DE2651129A1 - CONDENSER LENS FOR WORK PROJECTORS - Google Patents

Description

Condenser lens for work projectors

The invention relates to a condenser lens according to the preamble of claim 1

Condenser lenses are known to be used in projectors, e.g. B. slide projectors, episcopes and work projectors, and enlargers to increase the efficiency of the lighting through strict concentration and direction of the light.

In other words, condenser lenses should project the light source into a large solid angle (usually half or

108-x1922-HdHp

80982 0/0126

Full sphere) emitted luminous flux (usually together with a concave mirror on the opposite side of the light source) and through relatively narrow Bring diaphragms in the projection beam path through with the lowest possible loss.

The previously known condenser lenses for work or "overhead" projectors, which are used to the spoken Word of a lecturer by projection of text written simultaneously by the lecturer, e.g. B. formulas, support visually, but cannot satisfy, since they do not have a uniform image field illumination or illuminance distribution (brightness distribution) on the projection screen (in the image plane). Namely, all parts of the projected Template can be recognized without any special effort, especially in relatively bright rooms, so that the Listeners can take notes (e.g. lecture halls).

With the condenser lenses normally used in work projectors, the z. B. are plano-convex spherical, at the edge of the projection screen only a maximum of 50 % of the maximum illuminance is achieved in the center of the projection screen. This ratio can hardly be improved even with special spherical condensers; because the large drop in illuminance towards the edge is essentially due to the high light loss of the Fresnel lens towards the edge.

Aspherical condensers, such as those used e.g. B. bring a certain more even illumination with slide projectors, cannot be used with work projectors because

809820/0126

they are too short focal length and collect the light so strongly, that the edges of the usable area of the working projector can no longer be illuminated at all.

Long focal length spherical condensers also bring no noticeable improvement in illumination, as its surface is similar to that due to the long focal length of a spherical condenser.

In order to still achieve a more uniform image illumination, special work projectors have already become known (see brochure "Proki 1004"), which also only achieve an illumination of approx. 70 % , ie the illuminance at the edge of the projection screen is 70 % of the illuminance in the middle of the projection screen, although they are very complex and constructed as so-called two-chamber devices, in which the distance between the light source on the one hand and a Fresnel lens on the other, over which a pane of glass is located as a support for the original to be imaged, is kept very large. This means that the focal length of the Fresnel lens is very large. The edge rays therefore hit the Fresnel lens at a much smaller angle to the optical axis, and the slope of the individual lens zones at the edge can be kept much smaller. As a result, there are far fewer annoying reflections in the lens and the light losses can be kept lower.

Nevertheless, two-chamber work projectors have the following disadvantages:

a) To achieve this large distance between the light source and the iresnel lens, the light must come from the light source using an expensive mirror that adjusts precisely

8Ü9820 / 0128

must be directed from a first chamber to the ixesnel lens in the second chamber.

b) In addition, the dimensions are clearly significant larger than work projectors with only one chamber.

c) As for the rest, existing newer work projectors cannot be retrofitted to a two-chamber system will.

In contrast, it is the object of the invention to provide a condenser lens which, despite a relatively simple structure a very uniform image field illumination or illuminance distribution, which is even better than with Can be dual-chamber work projectors, and even in existing projectors, especially single-chamber work projectors, can be installed in place of the existing condenser lens to improve illumination.

This object is achieved according to the invention by the characterizing part of claim 1.

So it is crucial that in contrast to usual, in particular aspherical condenser lenses, the condenser lens according to the invention does not have an exclusively collecting effect, but also has rotationally symmetrical zones in which the lens has a dispersing effect or possibly has no influence at all on the beam path.

Thus, when the light rays leave the condenser lens, they are compared to the incident light ray in the The center of the condenser lens is directed outwards and inwards at the edge of the condenser lens. This way the illuminance can be adjusted reduced in the center of the picture and

809820 ^ 0126

edge can be raised. Light is transmitted from the center of the image to the edge of the image.

If the condenser lens is designed so that the side facing the light source contains the scattering effect in the center, in this way, the light source can be brought closer to the lens than with the condenser lenses previously used and at the same time the collecting effect at the edge of the condenser lens can be increased. So the solid angle (ii in Fig. 2), which the condenser lens detects in relation to the light source (3 in Fig. 2), increases and thus the detected useful luminous flux increased, whereby the overall brightness in the image plane is increased.

In an advantageous development of the invention, a condenser lens that is particularly easy to manufacture is provided by the Teaching according to claim 4 specified.

To the condenser lens in an advantageous embodiment of the invention optimally the complicated in a work projector Distribution of the illuminance on the projection screen adapt, the teaching of claim 3 is appropriate. Because the complicated distribution of the (Relative) illuminance is the sum of several influences and is similar for most work projectors (Pig. 3), it is used to optimally balance this illuminance distribution just advantageous to provide the radial lens profile with Drehsvmmetrisehen zones that collect the light more or less strongly depending on the radius. So it can be B. happen that the radial Lens profile of the condenser lens has several points of inflection.

8 0 9 8 20/0126

The condenser lens according to the invention can in particular be designed as a Fresnel lens (also called step or ring lens).

The invention is explained in more detail with the aid of the drawing. Show it:

Fig. 1 shows the basic structure of a work projector known per se with the only schematically indicated condenser lens according to the invention j

2 shows a radial section composed of two parabolic sections and a straight line section Condenser lens profile;

3 shows the relative illuminance distribution on a projection screen as a function of the radial distance from the center of the projection screen; and

4 shows an embodiment of the condenser lens with different zones as a Fresnel step lens.

According to Fig. 1, which is a known working projector shows, light is in a projector housing 1 from a lamp 3 via a concave mirror 2, a condenser lens 4 » a Fresnel lens 5 and a glass pane 6, which carries a template (not shown) to be projected, onto one Projection head 7 and projected from there onto a (not shown) projection screen.

A particularly simply constructed condenser lens according to the invention is shown in FIG

809820/0126

radial lens profile consists of two parabolic sections, as the following formally states:

2
ζ = ar + Zq 0 cc r; cr _g

^(r " ^r 1 ^{) 2} * ^ ^z 0 ^{+ ar} S ^r 1> r _s ^ r ^ R

^{with: -:} ■ - ;: ■■ "■" - '■' ■■

r = radius,

ζ = axis coordinate

a, r _g -, .r ^, R, z _Q = const.

The factor of (rr ^) is chosen so that the two parabola sections at point r _{g have} the same slope, while the constant term in the equation for the second parabola section is chosen so that the parabola sections in Point r «also have the same ζ-value.

According to Fig. "2, the light beams S1 and S2 are scattered, on the other hand, the light beams S4, S5 and S6 collected, while the light beam S3 from the condenser lens (in its Angle of inclination) is not influenced. Uach.dem the rays of light have left the condenser lens 4, they get into the Fresnel lens 5 and from there over the glass pane 6 into the projection head 7.

When dimensioning the lens parameters, care is preferably taken to ensure that the outermost of the condenser lens detected light rays S6 reach the outermost edge of the Fresnel lens safely. In this way one achieves that the lens is not oversized.

When dimensioning the lens parameters, it is also advantageous if the outer lens radius R is the same as that previously

809 8 20/0128

Consensor lenses used, since the condenser lens according to the invention is then easily compared to conventional ones Condenser lenses can be exchanged.

Fig. 3 shows the complicated distribution of the illuminance on a projection screen as a function the distance from the center of the projected image.

In order to compensate for this irregular illumination of the projection image, the incline of the generatrix is shown in FIG K of the condenser lens as a function of this same illuminance distribution on the projection screen 3 individually matched in a larger number of points r. It can then turn out that the Condenser lens contains several less or more condensing zones, see FIG. 4. In FIG. 4, F then denotes the radial profile of a Fresnel lens, that of the generatrix (the radial profile) K is assigned to the condenser lens.

In this way, for the first time, an almost uniform illumination can be achieved in spite of the fact that the Fresnel lens itself conditional complicated illuminance distribution can be achieved. Even with two-chamber work projectors this was previously not possible.

809820/0126

E e r a l e e s

Claims (7)

Expectations Condenser lens - for Arheitsprojektors with different formed rotationally symmetrical zones, thereby g e k e η η ζ e i c h η e 't that the central zone is dispersive and at least one zone has a collecting effect, so that the radial illuminance distribution in the image plane is as uniform as possible. 2. condenser lens according to claim 1, characterized in that that at least one zone is neither dispersing nor gathering. 3. condenser lens according to claim 1 or 2, characterized in that the slope in each point of the radial Lens profile "(Κ) according to the uniform brightness distribution is selected in the image plane (Pig. 4). 4. Condenser lens according to one of the claims, characterized, that the radial lens profile z (r) is composed as follows: 2 ζ = ar + Zq 0 ίτ r <; r _s r. ^ r ^r 1 » r = Radius, ζ = Axis coordinate, ♦ ^r S » ² O = constc 2 0/0126 5. Condenser lens according to one of the preceding claims, characterized in that the light source facing Lens surface is flat. 6. Condenser lens according to one of the preceding claims, characterized in that it is designed as a Fresnel lens is (Fig. 4). 7. Condenser lens according to one of the preceding claims for a work projector, in which immediately below the glass pane carrying the template a Fresnel lens is arranged characterized, that the outer radius (R) of the condenser lens (4) is chosen so that the outermost of the condenser lens is still covered Light beam (S6) in the outermost edge of the Fresnel lens (5) reaches directly below the glass pane (6) (Fig. 2). 809820/01 26