Vista Diablo Observatory with 10 inch Yolo Telescope

Vista Diablo Observatory

“Vista Diablo Observatory”, was built by Jack Borde in 1962. He named it because of the view it has near Mount Diablo, California. Under the 16 foot dome, sits the largest working Yolo telescope in the country, (since the dismantling of Arthur Leonard’s 12 inch Yolo at Colfax). This telescope is still in fine working order, 44 years later!
The 10 inch yolo is in the dome to the right. The roll off roof houses an 8″ celestron. To the right of that is his wood shed and grandchildren playhouse over head.

Jack Borde at the observing position of the Vista Diablo Observatory 10 inch Yolo telescope

This 10 inch F15 Yolo is of the classic Leonard design. The 10 inch primary mirror has a spherical figure with a radius of curvature of 40 feet. The 8 inch secondary mirror also has a spherical figure, with a radius of curvature of 40 feet, and is mechanically bent into a toroid shape to remove astigmatism.

Secondary mirror mounting of the Vista Diablo Observatory 10 inch Yolo telescope

The secondary mount:
The secondary tension adjustment is made while observing at the eyepiece by turning an adjustment rod that runs the length of the telescope. The warping tension on the glass is about 35 pounds.

The reason this works so well is because the bar shaped tension pads, that push on the secondary mirror, are well outside the illuminated area of the glass. They are located near the edge of the 8 inch glass. The secondary is then apertured to a diameter of 6.5 inches. This central area forms an excellent toroid shape with no “spiking” effects seen around star images.

The secondary mirror also has a worm gear in its mount to tweek its rotational axis.
The entire telescope weighs about 600 pounds.

The two photos are the same device taken from both sides.

Front end of Vista Diablo Observatory 10 inch Yolo telescope with baffle tube and secondary mirror removed

Looking from front end of telescope at 10″ primary with the secondary mirror removed.

A disconnected adjustment rod and turnbuckle can be seen in front of the 10 inch primary.

Notice the system of baffles to elliminate stray light.

Jack Borde at the observingg end of the Vista Diablo Observatory 10 inch Yolo telescope showing the focuser and large Erfle eyepiece

Seen here is Jack’s 20 pound Erfle eyepiece mounted on a 4 inch focuser. This particular eyepiece gives a wide field of ½ degree. Stars appear as “Hot Diamonds”. Three distinct colors are noticed in the Orion nebula. Jack has also shown many visitors the ninth planet Pluto and many Mars oppositions with his telescope.

Jack Borde in the instrument calibration lab at the University of California

Here Jack is seen in the instrument calibration lab at the University of California.