View Full Version : Accessories Katz Eye Optics Focusing Screens

First Light
12-02-2005, 06:36 AM

Custom focusing screens are available from at least two sources for the E-1. One of these is Katz Eye Optics (http://www.keoptics.com) (KEO). The major feature of KEO custom focusing screens are a split prism surrounded by a microprism collar. The split screen is available in a standard form which begins to darken at apertures smaller than f6.7 and a "plus" version which is usuable at much higher f-stops. An optional low-light treatment is available for the focusing screen, itself, and the user can order virtually any arrangement of engraved grid lines.

The drawing above shows optional 1/3 grid lines. Also notice that a large circle is present on all of the KEO focusing grids. The closeup below shows the pyramid pattern of the microprism collar. It is very helpful when focusing on small details.


First Light
12-02-2005, 06:44 AM
Perhaps to come...

First Light
12-02-2005, 06:45 AM
Do you know of any?

First Light
12-02-2005, 06:48 AM
To be completed...


More to come...


And more...


12-07-2005, 05:07 PM
Jebir Wrote:

Quote from First Light:
Did you test with any 4/3rds lenses?
Hi First Light,

yes, I tested also the 14-54 and the 50-200:


As you see, the exposure error with the Katz Eye screen is different in magnitude for the lenses but follows very much the same trend.

I tested four ZD lenses and the 50mm f2.0 macro prime was the only lens that had perfect exposure accuracy with the KEO screens.
I think that is a pure coincidence that it happens to be OK at full opening (where the camera is doing the metering)

Where did you obtain the modified OM screens? Did you mod them yourself?
Yes, I modified them myself. Not difficult except to get the final thickness (height position in the camera) correct.

I haven't had a chance to test any legacy lenses yet.
My results on legacy lenses show that the KEO Plus Hilux produces acceptable exposure (about ±1/2 EV error) at large apertures (f/1.8 - f/2.8) but it always gives unacceptable exposure (more than +2.5 EV error) at small apertures (f/8 - f/32). However, in accordance with your observation for the ZD 50/2.0 and ZD 150/2.0, I also see that the exposure error is different for different focal lengths even at f/2.8.

All this is a huge pity because it is for use with MF legacy lenses (which is about 90% of my photography) that I bought the KEO screen. I was hoping that it would be a good allround screen so I even invested in special less intrusive tick marks instead of the standard grid lines:


I'm now not sure wether or not I'll keep this screen. :(

Quote from tspore:
Do you guys think that the KEO would have correct exposure accuracy with the 35-100mm because it has a constant aperture?
Hi Tony,

I don't know but the observation above that acceptable results are usually achieved at large apertures imply that it should be pretty consistent with a constant aperture zoom if the aperture is large.

However, my impression is that what determines the exposure error is far more complicated than just what aperture is used for metering. I think it has to do with the existence of a Fresnel lens pattern on the KEO-screen in combination with a varying degree of telecentricity at different focal lengths. (My hypothesis is that the Fresnel lens pattern will reflect different amounts of light back onto the light sensor for different focal lengths.) The E-1 screens lack this Fresnel pattern.

However, it also depends on what you mean with "correct exposure accuracy". My maximal measurement errors in the graphs above can be as large as ±1/3 EV as I used the internal meter of the E-1 to set correct exposure. (It has 1/3 EV as the finest step.)

By the way Tony; maybe you could move (or copy) these posts over to the thread where FL presented his data on the KEO screens? I think they are slightly OT here and it would make sense to have them collected in one place.

Cheers to everyone! Jens.