The Hotech Advanced CT Laser Collimator the bugs and the stray cats, maybe using that old standby,...

One of the first things Joe and JaneNew Amateur learn is, “You’ve gotta col-limate.” If you use a reflecting type tele-scope, you will have to master the art ofadjusting your telescope’s mirrors so theyare aligned properly if the scope is to de-liver all the image quality it’s capable ofdelivering. Collimation isn’t just some-thing you need to do to a new telescope,either; it is a constant fact of life for mostamateur astronomers. If you own a New-tonian reflector, you will collimate,maybe once in a while, maybe every timeyou use the telescope.

Schmidt Cassegrain owners arelucky. SCTs require collimation, but if itis done correctly they can go months oreven years before re-tweaking is required.Not that we’ve always considered our-selves lucky. Heck, many SCT owners areafraid to collimate their telescopes. Whilethe Schmidt Cassegrain is at heart a sim-ple little beast, to the new owner it looksscary-high-tech, and the very idea of at-tacking the screws on the front of the sec-ondary holder sounds like a bad idea.

Which is ironic. SCT collimation iseasy. It’s a walk in the park compared to

Newtonian alignment. With a Newton-ian, you have two optical elements to ad-just, the primary and secondary. And thatsecondary can be moved in three axes.The Schmidt Cassegrain, on the otherhand, has only one user-adjustable com-ponent, and all that is adjustable is its tilt.

All you must do to get an SCT prop-erly adjusted is focus on a medium-brightstar, defocus just a little till you can seediffraction rings, making the star looklike a bull’s-eye target, and, with this “tar-get” centered, adjust the collimationscrews until the rings are concentric, notsquished on any side. There are a few“rules” to the SCT collimation game;you, for example, should always collimate

by tightening screws only if your scope isto hold collimation for any length oftime. But mostly it’s straightforward andeasy to do with only a little practice.

Yep, SCT collimation is so easy evena caveman can do it—unless you want tocollimate inside your cave. Polaris is theultimate collimation tool, but it is, ofcourse, only available under a dark, clearsky. You can use other stars, too, but attimes it would be nice to be able to colli-mate indoors. You want to take a quickweeknight look at Saturn, only have afew minutes to spend with the ringedwonder, and know your scope is badlyout of alignment. Or you need to startobserving right after sundown before

The Hotech Advanced CTLaser CollimatorBy “Uncle” Rod Mollise

Adventures in SCT Collimation withUncle Rod and the Hotech CT Laser

Image 1 - Schematic describing the basic Hotech Advanced CT Laser Collimator system.

44 Astronomy TECHNOLOGY TODAY

clouds roll in. Newtonian owners cancollimate indoors or in the daytime withease. Shame SCT owners can’t. Or could-n’t till now.

There are several ways to collimate aNewtonian without looking at a star, butone of the most popular over the lastdecade has been with a laser. Put a lasercollimator in the focuser, center the redspot on the primary and secondary, andcollimation is dead on. Unfortunately,SCT owners who tried the new collima-tors on their scopes quickly discoveredlaser collimation was a recipe for SCTmis-collimation.

Why were laser collimators denied toSCT Users? Because for a standard lasercollimator to work, everything—the tele-scope’s primary mirror, baffle tube, rearport, and visual back—has to be preciselymechanically aligned. Which isn’t oftenthe case for SCTs. That doesn’t do a thingto harm image quality or prevent precisecollimation, but it does preclude the useof a Newtonian laser collimator.

In addition, forperfect collimation, youneed the collimator’sbeam to be reflected offboth a telescope’s mir-rors. Insert a laser in anSCT’s visual back and itis easy to see its beam isjust hitting the second-ary and being reflectedback on itself. The pri-mary is not in play.

So there is no wayto collimate an SCT in-doors? That’s not ex-actly true. You can usean artificial star, butthat’s always inconven-ient and sometimes impossible. An arti-ficial star, even one of the fancy new LEDartificial stars, has to be far enough fromthe telescope so you can get it closeenough to focus to see diffraction rings.You do not have to have the target hun-dreds of meters away as you may have

read—long distances are only needed tostar test for optical quality—but you doneed enough space to focus properly.

Alas, most homes don’t have a longenough run of interior space to permitthat. I can place an artificial star in ChaosManor South’s kitchen and a C8 in the

Astronomy TECHNOLOGY TODAY 45

Image 2 - Hotech Advanded CT Laser Collimator system set-upin the author’s observatory.


THE HOTECH ADVANCED CT LASER COLLIMATOR

living room and barely collimate, but Ican’t do a C11 at all, and our Old Manseis probably larger than most folk’s homes.

Sure, you can collimate outdoorswith the bugs and the stray cats, maybeusing that old standby, the sun shiningon a power pole insulator or reflecting off

the chrome bumper of a car.Unfortunately, today’s cars aredeficient in chrome, and what ifit’s cloudy? You can use an illu-minated artificial star, but manypeople may still not have thespace to achieve proper focus.

A laser would be the perfectanswer to the daytime/indoorSCT collimation conundrum ifone could be made to workwith our telescopes. Severalmanufacturers have marketedlaser collimators designed foruse with Schmidt Cassegrains,but, while some worked betterthan others, none worked well.

When I heard David Ho(Hotech) was preparing to market anSCT laser, I was skeptical. Yeah, I knewthe man’s reputation for quality, but we’dbeen down this road before hadn’t we?Still, I kept my ear to the ground, andeventually heard the Hotech CT(“Cassegrain Telescope”) collimator was

an SCT laser of a new type.Naturally, I was anxious to get my

hands on the CT for a review, and whenDavid H. agreed to send me an evalua-tion unit, I was right excited. And maybea little bit apprehensive. One other thingI was hearing was that the Hotech CT re-quired a far more complicated setup thanjust sticking a laser pointer in the rearport. Would I be able to make the dangthing work? I’ve used SCTs for nearly 40years, and I know a thing or two about‘em, but, as my friends will tell you, I amat heart a fumbler and a bumbler when itcomes to technology.

When the collimator arrived, I wasimmediately impressed by Hotech’s at-tention to detail. This is a nice package,with the laser and its accessories con-tained in a soft case not unlike what you’duse for a laptop computer. In addition tothe collimator itself, in the case was a pairof eye-piece-looking things, a 1.25-inchand 2-inch. Turned out these were mir-rors that are inserted in the scope’s visual

Image 3 - Individual lasers mounted on the back of the CT Target.

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back to get the beam from the laser,which is pointed down the corrector endof the telescope, propagating through theoptical system, hitting the primary mir-ror as well as the secondary.

How about the laser itself? Actuallyit’s an enclosure equipped with multiplelasers. There are four of them mountedon the unit’s back. The whole shebang ispowered by a single (included) CR123battery. The opposite face of the colli-mator, the side that points to the tele-scope, is emblazoned with target rings.

What else? There was some scary-looking stuff. Several ruled measuringtapes, a fabric strap with a metal buckle,and some funny-looking plastic “tabs.”Looking at the tapes, I began to feel a lit-tle apprehensive. In addition to beingtold I’d have to precisely square the laserwith the telescope’s corrector, I had heardthat would be particularly difficult witha Celestron SCT (all I own).

The shipping box also contained oneadditional and, I believe, optional item,

a tripod fine adjuster. You’veno doubt seen these before:altitude-azimuth fine-tunersthat attach to a photo tripod’shead. If you are contemplat-ing the CT, I urge you to getone, as being able to makefine adjustments of the laser isextremely helpful, and canpreserve your sanity and yourhairline. A sturdy tripod isalso desirable—the CT ismounted on a 1/4-20 threadtripod for use. I used ourManfrotto, though I found aninexpensive Focal tripod (K-Mart) was useable.

What next? A look at themanual. Some of the picturesin this laser-printed sheaf of pages were alittle small and a little dark, and some ofthe wording was a bit awkward: “focuser”instead of “visual back,” “intercept”when “overlap” is meant, “tangent” when“perpendicular” would have been a better

word choice, etc. However, the instruc-tions were good enough; especially whenused in concert with the instructionalvideos available on YouTube. The goodnews is that David has revised the man-ual and the all-important instructions are

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Image 4 - Laser return spots displayed on the face of the CT Target.





now easier to follow.Let me make sure I am clear

about something: I know you areused to me being cavalier about andjoking about instruction manuals.I’ve often told y’all that the firstthing I do when I get a new piece ofkit is throw the manual in the oldrubbish bin. Not this time. READTHE INSTRUCTIONS. Thenread ‘em again—several times.Watch the videos. Then watchthem again, several times. I guar-ron-tee that if you don’t, you willnever figure this thing out.

“Time to get cracking. Let’s takeone last look at the manual.”Which was when I hit the firstbump in the road. The instructionswarn you not to set up on carpetedor wooden floors, only on a sturdysurface with no give. Well…I gotnews: Chaos Manor South ain’t gotnothing but wooden floors, and Isuspect many other folks, even

those who don’t live in ancient Victorianhouses, are in the same boat. I could gooutside, but one of the beauties of thisrig, I thought, was that you could use itinside. When all was said and done Ifound I didn’t have any trouble collimat-ing on a wood floor as long as I mountedthe collimator on a sturdy tripod.

The first step in the CT collimationprocedure is getting the collimator prop-erly square-on to the telescope. Doingthat with a Meade is fairly easy. With theCT’s rotary switch in Mode One (it hasthree modes), which projects a crosshairpattern, you aim the scope and collima-tor at each other so three screws insidethe tube near the primary mirror are il-luminated. The trouble for a Celestronowner is that Celestrons do not havethree screws spaced at 90 degree intervalsat the mirror cell end. I’d have to makemy own marks via the measuring tapesand “tabs.” Rut-roh.

Whether you’ve got a Meade or Ce-lestron, before you can point the colli-

Image 5 - A high-quality padded case is includedfor safe storage and transport of the Hotech Advanced CT Laser Collimator system.

mator to the screws or tabs, you first haveto place the collimator the proper dis-tance from the scope. That will dependon the scope focal length, but it’s lessthan one tube-length in front of the cor-rector for my C8. Start out about there,move the collimator and tripod forwardor back until the crosshairs are theirsmallest, then move toward the scope tillthe crosshair pattern projected onto thecollimator’s target-face extends to the firstbulls-eye ring.

Once you’ve achieved a goodcrosshair pattern on the CT’s target, youare approximately aligned as well as at theright distance. But you must be preciselyaligned to produce a good collimation.

Referring to the manual, I grabbedone of the lengths of measuring tape,which turned out to be surprisingly easyto use. No critical measurements are re-quired. Wrap the tape around the rearcell and mark the overlap point on thetape with a pencil. Remove the tape,keeping it overlapped. Fold it twice so it’s

one quarter its original length,and mark a starting “0” positionon the top of the telescope’s rearcell with a pencil or use someother convenient reference. MyC8 has a screw on the rear cellperfect for that. From there, usethe folded tape to mark two “90degree” positions on either side ofthe 0 mark.

90-degree marks made, all Ihad to do was wrap the suppliedfabric strap around the rear cell,fasten its buckle, and slide thethree provided plastic tabs underit at the three marked positions.It seemed kinda Rube Goldberg,but worked fine and was morethan precise enough. In practice,I found I could tell when the col-limator was properly aimed just by eye-balling the three laser spots on the edgesof the C8’s mirror. The tabs helped geteverything lined up properly, though,and if you are collimating a Celestron,

you should definitely use them. In fact,even if you have a Meade, you mightwant to use the tabs; I believe they willspeed up the process of aiming.

Getting C8 and CT positioned withthe three laser beam crosshairs on the

Image 6 - The CT Target face displays another Mode of the Hotect Advanced CT Laser Collimator.





tabs (in the case of a Meade that wouldbe “on the screws”) and the crosshair re-flection centered on the first target ringtook some doing, crying, and whiningthe first time out. The problem is thatyou’ve got so much freedom of adjust-ment when you combine all the possiblemovements of collimator and scope thatit gets confusing. How do you keep outof trouble and resist the urge to throw theCT against the wall?

FOLLOW THE INSTRUC-TIONS! If you do, you’ll find the align-ment process is a two-step affair with nomystery to it. First you aim the laser atthe tabs (or the screws), then you aim thetelescope so the projected crosshairs arecentered in the first bulls-eye ring on theCT. Keep doing these things in turn; ad-justing by small amounts, till the tabs orscrews are illuminated and the crosshairsare centered on the collimator.

Even with a fair idea of what I should

be doing thanks to themanual and the videos, Ieasily spent a solid hourgetting scope and CTproperly aligned the firsttime. Like anything else,of course, what was diffi-cult that first time waseasy the second. The nexttime, getting scope andlaser lined-up took all of15 minutes.

Since, as SCT mavenswill tell you, the SchmidtCassegrain’s mirror can

change position slightly depending onwhether the tube is level or pointing atthe sky, it might be a good idea to colli-mate with the laser elevated, so the tubecan be at an up-angle. The first time,however, you will have your hands fullgetting the feel of the CT, and I urge youto get comfortable with it with collimatorand scope both level. Having the SCT onan alt-azimuth type mount makes theprocess easier, too. While my C8 nor-mally rides on a German equatorialmount, I placed her on my Synta AZ-4alt-az for collimation.

With scope and laser properly posi-tioned near as I could tell, it was time tocollimate. Which turned out to beslightly anticlimactic. Once you masterthe art of squaring CT and SCT, all that’sleft is the old “which screw do I tweak?”routine. Well, almost.

Before you can begin collimation, youmust turn the rotary switch on the top of

the collimator to one of its other twomodes. Mode Two turns on the collimationlasers, and Mode Three provides a combi-nation of collimation laser spots andcrosshairs. I chose Mode Three so I couldbe sure the telescope and collimator werestill properly aimed (I am famous for kick-ing tripod legs).

When I switched the CT to ModeThree, the three laser spots I was supposedto see were nowhere to be found. What hadI screwed up now? I could see three smalllaser dots on the face of the CT if I (mis)ad-justed alignment a certain way, but fromthe instructions and the videos I knew Ishould be seeing three fat spots. I fiddledand fiddled, but nothing helped. Was Idone?

Thankfully, your silly old Uncle hadthe sense to read the instructions one moretime. There was indeed an entry on “Whatto do if you can’t see the laser spots.” Thefirst suggestion was to check the return mir-ror in the visual back. That seemed OK.What next?

The second troubleshooting suggestionwas slightly confusingly worded, but themeaning was clear. The telescope’s focusershould be close to the focus position it willassume with an eyepiece inserted directlyinto its visual back. Hey! Wait a minute! Thelast time I used the C8 was with my Stella-cam II and Meade f/3.3 reducer, whichthrows focus way off from visual. Maybe…

Sure enough, turning the focus con-trol to move the SCT’s mirror back to “visual position” caused three laser spotsto magically appear on the target.

Image 7 - Alignment tabs attached to the SCT’s rear cell.

With them visible, the rest was easy. Thethree spots were not all on the same bull’s-eye ring, so I adjusted the scope’s collima-tion screws till they were. I felt good,though the instructions warned me tocheck the scope on Polaris’ diffractionrings after the first collimation to be sureI’d done things right.

That very night I headed to our localclub’s dark site. There, I turned the scopeto the North Star and defocused slightly.I hoped the CT had worked, since I wasn’t in the mood for a full-blown collimation session. I didn’t have to do one; the star’s diffraction rings werenicely concentric.

My verdict on the Hotech CT Colli-mator? I hope to improve my setup time,but this unit will never be as quick to useas a Newtonian laser collimator. On theother hand, a Newtonian laser will notwork on an SCT, and using the CT Col-limator is significantly quicker than usingan artificial star in the daytime. TheHotech CT is an attractive piece of gear

with outstanding build-quality.Expect to spend some time fig-uring it out, but when you getto that “OH YEAH!” momentyou are gonna be right happywith this thing, muchachos. Igive it two thumbs up.

Stop the presses depart-ment: In the months since Ibegan following the CT’s devel-opment, one thing that has im-pressed me is how committedDavid Ho is to his product. Hecontinues to tweak and inno-vate and has recently developeda new procedure that makes ini-tial setup considerably easier. This is animportant breakthrough, since the onlything I (and most other users) foundeven marginally difficult was squaringcollimator and telescope.

The new procedure eliminates theuse of the tabs for alignment. Instead, apiece of frosted, matte-finish tape isplaced over the collimator’s center laser

to diffuse the beam. This causes a“donut” of reflected laser light to be pro-jected onto the collimator face. All theuser must do is adjust the telescope’s aimuntil this donut is centered on a targetring. You can still use the tabs, but be-lieve you me, this new procedure savestime, keeps the stress level down, andseems just as accurate.


Image 8 - Aligning the Advanced CT Laser Collimatorwith help of the alignment tabs.


The Hotech Advanced CT Laser Collimator the bugs and the stray cats, maybe using that old standby,...

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