Re: [ATM] Luri-Houghton prescriptions.

[Guy Brandenburg <gfbrandenburg@yahoo.com>]

Are your units in millimeters or inches or what?
What is the meaning of the pair of numbers after each
material? The second one looks like the ROC, but what
is the first one? THickness? 

By the way, if you have to make 4 separate curves with
4 separate radii, then the LH becomes much less
attractive to make than otherwise, because it becomes
extremely difficult to test all of those odd convex
surfaces. The reason Nagesh and I decided to do our LH
with only 2 radii is that the convex surface is
relatively easy to test against a matching concave
surface via the magic of monochromatic light
interference lines.

We already knew that it does improve the optics a bit
if you don't constrain the radii to be the same. But
all the same, we aint' gonna do it.

Guy
Guy

--- Bob May <bobmay@nethere.com> wrote:

> 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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> 


Guy  Brandenburg
Washington, DC
My home page:
http://home.earthlink.net/~gfbranden/GFB_Home_Page.html
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