This is the third web page I have made, it would be a good idea to read the first two before this page. The introduction and the refractor data entry pages cover some basics which I will not take as much time with here.
I want to make an OSLO lens file which starts off with a parabolic mirror. When this is completed I will add a second mirror to make a Cassegrain design. Let's start by making a New Lens.
This design only needs 1 surface, so enter 1 in the Number of surfaces box. Then click OK.
The Surface Data window will open. Enter the Entrance beam radius - I have entered 100mm as the semi diameter of the mirror. Then enter the Field angle, I have entered 0.5 degrees which is half of the full 1 degree field of view. Then it is best to enter a value into the THICKNESS box for surface 1, I have entered -1200mm. This is the distance to the next surface, which in this case would be the image surface.
Left click the gray box under GLASS, for surface 1 (AST) and click on Reflect, because this is a mirror.
Left click on the gray box under SPECIAL, move your mouse cursor over Plynomial Asphere, then left click on Conic/Toric.
This is the window which will open. Enter the conic constant, which is -1 for a parabola. Then click the green check mark in the upper left corner to accept this data. You may need to click this check mark twice, then this window will close.
Now you should see the Surface Data window again, which will show your paraboloidal mirror.
Left click the gray box under THICKNESS for surface 2 (IMS). You have a couple of choices here to find the focus. Since this is a reflector I have chosen On-axis (monochromatic). This may change the value in the THICKNESS column for the last surface.
Now you can save this file and give it a name. This is an 8" f/6 parabola.
ADD A DIAGONAL MIRROR
Now let's add a diagonal mirror at a 45 degree angle. I want to show you how to enter the data.
You can add another surface row by clicking on the gray box on the bottom left of the Surface Data window - it's identified as IMS. Now look in the upper right corner of the Surface Data window. There is a small icon which shows a small arrow pointing over a rectangular box. Click on this and you will add a new row. I want to have a total of 4 rows, so it will look like the image below.
I have also selected REFLECT under the glass type for surface 2.
Now click on the gray box under SPECIAL for surface 2, then click on Coordinates (C).
Enter 45 in the TLA Rotation Angles. Then click on the Tilt and bend box to select Yes. Accept these changes by clicking on the green check mark in the upper left corner.
Your Surface Data window should now look like this image below. And the drawing should look like this on the right when you click on the second icon, which looks like two small blue lenses. I will cover evaluation on a separate page.
This is the layout for a Cassegrain design. The conic constants are -1 for the primary, and -5.444 for the secondary mirror. Notice that I have entered a value in the IMS radius on the lower left corner. The optimum image surface is not flat, but has a radius of curvature of about -325mm.
This is the layout for a Maksutov Cassegrain design. This also has a curved image surface.
This is the Surface Data window for an eyepiece design which has been optimized for a 16" f/5 parabola. No real image if formed when an eyepiece is evaluated with an objective lens or mirror. The light coming out of the eyepiece is in parallel bundles. So, we will need to change the General Conditions to set this up for afocal evaluation. Click on the Gen box in the upper left corner, it's under the yellow "?" question mark.
Click on focal in the Evaluation mode, select Afocal. Then click on the green check mark in the upper left corner to accept this change.
I hope this page has been clear to explain how to enter data in OSLO. Obviously I have not shown how to enter ever kind of design. I will be happy to answer questions, and I hope that you will help me to improve this page if it is not clear.
Steve Fejes email@example.com