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7 Focusing screens

7.0 Introduction

Only the 330 series bodies have interchangeable screens. The standard screen resembles the Type 1 below. Some other bodies are known to have non-standard screens, either as a special order or a retro-fit. The fixed screen models usually have washers or shims fitted under the screen to obtain the correct focus. If you need to clean these screens it is strongly recommended that you attempt it from the lens mount, or have it done by a competent mechanic.

The C330s uses different screens and a different mounting method from the C330 and C330f. The difference in the two split-image types is the sensitivity of focus. The 6 degree version is most sensitive. According to a C330s manual, there was a checker screen that fitted into the finder (like the 55/65mm compensation plate). Note that not all screens have the exposure compensation scale. It appears that screens of C330 vintage do not have the scale. A PostScript program in section 6.4 can be used to create a finder insert.

At least one C220 is known to have had a C330-type screen fitted. The only advantage of this would have been to use the different split image screens to match different focal lengths. The exposure/parallax correction scale would have been of little value. This appears to have been done professionally, as the screen is correctly shimmed to match the film plane.

A number of cameras have been reported with screens refitted upside down, causing a focus problem. Generally this only occurs with fixed screen cameras, but the screens on the C330 can be removed from the mounting frame.

If you are buying a used screen, make sure that the box and the screen match. A lot of boxes were used to store the original screen when the alternate was fitted. Sellers do not always verify the contents.

7.1 C330

The C330 has three adjustable studs inside the mirror box that bear on three tabs on the screen itself. These are used to adjust the screen height for focus calibration. Since the screen is mounted into the screen frame with a foam separator, mounting the frame and screen assembly onto the camera applies sufficient pressure to ensure that the screen sits on the adjustment points. The mounting points can bee seen in the top and bottom right and 1/3rd up on the left in the mirror box picture at .

A range of seven screens was produced:

1. Matte Matted entire surface backed by Fresnel lens except centre spot. Exposure compensation scale. This is the standard screen.
2. Rangefinder (split image), 4 degree spot Matted entire surface except centre horizontal split image and surrounding annulus. Without exposure compensation scale according to some sources, but includes it according to a C330f Focusing Screen insert.
3. Rangefinder (split image), 6 degree spot As 2, but incorporates exposure compensation scale. Split image rangefinder is more sensitive. May not work well with longer (180mm plus) lenses.
4. Microprism As 2, but with microprism in place of split image.
5. Cross hair (ground glass with cross in central circular spot) Matted entire surface with clear centre spot and cross-hair. Suggested for close-up, dim views and astrophotography. To focus using this screen, use a strong (x8-x10) magnifier and adjust the focus until the image remains steady with respect to the cross-hair when the eye is moved from side to side.
6. Checker / grid Matted entire surface with Fresnel lens except clear centre spot. Incorporates exposure compensation scale.
7. Microprism / split image Introduced with the C330f. Apparently the same as the C330s Screen E.

7.1.1 Changing screens

Remove the finder, and rack the bellows out a short distance. At the front of the focusing screen mount is a small catch. Pull this forward, towards the lens. The screen will lift off upwards and backwards. The screens are replaced by reversing the process. Screens can be taken out of the metal frame, but it must be done with care. These screens are plastic underneath a clear glass, unlike the glass fittings of older models.

7.2 C330f

These are the same as the C330 screens, but would have the exposure compensation scale as indicated in the previous section. Late C330f’s also had the option of a microprism / split image screen similar to the C330s Type E. This is designated as No.7, and combines a microprism with a diagonal spit-image. These screens are acrylic resin, and are comparatively soft. Avoid contact with solvents.

7.3 C330s

A range of seven screens was produced. Technically similar to the C330 equivalents.:

A. Matte. Matted entire surface backed by Fresnel lens except centre spot. Exposure compensation scale.
A2. Matte for wide-angle lenses. Incorporates the 55/65mm parallax plate.
B. Rangefinder (split image), 4 degree spot.
B2. Rangefinder (split image), 6 degree spot.
C. Microprism.
D. Cross hair.
E. Microprism / split image.

Also available was a checked overlay screen for mounting between the focusing screen and the finder.

7.3.1 Changing screens

The screen release catch is to the rear of the screen, and the screen frame hinges up at the front. The screen is positioned into the revealed recess, the frame lowered, and secured.

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