AP-900 Equatorial Mount


After working with the Atlas for a few years, it was time to move up. The Atlas was a great mount for the price in my opinion, but I really wanted something a little more solid, and eventually capable of moving to heavier scopes and longer focal length setups.

I considered a number of mounts, but eventually decided on an AP-900 from Astro-Physics. A big part of my decision process was availability, which is always questionable in this hobby! I was lucky in that a production run had just completed and some of the units had not been ordered. The mount is delivered in multiple boxes, packed exceptionally well, and arrived in January of 2011.

AP900 and Atlas EQ-G Comparison

The AP900 next to my original Orion Atlas EQ-G

As is customary with new equipment, rain arrived with the mount, so comparison photos are inside my house. The AP-900 is a significant step up from the Atlas, immediately obvious from a side by side photo. This became more and more obvious through the assembly process.

This photo was taken with the AP-900 on the Astro-Physics pier with 32″ rise. As I am entirely into photography, I chose a relatively short pier to keep things close to the ground, I was not worried about eyepiece placement.

While quite beefy, the mount is still relatively easy to transport. The RA and DEC axes come apart by simply unscrewing two thumbscrews and lifting the DEC from the RA. There are features on the face of the RA axis that make it foolproof to align the two pieces and engage them correctly. Astro-Physics recommends a small bit of oil be applied to the surfaces to prevent any seizure if they are together for a long time. I simply applied a little 3-in-1 to a paper towel and rubbed this on. Only a very small layer is required and protects the aluminum from potential seizure. This is probably never an issue with temporary (frequently disassembled) applications.

AP-900 Axes

The AP-900 with the RA and DEC axes disconnected.

I did not order any polar scope solutions. My thinking was that for photography I really needed a better polar alignment than a scope could provide, so save the money. I currently use PEMPro from CCDWare for polar alignment, and I cannot recommend it enough. I simply use a compass for rough alignment north, and a angle/level to set the latitude roughly (only necessary when I travel). That gets it close enough for PEMPro.

I did however choose to order the Rotating Pier Adapter, and would recommend it. Basically it allows you to secure the mount to the pier and use only the AZ adjuster knobs to tweak polar alignment. This prevents having to loosen the mount itself as the entire RPA plate rotates with it. This resulted in frustration with the Atlas because I found I had to loosen the mount to freely adjust AZ, and more “tinkering” just meant more error and slop in final alignment.

AP-900 RPA

AP-900 Rotating Pier Adapter

In the image at right you can see the RPA. The thumbscrews secure the mount to the surface of the RPA, and the AZ adjuster knobs push against the stud near the front of the image. The stud is fixed to the level below, and the top surface is free to rotate. I’ve never used the mount without it, but can say it makes the AZ adjustment very fluid and smooth.

If you have any questions I’d be happy to talk about the mount, email me or leave a comment!

And finally, the AP-900 carrying my Orion 8″ Newtoian, and other bits and pieces…

Orion 8" Newtonian on AP900

My Orion 8" Newtonian on an AP900

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