Multilayer solar filter reducing distortive diffraction

• US 3,897,140 A
• Filed: 06/14/1974
• Issued: 07/29/1975
• Est. Priority Date: 12/22/1972
• Status: Expired due to Term

• Current Assignee: Roger W. Tuthill
• Original Assignee: Roger W. Tuthill
• Inventors: Tuthill, Roger W.
• Primary Examiner(s): Stern, Ronald J.
• Application Number:
  US05/479,508
• Time in Patent Office: 410 Days
• Field of Search: 350/1,164,166,314,171 117/33.3,71R 161/1,4,408,183,214,216,220
• US Class Current: 359/888
• CPC Class Codes: B29D 11/00634 Production of filters
• CPC Class Codes: B32B 2255/10 on synthetic resin layer or on natural or synthetic rubber layer
• CPC Class Codes: B32B 2255/205 Metallic coating
• CPC Class Codes: B32B 2367/00 Polyesters, e.g. PET, i.e. polyethylene terephthalate
• CPC Class Codes: B32B 2551/00 Optical elements
• CPC Class Codes: B32B 27/08 of synthetic resin
• CPC Class Codes: B32B 27/36 comprising polyesters
• CPC Class Codes: G02B 5/205 Neutral density filters
• CPC Class Codes: Y10T 428/24322 Composite web or sheet

Abstract

A filter for blocking out harmful solar radiation for direct viewing or for photographic purposes employs a plurality of flexible, transparent resin film layers which are coated with metal to achieve optical clarity and to effectively shield the user from most of the sun'"'"''"'"'s energy while allowing enough light to pass through the filter. The total thickness of the resin material is not more than approximately 0.002 inch, and the total thickness of the metal on the film layers provides an opaqueness to allow passage of approximately 0.01 percent sunlight.

Claims

1. A solar filter for an astronomical optical instrument, the solar filter consisting essentially of a plurality of flexible, transparent resin film layers each having a metal coating, the metal coated film layers overlying each other, the film layers having a total thickness not more than approximately 0.002 inch and the metal coatings having a total thickness to provide an opaqueness to allow passage of approximately 0.01 percent sunlight, each of the film layers being of a thinness so that there are pinholes therein, whereby the possibility of a pinhole in one film layer being aligned with a pinhole in another film layer is minimized thus reducing the distortive diffraction effect of said pinholes.

2. A solar filter according to claim 1 wherein the film layers each have a thickness of approximately 0.00035 inch.

3. A solar filter according to claim 2 wherein each of the film layers is a polyethylene terephthalate.

4. A solar filter according to claim 1 wherein the metal coatings are of aluminum.

5. A solar filter according to claim 4 wherein the aluminum coatings provide a resistance of approximately 0.4 to 0.9 ohm per square unit.

6. A solar filter according to claim 1 wherein the plurality of film layers comprises two film layers each having a coating on one side only.

7. A solar filter according to claim 6 wherein each metal coating is aluminum having a resistance of approximately 0.8 to 1.8 ohm per square unit.

8. A solar filter according to claim 7 wherein the film layers each have a thickness of approximately 0.00035 inch.

9. A solar filter according to claim 8 wherein each of the film layers is a polyethylene terephthalate.

10. A solar filter for an astronomical optical instrument, the solar filter consisting essentially of a plurality of flexible, transparent resin film layers each having an aluminum coating on one side only, the aluminum coated film layers overlying each other, the film layers having a total thickness not more than approximately 0.002 inch, and the aluminum coatings having a resistance of approximately 0.4 to 0.9 ohm per square unit, each of the film layers being of a thinness so that there are pinholes therein, whereby the possibility of a pinhole in one film layer being aligned with a pinhole in another film layer is minimized thus reducing the distortive diffraction effect of said pinholes.

11. A solar filter according to claim 10 wherein there are two aluminum coated resin film layers, and wherein the coating on each layer has a resistance of approximately 0.8 to 1.8 ohm per square unit.

12. A solar filter according to claim 11 wherein each of the film layers is a polyethylene terephthalate.

13. A solar filter according to claim 12 wherein the film layers each have a thickness of approximately 0.00035 inch.