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Equipment Discussions >> Cats & Casses

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Calypte
Pooh-Bah


Reged: 03/20/07

Loc: Anza, California
Re: HoTech SCT Laser Collimator? new [Re: rmollise]
      #5846292 - 05/07/13 06:25 PM

Quote:

And all of my HotechUSA products say "Made in USA" on them.



My Astro Aimer G3 only states the manufacturer and his address, not where the product was actually made. We use them at Palomar Observatory to point out things during tours. That aside, there's always a simple solution if you think an astro product is too expensive: don't buy it! If enough people say "no," then the product's price will either come down or (more likely) the product will disappear. That'll show 'em! A few years ago I contacted the manufacturer of a line of eyepieces that I liked that were no longer made. I had this crazy idea that maybe with a little bit of money I could get him to start making them again, and I (thinking modestly) could become the US sales rep, and I'd travel to all the shows and star parties while showing off these eyepieces, and I'd be eating in fancy restaurants with industry bigwigs and the editors of S&T and Astronomy. The guy I contacted told me he thought it would require about $250K to bring back the product. For one thing (if nothing else), there'd need to be a minimum order from the factory in Japan, so if I indeed had that kind of money (I didn't), I'd end up with thousands of these eyepieces sitting in my garage, waiting, hoping, that someday I'd recoup my $250K. There were originally four focal lengths. Inevitably some would be more popular than others, so I'd probably go to my grave with some of the less popular FLs. And meantime I'd be reading posts that they cost too much, and why didn't I come out with some other focal length, and somebody's going to say they'll never buy any from me because they think I'm a schmuck for how I talked to them at RTMC in 1995, etc., etc. Meanwhile, somebody'd be saying that Explore Scientific has eyepieces just as good for $50 less. For me it was a bit of a reality check on the business. A lot of my own money would be on the line, and there'd be absolutely no assurance I'd ever get it back. The claim of "overpriced" for some of this stuff acquired new meaning.


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JJK
Carpal Tunnel


Reged: 04/28/08

Re: HoTech SCT Laser Collimator? new [Re: rmollise]
      #5846511 - 05/07/13 08:14 PM

Quote:

Quote:

Knowing that David Ho is a guy who really cares about his customers, I doubt that it is priced one dollar higher than it has to be to keep it as a viable product on the market.

And another point to consider. If it really was overpriced for what it is, David's arch-competitors would come up with a cheap Chinese clone of it and try to undercut his market.

And all of my HotechUSA products say "Made in USA" on them.

I hope this helps.




Bingo. The collimator is also _very_ well made.




I agree. I'm tempted to get it to help collimate a Meade/Wegat 125 Mak-Cass, which only cost me about $450 used. Collimating that scope under the stars would be an exercise in frustration. Access the primary mirror lock/alignment screws requires taking off the visual adapter and the protective cover, adjusting the screws, putting the cover and visual adapter back on, add an eyepiece, and then rinse, lather, and repeat over and over again. The Hotech tool avoids the need to use an EP to collimate the primary and center the optical train.


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gaz-in
scholastic sledgehammer
*****

Reged: 12/17/07

Re: HoTech SCT Laser Collimator? new [Re: JJK]
      #5847340 - 05/08/13 08:57 AM

Got one...really like it...I have learned lots about how my sct operates by fooling aroung with it....chated with the designer at NEAF. Like so many in this hobby, a real great guy!

So glad we have him designing and making tis type of product available....


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Wade Van Arsdale
super member


Reged: 10/25/07

Re: HoTech SCT Laser Collimator? new [Re: gaz-in]
      #5847691 - 05/08/13 12:39 PM

One of the best uses I've found for David Ho's Advanced CT Laser Collimator Kit is to check centering of the secondary mirror to the primary mirror's optical axis. It's the best tool I have for checking centering on the Planewave CDK scope also, not just SCT's.

David has a neat trick he uses of putting a piece of Scotch Magic Tape (translucent) over the center laser hole on the kit's faceplate (the large white square plate with the hashmark and circular grid stamped into it that catches the return beams from the laser).

This piece of tape diffuses the laser beam to a spread-out, large donut pattern that you use to check the secondary centering. On scopes such as the EdgeHD, centering of the secondary gets much easier since those models have 4 adjustment screws along the front collar.

While some designs like SCT's aren't particularly sensitive to decentering error, every little bit of precision alignment that you can get helps on performance, especially at the edges of the field on large-chip cameras used at long focal lengths and severe image scales for deep-sky imaging. This becomes especially true if the scope was way off-centered like some I've seen.

So far, I've used David's kit to diagnose and fix three decentered SCT's, one of which was badly decentered, and also diagnose a mis-machined focuser on the back end of a Dall-Kirkham that was tilted from the optical axis and couldn't be fixed without a replacement.

For me, the kit has been a great diagnostic tool for the *other* alignment problems of the scope besides collimation (although as said here already, if you take the time required to "landmark" the lasers properly on the OTA, it will do a very good rough-collimation for you).

I still find my best *final* collimation tool is a fast webcam to freeze the atmospheric seeing (star swim), and a real star near zenith for least atmospheric interference...but only after I've worked the scope over with the Hotech kit first.

As has also been said here already, the Hotech is a great learning tool too, so you can understand better all the alignment variables for your scope.

So many times an SCT or other compound mirror scope gets talked bad about for not performing when in reality it is just mis-aligned all the way from focuser to front glass, in ways *other* than just basic collimation. That's where the Hotech really comes into play the best, IMO.

Wade


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HowardK
Pooh-Bah
*****

Reged: 10/20/10

Re: HoTech SCT Laser Collimator? new [Re: Wade Van Arsdale]
      #5847736 - 05/08/13 01:05 PM

Wade

I still use Metaguide and my Mallincam on my Planewave 12.5 and my new 8" Edge.......its a great help in collimation to be sure

I remember your help


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Alph
Carpal Tunnel


Reged: 11/23/06

Loc: Melmac
Re: HoTech SCT Laser Collimator? new [Re: Wade Van Arsdale]
      #5848010 - 05/08/13 03:23 PM

Quote:

This piece of tape diffuses the laser beam to a spread-out, large donut pattern that you use to check the secondary centering.



This does not sound right to me. According to the user’s manual, the large donut pattern is used to square (align) the collimator with the OTA. I would think that a single test like that can’t be used to adjust reliably two different things! If the donut pattern is off, then you don’t know whether it is because of the secondary or the OTA misalignment.


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gaz-in
scholastic sledgehammer
*****

Reged: 12/17/07

Re: HoTech SCT Laser Collimator? new [Re: Alph]
      #5848471 - 05/08/13 06:53 PM

I think where folks are missing is this is so much more than just a collimation device.

As was mentioned, centering the secondary. David chatted with me at NEAF about how to check/fix this. I came home and found my secondary to be in need of centering. Using the Hotech tool I was able to adjust to much closer to center...

As far as diagnosing things, it helped me realize that I had a diagonal where the mirror was not at the correct angle...rotating the diagonal showed the diagonal mirror was not squared properly to the light path. Swapping diagonals really helped the view....


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Wade Van Arsdale
super member


Reged: 10/25/07

Re: HoTech SCT Laser Collimator? new [Re: Alph]
      #5849888 - 05/09/13 11:55 AM

Alph,
What I'm talking about re. centering the secondary to the primary probably isn't in the user's manual (haven't looked at his latest manual). I got the information about this directly from David Ho via phone and email.

David probably doesn't include this step in the manual because it is pretty uncommon on an SCT to have one so badly decentered that it makes a difference (although on one of my three SCT's I've worked over with this kit, it WAS badly decentered enough that it showed up in Roddier tests pretty clearly). And on a warrantied scope, you could mess up your warranty on an EdgeHD OTA if you touch the front collar adjustment screws...see disclaimer below!!

What you are talking about in the user manual is the *initial* part of the co-alignment of laser (white face plate of laser kit that sits in front of the scope) to *primary* mirror, not secondary. This is the "laser landmarking" procedure I mentioned earlier.

For this initial step, you use only the *outer* edge of the donut pattern and shift the white laser face plate and its printed grid to the donut. You're not adjusting anything on the OTA at this point, only the laser face plate in front of the scope.

But in the secondary mirror centering step, *after* you have the laser landmarked properly to the primary mirror and optical tube wall, you use the *inner* dark portion of the donut pattern with the diffuser tape in place and instead of adjusting the laser plate's positioning, you adjust the corrector's lateral positioning on the OTA until your center dark hole is orthogonal to the grid marks on the laser face plate. (Note, this is darn near impossible to get right unless you have a spider vane with adjustment screws or the newer Celestron OTA's with corrector adjustment screws around the front collar of the scope).

***IMPORTANT: to anyone reading this, you might void your warranty on an EdgeHD tube if you try to start aligning the corrector using the four front collar screws!!!! You do this at your own risk. If in doubt about what to do, check with Celestron *FIRST* before proceeding.

Also keep in mind, for SCT's, your secondary centering has to be WAY out of whack to make a difference in overall optical performance. So if you think it's close to within a couple of mm laterally, let it be!!

The center dark hole of the pattern in this step is just a "shine-through" of the secondary coming from the primary mirror only, not a laser bounce off the secondary. You're just sillouetting the secondary against the laser plate and using its shadow on the pattern projected onto the laser plate.

(Note, It's been awhile since I've conversed with them, but last I heard from them, Planewave uses this same kit and same procedure for centering their secondaries at the shop while assembling according to Allen Keller. They may still be doing it this way for all I know).

I hope this makes more sense now. It's very difficult to visualize just by reading when you don't have the kit and scope in front of you doing it, esp. for undocumented steps like this. But it really does work. The laser kit has several modes of laser beam shooting and you use different modes depending on what part of the steps you are on.

For final checks of back-end and focuser squareness and orthogonality, after you've done everything else, *then* you start using the return beam coming from the secondary mirror to the back end of the scope and out the focuser. But I like to collimate on a live star first before going to the back-end checks. This helps rule out everything from the primary mirror forward and isolate *just* the back-end and focuser.

This is also where you can check for mis-machined, out-of-square/sagging focuser or back-plate tilt.

I think of it as a systematic alignment from front to back, in this order:
1) Co-align laser face plate to primary mirror.
2) Align secondary to primary mirror--**CHECK-ONLY** just to verify when it's an SCT. Leave it alone if close!!!
3) Collimate on live star, using a fast webcam on star near zenith for best possible results.
4) Check back-end return beam from secondary (*after* collimation on a live star) for backplate tilt and focuser sag/tilt, mis-machined and not square to optical axis.

Note: focuser checks on SCT scopes only if using an aftermarket focuser (Crayford, etc...).



*STOP HERE UNLESS YOU'RE INTERESTED IN THE BACK-END TESTS*

*After* you have a verified precise collimation on a live star (I use a fast webcam and star near zenith for this to see the best possible diffraction ring pattern), to do the back-end tests, you do this:

1) If using an aftermarket focuser instead of factory knob, rack focuser in and outside of focal plane to see if the return beam from the secondary mirror coming down the baffle tube stays within a couple mm of the same spot on the kit's rear "eyepiece" reflector that you insert into the focuser drawtube. Remember, this a greatly magnified beam at the back-end, so 1-2mm of variation is OK for many scopes. You have a problem if the impact point of the beam swings several mm back and forth as you rack or rotate on the back. This may indicate drawtube sagging or focuser body to drawtube alignment is not square. (Note, this step is difficult because as you rack the drawtube, the impact point of the laser will enlarge and go out of focus. So just check the outer edge of the defocused beam both in and outside focus and see if its donut pattern stays roughly in the same place for its impact point).

2) If the focuser has a rotation feature built into it, rotate the focuser without moving the drawtube while *at* focus, then lock it back down. Do incremental 90 degree rotation stops and check after each one. See if the laser impact point stays square on the back end. If not, indicates slop in the rotation mechanism or off-square machining of focuser or adapter plate of focuser.

3) If possible, rotate the *entire* backplate assembly without touching the focuser and with the focuser rotation locked in place and the drawtube at the focused position (you can do this on Planewave scopes and some other brands). Same deal there...watch for laser impact point large swings.

This gives you a systematic approach to checking back-end machining squareness and orthogonality.

That's the value of this kit. It's NOT just a collimator even though it's sold primarily under that flag. I would call it more of an "aligner and collimator" kit.

Hope this clarifies,
Wade


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Kevdog
scholastic sledgehammer
*****

Reged: 07/11/12

Loc: Desert Hills, AZ
Re: HoTech SCT Laser Collimator? new [Re: Wade Van Arsdale]
      #5849990 - 05/09/13 12:53 PM

After spending 30 mins or so fiddling with the collimation last night and probably ending up worse than when I started, I know I'm saving my pennies to buy one of these.

Saturn is downright fuzzy, so I know I'm off somewhere and was trying to tweak it last night but I just can't quite recognize which way to go, no matter how many articles I've read. What I see in my eyepiece does not look like the pictures I see in the collimation articles no matter what I do. I'm sure I'm missing something simple, but for now I don't know what.

It'll be worth $400 and 1hr to "get it right" and then be able to fix it again later if I need to!


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mega256
scholastic sledgehammer
*****

Reged: 05/10/07

Loc: N of Tampa
Re: HoTech SCT Laser Collimator? new [Re: Kevdog]
      #5850096 - 05/09/13 02:04 PM

After buying a C14 and a C11-HD over the last 12 months,(7K)
This is money well spent.(IMHO)...
Yes star adjustments are good, but sometimes difficult to do
in unstable air.....most of the time its best guess....
(my practical experience)...
I was very lucky to find a used one and look forward to
using this device...Also for centering the corrector plate
will be a great help.(they are now adjustable with set screws).
I find that my artificial star just has to be too far for me to use.......
I have a C6 and AT6RC to try also,but I understand the min scope dia is about 7",but I plan to try it on them also..



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gaz-in
scholastic sledgehammer
*****

Reged: 12/17/07

Re: HoTech SCT Laser Collimator? new [Re: mega256]
      #5851439 - 05/10/13 06:50 AM

When I chatted with David he gave slightly different means to center the secondary. Once all set up and the the HOtech reflector is placed in the read of the SCT you will see three laser dots on the Hotech reflector installed in the rear cell.

1) adjust the focus so the three dots on the rear reflector converge.

2) if the converged laser dots are not centered on the reflector target (not the big target on the tripod, the one installed in the rear cell of the SCT), the secondary is not centered.

3) Loosen the outer screws on the corrector plate and slightly move the corrector plate and secondary assemble to get the converged dots near the center of the target on the reflector.

Edited by gaz-in (05/10/13 06:53 AM)


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gaz-in
scholastic sledgehammer
*****

Reged: 12/17/07

Re: HoTech SCT Laser Collimator? new [Re: gaz-in]
      #5851445 - 05/10/13 06:58 AM

"you adjust the corrector's lateral positioning on the OTA until your center dark hole is orthogonal to the grid marks on the laser face plate."

could explain a little more about what you mean by "orthogonal to the grid marks" I interpret "orthogonal" as meaning at right angles or perpendicular...is that correct?

Thanks tons..


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Wade Van Arsdale
super member


Reged: 10/25/07

Re: HoTech SCT Laser Collimator? new [Re: gaz-in]
      #5851670 - 05/10/13 09:59 AM

Lateral (side-to-side/up-down) only, not "tip-tilt".

"Concentric" would have probably been a better word to use there.

Wade


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Wade Van Arsdale
super member


Reged: 10/25/07

Re: HoTech SCT Laser Collimator? new [Re: gaz-in]
      #5851748 - 05/10/13 10:44 AM

Gaz-In,
This way will likely be more accurate, but might also be a little harder to achieve because it introduces secondary mirror tip/tilt (collimation errors) into the mix along with possible decentering error at the same time.

Using the front shadow as an initial step after co-alignment eliminates that potential problem because you're not using the secondary mirror to reflect the beam to the back end (yet).

I use anything from steel tape to digital calipers on the front plate and its grid marks to measure the secondary centering. But I think the procedure you listed would work great as a final check after the "shadow test" up front, then collimation on a live star or with the Hotech.

Often, when you start using the secondary bounce at the rear, final alignment out the back end turns into an iterative process (too many moving parts at same time as Alph mentioned earlier). But I definitely use the secondary bounce out the back end as the final part of the process after the other alignment steps are complete.

In a pinch if your skies are too bad for live collimation, the laser kit's collimation simulation will still get it pretty close....enough to do all the back-end steps you and I mentioned.

Best,
Wade


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Kevdog
scholastic sledgehammer
*****

Reged: 07/11/12

Loc: Desert Hills, AZ
Re: HoTech SCT Laser Collimator? new [Re: Wade Van Arsdale]
      #5852528 - 05/10/13 06:56 PM

Order made. Should have my impression of the kit and pics next week hopefully!

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gaz-in
scholastic sledgehammer
*****

Reged: 12/17/07

Re: HoTech SCT Laser Collimator? new [Re: Kevdog]
      #5852659 - 05/10/13 08:03 PM

I found that when I rotated my diagonal in the rear cell the pattern on the reflector eyepiece moved around. I assume this means the diagonal mirror is not aligned properly?

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Wade Van Arsdale
super member


Reged: 10/25/07

Re: HoTech SCT Laser Collimator? new [Re: gaz-in]
      #5853701 - 05/11/13 12:19 PM

Gaz-in,
If this was on an SCT with an aftermarket focuser, and nothing else on the back-end was moved any (or factory knob turned any) during diagonal rotations, the diagonal would be a likely cause: either mirror misaligned internally in diagonal, or diagonal body not machined square or has slop in its fit into the drawtube.

**But** one caution on reading too much into the movement:
You should expect a small tolerance zone even if the diagonal was the only thing that got moved during the test, especially if the diag. is a clamping-style, not rigid screw-in.

If the error is larger than a couple of mm, compare it to a different diagonal if possible, to see if both do it (keeping in mind they could *both* be bad).

To keep things as simple as possible, I like to do all the Hotech collimation steps and a live webcam star test *without* the diagonal first, then add the diag. back in at the very last.

If the errors are very small during the diagonal rotation test, it is unlikely they will show up in visual or camera use with the diagonal. Verify this with a live webcam collimation test if possible.

Do you have another diagonal or two you could try just to compare (or borrow a buddy's)? This might help zero in on the cause.

Hope this helps,
Wade


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Hamsterdam
super member
*****

Reged: 03/23/11

Loc: smack dab in the middle of the...
Re: HoTech SCT Laser Collimator? new [Re: Wade Van Arsdale]
      #5854466 - 05/11/13 10:02 PM

For 1.5 years I have had an efficient, and free collimation system....a 10" SCT that wouldn't focus. 2 times in the field looking at bright donuts with a perfectly centered black hole for hours, trying spacers, etc, to achieve focus. The guy that lead me to the solution told me, "well, at least you know you don't need to collimate!" Then, as silly as it sounds, I super tightened the set screws on the focus knob, and now I can see stars, rather than donuts. Had the mirror not shown full throw when tested at home, this could have been diagnosed the first time, but it gave me variable symptoms. Ultimately it was use, a brass ferrule w/steel set screws to chew through the ferrule, then it would work indoors because of warmth, and dry air. When in the field, I suspect that humidity (slippage) and cool air causing metal contraction were the deceivers in my mind bending mystery. No matter how embarrassing a solution is, if it is free, and solves the problem... Please —embarrass me to death with my other malfunctioning machines!

One, mostly on topic question to add. If one were to switch to Bob's Knobs, you would expect to have to re-collimate immediately, no?


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Wade Van Arsdale
super member


Reged: 10/25/07

Re: HoTech SCT Laser Collimator? new [Re: Hamsterdam]
      #5854585 - 05/11/13 11:18 PM

Quote:


......If one were to switch to Bob's Knobs, you would expect to have to re-collimate immediately, no?




Yes, it's very likely you'd need to re-collimate after a changout of collimation screws/knobs.

Wade


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mega256
scholastic sledgehammer
*****

Reged: 05/10/07

Loc: N of Tampa
Re: HoTech SCT Laser Collimator? new [Re: Wade Van Arsdale]
      #5857205 - 05/13/13 10:58 AM

WoW just got mine,and what a well made device and a great
soft case to store it in...A very nice pro product !
Im happy,now the fun begins...lol...


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