OPINION

The matter is here on the appeal of Donald W. Norwood, plaintiff below, from a judgment holding claims 1 through 4, 6, 7 and 9 of his U.S. Patent No. 3,304,435 (the “435” patent) invalid and not infringed by defendants’ accused device. 322 F.Supp. 898 (C.D.Cal. 1970). We conclude that the trial court’s decision was correct on both grounds.

The “435” patent was granted plaintiff on February 14, 1967, pursuant to an application filed July 18, 1963. It covers a “photometric device having greater response to a preferential central portion of a scene.” In common parlance, the device is a meter (for use principally in photography) employing a photoelectric cell to measure the intensity of light reflected from objects; its particular feature is its fabrication to “indicate an intermediate value between the average brightness of the preferential central smaller portion of [a] scene and the average brightness of the remaining larger portion of [that] scene.” “435” patent, claim 9, col. 10, lines 16-20.

Emphasis on the central portion of the scene, which normally contains the object or objects of interest to the photographer, is achieved by interposing a filter having an aperture at its center between the photoelectric cell and the viewing lens [see FIGURE IA]

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The size of the aperture at the center of the filter (or the central surface area of the photoelectric cell which is more light receptive than the peripheral surface area of that photocell) is fabricated to correspond to the ratio which the object of interest in a scene generally bears to the whole. By reason of the differing intensities of light passing through the filter and aperture (or reaching the desensitized periphery and more responsive central portion of the surface of the photocell), the “reading” of the light reflected from the scene is weighted toward the intensity of light reflected from the object of interest.

*6Defendants are sales representatives for the American corporation which imports the Nikon F Photomic, the Nikon Photomic FTN, and the Nikkormat FTN cameras from their Japanese manufacturer. The accused device contained in these cameras sold in the United States by defendants is a light metering system structurally different from the devices described in the “485” patent. In the accused system, light from the scene sought to be photographed passes through a taking lens, strikes a mirror (which retracts during an exposure . to permit the light to reach the film), and forms an image of the scene at a focusing screen. Light from the focusing screen image is thereafter transmitted through a pentaprism and eyepiece lens to the eye of the photographer using the camera. Such light is simultaneously transmitted through the pentaprism to two aspherical lenses, each of which forms an image at a field stop (a diaphragm or masking device) positioned between that aspherical lens and one of two corresponding small photoelectric cells. As found by the district court, a “center-weighted response is obtained by positioning the aspherical lenses, field stops, and photocells so that they receive light from portions of the focusing screen image which partially overlap at its center.” Hence the integrated “reading” of the two “cross-eyed” photocells emphasizes the intensity of light at the center of the focusing screen image. See FIGURE II.

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*8We fully agree with the district court’s determination that claims 1-4, 6, 7 and 9 of the “435” patent1 are invalid for obviousness.2 In the leading case of Graham v. John Deere Co., 383 U.S. 1, 86 S.Ct. 684, 15 L.Ed.2d 545 (1966), the Supreme Court indicated that the issue of “obviousness” should be resolved by the district court’s conducting factual inquiries respecting (1) the scope and content of the prior art, (2) the differences between the prior art and the disputed claim or claims, and (3) the level of ordinary skill in the pertinent art. 383 U.S. at 17, 86 S.Ct. 684. See also Anderson’s-Black Rock, Inc. v. Pavement Salvage Co., 396 U.S. 57, 62, 90 S.Ct. 305, 24 L.Ed.2d 258 (1969); Alcor Aviation, Inc. v. Radair Incorporated, 527 F.2d 113, 115 (9th Cir. 1975).

Here the district court’s opinion, see 322 F.Supp. at 902-903, and its extensive findings of fact manifest its consideration of these factors.3 The court correctly found that plaintiff’s broad construction of his claims so as “to make them read upon the optical systems of defendants’ accused devices” causes them “to the same extent [to] read upon the prior art Elwood Densitometer and Light Meter . . . [and] the prior art Nelson patent No. 3,060,823.” Moreover, the court properly determined that other prior art patents, including the Rath patent No. 2,444,674, the Stimson *9patent No. 3,232,192, and plaintiff Nor-wood’s own earlier patent No. 3,121,170 (the “170” patent), all of which in some fashion employ the concept of “center-weighting” or “differential response,” demonstrate that the concept was well known in the art relating to light meters long before plaintiff’s purported invention of the subject matter of the “435” patent. Finally, the court correctly concluded that the device of the “435” patent is merely a structural improvement over the device of plaintiff’s earlier “170” patent.

*8“A patent may not be obtained though the invention is not identically disclosed or described as set forth in section 102 of this title, if the differences between the subject matter sought to be patented and the prior art are such that the subject matter as a whole would have been obvious at the time the invention was made to a person having ordinary skill in the art to which said subject matter pertains.”

*9In this connection, we note that the statutory presumption of nonobviousness,4 here heavily relied on by plaintiff, is substantially dissipated where there is a showing that the patent examiner failed to consider the prior art. See Alcor Aviation, supra, 527 F.2d at 15; Hewlett-Packard Company v. Tel-Design, Inc., 460 F.2d 625, 628 (9th Cir. 1972). And here the record is clear that the patent examiner, in awarding plaintiff his “435” patent, neither cited nor considered the prior art devices of Elwood, Nelson, Rath, Lange and Stimson.

In sum, we can only conclude that the district court’s determination—that the subject matter of plaintiff’s “435” claims would, at the time his asserted “invention” was made, have been obvious to a person having ordinary skill in the pertinent art—was wholly correct.

We similarly agree with the district court’s determination that none of the disputed “435” claims are infringed by defendants’ accused devices. Plaintiff’s essential position on infringement, taken at trial and maintained here, is that defendants’ focusing screens, some of which have “optical apertures” at their centers,5 permit the formation of a focusing screen image with a greater intensity of light at the “optical aperture” and hence create a “centerweighted” effect in the same manner as plaintiff’s “435” devices. The district court correctly rejected this contention, and so do we. Defendants, who style the “optical aperture” at the center of some of their focusing screens a mere visual aid in focusing, presented substantial expert testimony that there is no significant difference between the light transmissivity of the accused A-type focusing screen and the non-accused (because it has no aperture) D-type focusing screen. Defendants’ expert further testified that substantially identical photographic results were obtained by the accused cameras under identical photographic conditions using, alternatively, the accused A-type screen, the non-accused D-type screen, and no screen at all.

In addition, the district court correctly relied on the doctrine of file wrapper estoppel in rejecting plaintiff’s contention that the accused optical system infringes any of his “435” claims. When the patent examiner rejected a number of plaintiff’s original “435” claims on the ground of double patenting because those claims could be read to include “the plural photocell arrangement” described in plaintiff’s earlier “170” patent, plaintiff cancelled certain claims and amended all of the remaining “435” claims in the application so as to limit those claims to a device which entails “a single lens structure” (claim 2) or “a single means” (claim 7) “for forming a single image of a scene” and to “a single means responsive to the light of [the] image and operable to vary an electrical signal in accordance with [its] brightness.” The accused system, however, comprises three lens structures and two photocells. It is well settled that a claim in a patent must be interpreted *10with reference to claims which have been rejected, and allowed claims cannot be read to cover that which has been eliminated from the patent by the inventor’s own limiting amendments. See Exhibit Supply Co. v. Ace Patents Corporation, 315 U.S. 126, 136-137, 62 S.Ct. 513, 86 L.Ed. 736 (1942); Oregon Saw Chain Corporation v. McCulloch Motors Corporation, 323 F.2d 758, 768-769 (9th Cir. 1963), cert. denied, 377 U.S. 915, 84 S.Ct. 1180, 12 L.Ed.2d 186 (1964). Hence plaintiff is estopped from urging a sufficiently broad construction of his claims to cover defendants’ accused, devices.

On the record before us, we are unable to say that the district court’s findings of non-infringement are clearly erroneous.

Affirmed.