Pentax Focusing Screens
In addition to laterally reversing the image, most SLR cameras incorporate one more very important function into the viewfinder — the camera’s light meter. Apparently this is the easiest and cheapest solution, but it is not necessarily the best. Because the light meter is situated between the focusing screen and the opening for the photographer’s eye, it can be negatively affected by light entering through both. Replace the focusing screen with a "darker" one, and the camera overexposes. Take a picture without holding your eye close to the viewfinder’s opening, and the camera underexposes. Think of it this way: the light meter’s sensitivity is adjusted precisely to the mirror’s reflectivity and the screen’s brightness. When you replace the screen with one that transmits more light, the light meter receives more light than the film, and the picture is underexposed. Three possibilities exist for correcting this effect: recalibrate the light meter, adjust the film’s ISO rating to a lower EV value, or manually overexpose each exposure. If you replace the screen with a less transparent one, you must follow the reverse procedure. The one important exception to this rule is the LX, whose light meter is in the mirror box, and is not affected by variations of the screens and viewfinders.
The quality of focusing screens has improved constantly, and each new generation is finer and looks brighter. The designations of the Pentax focusing screens use two letters and normally two digits. The first letter indicates the screen’s dimensions, and distinguishes between screens with different designs, patterns, focusing aids, etc. The numbers indicate the screen age or generation. Higher numbers normally indicate more modern (and usually better) designs. Screens without numbers or with a single digit are from the first (level-10) generation.
The following sections list all Pentax cameras that support interchangeable screens and the screens that fit them.
Screens for the MX and LX
Screens for the MX and LX cameras have the same dimensions, and all have designations with first letter ‘S’. Screens for the original LX (those with numbers lower than 40) seem to be about 1/3 EV brighter than the screens for the MX. Screens for the LX 2000 (those with numbers between 60 and 70, sold only for a short time in 2001) seem much brighter than the original ones, but in reality the difference is no more than 1/6 EV.
Like previously discussed, screens designed for the MX can be used in the LX without the need for adjusting the light meter. LX screens in the MX will cause a 1/3 EV underexposure, but such a small difference will be virtually unnoticeable.
| Description | Screen Name | Catalog Number | Suited For | Specifically Designed for... | Suitable for Use with... |
|---|---|---|---|---|---|
| Matte with microprism center | SA-1 | 30831 | MX | — | Most lenses with f less than or equal to 300 mm. |
| Matte with microprism center | SA-21 | 30862 | LX | — | Most lenses with f less than or equal to 300 mm. |
| Matte with microprism center | SA-3 | 30833 | MX | Lenses with widest apertures between f/1.2 and f/2. | Lenses with widest aperture of f/2.5 or f/2.8. |
| Matte with microprism center | SA-23 | 30863 | LX | Lenses with widest apertures between f/1.2 and f/2. | Lenses with widest aperture of f/2.5 or f/2.8. |
| Matte with microprism center | SA-26 | 30882 | LX | Refractive lenses with f greater than or equal to 400 mm. | Refractive primes lenses with f greater than or equal to 100 mm and widest aperture smaller than or equal to f/2.5. Most refractive zooms. |
| Microprism with finer microprism center | SA-32 | 30885 | LX | — | Most lenses with f less than or equal to 300 mm. |
| Microprism with finer microprism center | SA-37 | 30884 | LX | Refractive lenses with f greater than or equal to 200 mm. | Most lenses with f greater than or equal to 100 mm. |
| Matte with split-image center | SB-1 | 30834 | MX | — | Most lenses with f less than or equal to 300 mm. |
| Matte with split-image center | SB-21 | 30864 | LX | — | Most lenses with f less than or equal to 300 mm. |
| Matte with split-image center and a microprism collar | SC-1 | 30835 | MX | — | Most lenses with f less than or equal to 300 mm. |
| Matte with split-image center and a microprism collar | SC-21 | 30861 | LX | — | Most lenses with f less than or equal to 300 mm. |
| Matte with split-image center and a microprism collar | SC-26 | 30881 | LX | Refractive prime lenses with f greater than or equal to 400 mm. | Refractive primes lenses with f greater than or equal to 135 mm and widest aperture smaller than or equal to f/2.5. Most refractive zooms. |
| Matte with split-image center and a microprism collar | SC-69 | 30869 | LX | Refractive prime lenses with f greater than or equal to 400 mm. | Refractive primes lenses with f greater than or equal to 135 mm and widest aperture smaller than or equal to f/2.5. Most refractive zooms. |
| Matte with center cross | SD-1 | 30832 | MX | Macrophotography. | Most lenses with f less than or equal to 300 mm. |
| Matte with center cross | SD-21 | 30865 | LX | Macrophotography. | Most lenses with f less than or equal to 300 mm. |
| Clear-glass with center cross | SD-11 | 30839 | LX | Astronomy, microscopy. | Most lenses with f less than or equal to 300 mm. |
| Matte with circle | SE | 30837 | MX | — | Most lenses with f less than or equal to 300 mm. |
| Matte with circle | SE-20 | 30866 | LX | — | Most lenses with f less than or equal to 300 mm. |
| Matte with circle | SE-25 | 30883 | LX | All lenses with f greater than or equal to 400 mm. | All lenses with f greater than or equal to 135 mm. |
| Plain matte field | SE-60 | 30850 | LX | Star lenses, mirror lenses. | All lenses except those wider than 28 mm and slower than f/3.5. |
| Matte with circle and grid | SG | 30838 | MX | — | Most lenses with f less than or equal to 300 mm. |
| Matte with circle and grid | SG-20 | 30867 | LX | — | Most lenses with f less than or equal to 300 mm. |
| Matte with grid | SG-60 | 30870 | LX | Star lenses, mirror lenses. | All lenses except those wider than 28 mm and slower than f/3.5. |
| Matte with circle and millimeter scale | SI | 30836 | MX | — | Most lenses with f less than or equal to 300 mm. |
| Matte with circle and millimeter scale | SI-20 | 30868 | LX | — | Most lenses with f less than or equal to 300 mm. |
SFXn/SF1n and SFX/SF1
Three screens were available in addition to the standard one: FD-41 (Scale matte Screen for Photomicrography and macrophotography), FG-40 (AF sensor field surrounded by a grid) and FI-40 (AF sensor with a horizontal and a vertical millimeter scale). Both screens are well suited to scientific, architectural, and macrophotographic work.
Z-1p/PZ-1p, Z-1/PZ-1, Z-5/PZ-5
Screens for all these bodies have the exact same dimensions, but 60-series screens are about 1 EV brighter than the 50-series. All screens have matte backgrounds and different markings.
| Description | Screen Name | Catalog Number | Suited For |
|---|---|---|---|
| AF sensor field (the standard screen) | FF-60 | unknown | PZ-1p |
| AF sensor field (the standard screen) | FF-50 | unknown | Z-1/PZ-1, Z-5/PZ-5 |
| AF sensor field with a 6 mm grid | FG-60 | unknown | PZ-1p |
| AF sensor field with a 6 mm grid | FG-50 | unknown | Z-1/PZ-1, Z-5/PZ-5 |
| AF sensor field with vertical and horizontal scales | FI-60 | unknown | PZ-1p |
| AF sensor field with vertical and horizontal scales | FI-50 | unknown | Z-1/PZ-1, Z-5/PZ-5 |
| AF sensor field with golden section | FK-60 | unknown | PZ-1p |
| AF sensor field and spot-meter field | FS-60 | unknown | PZ-1p |
| AF sensor field and spot-meter field | FS-50 | unknown | Z-1/PZ-1, Z-5/PZ-5 |
MZ-S
There are two screens available for this body: the standard GF-60 (plain matte) and the GG-60 (matte with grid lines).
