Re: [ATM] Luri-Houghton prescriptions.

["vladimir" <svla@isp.com>]

Rutten/Venrooij TDesign came up with this 350mm f/4.59 system:

R1/3: +/- 2578.45mm
R2/4: -/+ 6690.87mm
thickness 1/2: 16.98/8.75mm
spacing: 3.81mm
corrector-to-primary: 1400mm
R5: -3200mm

Center spot is somewhat over 4um, but that's the paraxial
focus. Slight refocusing to best focus location has the spot
reduced to little over 2um, and the circle of least confusion 
is just over 1um. This is roughly 1/40 wave p-v
of spherical aberration level (overcorrection). It could be
further reduced by slight tweaking (this is a non-optimized
design), but it isn't worth it.

Some coma can be noticed, but it's inconsequential - it is
astigmatism that determines blur size/shape farther off-axis,
where it matters. Image curvature is relatively weak, 
but does require slight refocusing 
(4-5um away from the primary) for nearly
round off-axis spot size. That would result in little over
3um center spot, and still only ~7um at 16mm off-axis.

Vlad

----- Original Message ----- 
From: "Bob May" <bobmay@nethere.com>
To: <atm@atmlist.net>
Sent: Wednesday, October 12, 2005 7:52 PM
Subject: [ATM] Luri-Houghton prescriptions.


> I've been playing with the Lurie-Houghton prescription on the two
> lenses and seem to find that the equal radius pairs of curves
> doesn't seem to do the best job.  The equal radius curves seem to
> do some inverse coma along with more astigmatism than doing
> different radius curves for each surface.
> What I've come up with is the following set of curves for the
> typically specified lens set:
> Object
> 0 12.5
> Refraction
> BK7 0 -96.3
> Refraction
> Air -0.81 275.9
> Refraction
> BK7 -0.96 96.3
> Refraction
> Air 1.457 -275.9
> Mirror
> -61. 119 0 13
> FocalPlane
> -1.69403
> WAVELENGTH
> 0.643 0.54 0.486
> while a much better result is:
> Object
> 0 12.5
> Refraction
> BK7 0 -107.09
> Refraction
> Air -0.745 201.726
> Refraction
> BK7 -0.78739 94.3063
> Refraction
> Air -1.27146 -271.735
> Mirror
> -61 119 0 13
> FocalPlane
> -1.57512
> WAVELENGTH
> 0.486 0.54 0.582
> ANGLE
> 0 0.0066 0.01
> FOV
> 0.0005
> the format is in Dave Rowe's TRACE program where the first number
> is the distance and the second is the ROC of the surface.
> The first data set gives a spot size of 0.00024" in diameter
> while the second gives a spot size of 0.00012" in diameter.  The
> images of the spots on the first show that the off-axis spot has
> a bit of inverse coma and the size of the spot is about twice the
> size of the second set of spot diagrams where the way off-axis
> spot shows a nice oval which indicates only astigmatism.
> Any comments?  I've got a guy that is about to build the scope
> and I'd want to make sure that he builds the best possible.
> Bob May
> bobmay at nethere.com
> http: slash /nav.to slash bobmay
> http: slash /bobmay dot astronomy.net
> Addresses have been munged up to keep spammers from bothering me.
> replace the obvious words with the proper character.
> Thank you for your understanding!
> 
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