[Raytrace] where to start?
John D. Upton
jd-upton@texas.net
Sat, 08 Dec 2001 19:40:08 -0600
Tim, Joe,
This sounds okay to me. We don't seem to have had any takers yet, so
here is my attempt to start this process.
At 08:28 PM 12/7/2001 -0800, Tim Rickard wrote:
> > What say you, List? Can we do both effectively?
>
>My two cents: For now, we could standardize on OSLO LT, or some other
>program
>if it is generally preferred, to make things more manageable. As Ken
>suggested, we could start with a simple Newtonian, since presumably all of
>us are generally familiar with it. The goal would be to make sure everyone
>has the software and the newt. file working, and to begin exploring how to
>do various analyses (e.g. wavefront, vingetting effects of various aperture
>stops, spot diagrams, etc). Then a central obstruction could be modeled, and
At 07:43 AM 12/8/2001 -0600, Joe Mayenschein wrote:
>I like this idea.
>
>And if we actually work out a step by step an actually constructable
>scope. all
>the better. Like One i have been thinking of,,(he he he) but yet have been
>able to figure out how to get it into the $#%&!#* programs. he he he.
>
>It starts out as a simple 10" f- 6 Newtonian.
Here is the text prescription for the 10" F/6 Newtonian. The full
text of the OSLO-LT file appears at the bottom of this post. Cut the text
between the lines and paste it into a file named "newt_10_F6.len" to
reconstruct your own copy.
*LENS DATA
10" F/6.0 Newtonian
SRF RADIUS THICKNESS APERTURE RADIUS GLASS SPE NOTE
OBJ -- 1.0000e+20 1.0000e+14 AIR
AST -120.000000 -60.000000 S 5.000000 AS REFL_HATCH *
IMS -- -- 6.0000e-05 S
You can also just follow the steps below to create this file
yourself. I am using OSLO-LT version 6.1 for this example.
1. Open OSLO-LT.
2. Select File | New Lens...
3. For the file name type newt_10_F6.len
4. For number of surfaces, enter 1. The mirror is the only optical
surface in this example.
5. Select OK. The "Surface Data" window will open. Note that there are
three lines and multiple columns in the "spreadsheet". The first is
labeled OBJ for object, the second is labeled AST for aperture stop, and
the third is labeled IMS for image surface. Since there is only one
optical surface in this example, that is where the aperture stop must be
placed. If there were multiple surfaces, the aperture stop could appear on
any one of them and the others would have a number in the SRF label
column. The surface numbers would be in listed in the order that light
strikes them.
6. In the "Surface Data" Window, select the Gen button.
7. In the "General Conditions" Window, select the Units button and set to
inches.
8. In the "Lens:" field, enter a name for the design. I am using '10"
F/6.0 Newtonian' for my name. (This is actually a description of the
design, not a file name, so it can be almost anything you want. If you
want, you can enter even more notes by pressing the "Notes" button and
entering your extra data.)
9. Click on the green check mark in the upper left corner. This always
accepts the data and can be used to close the window.
10. In the "Surface Data" window, click in the "Ent beam radius"
field. Enter the value of the entrance beam radius. This will be the
radius of the mirror for this example. Enter 5.0 or you can use the built
in formula capability by typing 10.0/2.0 (or 10/2). Press the enter key or
click on green check mark. (If you happen to click twice, the "Surface
Data" window will close. Open it again by selecting Lens | Update lens data...
11. Click in the RADIUS field of the AST line. Enter the radius of
curvature of the mirror. Remember the data entry conventions presented in
an earlier post. Since light starts out moving left to right, the concave
mirror will have its center of curvature to the left of the mirror
itself. This means that the ROC must be entered as a negative
number. Again, I will just use the formula capability to enter the ROC of
the 10" F/6 mirror. I type -10*6*2 and press enter.
12. Now I have to tell OSLO that this surface is a mirror. I select the
button in the GLASS column of line AST and choose Reflect (hatch). We now
have a spherical mirror described in the spreadsheet. Save this
intermediate result by selecting File | Save.
13. To tell OSLO this is a paraboloidal mirror for a Newtonian, we need to
specify its conic constant. Click on the button in the SPECIAL column of
the AST line. Select Polynomial Asphere | Conic / Tonic. In the "Conic /
Tonic Data" window, enter -1.0 in the Conic constant entry field. Close
the Conic / Tonic window by clicking the green check mark.
14. Finally, let's let OSLO find the focal length of the mirror for
us. Click on the button in the THICKNESS column of the AST line. Select
the Solves | Axial ray height... item. In the "Axial Ray Height" box that
pops up, enter 0 and select OK. We just told OSLO we wanted it to find the
place where the ray has an axial height of 0 -- in other words where is
crosses the optical axis. That marks the paraxial focal point.
We are done. Save the file. You now should have a file that is the
same as what I have appended in text form below. If you select the "Len"
button in the OSLO "TW 1" text window, it should print the same human
readable lens prescription that I included at the top of this note. Study
its format. It actually contains almost all of the data pertaining to this
design. The only thing missing is the conic constant for the mirror. That
can be included also by clicking the Spe button in the "TW 1" text window.
The contents of this window may be copied and pasted into any text
application -- like this post.
Cut this and paste into a new notepad file named "newt_10_F6.len".
===CUT BELOW THIS LINE===========================
// OSLO 6.1 41540 0 0
LEN NEW "10\" F/6.0 Newtonian" -60 2
EBR 5.0
ANG 0.0000572957795
DES "OSLO"
UNI 25.4
// SRF 0
AIR
TH 1.0e+20
AP 9.9999999995e+13
NXT // SRF 1
RFH
RD -120.0
PY 0.0
CC -1.0
NXT // SRF 2
AIR
WV 0.58756 0.48613 0.65627
WW 1.0 1.0 1.0
END 2
===CUT ABOVE THIS LINE===========================
Let me know if I have messed up this description. Doing a "tutorial"
like this real time, I often don't recognize mistakes since it is still too
fresh in my mind.
John D. Upton
Georgetown, TX
<http://www.atm-workshop.com/> "The ATM's Workshop"
<http://members.aol.com/RonWin20/> "Ronchi For Windows Home Page"