DE7635394U1 - 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 aioeix projectors, and magnification devices to increase the luminous efficacy 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

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

The previously known condenser lenses for .work or "Overhead" projectors that are used to track the spoken word Word of a lecturer by projecting text written at the same time by the lecturer, e.g. B. formulas, to support visually, but cannot satisfy, since they do not have a uniform illumination of the image field or illuminance distribution (brightness distribution) on the projection screen (in the image plane). Namely, all parts of the projected Template be recognizable 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. with slide projectors bring a certain more even illumination with them, cannot be used with work projectors, because

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

Long focal length aspherical condensers also do not bring any noticeable improvement in the illumination, because its surface is similar to that of a spherical condenser because of the long focal length.

In order to still achieve a more uniform image illumination, special work projectors have already become known (see brochure "Proki 1004") »which only achieve an illumination of approx. 70 % , ie the illuminance at the edge of the projection screen is 70 % of the illuminance in the center 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 disruptive 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 Fresnel lens, the light must come from the light source via an expensive mirror that adjusts precisely

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must be, coming from a first chamber to the

£ · Fresnel lens can be steered in the second chamber.

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

c) In addition, existing newer work projectors cannot be retrofitted to a two-chamber system.

In contrast, it is the object of the invention to provide a condenser lens which, despite a relatively simple construction a very uniform image field illumination or illuminance distribution allowed, which can be even higher than with two-chamber work projectors, and even in existing ones Projectors, especially single-chamber work projectors, to improve the illumination instead of the existing ones Condenser lens can be installed.

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 divergent effect or possibly none at all Affects the beam path.

So 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

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

If the condenser lens is formed so that the side facing the light source holds the scattering effect in the center , the light source can be brought closer to the lens than with the previously used condenser lenses and at the same time the collecting effect on the condenser lens edge can be increased. Thus, the solid angle (st in Fig. 2) that the condenser lens detects in relation to the light source (3 in Fig. 2) is enlarged and thus the detected useful luminous flux is 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 optimize the condenser lens in an advantageous embodiment of the invention that is complicated in a work project Adjusting the distribution of the illuminance on the projection screen is the teaching of claim 3 expedient. Because the complicated distribution of the (relative) illuminance is the sum of several influences and is similar for most work projectors (Fig. 3), it is to optimally compensate for this illuminance distribution just advantageous to provide the radial lens profile with rotationally symmetrical zones that collect the light more or less strongly depending on the radius. So it can z. B. happen that the radial Lens profile of the condenser lens has several turning points "

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The condenser line according to the invention can be designed as a FreeneX line (also called step or ring line).

The invention is explained in more detail on the basis of the drawing

Flg. 1 the basic structure of a self-contained | known working projector with the only schematically indicated condenser lens according to the invention ;

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 shows a known work projector, light is emitted 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 contains an original to be projected (not shown ) carries, projected onto a projection head 7 and from there onto a projection screen (not shown).

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

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radial lens profile consists of two parabolic sections b · stands, wlt di · to & ftade formally indicates t

z · ar + Z _n 0 «sr ss r _Q

ζ. a -rlar (a? - ^) ² + (»" + ap-p,.) p _fl «r ^ R

. Rf / T \ A _n XOXrJO .., i X ' _e

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r «radius,
ζ = axis coordinates a, r _s , r _4> 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 _s also have the same z-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. After the light rays have left the condenser lens 4, they arrive into the Fresnel lens 5 and from there via 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 linear radius R is the same as that previously

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Consensor lenses used, since the invented " load sensor lens" can then be exchanged for he? kö "Blloh condenser lenses without further ado *

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

In order to compensate for this irregular illumination of the projection image, according to Flg. 4 the slope of the generators K of the condenser lens as a function of the 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 strongly converging 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.

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Claims (7)

I t KU Il it it t «·» II for ^r f • · »II III III · Il Expectations 1 · Condenser lens for work projectors with different developed rotationally symmetrical zones, d'a d u r ο h characterized in that the central zone is dispersive and at least one zone acts collectively, so that the radial illuminance distribution in the image! level is as uniform as possible 2. Condenser lens naoh 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 that the slope in each point of the radial lens profile (K) corresponds to the uniform brightness s distribution in the image plane is selected (Fig. 4). 4. condenser lens according to one of the preceding claims, characterized, that the radial lens profile z (r) is composed as follows: ζ = ar ² + Z ₀ 0 6 rsr _g (rr ^ ² + (z _o + ar _s r.,) r _g «: r ^ R S 1 ^mii; r = radius, ζ = axis coordinate, a, r _g , T ₁ , R, Zq = const. 7635394 07/28/77 III I • I> ■ Il <I. I III t I I > I I - 10 - 5. Condenser lens according to one of the preceding Aaeprüche, characterized in that the lens surface facing the light source is flat. 6. Condenser lens according to one of the preceding preparations, characterized in that it is designed as a Fresnel lens (Pig. 4). 7. Condenser lens according to one of the preceding claims for a work projector with a Fresnel lens directly below the glass pane carrying the templates arranged 1st, 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) reaches the outermost edge of the Fresnel lens (5) immediately below the glass pane (6) (Fig. 2). 7635394 28.U7.77