Abstract In certain astronomical applications, it is desirable to photograph (or otherwise observe) a celestial body (e.g., spectroheliograms of the sun) at a very narrow spectral bandwidth (i.e., substantially monochromatically). It is proposed to modify an otherwise conventional astronomical telescope so as to allow the simultaneous photographing (or other recording) of, for example, the sun at a plurality of different extremely very narrow wave bands (i.e., discrete, substantially monochromatic spectroheliograms). This may be accomplished by providing a series (say, four) of discrete apertures at the entrance end of an otherwise conventional telescope; and means at the image or exit end of the telescope for separately forming an image from each of the four separate entrance beams. By providing different narrow band-pass filters (or other means for rendering each of the beams monochromatic at a different wavelength), a simultaneous photograph (or other measurement) of the sun at different spectral lines may be made. Comparison of such simultaneous photographs can yield information concerning relative intensity of spectral lines from any part of the sun, free from uncertainty due to, for example, the fluctuating intensity with time of the source (e.g., the sun) itself. Preferably the entrance apertures are provided with moderately broad-pass reflecting filters for rejecting (i.e., reflecting away) most of the radiant energy outside of the vicinity at which each of the separate spectral measurements are being made.
A spectrographic apparatus according to claim 1, in which: each said first filter means is of such construction as to reflect substantially all of the undesired radiation outside of its respective moderately narrow spectral band-pass; whereby said first filter means reject all such undesired outside radiation without substantial absorption and the attendant heating problems.
Claim 2
Dependent Claim
28 words
A spectrographic apparatus according to claim 2, in which: each said first filter means is of the induced transmission type having at least one very thin metallic layer.
Claim 3
Dependent Claim
59 words
A spectrographic apparatus according to claim 1, in which: said means for rendering each of said separate beams substantially monochromatic comprises a plurality of second filter means; each said second filter means being of such construction as to pass only an extremely narrow spectral interval within the moderately narrow spectral band of the first filter means optically associated therewith.
Claim 4
Dependent Claim
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A spectrographic apparatus according to claim 4, in which: each said second filter means comprises an interference filter of the type comprising a plurality of extremely thin alternate layers of two different dielectric materials.
Claim 5
Dependent Claim
89 words
A spectrographic apparatus according to claim 1, in which: a field lens means is positioned at least in the vicinity of the original solar image formed by said telescopic optical system; said field lens means being of such dioptric power and such relative position as to form a conjugate image of said first filter means substantially onto the entrance pupil of said reimaging means; whereby separation of each of said separate substantially monochromatic beams is more completely obtained, and the field angle requirements of said reimaging system substantially reduced.
Claim 6
Dependent Claim
60 words
A spectrographic apparatus according to claim 1, in which: said recording meanS comprises at least separate portions of at least one photographic material; whereby a permanent record is obtained of the manner in which the various parts of the sun, corresponding to the parts of the solar image formed, emit radiation in each of the extremely narrow spectral intervals photographed.