Jump to content


Photo

HoTech SCT Laser Collimator?

  • Please log in to reply
86 replies to this topic

#51 gaz-in

gaz-in

    Viking 1

  • *****
  • Posts: 821
  • Joined: 17 Dec 2007

Posted 10 May 2013 - 05:50 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.

#52 gaz-in

gaz-in

    Viking 1

  • *****
  • Posts: 821
  • Joined: 17 Dec 2007

Posted 10 May 2013 - 05:58 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..

#53 Wade Van Arsdale

Wade Van Arsdale

    Vostok 1

  • -----
  • Posts: 107
  • Joined: 25 Oct 2007

Posted 10 May 2013 - 08:59 AM

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

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

Wade

#54 Wade Van Arsdale

Wade Van Arsdale

    Vostok 1

  • -----
  • Posts: 107
  • Joined: 25 Oct 2007

Posted 10 May 2013 - 09:44 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

#55 Kevdog

Kevdog

    Apollo

  • *****
  • Posts: 1275
  • Joined: 11 Jul 2012
  • Loc: Desert Hills, AZ

Posted 10 May 2013 - 05:56 PM

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

#56 gaz-in

gaz-in

    Viking 1

  • *****
  • Posts: 821
  • Joined: 17 Dec 2007

Posted 10 May 2013 - 07:03 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?

#57 Wade Van Arsdale

Wade Van Arsdale

    Vostok 1

  • -----
  • Posts: 107
  • Joined: 25 Oct 2007

Posted 11 May 2013 - 11:19 AM

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

#58 Hamsterdam

Hamsterdam

    Vostok 1

  • *****
  • Posts: 171
  • Joined: 23 Mar 2011
  • Loc: smack dab in the middle of the US (almost)

Posted 11 May 2013 - 09:02 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! :crazy:

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? :question:

#59 Wade Van Arsdale

Wade Van Arsdale

    Vostok 1

  • -----
  • Posts: 107
  • Joined: 25 Oct 2007

Posted 11 May 2013 - 10:18 PM

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


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

Wade

#60 mega256

mega256

    Viking 1

  • *****
  • Posts: 925
  • Joined: 10 May 2007
  • Loc: N of Tampa

Posted 13 May 2013 - 09:58 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...

#61 mega256

mega256

    Viking 1

  • *****
  • Posts: 925
  • Joined: 10 May 2007
  • Loc: N of Tampa

Posted 14 May 2013 - 08:55 AM

After a 4 hour learning session...Cool got it..
And it WORKs!..Checked it out on Saturn and some stars...my adjustment was right on..
From what I understand there are 3 versions of the manual...
Ver 5,8 and new 9.
Mine came with both types of 2" mirror's...normal and a new one that is transparent,with a crosshair rectical that shows the laser dots behind the EP mirror.
Its now much easyer to use in setups,no need to find the screws at 90deg..
And by removing the secondary in my new C11HD I could check the total optical path,including my jmi focuser first,looking at the cross at the EP and over laping the hole reflection in the round screen,,,it was fast setup!
My confedence level is now very good!
I did not want to touch my new HD scope,until I could spend
the proper amount of time to set it up..
I now have no worries about removing secondary ,for fastar,
and cleaning corrector plates on my cats..
So for the price of a good EP,this is justified.

http://www.hotechusa...irror-p/rm2.htm

#62 Ed Wiley

Ed Wiley

    Apollo

  • -----
  • Posts: 1013
  • Joined: 18 May 2005
  • Loc: Kansas, USA

Posted 14 May 2013 - 11:21 AM

At the TSP two observing buddies who are expert collimators assisted me in collimating my C11 Edge using Arcturus. No tools, only the star and Bob's knobs. I learned a lot. Result: spot on collimation and resolution under the Dawes Limit as confirmed by a resolution target.

Ed

#63 mega256

mega256

    Viking 1

  • *****
  • Posts: 925
  • Joined: 10 May 2007
  • Loc: N of Tampa

Posted 14 May 2013 - 01:44 PM

Yes I agree with you..and a good night with stable
skys and temp right does a good job.But I seldom
have those in SW florida.Now I don't have to spend time
at night.I was able to center the total optic system,including the corrector and my JMI electric focuser
in my living room.
BTY after centering the lasers,by removing the secondary
and using the new 2"crosshair mirror ep.I was able to center all 3 retun beams on target(only had 2 b4)and found
that all 3 screws had to be redone to move to the center line.Now inter and outer focus on a star is the same ,with almost no focus or image shift..This was on a brand new C11edge.Sending it back to celestron was not an option for me as shipping cost and shipping back may have done the same. My problem (I think) was that the screws were lose to start with? Last night was not clear but Saturn was the same and did not shift with inter/outer focus.
I will have to give celestron an ata boy in design that removing and repacin the seconday had no effect on alignment.
By the way....this device does not work(as advertised) on a 6" scope,both my C6 ant AT6rc are too small to get the 3
laser beams through that diameter..must be over 7" to work.

#64 Kevdog

Kevdog

    Apollo

  • *****
  • Posts: 1275
  • Joined: 11 Jul 2012
  • Loc: Desert Hills, AZ

Posted 15 May 2013 - 04:27 PM

Unit arrived today. As others have said, very very well built!

The kit has changed since the original. No longer do you need to put the tabs on the back of the celestron telescope with the strap! Whee! That was the part I was dreading the most. Now David uses diffraction tape over the crosshairs to form a donut to center the telescope's primary mirror. But it looks like it went even one step further as it appears that the reflector has it built in now? I got (a dim) donut back without the diffusion tape. If I blocked the sunlight through the window then I could easily see it. (And that's AZ sun). Putting the diffusion tape on showed the same (but brighter) donut so it was good for aligning it.

After aligning the donut with the target, I then aligned the crosshairs back on the target with the fine adjustment stage knobs. Once that was done I switched to laser dot mode (mode 2) and looked for the dots. I saw one way off to the side and no others. As I thought, my collimation was way off. Even though the highly OOF donut through the eyepiece had been centered, my secondary was still quite far off.

When I looked back at the reflector in my diagonal, I saw a single laser dot off to the very edge of the target. So I started adjusting the secondary until I got the dots near the center of the target in the reflector. Then they appeared on the main target.

Spent several times fiddling with the collimation, then double checking the alignment of the scope and target and then double checking the collimation again.

After reading the manual and all the threads on how to do it several times, plus watching the youtube videos, it only took me 30 mins to complete the procedure. The new "donut" alignment made that process much quicker! I'm glad I paid for a new one with the upgrades. It was worth the extra $$$.

I doubt it is perfect yet, but I'm sure it's much much better than it was. Hopefully I can get out tonight and try Saturn. Will follow up when I've had a chance to get it under the stars. But so far 5 star recommendation!

#65 Kevdog

Kevdog

    Apollo

  • *****
  • Posts: 1275
  • Joined: 11 Jul 2012
  • Loc: Desert Hills, AZ

Posted 20 May 2013 - 03:23 PM

So had another go as the first time I didn't take enough time doing the alignment of the scope and the collimator. Did it much more carefully this time and I think I have it. Have to star test again sometime this week. Also kept rechecking the centering to be sure nothing moved.

Here's my final alignment. Hard to see with the cell phone camera. Forgot to bring my good camera :(
Posted Image

Saw the 3 dots do converge on the reflecting eyepiece off center. I'm guessing this means my secondary isn't quite centered? Rotating the eyepiece didn't change it, neither did rotating the diagonal.
Posted Image

#66 Alph

Alph

    Surveyor 1

  • -----
  • Posts: 1759
  • Joined: 23 Nov 2006
  • Loc: Melmac

Posted 20 May 2013 - 04:24 PM

Saw the 3 dots do converge on the reflecting eyepiece off center. I'm guessing this means my secondary isn't quite centered? Rotating the eyepiece didn't change it, neither did rotating the diagonal.


You should not have used a diagonal. I think your are still off. The doughnut is not centered and the bottom laser return is off.

#67 Kevdog

Kevdog

    Apollo

  • *****
  • Posts: 1275
  • Joined: 11 Jul 2012
  • Loc: Desert Hills, AZ

Posted 20 May 2013 - 06:21 PM

My diagonal is an SCT diagonal. I can't remove it as it screws onto the 2" SCT threads in the back (no 2" visual back). Plus I use it for observing, so it better be collimated with it in.

I really should have had my better camera. The donut looked centered from what I saw.

What is still odd though is the top 2 lasers are oval in line with the axis of the center of the target. The bottom laser is oval is tangent to target circles, which makes it hard to verify that they are in fact on the same axis line! I wonder if that bottom laser needs rotated slightly?

I may set it up tomorrow again and bring my good camera for better pictures and try it again. See if the results again match.

#68 HOTECH

HOTECH

    Vendor - Hotech

  • -----
  • Vendors
  • Posts: 52
  • Joined: 23 Oct 2008

Posted 21 May 2013 - 04:10 AM

Hello Kevdog, Great setup!
1. Can you move the collimator closer toward the telescope so the inner tip of the crosshair lines expand to ring 1.5. This way, it is easier to identify if your secondary mirror is concentric to the primary optical axis.

2. The converged three dots on the reflector mirror's target:
Your mirror is properly positioned in the focal point because the three dots are converged into one. But they are not centered as you mentioned. Your guess is correct that most likely the secondary mirror is optically decentered if the co-alignment is properly done.

3. Before you begin any adjustment, I like to know what are the available adjustments you have and you can do on your scope.
a). Do you have tilt adjustment on the fouser? This can help you to square up the focal plane to the primary mirror's optical axis. You can shim the diagonal locking thread to achieve this.
b). Can you detach the secondary mirror assembly? Not a very hard task but you will need to pre-index the orientation of the assembly first. This adjustment will allow you center position your secondary mirror to the primary optical axis and help you to square up the focal plane to the primary mirror's optical axis.

Thanks for your posts, and I will do my best to walk you though.

Clear Skies!
David

#69 Kevdog

Kevdog

    Apollo

  • *****
  • Posts: 1275
  • Joined: 11 Jul 2012
  • Loc: Desert Hills, AZ

Posted 21 May 2013 - 10:20 AM

Thanks, you have a great tool. Very very well made.

1. Yes, I'll do it closer on the the next go around today. I'll take a picture once I have that set up. Still don't have the good camera with me, but I'll try and get a better picture.

2. I do have the removable secondary for the faststar system. I've read that unless it is highly decentered, don't mess with it. I'll do the alignment like you said in step 1 and see what it shows.

3. I have the Williams Optics 2" CF diagonal here:
http://agenaastro.co...ar-mirror-di...

I am currently using it with the SCT adapter, then planned to get a crayford focuser later and switch it to refractor mode. So I currently only have the standard focusing mechanism on the C11.

a) No aftermarket focuser yet, so just the SCT diagonal directly connected to the 2" threads of the SCT back

b) It's a faststar system, so it easily unscrews. I'm guessing that the faststar system only screws on one way, so it's automatically "indexed" for me. Not sure if the faststar system has any adjustements built in for centering?

So I have the old carbon fiber tubed Fastar C11 with the WO CF diagonal. Everything else is stock.

Thanks for your help!

#70 mega256

mega256

    Viking 1

  • *****
  • Posts: 925
  • Joined: 10 May 2007
  • Loc: N of Tampa

Posted 21 May 2013 - 11:43 AM

Yes the fastar is keyed and goes back with no problems.I was surprised that my settings held very well when putting the secondary back in..

I found out that removing the secondary first and then center the lasers in the focal plane,was fast and gave me some insite on how things were lined up...(corrector,focuser,ect)

Then put the secondary back in and proceeded to do the rest.
Im looking forward to the new setup instuctions with the new crosshair mirror.
I will say a stable secure tripod to mount the laser ,makes it much simpler job to do.

BTW David told me how to check the device for alignment:

Turn and square to a flat wall and one of the beams should
be in line with the X pattern on the wall..The other 2 will
be off the X ,but in good spacing.

#71 Kevdog

Kevdog

    Apollo

  • *****
  • Posts: 1275
  • Joined: 11 Jul 2012
  • Loc: Desert Hills, AZ

Posted 21 May 2013 - 03:19 PM

Okay, so had another go. I put the target closer at first just to see if the secondary is off center. It is, but not by much (1/2 a circle or less when the outer ring of the donut was on the 3)

I then moved it back again for another collimation run. Made sure to carefully center the crosshairs/donut and align the crosshairs to the target. Fixed the collimation (it was close).

Then I reset the target to a different location (higher and a bit farther away), so then I realigned, retargeted and the alignment was still right on, so I'm happy with that.

The dots in the eyepiece reflector are still a bit offcenter as in my previous picture, so that still matches with the secondary being offcenter.

Then also took the diagonal out and tried just holding the reflector against the 2" SCT opening on the back of the scope. Had to refocus, but then the collimation was still on.

The dots in the eyepiece reflector were still the same amount offcenter doing it this way, so I think my diagonal is fine.

Thanks for all the help. Now gotta get it under the stars again.

#72 HOTECH

HOTECH

    Vendor - Hotech

  • -----
  • Vendors
  • Posts: 52
  • Joined: 23 Oct 2008

Posted 21 May 2013 - 06:42 PM

Thanks Mega256! I would also like to touch up from your description in the following as well.

1. Kevdog needs to check if the focal plane at focal point is square to the primary optical axis first.
- Remove the secondary mirror assembly.
- Co-align the primary to the collimator crosshair by lining up the reflected crosshair back on the collimator target symmetrically. Make sure the outer tip of the crosshair lines are all on the same track, and the crosshair lines are also lined up to the target cross lines. At this point, your primary mirror is optically aligned to the collimator.
- Install the reflector mirror in the focuser. You can try both with and without the diagonal and see if the diagonal corresponds to the visualback focal plane.
- Observe the reflected crosshair from the reflector mirror and see if the crosshair laser is also reflecting back to the center of the collimator target. You should see two crosshair overlapping on the collimator target. One larger diameter (from the primary) and the other smaller from the reflector mirror/focal plane.
- If the small crosshair don't coincide on the target, your focal plane is off/tilted.
- If the crosshair exhibit behind the reflector mirror's target is not centered, your focal plane is decentered.
- Correct the tilt first by shimming the connection between the focuser and the visualback. Usually, I will use a third party focuser has tilt capability to square this up.
- The tilt can also came from mirror flop. You can adjust the primary mirror focus (in/out) and see if the primary mirror crosshair shifts. If you can control to make the change and line up both crosshair reflection. Lock down the primary focus after achieving this. And this will keep the whole scope optically and mechanically lined up from the primary optical axis to the focal plane/focuser.
- The next step will be optically centering the secondary mirror in the primary's optical center.

Before we start the secondary centering procedure, I would like to emphasize a few fundamental requirement on a good scope.
The whole scope should build around the "optical axis" of the primary mirror. Then the rest of the optical train elements will follow accordingly. Often time, the mass produced telescope makers assume that the mechanical axis is the same as the optical axis, then they slap the rest of the parts under mechanical alignment. A good scope maker will allow some room to shift around to correct the inherited tolerance (both optical and mechanical) discrepancy, but most will just glue the whole thing together without any feedback system. This is the trade off for "ready to use" scope. But the adjustments are far cry limited if the mfg. did not do it right on the first time. The scope is pretty much stuck on its performance without any possible optimization. Some people would say it is time for a 'better' scope. But in fact, if you can do some adjustment with the help of the collimator, you can revive the scope with your well spent effort in it.

This is where the hobby fun kicks in. We will find anyway to tweak each part to improve the ever ending optimization quest. A full collimation process can elevate your understanding of the instrument you use and built confidence in you with no fear of adjustment on each optical element. In the process, we learn, share, and enjoy the hobby. :jump:

#73 HOTECH

HOTECH

    Vendor - Hotech

  • -----
  • Vendors
  • Posts: 52
  • Joined: 23 Oct 2008

Posted 21 May 2013 - 07:53 PM

The following is the general guideline to the collimation procedure.

Co-alignment distance: Find a good distance that the central shadow cast by the secondary mirror is at least on one of the target ring between ring 1 and 2 as I've mentioned earlier.

1. Line up the focal plane to the primary mirror's optical axis.
- Remove the secondary mirror with the corrector plate.
- Co-align the primary optical axis to the collimator.
- Make sure the outer tip of the crosshair are symmetrical to the same ring on the collimator target.
- Make sure the crosshair are also lined up to the target printed crosshair.
- Install the reflector mirror in the focuser.
- Adjust the focuser tilt to center the reflected crosshair back on the center of the collimator target.
- Make sure both reflected crosshair (from the primary mirror and from the reflector mirror in the focuser) are all lined up to the printed cross on the collimator target.
- At this stage, your focal plane is guaranteed orthogonal to the primary optical axis.

2. Center the secondary mirror in the primary mirror's optical axis.
- Position the secondary and the corrector plate back on the scope. Do not lock it down yet.
- There will be some weight difference where the scope will slightly point down. So you will need to touch up the co-alignment.
- Observe closely on the four inner tips of the crosshair lines (cropped by the secondary mirror assembly).
- Shift the secondary mirror to bring all four inner tips on the same track. Then lock down the secondary mirror assembly.
- At this stage, both the outer and inner tips of the crosshair line are all symmetrical on its own rings. And this means the secondary mirror is positioned concentric in the primary's optical path plus the focal plane from the focuser is also square up to the same primary optical axis.

3. Adjust the secondary mirror tilt to collimate the final optical train.
- Adjust focus to bring all three converging laser dots exhibit behind the reflector mirror to a single point.
- Adjust the secondary tilt to line up the three dots on the collimator target onto the same track.
- Check if the converged laser behind the reflector mirror are also concentric on the small bull's eye target.
- If not, the secondary mirror is still offset positioned from the primary optical axis. You will need to iterate the same process in step two to correct this.
- At this point, your secondary mirror aims parallel to the primary's optical axis.

4. Verify focuser travel is parallel to the final optical axis.
- Adjust the focuser from minimum to maximum distance and observe the three laser dots on the collimator target.
- If all three converge and expand symmetrically on the target, your focuser is parallel to the final optical train axis.
- Your scope is ready for the first light and you should only need small or no adjustment to touch up the image.

The above guideline is based on available adjustments on your SCT scope and most RC scopes like the ATRC. The sequence may slightly switched depending on the type of scope, e.g. MaK with fixed secondary mirror in the OTA will be aligned based on the secondary mirror's optical axis.

Clear Skies!
David

#74 ahopp

ahopp

    Messenger

  • -----
  • Posts: 402
  • Joined: 24 May 2012

Posted 22 May 2013 - 07:59 AM

Maybe David could start a rental service for the collimator, I would happily pay $100 to rent for a week.

Tony

#75 Kevdog

Kevdog

    Apollo

  • *****
  • Posts: 1275
  • Joined: 11 Jul 2012
  • Loc: Desert Hills, AZ

Posted 22 May 2013 - 04:25 PM

I have no idea how to shift the secondary on an old CF tube C11. Anyone know? If its not too hard I might give it a go. If it's too involved I might just be happy with "good enough" for now.

Thanks for all the info!






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics