Yolo Telescopes

The Yolo telescope was invented by Art Leonard, and consists of a concave primary which is tilted to the incoming optical rays, and a concave secondary which is also tilted back across the light path to be focused at the rear of the telescope tube. The tilt of the primary is set to make the telescope unobstructed and the secondary is tilted to remove coma. To remove the remaining astigmatism, the secondary is deformed, either by a warping harness, or by polishing or in extreme cases grinding in the necessary correction.

I have been interested in tilted component telescopes for quite some time. I have had the opportunity to look through a number of schiefspieglers and trischiefspeigler telescopes, and have been well pleased with the high contrast views they give. I hope to embark on a project constructing one fairly soon.

Toward that end, I have written a simple C program based on the formulas that Jose Sasian gave in his Telescope Making article on Yolo design. You enter the sizes of the mirror blanks that you have for the primary and secondary, and it calculates the necessary separation, tilts and final focal ratio for the combined system.

I also have a copy of Jose Sasian's TCT program for tilted component telescope design. It is a bit obtuse sometimes, and locks up occasionally, but seems to work quite well. I can take designs that my program outputs and raytrace the optics to find the residual aberrations.

An example run of my C program produced this as output:

Aperature of Primary	6
Aperature of Secondary	4
Radius of Curvature of Primary	180
Radius of Curvature of Secondary	180
Desired field of view	0.5 degrees
Distance from Primary to Secondary	30.115898
Distance from Secondary to Image Plane	36.123213
Tilt of Primary	5.028260
Tilt of Secondary	4.242595
Secondary Alternate Focal Length	184.191745
Overall Focal Length	54.184819
Primary K-Factor	-4.160494

This design is corrected for spherical aberration, coma and astigmatism on axis. Later, I will try to analyze it for off axis aberrations as well.

This page Copyright 2001, Mark T. VandeWettering. Permission is granted to reproduce and distribute these files for non-profit, personal use.

Mark T. VandeWettering