[Raytrace] TCT (Tilted Component Telescope) designs
Michael Peck
mpeck1@ix.netcom.com
Sun, 20 Jan 2002 11:29:36 -0600
At 19:22 1/17/2002 -0500, JulesFran@aol.com wrote:
>Hello list,
>
>I'm new to this list and have a few questions:
>
>Has anyone modeled a four mirror TCT design with OSLO Lt? I would like to use
>this as a starting point to evaluate a few designs I have been playing with.
>Up til now I've been using David Stevick's software which is wonderfully
>simple to use but doesn't have the horsepower I need to go to the next level.
I hate to say this, but good luck. I've tried exactly one TCT design,
namely the "Stevick-Paul" which consists of 3 mirrors plus a flat. I saw no
obvious way to turn Stevick's specifications for tilts into an OSLO
prescription. What I ended up doing was sitting down with paper and
calculator and working out tilts by hand, with some additional trial and
error experimentation. I think I also used some OSLO optimization to work
out the tilt of the focal plane. I ended up not even trying to produce a
buildable design. All I was really interested in was comparing the
theoretical performance of the TCT to an axially symmetric version.
The "Stevick-Paul" is kind of an interesting design. The axially symmetric
version of this was discovered by Maurice Paul - optically it is equivalent
to an all-reflective Schmidt, with the only third order aberration being
field curvature. Stevick mentions that his version is actually
axisymmetric, but it's almost impossible to tell that from either his
specification or an OSLO version. It turns out though that what he is doing
is rotating the two spherical elements around their respective centers of
curvature to catch off-axis light from the primary. The reason it works so
well at moderate focal ratios is because residual higher order aberrations
are small, so correction is good even several degrees off-axis.
There's a guy who's been on and off the ATM list a few times who likes to
evangelize for this design. Bob May likes it too. Personally I think it's
the only TCT that might possibly be worth building, but then I'm pretty
ignorant of these things.
Anyway, here is the text description -
******
*LENS DATA
No name
SRF RADIUS THICKNESS APERTURE RADIUS GLASS SPE NOTE
OBJ -- 1.0000e+20 1.7455e+18 AIR
AST -4.7000e+03 -1.4100e+03 100.000000 AS REFLECT *
2 -1.8800e+03 1.8800e+03 64.611642 S REFLECT *
3 -1.8800e+03 -940.000000 S 146.650447 S REFLECT *
4 -- -- 41.019403 S AIR
IMS -2.3500e+03 -- 41.019403 S *
*CONIC AND POLYNOMIAL ASPHERIC DATA
SRF CC AD AE AF AG
1 -1.000000 -- -- -- --
*TILT/DECENTER DATA
1 DT 1 DCX -- DCY -- DCZ --
TLA 3.050000 TLB -- TLC --
2 DT 1 DCX -- DCY -75.022000 DCZ --
BEN TLA -2.287000 TLB -- TLC --
3 DT 1 DCX -- DCY -100.030000 DCZ --
BEN TLA -5.337000 TLB -- TLC --
5 DT 1 DCX -- DCY -34.581954 DCZ --
TLA 12.585325 TLB -- TLC --
****
and the oslo file:
****Stevick-Paul.len****
// OSLO 5.40 61115 9635 23731
LEN NEW "No name" -2350 5
EBR 100.0
ANG 1.0
DES "OSLO"
UNI 1.0
// SRF 0
AIR
TH 1.0e+20
AP 1.7455064928e+18
NXT // SRF 1
RFL
RD -4700.0
TH -1410.0
CC -1.0
DT 1
TLA 3.05
NXT // SRF 2
RFL
RD -1880.0
TH 1880.0
DT 1
DCY -75.022
TLA -2.287
BEN
NXT // SRF 3
RFL
RD -1880.0
PY 0.0
DT 1
DCY -100.03
TLA -5.337
BEN
NXT // SRF 4
AIR
NXT // SRF 5
AIR
RD -2350.0
DT 1
DCY -34.581954245978
TLA 12.5853253995054
CBK 1
WV 0.58756 0.48613 0.65627
WW 1.0 1.0 1.0
END 5
DLNR 2 3
DLMN 2 -1.0
DLMX 2 1.0
SDSA On
OPDF 3.7920964
OPOC "*oprays"
VAR NEW
V 1 5 0 DCY 0.0 0.0 1.0 1.0e-07
V 2 5 0 TLA 0.0 0.0 1.0 1.0e-07
END
OPE NEW
O 1 "OCM12" 1.0 ""
O 2 "OCM15" 1.0 ""
O 3 "OCM25" 1.0 ""
O 4 "OCM28" 1.0 ""
END
****end****
_________________
Michael Peck
email mpeck1@ix.netcom.com
Wildlife photography page http://home.netcom.com/~mpeck1/index.html
Amateur telescope making http://home.netcom.com/~mpeck1/astro/astro.html