An Imaging Platform is Born

In the spring of 2017 an anonymous donor (hereafter called 'AD') came forward with an offer to fund what was needed to make the Minnesota Astronomical Society's dark sky site at Cherry Grove a high-end imaging site. Basically the AD was volunteering to fund the purchasing of a new imaging platform. The money would come with a few strings:

• The platform would make use of an existing underutilized mount in the observatory. This mount was a Mathis MI-500, a huge mount capable of carrying 180 pounds of imaging gear. The mount is already outfitted with an Astro-Physics GTOCP4 control box and handset.
• The platform must be easy for beginning imagers to use.
• Purchased telescopes must to be able to fit under the roof. The purchase of large refractors like those installed at the club's other two sites was discouraged along with truss-tube scopes.
• A person or people need to be found who will maintain the platform
• Adequate training must be provided for those wishing to use the platform

Existing Facility

Cherry Grove Observatory (CGO) is a large roll-off roof building located in Goodhue county, Minnesota, about 23 miles northwest of Rochester and 20 miles south of Cannon Falls. While it's not a truly dark site (light green zone), it's far darker than the other club observatories. Horizon glow from the metro area of Minneapolis/St. Paul 60 miles to the north can be seen, as is a growing glow of light in the southeast from Rochester.

Cherry Grove. Warming house at left, observatory on right

The Process

The task of choosing gear for the Imaging Platform was passed to the small committee that oversees CGO. None of the committee members are imagers, and they thought it best to form a task force of imagers to make recommendations for what to purchase. That's when I entered the story.

Recruiting task force members went reasonably well for something like this. Some people agreed to help, others said they weren't really qualified or had other obligations. Five volunteers were quickly selected and I was designated the chairperson, probably because I had advanced some ideas for what might be done in an earlier request for help from the CGO committee.

The early going was hindered by a lack of any idea for what the AD was willing to spend. We quickly settled on a two-tier recommendation for what might be possible at around $10K and $20K.

Guiding Thoughts

Beginners will be using it, many with DSLRs but a few with CCDs or newer cooled CMOS cameras. Astrographs for which no flatteners are needed are simple and convenient. Beginners wouldn't have to be concerned about having the correct spacing rings.

What will people want to image? Probably the objects that image well from dark sites: Diffuse and dark nebulae, but not solar system objects. That suggests a telescope with short focal length and fast optics.


Many objects are small. After diffuse nebulae likely targets will be planetary nebulae, globular clusters, and external galaxies. The way to image them is with a longer focal length scope. Since these tend to have higher surface brightness than many diffuse nebulae optical speed is less of an issue.

Beginners will bring a wide variety of learning skills. Some will be happy to learn how to use software to control the mount and camera while others may be reluctant to use more than the mount's hand control. We should try to accommodate as many people as is reasonable.

Given all of these factors we decided to go with a platform that would provide two imaging astrographs in tandem-one short focal length, the other much longer for those tiny planetaries and galaxies.

As we looked over the available scopes it became clear we the low cost option of about $10K was unrealistic. In fact given the cost of all the accessories, shipping and taxes the higher tier of $20K would be inadequate, too! After a talk with the AD it was decided to go with a budget of between $30K and $35K.

At that point we were ready with our recommendation: A Takahashi FSQ-130ED as the short, fast scope and a Planewave 12.5" CDK. Along with the Tak we decided to get the 0.6X focal reducer and 1.6X tele-extender to provide three focal lengths: 390mm, 650mm, and 1040mm.

Current Status

The club's Board signed off on the purchase and we placed our order with Oceanside Telescopes.

The Tak has arrived and is on the mount for testing. So far it's living up to the Tak reputation: Exceptional optics and build quality. It's a great scope!

Takahashi FSQ-130ED on the Mathis mount (to be remounted when the Planewave arrives)

The Planewave is scheduled to arrive in July.

We hope to have the platform fully functional by autumn -- if this year's run of cloudy nights will ever relent!  I'll post images taken using the platform as they are created.