SDM#071 – 22″ f/3.8

Owner: Rod Stubbings of Tetoora Road Observatory in Victoria
Primary: 22″ x 1.6″ thick. A fabulous mirror made by James Mulherin of OMI
Secondary Mirror: 5.5″
Known As: “Infinity”
Extras: ServoCATNexus with built in GPS and WiFi

The Story Unfolds
Q: Tell me, who is the owner of this new scope?
A: Rod Stubbings. He is a variable star observer. Not a casual observer but a man with a passion for variable stars. It’s taken him 22 years but he has just completed 250,000 logged observations and has completely worn out his old 16″ Meade.  He wanted a new scope – something easy to use that would take him deeper. So Rod asked me (Peter Read of SDM telescopes) if I could build him a new scope to fit in his new observatory.

Q: The first thing I notice is the colour. Have you ever made a scope like this before?
A: You noticed…. it is red and it is striking! It’s a two pack Mirotone polyurethane called “Cosmic Fire”. This is a unique colour for a unique scope for a unique observer.

Q: The other very noticeable thing about the scope is the very deep mirror box and the two UTA’s…. can you tell us about that?
A: One of the design criteria was that the scope must be able to see over the dome wall down to 20 degrees with the full unobstructed mirror….. BUT the scope had to be ladder free (or very nearly) when pointed to the zenith.

The big challenge was the observatory wall… is 49″ tall (over 1200mm).

This was going to be difficult. The only solution was to make the mirror box as deep as possible thus creating a very high pivot point and have an extra-long intercept distance (distance from secondary to focus) and then to balance the scope by adding as much weight as needed to the top end. It struck me to build a second UTA with extra finder boards to solve the lack of weight in the top end and it has the added benefit  of acting as a light shield and dew shield.

Q: Normally a 22″ f/3.8 would have an eyepiece height at zenith of 6’8″ What is the eyepiece height of “Infinity”?
A: By sinking the scopes’ groundboard below floor level and having an oversize secondary we have managed to get the eyepiece height at zenith down to 5’9″

Q: How does it perform?

Here’s what Rod had to say on its first light.

“First light for me last night was under a near full Moon and I recorded a 15.4 magnitude pin point star! The Moon was Simply stunning! Peter Nelson came around and we were both floored with the image of the Moon. Never in 22 years have I seen it so sharp. Peter said he wants one! We put it up to almost 400X and the image was still great. Can’t wait to see what it can do under a dark sky”.


” Will keep you informed when the Moon goes and I get a dark sky. Even did a few variables last night, I’m almost getting lost with the deeper field!”

And finally:

“Well my first dark night observing and I can tell you I observed 17.3 mag. stars! The scope fits like a glove, love it. Now I have to learn all my fields again for the deeper comparison stars!”

…that’s pretty amazing.