Nov. 18, 2012:  A 20" f/3.0 and a 30" f/3.0 are born

20" f/3 JPAstrocraft telescopeIt was an uncharacteristically nice week in November when two fast telescopes recently came into the world - one, a visual instrument, the other, purely for imaging.  Amazingly, both made their debut during a string of clear nights in a month that can be notoriously cloudy here in central Illinois, somehow avoiding the "new telescope curse" or multiple weeks of cloudy weather.

First, let's start with an absolutely amazing 20" f/3.0 instrument, seen at right, custom-built by John Pratte of JPAstrocraft.

The mirror comes is from the same batch of 1.25"-thick Pyrex blanks that the mirror for my own 20" f/3 Starmaster came from.  I also figured the 5.0" m.a. flat elliptical secondary mirror.

The rest, as you see it here, was pure John Pratte.  He created a superb mirror cell with excellent edge support (which we tested in my shop with the nearly-spherical mirror), a fantastically stiff structure, beautiful woodwork, and numerous custom features.

You see, this is not a normal visual telescpe.  It is configurable for monocular viewing with a SIPS (Starlight Integrated Paracorr System), for binoviewing, and for using a Mallincam for "video astronomy".  Each application utilizes a different set of adapters to which the upper cage and truss poles attach.  This avoids any compromise in the structural integrity of the telescope.

I'm sure we'll hear more about this telescope after the finishing touches are done.

Bob Holmes' new 30" f/3 at the Astronomical Research InstituteNext, we take a short trip from JPAstrocraft out to the Astronomical Research Institute, where a new 30" telescope had first light in mid-November.

This telescope and tracking mount originally came to Bob as a 30" R-C telescope in need of work.

After it was picked up in New Mexico, the telescope drive electronics were not really usable, but the mechanical parts and optics were in working order.

New motors and a new drive system were procured and installed, and of course an observatory was built to house the new instrument.

First light with the Cassegrain telescope showed images, but they were fairly disappointing.  Stars were not as sharp as those imaged with Bob's 24" and 32" instruments.

After considerable frustration, Bob decided to convert the telescope to a prime-focus Newtonian.  In order to fit in the observatory, it would need to be f/3.0, and the telescope would need to be moved north within the building.  Bob took care of this by pouring new concrete piers to support the base of the telescope.

I was contracted to make the mirror, which was completed in November of 2012.  It was coated within a week, and by the next week it was in the telescope!

Bob certainly doesn't mess around when it comes to building instruments and getting them running.

It appears that the instrument is already a success - in its first few days of operation its wide field and excellent image quality allowed it to recover several "lost" NEOs, or NEOs that were not where they were expected to be based on a calculated orbit that was a bit off of the true orbit.  So, this is truly an instrument that fills a niche for Bob and his collaborators.

Below, the 30" f/3.0 is pictured as the sun sets before another night of data gathering.

The sun sets over the 30" f/3.0

Finally, we step inside the building that is right next to the observatory housing the 30", and we see a true monster.  This is the massive fork mount that will soon support the 50" f/4 instrument.  For those who speak metric, that's 1.3 meters.

I'll end this installment with this photo, and no doubt you'll hear more about it in the future.  Stay tuned.....

The massive fork mount of the 50" f/4

Please check back for future installements of "In the Shop".

Mike Lockwood
Lockwood Custom Optics

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