[Raytrace] Dall Null

[John D. Upton]

Tom,

     Sorry for the name confusion.

At 12:38 PM 9/4/2002 -0700, Robbin Palmer wrote:
>With regard to John’s suggestion of viewing a rectangular strip across
>the mirror to reduce wavefront error: The center point of the wavefront
>I get with the pinhole and lens off axis is a saddlepoint.  Moving in
>+/- x the slope decreases, +/-y the slope increases (depending on the
>direction you tilt).  The max in y is on the same order as the min in
>x.  So instead of placing the rectangle along x or y, it must be placed
>at an angle for the least wavefront error.  If the off axis error is on
>the order of 2 waves, then it can be brought down to a useful level
>using a rectangular strip of about 1” or less height. The strip reduces
>the error by a factor of ten or so ­ somewhat more of course for smaller
>heights. I feel like I have tried about everything.  Anything I have
>missed? Thanks for your help John.  OSLO is a wonderful tool to have.

     We may have set up the tilts a little differently.  Also, I assumed a 
4mm center thickness for the lens.  I didn't recall you specifying 
that.  It may make a small difference.  Here is the OSLO-LT file I ended up 
with.  It looks to me like the test is usable for this mirror but, again, 
you will need to visually ignore the very top and bottom of the astigmatic 
image.  For a 2" high mask, I get a null of about 1/10 wave on the 
wavefront (~0.95 Strehl) across the saddle without having to tilt the mask 
along a diagonal of the mirror.

OLSO-LT File:
======================
// OSLO 6.1 58827 49397  7379
LEN NEW "22 Inch F:4.5 Dall Null tilt 0.5" 386.36 4
EBR  18.0138770724419
ANG  0.0000572957795
DES  "OSLO"
UNI  1.0
// SRF 0
AIR
TH   157.8418700893456
AP  0.0001578418701
NXT  // SRF 1
GLA BK7
RD   156.4029023110757
TH   4.0
NXT  // SRF 2
AIR
TH   4784.2970976889228
NXT  // SRF 3
RFH
RD   -5029.1999999999989
PY   0.0
CC   -1.0
DT   1
TLA  0.5
APN  1
AY1 A -25.0
AY2 A 25.0
AX1 A -279.4
AX2 A 279.4
ATP A 2
AAC A 4
NXT  // SRF 4
AIR
TH   -0.5293006138251
WV 0.58756 0.48613 0.65627
WW 1.0 1.0 1.0
END  4
OPDF 1.0e-08
VAR NEW
V 1 0 0 TH 0.1 10000.0 1.0 0.0018013877072
END
OPE NEW
O 1 "OCM41" 1.0 ""
END
==============================

Sincerely,

John D. Upton
Georgetown, TX
<http://www.atm-workshop.com/>     "The ATM's Workshop"
<http://hometown.aol.com/RonWin20/> "Ronchi For Windows Home Page"