From Wed Jun  4 11:07 CDT 1997
Received: from by 
	id LAA01767; Wed, 4 Jun 1997 11:07:42 -0500
Received: from ( []) by with SMTP (8.7.6/8.7.1) id LAA08666 for 
; Wed, 4 Jun 1997 11:19:59 -0500 (CDT)
Received: by (4.1/SMI-4.1)
	id AA08885; Wed, 4 Jun 97 11:36:05 CDT
Date: Wed, 4 Jun 97 11:36:05 CDT
From: (Tom Renbarger)
Message-Id: <>
Subject: Re: SPARO optics
Content-Type: text
Content-Length: 2353
Status: RO

Jessie, Giles:

Here are the preliminary results for the new set of SPARO lenses.

Viper Telescope (assumes we illuminate a diameter of 70 cm on the primary)

	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)


	Field Lens (quartz, n = 2.1075)
		f = 4.69"
		R = 5.19" (plano-convex)
	 diameter = 0.75"
	thickness = 0.10"

We have three lenses of f = 4.65", which could be used as backups in a 

	Pupil Lens (quartz, n = 2.1075)
		f = 2.625"
		R = 5.81" (convex-convex) 
	 diameter = 1.75"
	thickness = 0.18"

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)
	 diameter = 0.75"
	thickness = 0.10"

We have two f = 5.25" lenses, so we're OK although lacking any backups.

Beam Size (assumes we illuminate 70 cm diameter on Viper primary)

	Beam Size = (Plate Scale)*(entrance aperture of Winston cones)
		  = 7 arcmin.


The image of the primary on Viper is at the chopper.

X-vertex and Z-vertex in Jessie's notes correspond to the point where the
central ray hits a given optical element on Viper.

The array will have a diagonal length of the Winston cone aperture (3.05 
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 
lens was therefore specified to have a 0.75" diameter for relative ease of
mounting at the lowest possible price.

The spacing between array and pupil was determined for a 1.5" pupil 
at F/3.5.  A pupil lens diameter of 1.75" was chosen to give a slightly 
sized pupil even after mounting to optimize throughput.

The one assumption I could not verify was whether we actually would 
70 cm on the Viper primary.  I would certainly agree that IF we illuminate 
cm on the primary THEN the beam size would be 7 arcmin.  However, I lack 
the information or the know-how to verify this.

See how this looks to you, and we can talk about it next week.  By the 
the prices for one field lens and one pupil lens would be about $1100 with 
four week lead time.