Designing a Yolo example: Let's imagine that you would like to design a 10 inch Yolo. You want a focal ratio of F11.  (Remember that the difficulty to build one increases as that focal length gets shorter.) You want a hyperbolic primary and a toroid secondary. You also would like the length from secondary to focus to be 20 inches longer than the mirror spacing, as you plan to buy one of those bino-viewer attachments and need the extra length. Start by opening the Yolo Calculator Spreadsheet and the Winspot program side by side on the computer screen.

Select the worksheet titled "Yolo_Toric_Sec"

Enter 10 for the diameter.  Now for a little trial and error, enter values for the radii.  To make the F-ratio lower, try lower values for the radii.  Usually, both mirrors have about the same radius of curvature value.  Here the value 340 was just about right.

Try entering values for surface1 separation in order to arrive at a value that is about 20 less than The Surface2 separation value.  This will extend the focus out for that bino-viewer you want to get.

Changing the separation now has changed the F-ratio to F10.  To get the F-ratio higher, go back and increase the radii values.  Then adjust the separation value again.  You will find that changing one parameter, effects a few others.  Now the values are close to our original goal.

Now to enter this initial design in Winspot.  Select File>New.

Enter 2 for mirror count. Click OK.

Enter the first row of values from the spreadsheet into Winspot.  Click OK.

Enter the second row of values from the spreadsheet into Winspot.  Check if toroid, must be checked.  The separation value for surface 2 need not be entered.  Winspot recalculates this.  Click OK.

Focal plane parameters, just click OK.

Now enter aperture and 0.25 for the semi-field.  This value is used for the spot plot, showing the focus at the edge of the field.

Now Winspot shows you a diagram of the telescope.  Click the focus button, will calculate the separation value for surface 2.  From the diagram now it is obvious that the secondary mirror is In the incoming light path.  Now, start increasing the surface1 tilt and watch the diagram.

Here it looks like a tilt angle of 4.6 is just enough for the secondary mirror to clear the light path.

Now go back to the spreadsheet and enter this new value for the surface1 tilt.  The spreadsheet now has new values that must be transferred over to Winspot.

Here we have the final design!

Select Plot>Standard Plot to see the spot plot of how the telescope will perform.

Here is the spot plot of our design.  Click the Airy! Button and see the size of the Airy disc.  The goal here is to have the spots within the circle.  The center of the field is excellent.  The spots at the outer edge show some coma and astigmatism.  However, in order to see that out at 0.25 degrees from center, you would be using a very low power eyepiece and that problem would be hardly noticeable.