DE950411C - Three-part enlarging lens - Google Patents

Description

ISSUED OCTOBER 11, 1956

A 20868IX142 h

The subject of the invention is a magnifying lens which consists of three members, of which each of the two outer members is a cemented member of positive refractive power composed of a converging and a dispersing part, which contains a converging cemented surface raised against the lens interior, while the inner member is a biconcave single lens whose more curved hollow surface r ₅ faces the negative plane and has a radius of curvature whose value is between 0.4 and 0.6 times the absolute value of the radius of curvature of the less curved hollow surface r _{4 of} this lens.

The triplet and tessar type lenses have hitherto been the preferred magnifying lenses, which, however, only provides a relatively good and constant image quality for a low magnification range and were only corrected for a narrow spectral range. However, they are sufficient the increased and sometimes different requirements, such as those placed on the image quality of modern times Magnifying lenses need to be provided, no more.

The invention therefore seeks to provide magnifying lenses whose image quality is so improved that the modern recording

objective achieved gain in image sharpness also in the enlargement, over the entire enlargement range is retained and in which the error correction is based on an expanded spectral range (about 350 to 720 πιμ) extends. The expansion the correction to the thus expanded spectral range should, on the one hand, make it possible to use the high Actinity especially of cold light sources containing strong UV components for black and white enlargements to take advantage of; it is, on the other hand, necessary in view of the fact that - as opposed to the material used for black and white enlargements - that used for color enlargements is additionally sensitized up to about 720 ΐημ.

This goal can be achieved in the case of the lenses of the construction described above, if according to the invention the length of the lens

is at least 15% larger than the opening diameter corresponding to the largest lens diaphragm (P ₁ on the outer surface of the lens facing the positive plane and at the same time both the diffusing parts of both cemented elements and the biconcave individual lens consist of glasses n ₂ , K ₃ , M ₄ whose refractive index for yellow light (587.6 ΐημ) is at most 1.58 and is at least 0.04 smaller than the refractive index of the glasses used for the collecting parts of both cemented elements and if the v-value of the glass is biconcave single lens (v _a ) is at least 48 and is at most 10 smaller than the arithmetic mean of the v- values of the glasses for the individual parts of both cemented links

^v i + "2 +" 4 + "5

By simultaneously fulfilling these conditions, a magnifying lens has been made available in which the error correction is carried out so far and evenly that the image performance, that the lens has at full aperture is hardly increased by stopping down. That applies to all standard scales for enlargers. This exquisite image performance is what makes the spherical correction as well as the correction in the lateral parts of the image, can be attributed to that even if you do without high-refractive index, sometimes very expensive glasses, you can use the prescribed Measures the proportions of the individual lenses in the total refractive power of the lens like this let determine that both the partial area coefficients for the aperture error are proportionate become small as well as a remarkably small Petzval sum is reached.

In order to reduce the additional decrease in brightness caused by the relatively large overall length of the lenses according to the present invention and, moreover, to ensure a high degree of uniformity in the illumination, the lens diameters of the two outer members are enlarged beyond the effective opening diameter. For this reason, it is advisable to keep the mean thickness for the collecting parts of both cemented links d _lt d ₅ greater than 6% of the focal length f of the lens.

It is within the scope of the invention for the rules given above to be the same for taking lenses To apply the basic structure.

The lens example given below has the features according to the claims. It is specified for a focal length f - r, oo and an aperture ratio ι: 4.5. The radii are with r, the mean thicknesses the. Lenses with d, the air gaps with I, the refractive indices of the glasses with n, their Abbe number with ν . The refractive indices refer to a wavelength of 587.6 ΐημ. All components are numbered consecutively, in the direction of the negative plane (film plane).

H = +0.311830

d _x = 0.071570 M ₁ = 1.62041 V ₁ - 60.3 r ₂ = -0.583253

d ₂ = 0.020399 ^W 2 = 1.56138 «2 = 45.3 's = + 5.512448

I ₁ = 0.047679 "5

u = - 0.539667

d ₃ = 0.011064 M ₃ = 1.54041% = 50.9 ^ = +0.256505

_{,, o} J ₂ = 0.074436
r ₆ = -6.136018

dt = 0.011064 ⁿ i = 1.52310 Vi = 50.9 r ₇ = + 0.256505

d ₅ = 0.065383 M ₅ = 1.62041 D ₅ = 60.3 »'s = -0.425729

The drawing shows the section through a lens according to the example given, for a focal length f = 200 mm.

Claims (3)

PATENT CLAIMS: i. A magnifying lens consisting of three members, each of the two outer members being a cement of positive refractive power composed of a converging and a diffusing part, which contains a converging cement surface raised towards the inside of the lens, while the inner member is a biconcave single lens The more strongly curved hollow surface (r ₅ ) faces the negative plane and has a radius of curvature which is between 0.4 and 0.6 times the absolute value of the radius of curvature of the less curved hollow surface (| r ₄ |) of this lens, characterized in that the Overall length of the lens is at least 15% larger than the opening diameter corresponding to the largest lens aperture {Φ ^} on the outer surface of the lens facing the positive plane and both the diffusing parts of both cemented elements and the biconcave individual lens are made of glasses (m ₂ , m ₃ , « ₄ ) whose refractive index for yellow light (587.6 ΐημ) is at most 1.58 and is at least 0.04 smaller than the refractive index of the glasses used for the collecting parts of both cemented elements, and the j »value of the glass the biconcave single lens (v ₈ ) is at least 48 and is at most 10 smaller than the arithmetic mean of the v-values of the glasses for the individual parts of both cemented elements (Vl + Vj + Vi + vA 2. Lens according to claim 1, characterized in that the mean thickness of the collecting parts of both cemented members (^ ₁ , d _s ) is greater than 6% of the lens focal length (f). 3. Lens according to claim 1 and 2, characterized by the data in the description specified embodiment. For this purpose ι sheet of drawings © 509 704/158 4.56 (609 644 10.56)