Astro-Physics 1100 GTO mount
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This mount came to replace my trusty 900GTO after 10 years of flawless service.
This successful new version offers many innovations and cleverness for increased performances in terms of tracking accuracy, rigidity, strength, load capacity and ergonomy.
Its extremely low ripple and smoothly variant PE makes deep sky imaging with long exposure times trouble free, and the mount is virtually "invisible" so you can concentrate on other tasks.
The new RAPAS polarscope delivers also outstanding performances for quick and easy polar alignment.
The major differences lie in the mount itself. The axis have been redesigned: large diameter hollow axis (allowing internal cable management) directly fitted on the worm wheels (that are now identical), oversized preloaded bearings strategically located, new clutch system, powerful motors, redesigned worm gear, gearbox and motor housing assembly, new worm mesh adjustment system, improved ergonomics, combine everything and you get a mount lighter than the 900GTO with a 50kg telescope load capacity!
Beside its load capacity, it is very lightweight thanks to the CNC machining techniques, and its compact design. More, it comes apart in two separate elements without tool!
It's extremely rigid, which is very important in high resolution deep-sky imaging with a long instrument with moment-arm or a side by side configuration.
It carries easily the 155 f7 StarFire EDF refractor with its finderscope, mounting rings, two mounting plates, a heavy CCD camera with field flattener or telecompressor and eventually other accessories.
I decided to fit it on a Losmandy HD tripod, using the LT2APM and 119FSA adapters. The overall rigidity is not impaired and levelling is easy on eneven terrains.
Tracking and pointing accuracy are impressive. With an instrument like the refractor, the object is always centered onto the CCD chip, even after a meridian flip. By the way, the big advantage of this mount is its ability to point and track up to 6h before or after the meridian without having to flip the mount, without any tracking performance degradation.
The periodic error is extremely low, between 2.7 to 3.0 arc sec peak to peak, without any error correction applied. With PEM error correction enabled, PE is reduced to a mere 1 arc sec.
The other big advantage is the smoothness of the curve, allowing long autoguiding times for those having filters in front of the guider, up to 20 seconds, without noticing any tracking deterioration.
Mount's control doesn't need a computer , this is precious when a computer failure occurs in the field.
Several features like focusing, reticle, can be ajusted with the keypad.

Technically and aesthetically, this mount will undoubtly fulfill the avid astrophotographer or visual observer.

Again a perfect product from Astro-Physics!!!

The Astro-Physics 1100 GTO mount in action

"The single most important item for the imager is the mount. next comes the mount. Then comes the mount.... Get the picture?"
Roland Christen
Texte et images non utilisables sans demande préalable


Guided tour:

Overall view on the left, all cables removed.
Like the other mounts of the range, the black knobs are used for tightening or various adjustments, like clutches, elevation or azimuth.
The silver knobs are used to secure elements that can be separated without other tools.




















Final result with factory PEM enabled.
1.04 arc sec peak to peak. What more?






















Histogram (also called Spectrum) is very important. It shows any tiny defect in the drive system.
Except the first order, which is the gear worm sine, the highest harmonic is only 0.2" which is almost negligeable.




















Here is the averaged curve for 7 cycles, 3 arc sec peak to peak, very low and smoothly variant, with no ripple.
Such a smooth curve is easy to correct with PEM and can be obtained only with a high quality gearbox that prevents harmonics, which are crippling for deep-sky imaging as well as planetary imaging with modern high speed cameras.


















Here are the results on the sky for 7 successive cycles, note the perfect repeatability of the curve, the low amplitude, and how they overlap perfectly.





















Periodic error measurements:

With the advent of the new CP3 controller, a few years ago, the periodic error measurement done at Astro-Physics during the final steps of the mount control could be stored into the control box and a PEM curve generated and directly  programmed into the electronics. The user just has to turn it "on" with the keypad to get a value close to "nothing".
PemPro software included with the mount allows direct reading at any time of the PE curve stored into the memory of the CP3.
Here is the result for my mount, 2.70 arc sec peak to peak "out of the box", without any PE correction, with an ultra smooth curve.
Now it's time for actual measurements on the night sky.












3. Measurement of the altitude drift using PemPro after 15 minutes...no noticeable drift again...better not to adjust further!










2. Measurement of the azimuth drift using PemPro after 15 minutes...no really noticeable drift, with no noticeable direction.










Performances in actual conditions under the sky:

1. Performance of the RAPAS polarscope.

Polar alignment is performed using the Astro-Physics driver or using the Android or IOS Apps.







The CP3 control pannel:
it is actually the "brain" of the mount. It  centralizes connectivity, it has strong and reliable connectors, with all the stuff you need to control your mount using a computer.
It is now mounted vertically to protect it from humidity. It's immediately removable using a dovetail.





















Another hatch is located on the west side of the declination axis, for internal cable management of the declination motor or absolute encoders cables when necessary.
























Two cables channels are located at the top of the declination axis.
The access is immediate from the top without tools.

























The new RAPAS polarscope is directly mounted into the mount's axis using a captive thumbscrews / locating pin combination.
Once calibrated on the mount using push-pull screws, the adjustement is definitive, since it is done on the mount's plate itself.
It can be removed and attached again without losing alignment, so it can be used with several mounts.
Magnification is 8x, field is 6 degres and its accuracy is unrivalled. See below for more details.
Small hatches located below the RAPAS allow internal cables management, without obstructing the view into the polarscope.

















The azimuth adjustment (black engraved knob) has been moved to the rear of the mount for ergonomic purposes. It is micrometric and backlash free, and it's now embedded into the mount's assembly.
The integrated rotating adapter is also now part of the mount's base, and provides smooth movement regardless the telescope load.
The set screws allow fine adjustement of the friction of the rotating adapter.
The mount is easily fitted on a Losmandy HD tripod using the LT2APM and 119FSA adapters. Everything is bolted and rock solid.











The latitude adjustement is made with a large captain's wheel knob, the major adjustments are made by moving the bar into a serie of predefined slots, from 0 to 78 degrees, which can come down instantly to 0 for a quick and compact storage during transport.























The mount is fitted with a precision bubble level, which  is used for polar alignment and to help overall levelling in the field.
Two removable post-knobs are located on each side of the base to hang securely the mount's keypad.