Slide projector

A slide projector is an opto- mechanical device that can be projected with the mounted slides with light onto a screen. It consists essentially of the illumination system having the light source, the imaging system comprising the lens and the slide holder with a replacement system.

Leitz Prado slide for manual change images

Mature slide projector Braun Paximat with wired remote control

Liesegang Fantimat with Universal Magazine according to DIN 108

Lighting system

The illumination system determines the type of operation of a slide projector. Criteria are the size of the slides, the light power required and the uniformity of the illumination. On the imaging side, the lens is determined by its focal length, the size of the projected image and projection distance to the screen. The optical path of the illumination system and the imaging lens form an entangled beam path.

The lighting consists of the bulb, the concave mirror behind it, and the condenser. The light from the lamp passes the slide and the filament of the lamp is shown in the lens. The lens projects the illuminated slide by on the screen.

For smaller slides Elipsoidspiegel a lamp, instead of the condenser lens in front of the lamp, can be used. Again, there is an interwoven beam path and the filament of the lamp is shown in the lens.

The lamp, the lamp has changed significantly from candles, Petoleumslicht, light bulbs, halogen bulbs up to metal halide lamps. The luminous fluxes thus achieved are greater and thus the loading of the slides is in particular increased due to the absorbed heat radiation from the lamp. Reducing the temperature on the slide is achieved by means of heat-absorbing filter and the infrared transmitting filter on the concave mirror, or infrared reflectierende lens coatings. In addition, the slide is cooled by targeted air routing.

Projection lens

The projection lens is used for optical- geometrical illustration of the projection template on the screen. They are generally made ​​up of 3 to 5 lenses, while the aberrations should be largely corrected.

The lenses are designed with a fixed focal length or variable focal length as a varifocal lens. More designs are shift lenses and the CF- lens ( Curved Field) adapted to the curvature of a non- framed between glass slides, which has heated up in the projection.

When changing the focal length of the lens, you can switch the field lens to adjust the interwoven beam paths or in another position in the lamp house.

To focus the lens in the optical axis must be displaced, for example by a coaxial threaded guide.

The resolution describes the properties of lenses, nor to separate closely spaced details. ( Modulation Transfer Function MTF, engl. ) Or contrast transfer function, is generally in the image in line pairs / mm, Test mark according to DIN 19051, or by the modulation transfer function, and modulation transfer function measured.

Projection distance - Resolution

The relationship between projection distance A to B image size on the screen is given by the ratio of the focal length f of the lens to Diabreite b.

Comments: It is assumed that focal length f is much smaller than the projection distance. The nominal size of the slide, for example, the record format specified with 24 mm x 36 mm, the mask in the slide frame but has a size of 23 mm x 35 mm.

Automatic focus

The focus of the projected image on the screen is usually done by turning the lens. Thus, the distance between lens and slide is changed. This set distance can be changed by different slide frames. In addition, the slide is heated in the beam path during projection and bulges, it "jumps". The autofocusing corrected this change by shifting the lens and adjusts the distance manually set restore.

Slide Transitions

Inserted slides over chute

Inserted slides over long magazine automatically

Inserted slides on circular tray automatically

For projectors with manual slide feeder the mounted slides are brought individually by changing slide or through a chute into the projection beam path.

For projectors with slide feeder from a slide tray, a manual or automatic slide change slide change is possible. The triggering of the forward or the reverse ( Image Repeat ) can be controlled by different buttons or by the pulse length. The automatic slide change can, according to the features of the projector, be triggered by a button on the projector or remote control, by a time switch or controlled by a tape recorder.

Magazine for slide projectors

Magazine for slide projectors, long magazine or round magazine, can be used for slide frames of nominal sizes 3x3, 5x5 or 7x7 cm. The slide trays differ in their capacity, ie the number of recorded slides and the shelf width for the slide frame. The compartment widths for receiving the slides are: up to 1.2 mm or to 3.2 mm.

For an endless demonstration is especially suitable round magazines. These magazines are designed depending on the manufacturer for different capacities. For magazines that are arranged horizontally on the projector, the slides will be led from the top into the illumination beam path, in magazines, which are located next to the lighting system, the slides are pushed laterally into the beam path. Round magazines of the nominal sizes 3x3cm and 5x5cm slides are also provided for.

Additional equipment and accessories

• Timer, adjustable interval for automatic slide change
• The functions of the projector can be controlled by an IR remote control.
• Saving switch that reduces the voltage across the lamp by 5%, the luminous flux is reduced to approximately 20%, the lamp life increases by approximately 100%.
• AV control socket, this socket, the lamp, according to the programming of a control device, are controlled for transitions.
• A light pointer can be incorporated into the remote control. With the light characters can be made to details in the projected image.
• With Diavorbetrachtung, a single slide in front of the projection are regarded as on a small screen.
• With a picture book approach 35 mm film strips can be projected with still images.
• A micro approach is used for projection of transparent microscopic slides.
• A tape controller controls over, be played on one track of the tape impulses, the slide change the projector in sync with the sound being played.
• A Multi- Vision is a projection with multiple projectors, controlled by a multi-vision control, on a large screen.
• A projection unit consists of a projector with a transparent screen which is fixedly connected to the projector or a fold-out screen.

History

The history of slide projection to the beginnings of the magic lantern, described by Joh. Porta back in 1589. The first projected templates were shadow projections or drawn templates. Until about photography, first by means of coated photographic plates and then developed over the 35 mm film, the small picture slides 1925 and the first small -screen slide projector by Leitz in 1926 came on the market.