The BEST Autocollimator

[FLO]

We normally recommend buying Jim Fly's Catseye Infinity XLK Autocollimator as part of a Catesye Combo Set or Triple Pack but some customer's have asked us to make it avalable as a stand-alone item, so here it is

Members of the American forum Cloudy Nights will probably recognise the XLK Autocollimator because it was discussed, designed and developed in real-time on that forum. This excellent thread by Jason D, who also posts here on SGL, is probably the most detailed (you'll need a strong coffee!) so if you are interested in the history and development of autocollimators do take a look. But don't let it put you off, It is much easier to use an autocollimator than to explain it's physics.

Not a lot of people know this but the 'K' in Infinity XLK is a tribute to Ghassan 'Jason' Khadder (Jason D) for his contribution to the design, development and analysis of the product.

Catseye also have a more affordable autocollimaor, the Infinity XL, with a single view-hole. So far most of the enquiries we recieve have been for the higher specified Infinity XLK (shown here) with both a central and off-set view hole, so that is the one we offer. Having said that, we have noticed some pre-launch advertising for what is essentially a copy of Catseye's single-hole Infinity XL. We won't be stocking the copy but we will import and offer the original Catseye product.

HTH,

Steve

[Capricorn]

Going to have to make a bigger coffee before I start reading the CN entry.

Are you going to have one at the SW AF (assume you will be there?) that would enable people to see one and how they are used and display when in a scope.

[FLO]

Good idea. We are attending the South West Astronomy Fair and the higher specified Infinity XLK autocollimator is in stock (we began importing them over a year ago) but the cheaper single-hole XL might not arrive in time for the show.

[Capricorn]

My idea was that showing it and how it is used/operates would reduce the "trepidation" associated with collimating, and if people try one and find the operation/action straight forward it may well bias them towards one in the future.

Only concern could be the cost as usually the Catseye items are not inexpensive.

Would be good though to see one in the flesh and how it all operates.

[FLO]

I know what you mean, it does sound complicated when you read the description but you don't need to understand the physics to use it and lining up reflections is not difficult. It's a bit like the internal combustion engine, we all drive but only a few of us know how it works.

As for price, having put time energy and emotion into developing and popularising the product, not to mention his obsessive attention to detail and manufacturing tolerances, Jim at Catseye can be forgiven for being more expensive. Besides, those companies who choose to copy a product 'should' charge less. Imitation is easy, innovation is not. Innovation is what sets leaders apart from followers. They take time to understand a customer's requirements and provide a solution. True innovation is also a good long-term business strategy.

I'll get off my soap box now

[FLO]

The price was wrong

I miscalculated the UK 'landed' price. The price displayed now is correct.

We'll add the cheaper Infinity XL (with single view-hole) as soon as they arrive.

[FLO]

Just found this animation at the Catseye website which shows the autocollimator in action

[FLO]

We'll add the cheaper Infinity XL (with single view-hole) as soon as they arrive.

The original Catseye Infinity XL Autocollimator in now in stock

[Jason D]

All autocollimators have an eyepiece case, a mirror, and all show multiple reflections of the primary mirror center spot. That does not mean much. A true autocollimator has to meet a high standard of quality and precision. If it lacks precision then it will not provide any additional collimation improvement beyond a mass produced laser collimator.

Here is a detailed criteria to evaluate any autocollimator:

1) How many center spot reflections can you see with reasonable clarity? Four is excellent. Less than four is poor. Note that two of the center spot reflections might look fuzzy. That is OK. The degree of fuzziness is dependent on vision acuity and the scope focal length. The smaller the focal length the fuzzier two of the reflections. Seeing the fourth center spot reflection will enable a procedure called “CDP” introduced by Vic Menard. CDP will make it easier to align the focuser axis with high precession.

2) Rack the drawtube until the autocollimator mirror is close to the primary mirror focal plane. Unstack the center spot reflections until you see all four reflections then rotate the autocollimator in the focuser without tightening any focuser setscrew. Test it at 90, 180, and 270 degrees. To validate the test, rotate the autocollimator 360 degrees and check – repeat few times. If reflections stay close to their original location after each 360 degree rotation then this test is valid. Do reflections shift significantly at 90, 180, and 270 degrees compared to their original locations? If yes then the autocollimator quality and precision is poor. It is almost impossible for any autocollimator to pass this test with 100% accuracy. This is a highly sensitive test. Small shifts by around ¼ the diameter of the center spot is acceptable. However, if the shift amount is larger than a full diameter of the center then the autocollimator is of poor quality. This test checks the squareness of the autocollimator mirror against its casing and it checks for registration errors of the autocollimator with respect to the focuser.

3) Look for distorted center spot reflections. If some of the center spot reflections are noticeably distorted then that is an indicated of poor autocollimator mirror flatness. If some of the reflections have a slightly different size but otherwise are undistorted, that is OK. Size difference is an indication the autocollimator mirror is located away from the focal plane.

4) When the scope is collimated and the autocollimator background reflection is dark, how dark is it? The darker the better. Gray’sh background is an indication of poor autocollimator mirror flatness and possibly poor reflective surface.

5) How centered is the central pupil of the autocollimator case? Off-centered pupil will introduce errors.

6) How large is the central pupil? Around 2mm is good and reasonable. Larger pupil hole will introduce parallax errors.

7) How large is the non-reflective area around the central pupil from the autocollimator mirror side? This is important. If this area is large then a measurable error will be introduced. The reason is somewhat complicated but I will try to summarize it. A large non-reflective area around the central pupil will cause two of four center spot reflections to disappear prematurely. As all four center sport reflections start merging, two of the reflections will quickly and prematurely disappear and you will be left with two reflections. Stacking two center spot reflections is far from being acceptable. You need to stack a minimum of three reflections.

8) The reflective area of the autocollimator mirror has to be free of artifacts – especially around the central pupil. Again, the reasoning is somewhat complicated but I will try to summarize. As reflections merge, if the reflective area around the central pupil has rough surface or poor reflection then the background will suddenly brighten reducing contrast and two center spot reflections will potentially disappear.

9) How large is the reflective surface? In general, 2” autocollimator should be used when possible. The large reflective area will make it much easier to see all center spot reflections. For 2” autocollimators, it is desirable to have thinner case walls and more reflective area.

10) Is it a single or dual pupil autocollimator? Not only the dual-pupil autocollimator provides more accuracy but it will also catch errors explained in items 7 & 8 in this list.

As someone who evaluated multiple Catseye autocollimators, I can attest that all have passed the above outlined criteria.

Anyone who owns an autocollimator regardless of the vendor can evaluate their autocollimator based on the above.

Jason

[FLO]

All autocollimators have an eyepiece case, a mirror, and all show multiple reflections of the primary mirror center spot. That does not mean much. A true autocollimator has to meet a high standard of quality and precision. If it lacks precision then it will not provide any additional collimation improvement beyond a mass produced laser collimator.

Here is a detailed criteria to evaluate any autocollimator:

Thank-you Jason

Some will think I asked you to post that. I didn't but I'm glad you did. We are about to create a new and more convenient section for Catseye collimation products on our website, would you mind if I include your comments please?

Steve

[Jason D]

Feel free to copy the list to any website you choose.

I have spent a significant time studying the autocollimator reflections and how best to interpret them. I continued the excellent autocollimator studies published by Nils Oolf Carlin and Vic Mendard. The autocollimator is an excellent collimation tool providing:

1) A high quality autocollimator is used. An average quality autocollimator will not add value above and beyond other good collimation tools. A poor quality autocollimator will actually make things worse.

2) Good knowledge of how to use an autocollimator is important. I have read gross instructional inaccuracies written by one vendor. The vendor claims that getting a darkened autocollimator background is always an indication of excellent collimation. The same vendor continued claiming that having a primary mirror center spot is optional with an autocollimator. Both claims are grossly inaccurate. Another vendor claims that since each subsequent reflection of the center spot is more sensitive than the previous one; therefore, seeing and using the 4^th reflection is an overkill. Again, this is grossly inaccurate. Each reflection of the autocollimator serves a different purpose including the 4^th reflection. The 4^th reflection is needed to perform a procedure called CDP which aligns the focuser axis with the center spot. Actually, the 3^nd center spot reflection is more sensitive than the 4^th reflection – unintuitive but true. Reflections between two flat mirrors placed opposite to each other are very different compared to placing a flat mirror opposite to a concaved mirror. Reflections of the latter are unintuitive and more complex.

Jason

[FLO]

Thank-you Jason

Steve