CATSEYETM 2" Autocollimators

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ATTENTION Imagers with Newtonian ASTROGRAPHS:
The Extended-barrel XLKP'S are now available!
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Newtonian astrograph users can now confidently take autocollimator focuser-axis alignment to the next level of precision WITHOUT THE NEED FOR A FOCUSER DRAWTUBE EXTENSION!

Extended-barrel INFINITY XLKP Family
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By design, Newtonian astrographs incorporate a "back-focus" position of the primary's native focal plane to facilitate image focus at the camera CCD chip. To negate collimation visual queue parallax error, an autocollimator's mirror surface must be at or near the position of the Primary's native focal plane. Heretofore to compensate, imagers stacked an appropriate-length extension tube under their autocollimator to satisfy this constraint. Unfortunately, the increased focuser-axis skew potential of an additional mechanical section in the optical train is counter to collimation precision and has long been a common nemisis complaint.

Enter the solution! CATSEYE is pleased to introduce the INFINITYTMXLKP autocollimator in 4 barrel extension lengths: 1.0 ", 1.5", 2.0", and 2.5". Additionally, all autocollimators are now enhanced with flat-black anodized barrels and identified with a handsome laser-engraved logo/Model graphic.

Which Extended-Body Length Do I need?

Collimation using CATSEYETM tools is always done WITHOUT a corrector/reducer component in the optical path. To acertain the appropriate Extended-Body autollimator length to use, the Primary's native focal plane location (prime focus) relative to the focuser must be determined. This can readily be accomplished by first racking the focuser all the way down and then aiming the telecsope at the moon or distant terrestrial object. Place a translucent screen (example: waxed or parchment paper) above the focuser and move the screen up or down until the image is in focus. Measure the mm distance from the screen to the lip of the focuser drawtube (or 2" adapter). Use the chart in the diagram below to determine the extended-body length to use.

Focal Plane Distance Diagram
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For Extended-Body A/C Selection options with precise focuser adjustment position settings, download this Excel Spreadsheet Calculator:

Extended-body Autocollimator Selector Calculator
Bernd Goosman shares his first-time experiences using CATSEYETM tools including the 1.5" extended-body XLKPTM. Below are his comments and imaging results using his both his 6" and 10" Newtonian astrographs:

3/19/2018 - "Yesterday night I tried the new extension-body autocollimator.... The toolset you sent me is VERY easy to use and TOTALLY uncomplicated! ... I was able to run my 6" f/2,8 and I got it collimated VERY quickly! This system is an original f/4 with an ASA-0.73x-reducer... Your system gives an extreme precise (and quick!) collimation even in the dark! I'm very happy having your tool as my first choice for collimation! Please see the picture (Makarian's Chain) attached ... The slight "out of shape"-stars in the edges of the picture are due to non exact focus because of temperature drop down during the 3h-capture. During initial focus the picture was undistorted and clean!"

3/20/2018 - "... I captured M101 (Fireworks Galaxy) for 5,5h with my 10" Newtonian reduced to f/3.5 with the 0.73xASA-Reducer, ATIK460EXm on my G11. Temperature was around -3deg Celsius and winds around 10km/h. I squeezed it through PixInsight and I'm happy to see a "PERFECTLY collimated galaxy". Your toolset was totally save and uncomplicated to use as the night before! The only downside of the picture are some hotpixels which I didn't exterminate because I only used flats but no darks and no bias..."

Virgo Cluster (Makarian's Chain) - 3.0 hrs Virgo Cluster (Makarian's Chain) - part of Virgo/Coma Berenices
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M101 (Fireworks Galaxy) - 5.5 hrs M101 (Fireworks Galaxy)
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INFINITYTMAutocollimators Exclusive Features
  • A CATSEYE-exclusive "first-Surface" Mirror that incorporates:
    • Premium optically-flat glass.
    • Guaranteed internal orthoganal mirror registration.
    • SiO2 coated aluminum.
  • Generous 1.625" Aperture for faster off-axis "ghost" image discovery.
  • 1.5" barrel length for maximum drawtube-axis alignment.
  • Precision-Machined "Black" Delrin Eyepiece and 6061-T6 Aluminum "black-anodized" barrel.

The World's Most Precision 2" Autocollimator!
This is the most discriminating axial-alignment assesment tool available ...

* Buy It Now! *
New 2.00" INFINITY "XLKP" Pic - Front View
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New 2.00" INFINITY "XLKP" Pic - Oblique View
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For a Step-By-Step Pictorial of the INFINITY XLKPTM Collimation Procedure:


For a comprehensive tutorial on AC funtionality, an excellent read is:
"Concise thread about autocollimators+improvements"
by Jason Khadder, 12/31/2009
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To meet the demand for the more critical alignment needed in todays' big, fast Newts, CATSEYETM 2" autocollimators have been carefully engineered and assembled to achieve a new benchmark in precision and visual clarity. In a few short years since the introduction of the first INFINITYTM autocollimator and subsequent leap forward with the XLKTM 2-pupil model, the CATSEYETM line of autocollimators are recognized as the definitive "gold standard" by performance-minded astronomers world wide.

While viewing with the 2" INFINITY XLPTM or central pupil of the XLKPTM, 4 images of the reflective triangle are usually seen. Convergence of these multiple images, concurrent with the proper Cheshire view, validates precision alignment of the Primary and focuser axes.

Click Each Image For a Closer View.
If Animations stall, refresh your browser.

Primary Tilt Animation Secondary Tilt/Rotation Animation
Telescope Animation Frames Modeled & Rendered with POV-Ray
2" INFINITY(TM) displaying 4 triangle center-spot images
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The INFINITY XLKPTM Autocollimator
Its predecessor voted #8 in the CN Top 10 Astro Gear of the Year 2010 Reader's Choice Poll

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2" INFINITY XLKP(TM), Offset Pupil View w/Perfect Collimation
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The continued refinement of this amazing tool is the direct result of the "out of the box" thinking and analysis by Ghassan "Jason" Khadder on the Cloudy Nights Astronomy Forum. The "K" in the tool's name is a tribute to Jason's extrodinary insight in facilitating the conversion of his autocollimator modeling theory to reality.

The 2nd "offset" pupil of the INFINITY XLKPTM provides a unique "spit-pair" view of the 4 center spot reflections that facilitates additional axial-error resolution/correction after they have eluded viewing in the central pupil at close reflection convergence.

INFINITY XLKP Central and Offset Pupil Views

The conventional central pupil view on the left shows a single stack of multiple images that "appear" correct while the 2nd offset pupil view on the right reveals that incremental residual errors are actually still present in the axial alignment.

The INFINITY XLKPTM surpasses the axial alignment capability of its XLKTM legacy with a 21% reduction in pupil diameter for even more axial-error resolution before the central-pupil images disappear during the iterative convergence collimation method.

Additionally, a new novel mirror manufacturing process produces a long-awaited improvement in the consistency and precision of mirror-hole circular definition and spacing to facilitate precision alignment with the tool's eyepiece pupils.

INFINITY "XLK" and "XLKP" Mirrors
Side-by-side look of a typical XLKTM mirror with irregular (approximately 0.125") pupils and the new XLKPTM mirror with "perfect-circle" 0.100 pupils.


When "perfect" collimation is "close at hand", 4 center-spot reflections can be seen in the INFINITYTM autocollimator and are the result of multiple reflective interactions between the 3 mirror components of Primary, Secondary and Autocollimator.

In these simulations below, both Primary and Focuser optical axes alignment errors are present resulting in the reflections being spread apart from their "perfect collimation" stacked position.

You might see something like this ....

Autocollimator View Showing 4 Spot Images

or perhaps this ...

Autocollimator View Showing 4 Spot Images

  • Reflection "P" is the "Primary" or "first" reflection and is the direct reflected image of the spot itself via the Diagonal mirror after 1 FL pass. Reflection "P" is what is visible "without" the autocollimator whereas images (#1, #2, & #3) are reflections of "P".

  • Reflection "1" is generated from reflection "P" after an additional reflection back from the A/C mirror, via the diagonal to be reflected off the Primary and back via the diagonal to the eye for a total of 3 FL passes from the original spot. It's sensitivity to Primary axis error is 4X and to Focuser axis error is 2X.

  • Reflection "2" (inverted) is generated from the "real" image response from the (parabolic) Primary mirror at its Center of Curvature (COC at 2 FL's away) from the spot reflection it sees in the Autocollimator mirror (which is 1 FL away). The trick here is that the autocollimator reflects (or "folds") the real image back onto the Primary surface where it is then seen via diagonal reflection by the eye (just like reflection "P") - it is a total of 5 FL passes from the origin.

    The reflection "2" sensitivity to both Primary and Focuser axes errors is 4X each. Total distance between reflections "1" and "2" is the vector sum of the primary mirror and focuser axial errors. When the other axial error has been removed, this distance is either 8X the primary mirror axial error or 6X the focuser axial error.

  • Reflection "3" (inverted) is a reflection of reflection "#2" following a path like that of reflection "#1" (generated from reflection P) for a total of 7 FL passes to the eye from the original spot. When the faintest reflection (#3) is in view, the distance from "P" to "3" represents a sensitivity to focuser axis error of 2X regardless of the Primary axis error.

    It is this unilateral sensitivity to the focuser axial error that allows us to use this reflection to "zero" the focuser axis with Vic Menard's "Carefully Decollimated Primary Mirror" protocol, leaving the primary mirror axial error, magnified 8X, visualized as the distance between reflections 1 and 2.

    The distance and direction between reflections "#2" and "#3" is always equal to that seen between "P" and "1" and between the two A/C pupil reflections; thus, these two spot reflection "pairs" will always be arranged with their centers forming 2 separate parallel lines that are also parallel to the A/C pupil reflections.

*** Many thanks to Vic Menard and Nils Olof Carlin for their insightful contributions and editing assistance ***
Read: Nils Olof Carlin's "The Autocollimator and its Reflections" updated July 2010
Read: Vic Menard's Autocollimator comments:
Click to see Vic's

INFINITY(TM) Image Sequence 3 Movie Clip (57 FRAMES)
Autocollimator Image