manual and I pay constant attention to exposure, this is not a big deal for me. Even if I lost spot-metering altogether, trading spot metering for much improved focusing would, I think, be a fair trade off.
Note that the Katz Eye affects only manual focusing and metering. It does not affect the taking of the actual shot. In the gallery of test shots to which I just linked, there are two shots taken with precisely the same exposures, one using the Katz Eye and one without the Katz Eye installed. The Katz Eye shot looks slightly darker, but this has to be an accident of the light, as the focusing screen is out of the way when the shot is actually captured by the sensor, and the settings for the two shots were identical. The Katz Eye screen does not affect the camera's ability to focus automatically, although I would note that, with the Katz Eye screen installed, I have occasionally noticed that the autofocus wasn't quite perfect. At such a moment it's nice to be using one of the Pentax lenses that allows you to adjust the focus manually even while the camera is in auto-focus mode.
I didn't get the opti-brite treatment on my screen, and I didn't get any special etching.
I am very happy with the Katz Eye screen and find myself much more willing to switch to auto-focus now than I was before. As a result I have noticed a slight improvement in the sharpness of my photos, and even if perfect focus were not more frequently attained with the Katz Eye, it is certainly more easily and comfortably attained.
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