Re: [ATM] additional lurie-houghton degrees of freedom

["Ukyo Chen" <ukyochen888@hotmail.com>]

Obviously that one Guy mentioned is not optimized yet. I played in OSLO for 1 min and get below which is much better now:
 
 SRF      RADIUS      THICKNESS   APERTURE RADIUS       GLASS  SPE  NOTE OBJ       --        1.0000e+20    1.0472e+18             AIR     
 AST    68.616629 V    0.700000      3.750000 A          BAK4 C     2   -307.036429 V    0.100000      3.740757 S           AIR     
  3    -68.616629 P    0.400000      3.737986 S          BAK4 C     4    307.036429 P   36.000000      3.738855 S           AIR     
  5    -80.000000    -39.932232 S    4.112132 S    REFL_HATCH     
PS: I do not recommend to use BAK4 as it is more (23.5%) heavy than BK7, below data is captured from OSLO:
BAK4: dens=3.10; trans=0.989; cost=1.40;BK7:   dens=2.51; trans=0.991; cost=1.00;
Best Regards,
Ukyo Chen



> From: vla@toast.net> To: atm@atmlist.net> Date: Sun, 17 Sep 2006 10:40:16 -0400> Subject: Re: [ATM] additional lurie-houghton degrees of freedom> > >  Guy Brandenburg wrote:> > >I was just doing some playing around with OSLO and >my 8" f/5 > >Lurie-Houghton design. I found that you have >to keep surface # 1 and > >surface #2 very, very close to >each other; if they are one inch apart, the > >spot diagrams >go downhill pretty fast. But if R2 and R4 are as much as >5 > >inches different, there seems to be essentiall no change >in the spot > >diagrams AFAICT.> > The two lens elements of the Houghton corrector> need to have near identical power (f.l.) of opposite> signs in order to keep secondary spectrum near cancelled.> Any changes in the radii that causes increase in the power> disparity between the two elements will increase secondary> spectrum. And if the change in  radii result in a nearly> similar change in power for the two elements, the amount> of secondary spectrum also won't change appreciably.> > Similarly, the sum of spherical aberration of the two> elements needs to nearly cancel that of the mirror. The> most significant element determining the amount of> aberration of the single lens element is its focal length> (the aberration changes with the third power of it).> If the radii change causes the two element powers to go> in opposite directions, the effect will bi much more obvious> than in the scenario where it causes both elements power> change in the same direction (sign), and in the similar amount> (this applies to spherochromatism as well).> > Interestingly, the R/V raytrace gives less than optimum s.a.> correction for the design (about 1/5 wave over-correction).> Their T-design gives zero s.a. radii (absolute values) as> R1,3=67.42" and R2,4=175.96" (which agrees with the>  formulae: http://www.telescope-optics.net/Houghton.htm ).> Lens thickness is about half of yours (probably too thin),> but it doesn't affect spherical correction.> > Btw, if the corrector radius is 3.75", isn't it a 7.5" f/5.3 system?> > Vlad> > _______________________________________________> ATM mailing list http://www.atmlist.net/
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