T 2303/10 – Only One Choice

This examination appeal deals with the correction of an error.

Claim 1 before the Board of appeal read (in English translation):

Objective lens having a housing (102; 202; 302; 402), an iris diaphragm (110; 210; 310; 410), and a plurality of lens groups (I, II, III, IV), wherein, for focusing said objective lens (100; 200; 300; 400) while minimizing a variation of an image angle, at least two lens groups (III/IV; II/III) are adapted to be moved relative to said housing (102; 202; 302; 402), one lens group (III; II) being arranged in front of said iris diaphragm (110; 210; 310; 410), and the second lens group (IV; III) being arranged at least partially behind said iris diaphragm (110; 210; 310; 410), characterized in that in the objective lens the condition

 f’(e) = f’(∞)/(1-f’(e)*β(e)/APF)

is fulfilled with a maximum deviation of less than 10%, wherein
f’(e) is the focal length of said objective lens when a distance e to an object is set;
f’(∞) is the focal length of said objective lens when a distance ∞ to an object is set;
β(e) is the imaging scale of said objective lens when a distance e to an object is set; and
APF is the distance between the exit pupil and the focal point. (my emphasis)

*** Translation of the German original ***

[2.1] Claim 1 on file is identical to claim 1 on which the decision was based. It is directed at an objective lens that fulfils the condition

f’(e) = f’(∞)/(1-f’(e)*β(e)/APF)

with a maximum deviation of less than 10%.

The original disclosure of said condition is found in claim 2 and on page 16 of the application as filed. There the function (Größe) β(e) is defined as “the imaging scale of said objective lens when a distance ∞ to an object is set”. During the examining proceedings the appellant has amended the original definition of the function β(e) in the description and in the claim such that β(e) is defined to be the imaging scale of said objective lens when a distance e to an object is set”. It has argued that this amendment is a correction within the meaning of R 139. The Examining Division (ED) has justified the refusal of the application by pointing out that the amendment of the definition of the imaging scale β(e) was not allowable within the meaning of R 139 and thus constituted a violation of A 123(2).

[2.2] It can be seen from the documents as filed that – in view of the fact that the function “f’(e)” is defined to be “the focal length of said objective lens when a distance e to an object is set” and the function “f’(∞)” is defined as “the focal length of said objective lens when a distance ∞ to an object is set” – the original definition of the function “β(e)” as “the imaging scale of said objective lens when a distance ∞ to an object is set” lacks consistency between the argument “e” of the function “β(e)” and the definition the latter as a function of the objet distance ∞. Thus, as the ED has correctly established in its decision, the original definition of the function β(e) is erroneous.

However, in regard of the correction of the obvious mistake, the ED in the impugned decision expressed the opinion that the skilled person would have had doubts whether in the original definition of the function β(e) “∞” had to be replaced by “e” or whether the function β(e) had to be replaced by β(∞) in the equation and in the definition of the function, so that the amendment was not allowable within the meaning of R 139.

However, the fact that the equation expressing the condition also uses the function “β(e)” and not “β(∞)” already pleads against a correction replacing “β(e)” by “β(∞)”. As the appellant has pointed out in its statement of grounds of appeal, the fact that the imaging scale β(e) of the objective lens is equal to zero when the object distance e = ∞ (as follows from the relationship β(e) = f’(e)/(e-f’(e)), which is well known to the skilled person of the relevant field) so that the equation of the claimed condition would be reduced to f’(e) = f’(∞), which clearly contrasts with the purpose of the invention and the claimed subject-matter, also pleads against such a correction. As a matter of fact, the claimed objective lens uses a movable lens group for focusing the objective lens and the claimed condition presupposes variable values of the focal length f’(e) of the objective lens as a function of the object distance. Moreover, […] the description discloses different values of both the imaging scale β(e) and the focal length f’(e) of the objective lens for each of the embodiments. It can be seen that these values are a characteristic feature (Kenngröße) of the objective lens for different object distances (and not, as assumed by the ED, a characteristic feature of the individual lens group of the objective) and represent a functionality depending on the object distance “e”.

Thus it is clear to the skilled person that a correction replacing “β(e)” by “β(∞)” in the claimed condition would be totally inconsistent with the disclosure of the application.

In contrast the second alternative mentioned by the ED, i.e. the correction of the definition of the function β(e) as the imaging scale of said objective lens when a distance e (rather than a distance ∞) to an object is set, is technically meaningful and completely in line with the disclosure of the application as filed.

Thus the skilled person of the relevant field (i.e. a skilled person working in the field of optical design, and in particular in the field of objective lens design) would directly and unambiguously realise that the original definition of the function β(e) is erroneous in regard of the object distance ∞ and that “β(e)” can only mean the imaging scale of the objective lens when a distance “e” to an object is set – in agreement with the notation that is usual in this field.

[2.3] The Board comes to the conclusion that the amendment criticised by the ED is an allowable correction of an obvious clerical error within the meaning of R 139 and that the amended [subject-matter] does not go beyond the subject-matter disclosed in the application as filed within the meaning of A 123(2) (G 3/89).

Should you wish to download the whole decision (in German), just click here.

The file wrapper can be found here.