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Learnings from Using Hotech Laser Collimator with EdgeHD Scope

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#1 Gary Imm

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Posted 11 March 2020 - 04:58 PM

A few months ago I purchased a Celestron C11 EdgeHD SCT scope together with a Moonlight Edge focuser.   I knew that collimation of such a long focal length scope would be critically important.  I convinced myself that purchasing the Hotech Advanced CT Laser Collimator for $455, a substantial sum for a calibration device, would be worthwhile.  After much effort, I have used this device to perform a good collimation of my scope.  This posting shares my learnings.  Please keep in mind that these learnings are specific to my setup. 
 

The device itself is simple and is well designed.  The challenge is using this device properly, and unfortunately the Hotech instructions fall a bit short in that regard.  Hotech has put quite a bit of work into the documentation - you will find various Hotech manuals (v8 and v9) and YouTube videos on-line.  All have pieces of useful information, but none of them had a complete solution for me.  My first collimation attempt, following the v8 instructions included with the collimator to the letter, resulting in a very poor star test that night.  I knew that the problem wasn't with the device but with how I was using it.   I wasn't going to let my $455 go to waste, so I did some more reading, research, and experimenting, and I was able to piece together a procedure which works. I don't think that most people have the time to do something similar, so I am posting the results here with no promise that it will work for you.
 

This is the most important thing:  Most people (and much of the Hotech instruction) focus mainly on the alignment of the 3 screws of the secondary mirror.  If this is the only alignment that you check, the collimation will not likely pass a simple star test.  Two other alignments also impact your collimation - the tilt of your focuser, and the centering of your secondary mirror.  All of these interactively work together to determine your collimation result.  The beauty and simplicity of the star test is that it incorporates all 3 of these effects, although a star test can only help you adjust the secondary mirror to get the best result.  In most cases, alignment of the secondary mirror alone through a star test will be sufficient to get good results.  The beauty of the Hotech system is that, if done properly, it aligns not only the secondary mirror, but also the focuser tilt and the secondary centering.  Alignment of all 3 of these results in the best collimation.
 

So here is my process.  It would help to watch the Hotech YouTube videos and to download and read the detailed Hotech v9 procedure before starting:

  1. Check your collimator  
    The Hotech collimator is not some magical, black box device.  It is "just" 4 lasers in parallel, but they have to be lined up exactly.  Check this by photocopying the face of the collimator and putting the copy up on a wall some distance from the collimator.  Point the collimator square at the copy and check if the lasers line up with the copy holes.  Mine lined up well.
     
  2. Optional - Create a jig 
    Hotech is right in that setup to achieve perfect alignment of the collimator is 90% of the work.  This is a tedious and frustrating process using the recommended telescope/tripod approach, especially since for most people the telescope has to be horizontal.  After messing with that twice, I decided to craft a jig for $10.  This jig enables much quicker and consistent alignment, at my telescope's normal elevation.  I attached a thin steel bar (36"x1/8") to the dovetail plate of my scope, and then attached the collimator holder to the steel bar.   I took apart the original collimator holder and reassembled it as shown in the image.  The holder adjusts for up/down tilt and left/right tilt.  The bar can easily be moved left/right, and I use weights at the end of the bar to adjust the elevation as needed.  The distance from the dovetail bolt to the holder bolt is 20-3/8" and never needs to be changed.
    Step 2a - Create a jig.JPG
    Step 2b - Create a jig.JPG
     
  3. Align the collimator 
    Turn on the collimator to mode 1.  Adjust the bar and collimator holder until the outer crosshair tips from the primary mirror reflection are centered on the same ring of the collimator.  This needs to be done accurately.    Keeping the outer tips are centered, adjust the collimator so that the crosshair lines are centered on the printed cross on the collimator.  This will take some time, so don't rush this process immediately before a night's imaging.
    Step 3 and 4 - Align collimator and center secondary.JPG
     
  4. Check the secondary mirror centering  Check the inner tips of the crosshair to make sure that the secondary mirror shadow is centered.  If not, use the Hotech guidance in the procedure to center the secondary mirror.
     
  5. Align the focuser  Remove the secondary mirror and install the reflector mirror in the focuser.  Turn on the collimator to mode 2.  The task now is to center all 3 crosshairs - the primary mirror reflection seen before on the collimator, the new reflector mirror reflection now on the collimator as well, and the crosshair seen on the reflector mirror in the focuser itself.  My Moonlight focuser had 2 methods of tilt adjustment -  I used the cam adjustment.  
    Step 5 - Align focuser.JPG
     
  6. Perform collimation  Install the secondary mirror and adjust the 3 secondary mirror adjustment screws until the three large reflected collimation spots are on the same collimator ring.  Check to make sure that each of the much smaller red dots are hitting the collimation holes.  In the focuser, the center of the 3 dots should be at the center of the reflector mirror.  Numerous iterations will be required, especially since you have to keep checking to make sure that all of the above alignments from the previous steps still hold true. 
    Step 6a - Perform collimation.JPG
    Step 6b - Perform collimation.JPG
     

Done properly, your collimation will be very close when starting a star test.  A star test is still required to make any minor final tweaks (lasers are not perfect, and neither is the alignment process, while star light always travels perfectly!).  Following my most recent Hotech collimation this week, I had to adjust two screws each by 1/32 a turn during the star test to achieve final "perfect" collimation. 

If you are reading this because you are thinking about buying this Hotech device so that you can quickly and simply calibrate your SCT, my advice for you is to stick with the simple but very effective star test instead.  I star test by using short exposure images of a defocused star and it works like a charm.  You just need to take your time and pay attention to detail.  The Hotech device is for those who are serious and have the time and money to take the next step.   I am happy I bought it for peace of mind that my focuser tilt and secondary mirror centering are now both good, which is hard to verify accurately through other means.  But I have to say that I expected such an expensive device would be a bit easier to use, especially after reading all of the Hotech ads and testimonials before purchasing it.

 


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#2 Benni123456

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Posted 11 March 2020 - 07:23 PM

Yes, this is the way it works with this hotech.

 

If one does not have an external focuser that can be aligned in tilt and horizontal/vertical directions, one may just use a tilting adapter and try it as best as it is possible.

 

In general, the lasers just seem to provide some first start. One has to fine adjust it with the stars anyway. But pre collimating with the hotech saves some time. 

 

It is simply too time consuming to turn collimation screws around for hours.Keeping the defocused star in the center with the mount after adjusting the screws simply takes time. And during collimation, one has to make this star smaller and smaller until one restarts at focus with the airy disk... this process usually takes one night...

 

With the hotech, one can set the system up before making the fine adjustment with the stars.

 

With the pre collimation with the hotech at home, it usually suffices to optimize the field and this adjustment then goes rather quickly, 1/2 hour or something....

 

Move the secondary screws until the stars in all corners are round.

 

Optimizing it with the starfield at the corners is really just a field optimization and not a collimation but it turns out that if you "optimize the field" that way, you usually tend to see a good airy disk in metaguide......

 

Especially when you have removed the tilt of the visual back with help of the hotech laser...


Edited by Benni123456, 11 March 2020 - 07:24 PM.


#3 Hobby Astronomer

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Posted 13 March 2020 - 06:06 PM

Nice post. Going to read in detail when I get home.



#4 Benni123456

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Posted 18 March 2020 - 04:23 PM

what i want to note is that from the hotech, you can see how important recollimation is when you change the imaging train. i recently changed my off axis guider from tsoag9 to tsoag16, the stars suddenly looked like elipses, elongated vertically... the hotech could confirm that the dots where shifted upwards....

 

And then one has to go via a tilting adapter or, better a recalibration of the focuser.

With the tilting adapter, the necessary changes are only fractions of milimeters. Usual tilters have a habit of changing during transport, so im almost tempted to buy something like this 

 

https://www.astrosho...ab_bar_0_select

 

or an edge 9 where i have enough space to insert a moonlight focuser in front of my  active optics...

 

Also, it is sometimes said that you can achive collimation just with the secondary screws regardless of the position of the corrector... this may work for a pure sc. apparently not the edge....

 

i tried that. the stars in the center looked round then, but on the edges of the field there were slight deviations from round, which are not there if i make sure that the corrector is centered...

 

to center the corrector do the following:

 

remove the secondary. It has a set screw on the side that holds it in the scope at some angular position. Remove that. Then reinsert the secondary and rotate it in the telescope. have the hotech at position 2 and look at the dots in the visual back and at the target plate. move the secondary collimation screws such that they have enough tension and that the dots do not change their position when the secondary is rotated inside the scope..

 

then re insert the holding screw into the secondary... it should now be exactly horizontal...

 

now you can position the corrector plate by losening the plastic ring on the corrector and tighting and losening the screws around the tube that position the schmidt plate vertically and horizontally in the optical axis...

 

place the corrector such that the dots at the visual back are in the same ring. Then fix it but not with too much tension... Since the secondary was made horizontal, this should center the corrector exactly on the optical axis...

 

Finally, move the tilting adapter or the focuser calibration screws such that the dots at the target plate are at the same ring...

 

of course during this,  one always  has to check that the hotech target plate is aligned to the primary...

 

But when you do all that... well this is basically the collimation procedure of an rc...

 

So you can buy an rc instead and get an f8 telescope, which is colimated similarly, where all optical elements have to be parallel and centered, with similar tolerances....

 

probably the collimation of an rc with a tak scope is even faster and easier than  with this hotech, whose output is very sensitive to the tilt of a target plate sitting on some imprecise plastic head and tripod...


Edited by Benni123456, 18 March 2020 - 04:45 PM.


#5 Gary Imm

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Posted 18 March 2020 - 04:56 PM

Benni,

 

Thank you for adding your thoughts and the collimation procedure to this thread.  I agree that the Hotech is useful for analyzing changes to the optical train.  Adding the reducer impacted the collimation for me and the Hotech showed that.

 

The procedure you describe above is also described in v9 of the Hotech manual.  I tried it but I could not find success with the step where one rotates the secondary mirror and then adjusts the secondary screws so that the dots "don't move".  When I rotated the mirror, the dots seemed to jump around enough to make it difficult to know when the final "non-movement" position is achieved.  I may give it another try.

 

Gary



#6 Benni123456

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Posted 18 March 2020 - 06:22 PM

 

When I rotated the mirror, the dots seemed to jump around enough to make it difficult to know when the final "non-movement" position is achieved.  I may give it another try.

Of course there is some play in the mirror.

 

But you should make the secondary as horizontal as possible. It must not be exactly aligned. Any remaining tilt of the secondary can be accounted for by aligning the focuser or the secondary with the collimation screws... 

Because the more aligned it is to the visual back and the primary, the better you get the Schmidt corrector into the center with this hotech...

 

Probably an even better procedure for aligning the schmidt plate would be this:

 

Add a small mark to the center of the secondary and use the takahashi collimation scope that is used by rc users...

 

Because in the end, the edge hd reacts like an rc... with the builtin flatener, it appears to be rather intolerant towards decentering.

 

Regarding this celestron reducer:

At least the reducer for the edge 8 will almost always need a new collimation, even if the reducer itself is perfectly built.

 

Why?

 

Because these geniuses at the factory where the reducer is assembled have positioned the threads of the reducer such that they begin at different positions than the thread of the edge hd...

 

This means that if you screw your imaging train on the telescope, it will be fixed at a different angle than if you screw your imaging train on the telescope with the reducer in between....

 

If your imaging train has just the slightest tilt, with the reducer screwed on, the sensor will look at a different direction than without the reducer.

 

And that means you need a recollimation, i.e. a different tilt of the secondary and a different position of the Schmidt corrector....

 

This is one reason to simply toss this reducer into the bin...

 

When they do not think things through, like where the threads have to begin.... then one can assume that not much thinking went into the design... 

 

To this comes that the Schmidt corrector is not a color free triplet, unfortunately, but a single complex lens. The handling of the chromatic aberrations is a challenge.

 

It is an interesting achivement that celestron was able to bring a flatener into the scope that looks good. But I guess the reducer was simply too much for the designers....

 

 

In the end, i think i will buy an rc if i have money again, since it appears the collimation is quite similar to the edge....


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#7 Gary Imm

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Posted 18 March 2020 - 06:42 PM

Very interesting post, Benni, thanks!  You are very knowledgeable in these issues and I appreciate you sharing that knowledge.


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#8 phileefan

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Posted 29 March 2020 - 07:04 AM

Gary,

 

Thank you for your very informative write up! waytogo.gif  I also have a EdgeHD 11 OTA with a MoonLite focuser so you can only imagine how happy I was to find an "easier to understand" set of instructions for the Hotech laser collimatorsmile.gif

 

I struggled with getting my OTA close to collimation with this device. I even contacted Hotech a few times and managed to get the V9 manual but like you said it left a bit to be desired! So being frustrated, it went into storage. 

 

So in the midst of this pandemic, I have a bit of time on my hands so that lead me to your post. I really like the idea of the jig you made. The tripod I purchased for my Hotech isn't the sturdiest so your jig idea should be more rigid. If you don't mind me asking, how did you attach it to your dovetail plate? confused1.gif

 

Thanks.................. 


Edited by phileefan, 29 March 2020 - 09:39 AM.


#9 Gary Imm

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Posted 29 March 2020 - 11:00 AM

phileefan, thanks for the feedback! It was a lot of work to write it up and I was hoping some folks would be able to benefit.

 

The jig works very well for me.  With it, and the instructions, my calibrations are always spot-on, which they never were before.  

 

I think that most dovetail plates, like mine, have a threaded hole towards the end in which you normally would thread a "stopper" to prevent the scope from sliding through the dovetail saddle if the screws are loose.  I removed the stopper and used that hole to secure the flat bar of my jig.  I had to drill a hole in the metal bar and find a short threaded bolt to use.  I attached a picture.

 

FYI, the collimator, at the end of the bar, bounces up and down a bit because my jig is flexible.  I like it that way - it would be much heavier if the bar was thicker, plus it is easy to add weights to the end of the bar to slowly bring the collimator down to the right elevation.  The problem is that you have to wait for the up and down vibrations to dampen out whenever you touch the bar to make an adjustment.

 

Let me know if you have any other questions.

 

Gary

 

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#10 Gary Imm

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Posted 29 March 2020 - 11:01 AM

Also, with just one bolt holding the jig, I can make slight left and right adjustments just by tapping the side of the bar.


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#11 TG

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Posted 29 March 2020 - 03:44 PM

I had high hopes of the HoTech collimator to achieve precise collimation without need of a star but I've since seen that this is probably not achievable. You can get close, and sometimes might even be spot on, but repeatable precise collimation is probably not something that the HoTech collimator can deliver on. Note that when I'm speaking of precise collimation, I mean collimation at the airy disk level with uniform diffraction rings all round and not the defocused disk.

 

Why do I say this? Even though I no longer own any SCT, I still have a 10" Cassegain with excellent mechanical construction. The collimator can be used in pretty much the same way except that I cannot remove my secondary (it's very accurately positioned anyway). After the initial co-alignment, I adjusted the secondary collimation screws to get the spots on the same radial line. However, I was curious how sensitive it was to the co-alignment part so I moved the scope in Az the slightest bit so that the crosshair lines barely moved on the collimator face. This resulted in the reflected spots moving significantly, showing that the collimator is very sensitive to the initial co-alignment. Not surprisingly, I found that the scope was not perfectly collimated and had to adjust it on a star.

 

Thus, the range of collimation produced by the star will be a function of the range of apparent perfect co-alignment that the user is able to discern. Due to the double pass setup and due to the fact that mirrors multiply ray angles by 2x the amount the mirror moves, I suspect that any error in co-alignment manifests itself as a 4x error in the spots' placement. This makes co-alignment very critical and no matter how accurately we place the spots, unless co-alignment can be done 4x better, it won't matter.

 

TL;DR: I think that the initial co-alignment step is the weak link in the collimator and sets a limit on the achievable accuracy.

 

Tanveer.



#12 Gary Imm

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Posted 29 March 2020 - 05:01 PM

Tanveer - thanks for your response.   You are correct that the co-alignment step is the most important one and one which dictates the final accuracy.  You are also correct that a final star test will always be needed, even with the Hotech collimator.  I usually end up turning one of the screws the tiniest amount for the ultimate precision collimation.

 

So if a final star test is always needed, what is the advantage of this collimator?  I see three:

1.  The resulting collimation is so close that any final adjustments are dead easy to make.

2.  The collimator also enables an alignment check of the focuser, which is not possible through just a star test.

3.  The collimator also enables an alignment check of the secondary mirror centering, which is not possible through just a star test.

 

Are these advantages worth the high cost of the collimator?  Probably not to most users.  But I image about 1,000 hours each year so it is worth it to me to have a system where I am confident in the alignment.


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#13 Benni123456

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Posted 30 March 2020 - 03:58 AM

I am thinking whether a takahashi collimation scope for rc telescopes would be even better...

 

Has somebody tried this? In order for that to work, one would need to mark the secondary with some circular spot in the middle..

 

I guess if you cut a donut out of self adhesive adress labels and then place it into the middle of the secondary, can one then use the takahashi collimation scope?



#14 TG

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Posted 30 March 2020 - 11:21 AM

I am thinking whether a takahashi collimation scope for rc telescopes would be even better...

 

Has somebody tried this? In order for that to work, one would need to mark the secondary with some circular spot in the middle..

 

I guess if you cut a donut out of self adhesive adress labels and then place it into the middle of the secondary, can one then use the takahashi collimation scope?

With an SCT, the secondary is spherical. There isn't much point to centering it precisely except for getting perfectly even field illumination. The Tak collimator could be useful in aligning the focuser, if you add an adjustable Crayford focuser but this might be better done using a laser which projects a pattern. Overall, nothing beats a simple star for collimating an SCT precisely.



#15 Benni123456

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Posted 30 March 2020 - 02:58 PM

the edge hd is not a simple sct design.

 

Because of its flatener, the centering of the corrector is, unfortunately, somewhat important....

 

I tried to just collimate it with the secondary screws... without centering the corrector i think i noticed some differences in the corner stars...

 

from what I see, the edge reacts similar to an rc, sensitive to focuser tilt, centering of the secondary and corrector and tilt of the secondary...


Edited by Benni123456, 30 March 2020 - 03:01 PM.


#16 TG

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Posted 30 March 2020 - 07:00 PM

the edge hd is not a simple sct design.

 

Because of its flatener, the centering of the corrector is, unfortunately, somewhat important....

 

I tried to just collimate it with the secondary screws... without centering the corrector i think i noticed some differences in the corner stars...

 

from what I see, the edge reacts similar to an rc, sensitive to focuser tilt, centering of the secondary and corrector and tilt of the secondary...

The secondary in an EdgeHD is still spherical and centering the secondary is not the same as centering the corrector since there is slop in the fit. Celestron is supposed to center the corrector accurately on a jig and that's why I always avoided pulling the corrector from my C11HD and C14HD scopes. I just had no confidence in being able to center it as it had been at the factory.

 

This thread will be of interest:

https://www.cloudyni...e/#entry7859305

 

One of the things the above thread (and its predecessor) mentions is that the secondaries are almost perfectly spherical under interferometric measurement. This means any decentering of the secondary can be compensated for by tilting it at the expense of slightly uneven field illumination.



#17 CA Curtis 17

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Posted 17 April 2020 - 02:48 PM

Gary,

 

I was just thinking this past week of a way to attach my HoTech CT Collimator to my scope to eliminate the wobbly tripod approach and low and behold I find your post.  First, I fully agree with your comments in post #12 for the advantaged of using the HoTech.  I also agree that the process can be very confusing at first and requires carefully reading the instructions and watching the video, several times, to get it right.  Frankly, it is not actually a complicated concept if one gets the big picture, which took me several runs through of the process.  But it is not for everyone.

 

I first used the CT Collimator to re-collimate my C14" Edge scope a year ago.  In using the Hyperstar I made the mistake one time of over-tightening it and could not get it off no matter how I tried.  I contacted Dean at Starizona and learned that the Celestron gasket between the secondary and the corrector plate tends to slip which prevented me from being able to remove the Hyperstar..  So I had to remove the corrector plate to take the Hyperstar off and I used a better gasket which does not slip from Starizona to reassemble everything.  I did my best to align the corrector as I thought it should be but I later fond slight coma in stars at the edge of my images.  Normal collimation of the secondary did not solve this problem.  So I bought the CT collimator used to check the positioning of the corrector plate as well as collimate the secondary.  I found another post on CN which suggested checking that the collimator lasers themselves were collimated.  I followed that procedure and found that at least one of my lasers was definitely out.  I sent it back to Hotech and they confirmed the problem and re-collimated the system at no cost other than shipping.  I re-checked it when I got it back and confirmed the lasers were spot on.  Then I went through the learning curve but finally finished the collimation of all three elements and also the Hyperstar.  When I checked images after that the stars were round all the way out to the edges.

 

I have always found the star test challenging because it takes some interpretation that leaves me uncertain even though I have read many discussions of what to look for.  I prefer data I can measure and see which the HoTech provides.  What I don't like about the HoTech approach is the fact that the Collimator is meant to be installed on a camera tripod.  Mine, and most unless you spend as much as a decent mount, tends to allow lots of vibration whenever you touch it to make an adjustment to the angle, distance etc.  It takes patience to wait out the vibrations.   Also, ideally an SCT scope should be collimated with the optical axis point up at an angle as it would be when viewing.  This allows the primary mirror to shift into a slightly different position from when the optical axis is horizontal.  I had to mount the tripod on a table to do this and it was challenging to get the collimator spaced correctly and still along the optical axis.  Eventually I made it work, but to me using a tripod and correctly positioning it is the weak point in the whole process.

 

Hence I thought about mounting the collimator directly to the optical tube similar to how you did it.  I appreciate your clever, simple and inexpensive approach but I was thinking of a more rigid setup.  I want to rigidly attach the collimator to the scope so there is no flex.  I was thinking of a piece of unistrut tube mounted to my ADM dovetail plate on top of my scope.  I would want to be able to move the collimator closer and further away from the corrector plate to get the best distance from the corrector plate.    I can think of a way to do with slotted holes on the unistrut.  The one thing I don't have a solution for is the ability to position the collimator up and down to get it centered on the optical axis.  Still thinking about how to do this.  If anyone has any suggestions I would be pleased to hear.

 

Once again, I applaud Garry for the concept and sharing it with us.

 

Best Regards,

Curtis


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#18 Benni123456

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Posted 17 April 2020 - 04:27 PM

what i want to say is that i removed the imaging train that was aligned with the hotech from my sct and i put it on my refractor...

 

my flat field refractor shows that stars are focused and round everywhere, so i guess the imaging train is now somewhat straight...

 

at least it appears i do not have to realign it everytime i switch my telescopes....

lets see how long it holds... 



#19 Gary Imm

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Posted 17 April 2020 - 05:01 PM

Curtis,

 

I appreciate your kind words above - thanks for that.

 

The reason that I used a thinner bar for the rig, and not a completely "rigid" beam or strut, is exactly the reason you mentioned - I wanted to have an easy way to position the collimator very slightly vertically up or down each time. The thin bar allows the use of simple weights (I use an assortment of smaller wrenches) to add or subtract from the end of the bar to adjust the elevation.    I wasn't concerned with being able to adjust the horizontal distance (closer or further away), so I locked that it in with a single hole and a bolt.  That has worked well - as long as you get the rings close to the right size, it doesn't matter too much if it isn't exact, unlike the vertical adjustment.  Ideally I would like to be able to lock in both the vertical and horizontal distances, but I couldn't think of an easy way to do that simply and cheaply.

 

Also, FYI, I have found it to be dead simple to align the 4 Hotech lasers myself.  Just make a copy of the target and put it on the wall 15 ft or so away.  Point the collimator at it and check the alignment.  It will be off.  For each laser, remove the warning label and unscrew the cap on the back.  You will then see the laser device and 3 hex adjustment screws at 120 degrees apart.  Turn each screw slightly to dial in the laser.

 

Good luck!

 

Gary


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#20 CA Curtis 17

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Posted 17 April 2020 - 10:12 PM

Gary,

 

Yes, your method is simple, cost effective and obviously works.  I just want to try something a little different.  I will let everyone know if I get it to work.

 

As for aligning the lasers myself, I do understand that is possible and understand the method.  I found this CN thread by Michael P where he explains how to do that https://www.cloudyni...or#entry9090440   I tried this method but believe that it is possible to fool oneself and make the collimation worse.  The key to collimating the lasers with the paper target is to get the actual collimator coplanar with the paper target, which is exactly the same as the first step in collimating the scope.  The difference is that with the scope you can align the cross hairs to the circles on the collimator.  In the picture here you can see that the cross hairs are much wider and taller because there is no obstruction to minimize them.  I tried doing this in my garage where I have a bigger wall to work with and tried to make sure that the ends of the cross-hairs were centered about the center of the target.  But my wall just wasn't big enough if I put the collimator any further than about 12ft from the wall.  It was clear to me that one of the lasers was out of collimation even if I wasn't confident that I could be sure about the adjustment.  So I sent the collimator to David at HoTech.

 

While my laser was off to be re-paired, I decided to try using a mirror attached to the wall instead of the paper target.  I got a small mirror at Home Depot.  Now I was chastised that a normal mirror would not work because I needed to use an optical flat.  I disagree in part.  If the mirror shows that my lasers are aligned I believe it as it would be impossible for imperfections in the mirror to exactly counteract a misalignment in lasers.  On the other hand, if the mirror says my lasers are off collimation I would not know if I could trust it because it could be due to an imperfection in the mirror.  In other words, this is a one sided test.  It will tell me if the lasers are accurately aligned but cannot give me certainty that they are misaligned.  When I got the collimator back from David I tried this and confirmed the lasers were now properly aligned.

 

Here are the before and after collimation of the lasers.

Attached Thumbnails

  • Image 4a.jpeg
  • Checking Collimation.jpg
  • Before Collimation 4.jpg
  • After Collimation 2.jpg

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#21 Gary Imm

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Posted 18 April 2020 - 12:00 AM

Thanks for the excellent report and pictures, Curtis!  I agree that David can do the best job of re-aligning the lasers.  I was just impatient and not willing to send it back.  When I first checked it, it looked much better than your "before" pic, but one of the lasers was slightly off (a bit more than the bottom right laser in your "after" pic).  My final result of the laser alignment may not quite be perfect but it seemed to do the job for me, in that I was happy with the end results and the final star tests.



#22 CA Curtis 17

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Posted 18 April 2020 - 09:27 AM

Gary

 

If one or more of the lasers on mine gets out of alignment in the future, I will use the mirror method I described above to re-align them.  Even though it is not an optical flat I think it gives an accurate result by having the laser spots reflect back onto the laser origins on the collimator plate itself.

 

By the way, the lower right laser spot shown in the after picture is actually well aligned to the hole.  The picture makes it look like it is shifted up to the 11 o'clock position because of the angle of the image.  Just don't want folks to think that David did not do a perfect job aligning these.

 

I bought a length of superstrut metal channel at Home Depot yesterday and am beginning to work out how to use it to attach my collimator to the scope.  The only challenge is to get the center of the collimator aligned with the center of the optical axis.  It turns out that the challenge with this is the fact that the collimator holder shown in your first picture is quite tall, relative to things and I need to account for that.  I think I have it mostly figured out and will share when I get it working.

 

Curtis



#23 Gary Imm

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Posted 18 April 2020 - 09:39 AM

Curtis,

 

I am eager to set your final setup.  Good luck and have patience - it will be frustrating at times, but worth it in the end.

 

Gary



#24 Reinhold Wittich

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Posted 04 May 2020 - 02:48 PM

Hi everybody,

 

I found Gary's setup at astrobin and I made a simliar setup for my RASA. 

Attached Thumbnails

  • IMG_DSC3819_1920.jpg

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#25 Gary Imm

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Posted 04 May 2020 - 03:46 PM

Reinhold,

 

Thanks for posting your improved setup.  It is much stiffer than mine and should be quite a bit easier to use.

 

Gary




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