When the Intenscreen™ is used in 35mm SLR's, Medium Format, or View Cameras, the user can expect an increase of viewing brightness of  1½ to 4 f-stops depending on the camera used. With the increased brightness it will become easier to focus in low light or poor contrast conditions, indoors or outdoors. 

Intenscreen™ helps the user achieve fast and accurate focusing while preserving detail and a brighter image. Intenscreen™ bright focusing screens is a combination of a specifically designed image surface and a fresnel lens. This reduces the amount of light required for image-forming and transmits the bulk of the light to your eye. Not only does this improve your depth of field, but it increases the sharpness of your own vision. The Intenscreen™ is custom-tailored for each type of camera to work best with it's features and optics.

INSTALLATION IS SIMPLE

In camera models with interchangeable screens installation of the Intenscreen™ is as simple as removing the present viewing screen and replacing it with the Intenscreen™. For some models of camera Intenscreen comes in component form, in which case installation instructions are included with the screen. The Pentax 6 x 7 and the Hasselblad 500C are the only cameras that require a technician to install.

Brightness Gains & In-Camera Light Metering

Depending on the camera, optics and accessories gains range from 1½ f-stops to 4 f-stops. Small format camera gain approximately 1½ f-stops; Medium format cameras 2 - 3 f-stops; and 6 x 7, 6 x 9 , 10cm x 12.5cm (4" x 5") and Panoramic Cameras 3 - 4 f-stops. Metering systems that read off the screen (see your user's manual) are affected by the Intenscreen™. The following methods can be used to compensate:

Changing the ASA film speed - Using your existing screen, set the camera lens at infinity and looking at an even light, such as a grey card or blue sky, note the meter reading. Install the Intenscreen™ and turn the ASA index dial until the meter needle returns to the old screen reading. Record this offset and tape to the back of your camera.

Changing the Exposure Value (EV) 1 EV = 1 f-stop - In modern cameras there is a button that can manually change the amount of exposure. Using your existing screen set the camera at infinity and looking at an even light, such as a grey card or blue sky, note the exposure reading. Install the Intenscreen™ and push the exposure button until the exposure needle returns to the old screen reading. Record this offset and tape to the back of your camera. An essential part of the design of the Intenscreen™ Plus bright focusing screen is that a very small proportion of the light is used through scattering to form the image and provide focus contrast. The remainder is transmitted through the screen and collected in a narrow cone by the special fresnel lenses used. The meter sensor cannot be in your line of sight and so is slightly off axis. This means that it may be in the "boundary layer" at the edge of the light cone and will therefore not record a significant change even though your eye may see major brightness changes.

Looking into the Future

Special screens have been made for medical, scientific and industrial purposes ranging from 3mm to 52.5cm in diameter. A few applications are, enlargers, custom printers, microscopes, endoscopes, telescopes, back projections of all types. In these cases Intenscreen™ will provide a better than twofold gain in light transmission over conventional ground glass.

FOCUSING & CAMERA FOCUS

Critical lens focus on the film depends on installing the correct components in the correct order. This should be determined at the time of ordering. The installation should be tested on a fine line target with high resolution film. If there is any doubt of the very short depth of focus lenses are being used, it would pay to have the camera checked on a collimator (Camerascreens will not be responsible for any focus errors).

LIGHT METERING

External meter and the modern slide in meter sticks that meter the image in front of the screen will not be altered. However, the Intenscreen™ is BRIGHTER. If you use a meter with a fibre optic probe (like Gossen) or an optical Type I spot meter (like Litemate\Spotmate by Photo Research), then the absolute EV readings will be different from any other screen, when you take readings off the eye side of the cover plate. If you wish to compare relative bright\dark areas, this works as before, but for absolute exposure, the direct meter at the lens should be used.

FRESNEL LENSES

The fresnel lenses on the back of the focusing screen are a 6" effective focal length plano convex lens for 6 x 9 and 4 x 5 view cameras and a 10.45" effective focal length plano convex lens for 5 x 7 and 8 x 10 view cameras, with convex portion towards the eye. For optical calculations the fresnel side conjugates are 6" and 10.45", both plano side conjugates are infinity for the fresnel lens with 6" EFL and 10.45" EFL, respectively. These choices suit most of the normal view camera lenses. 

Some points to consider: 1. If using a viewing attachment with a mirror inverter, everything is OK. If there is a magnifier lens included, it may cause vignetting and should be removed. 2. When using short wide angle lenses (Super Angulon etc.) see use of extra fresnel lens in the first part of this article. This is an identical fresnel to the fresnel on the focusing screen except it is installed with the plano convex side towards the other fresnel. This makes a Ramsden pair, for least distortion, which makes a combined focal length of about 3" which will cope with lenses down to Super Angulon 47mm.

MISCELLANEOUS INFORMATION