From tom@clark.phys.nwu.edu Wed Jul 16 13:46 CDT 1997 Return-Path:----- End Included Message -----Received: from relay.acns.nwu.edu by belmont.astro.nwu.edu. (SMI-8.6/SMI-SVR4) id NAA00245; Wed, 16 Jul 1997 13:46:55 -0500 Received: from clark.phys.nwu.edu (clark.phys.nwu.edu [129.105.151.58]) by relay.acns.nwu.edu with SMTP (8.7.6/8.7.1) id OAA24507 for ; Wed, 16 Jul 1997 14:00:23 -0500 (CDT) Received: by clark.phys.nwu.edu (4.1/SMI-4.1) id AA09254; Wed, 16 Jul 97 14:17:23 CDT Date: Wed, 16 Jul 97 14:17:23 CDT From: tom@clark.phys.nwu.edu (Tom Renbarger) Message-Id: <9707161917.AA09254@clark.phys.nwu.edu> To: novak@relay.acns.nwu.edu Subject: Re: optics Cc: jdotson@belmont.astro.nwu.edu Content-Type: text Content-Length: 3761 Status: R Giles, Jessie: Spoke with Ron Kappler after lunch. Should be able to make the change with no problems, but it will make the total price go up a little. Here is the updated version of the optics table for the webpage. ----- Begin Included Message ----- A revised table for the SPARO lenses. Viper Telescope F/3.5 (but see discussion below) Plate Scale = 2.35 arcmin/mm S0 = 43.7" (distance between image of primary and focal plane) Physical Lengths S1 = 5.25" (distance from focal plane to pupil, "a" in Jessie's notes) S2 = 5.25" (distance from pupil to array, "b" in Jessie's notes) Lenses Field Lens (quartz, n = 2.1075) f = 4.69" R = 5.19" (plano-convex) physical diameter = 1.00" open diameter = approx. 0.75" central thickness = 0.12" edge thickness = 0.10" We have three lenses of f = 4.65", which could be used as backups in a pinch. Pupil Lens (quartz, n = 2.1075) f = 2.625" R = 5.82" (convex-convex) physical diameter = 1.75" open diameter = 1.65" central thickness = 0.23" edge thickness = 0.10" We have two f = 2.53" lenses, not really good enough even as backups. Array Lens (quartz, n = 2.1075) f = 5.25" R = 5.81" (plano-convex) physical diameter = 0.75" open diameter = 0.50" central thickness = 0.11" edge thickness = 0.10" We have two f = 5.25" lenses, so we're OK although lacking any backups. Beam Size (assumes we have the proper plate scale) Beam Size = (Plate Scale)*(Winston cone aperture)*(magnification) = (2.35'/mm)*(3.05 mm)*(1) = 7 arcmin. Assumptions: The image of the primary on Viper is at the chopper. -True X-vertex and Z-vertex in Jessie's notes correspond to the point where the central ray hits a given optical element on Viper. -Also true The array will have a diagonal length of the Winston cone aperture (3.05 mm) times a geometrical factor of 2*sqrt(2) + 1, assuming a 3 by 3 array with adjacent cones touching. This length turns out to be about 0.47". The array lens was therefore specified to have a 0.75" diameter for relative ease of mounting at the lowest possible price. -Taken into account with the 0.5" open diameter of the array lens The spacing between array and pupil was determined for a 1.5" pupil diameter at F/3.5. A pupil lens diameter of 1.75" was chosen to give a slightly over- sized pupil even after mounting to optimize throughput. -Unless you've had a change of heart, this still stands, locking into place the values of S1 and S2, which in turn determines f for the pupil lens. The trouble with the illumination of the primary has evolved into the issue of the possible discrepancy between Viper's plate scale and its effective focal length. The focal length listed for Viper is 1.0m, while the inverse of the plate scale is 1.5m. This affects us in terms of the amount of the primary we ultimately illuminate. For our F/3.5 dewar, the effective diameter of the primary is either 30cm or 45cm. Furthermore, the effective F/# of Viper is not affected by the change in the effective focal length. Given the primary diameter of 2.0m, Viper is either an F/0.5 or F/0.75 telescope; faster than the dewar in either case. Since we are now calculating the effective diameter of the primary by D = f(effective)/3.5, Viper defaults to acting as an F/3.5 dish when SPARO looks through it. -I think this is right, but maybe I'm playing a little loose with what the F/ratio is. At any rate, still no update about this discrepancy, although it does not affect the lenses we should order. The price of two field lenses plus two pupil lenses will be around $2100, again with the 4-5 week lead time. -Price will be a little more than $2100, 5 week lead time Tom