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Collimation check! w/ pic

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#1 bazookaman

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Posted 04 December 2020 - 08:29 PM

Hey guys, so I got a Parallizer from Don and realigned the secondary. There was much less movement with the Parallizer and the laser collimator, but there was still some flex although it seemed to move back to the same spot which is good.

 

I then used the laser and adjusted the primary. I put the collimator cap back in (with the Parallizer) and this is the result.

 

thumbnail_20201204_173932.jpg

 

Is this correct, or does the circle need to center with the vanes? This is a cell phone pic through the coll cap so you can't see the mirror clips but they are there and the secondary mirror looks to be centered in the focuser perfectly.

 

Also, I tried to put the laser in my shorty 2x as I read that using a barlow can be more precise, but when I did this it just diffused the laser into a circle on the primary about 1" across. What am I missing?


Edited by bazookaman, 04 December 2020 - 08:30 PM.


#2 Asbytec

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Posted 04 December 2020 - 08:52 PM

Using the Barlow laser method is for aligning the primary center donut on the return target on the Barlow. It reads the image of the primary center mark at the Barlow, not at the primary center. Use the thin beam, un Barlowed laser to align the focuser to the primary center. The Barlow uses the diffuse return beam to collimate the primary axis, so you read it against the target on the Barlow lens. 

 

It's hard for me to make much sense of it using the picture above, there does seem to be a lot or parallax error to confuse things. But your offset looks right presuming the primary is in the direction along the spider vane at 4 o'clock. So, your secondary is nicely rotated, which is an indication you did a good job. The bright spot in the center should be centered in the larger bright cheshire ring, and both centered in the barely visible grey ring (reflection of the inside of the focuser). But that "error" may be another trick of parallax. The vanes mechanically hold the spider and have nothing to do with optical alignment. They may not and probably will not be on the optical axis in most cases. So they do not have to cross the reflection of the small bright primary center mark.

 

I don't really see anything wrong given the context of the picture. But, if as you say, the secondary mirror is centered under the focuser and if you can get the laser into the primary center, you should be collimated on both axes. At least very close. 

 

post-347275-0-40381600-1607131662.jpg


Edited by Asbytec, 04 December 2020 - 09:00 PM.

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#3 bazookaman

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Posted 05 December 2020 - 11:36 AM

Using the Barlow laser method is for aligning the primary center donut on the return target on the Barlow. It reads the image of the primary center mark at the Barlow, not at the primary center. Use the thin beam, un Barlowed laser to align the focuser to the primary center. The Barlow uses the diffuse return beam to collimate the primary axis, so you read it against the target on the Barlow lens. 

 

It's hard for me to make much sense of it using the picture above, there does seem to be a lot or parallax error to confuse things. But your offset looks right presuming the primary is in the direction along the spider vane at 4 o'clock. So, your secondary is nicely rotated, which is an indication you did a good job. The bright spot in the center should be centered in the larger bright cheshire ring, and both centered in the barely visible grey ring (reflection of the inside of the focuser). But that "error" may be another trick of parallax. The vanes mechanically hold the spider and have nothing to do with optical alignment. They may not and probably will not be on the optical axis in most cases. So they do not have to cross the reflection of the small bright primary center mark.

 

I don't really see anything wrong given the context of the picture. But, if as you say, the secondary mirror is centered under the focuser and if you can get the laser into the primary center, you should be collimated on both axes. At least very close. 

 

attachicon.gifpost-347275-0-40381600-1607131662.jpg

Ok, so I can ignore the vanes. That simplifies things.

 

On the barlow return, the light hitting the target looked like a diffused mess too. If there was a dot, it was in the target hole, but there was laser light scattered all around the target. I tried adjusting the focus knob thinking maybe it needed to be focused, but that didn't seem to have any affect.



#4 MellonLake

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Posted 05 December 2020 - 11:56 AM

Below are pictures of my XT10 using the Barlowed Laser technique. I hope they help.  The arrow shows the direction the shadow needs to move to be collimated.  I will say that it is hard to see the shadow on the cheaper lasers because the shadow is so big compared to the target and the lasers really are not that bright.  

 

In this image the Barlowed laser beam on the mirror.

 

Laser spot on Primary small.jpg

 

 

In this image I have intentionally de-collimated the primary to show the shadow of the Mirror marker.

 

Laser Tarket with shadow2 small.jpg

 

 

In this image I have intentionally de-collimated the primary to show the shadow of the Mirror marker and annotated

 

Laser target with annotation small.png



#5 bazookaman

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Posted 05 December 2020 - 12:38 PM

Perfect, I looked at it again and that's what I have as well.

 

Here is without and with barlow.

 

thumbnail_20201205_111231.jpg

 

thumbnail_20201205_111425.jpg


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#6 MellonLake

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Posted 05 December 2020 - 12:46 PM

Perfect!!!!

I bet if you do a star test it is bang on!!!  The telescope should but up the best views it can.  



#7 MellonLake

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Posted 05 December 2020 - 12:47 PM

FYI... I love the Parallizer, it is by far one of the best tools I have ever purchased.  It makes everything less "wiggly" and gives me confidence in my collimation.  Money well spent.


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#8 bazookaman

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Posted 05 December 2020 - 01:13 PM

Good to know. I've already seen the difference with the laser col. I can "bend" it with pressure, but it returns upon release, and the significant wiggle that happens when tightening is gone.

 

What I did notice last night was on dim stars, there appeared to be a small amount of coma across the entire field, even in the center. If I focus on one side of the focal plane, the coma points to around 4 o clock. If I focus in the other direction, the 4 o clock coma shrinks and a 6 o clock coma grows and replaces it. At no point were they both completely gone. It was a slight affect and didn't bother me too much, but it was enough for me to take note.

 

I didn't mess with it much so I can't even remember if it was more than one ep. Cloudy tonight so no testing. Maybe tomorrow. I have a Parracor 2 coming in this week so maybe that'll clean it up.

 

Any ideas?

 

Otherwise it seems sharp, I saw 5 of Saturn's moons before it set so I was pretty happy with that. I don't think I've ever noticed more than one before.


Edited by bazookaman, 05 December 2020 - 01:14 PM.


#9 MellonLake

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Posted 05 December 2020 - 01:27 PM

If you are getting issues with Coma varying across the field;

 

1) Do a star test (Polaris is easiest) with star in the middle of the field of view.  If the diffraction rings on defocusing (outward focuser movement) do not move outward concentrically your collimation is off.

2) Make sure both the eyepieces and the laser are registering the same way.  Only use on screw to hold in the Parallizer, it should be opposite the set screw in the Parallizer  Even if the collimation is good if the eyepieces are not sitting square you will get this issue.  

3) Put the laser in the Parralizer and the then run the focuser all the way in and out, the dot should not move.  if it does you have an issue with secondary collimation (could be the laser).

4) These cheap lasers are often misaligned from the factory (have you aligned it). Put the laser in the Parallizer and clamp it only lightly, rotate the laser and let go, repeat every 45 degrees.  Watch the spot on the mirror if it moves in a circle your laser is internally misaligned.  There are directions here on CN on how to align it.

 

The star test is really the best test of collimation (see below).  FYI collimation is much more critical with the Paracor for it to work right.

 

air disc.gif



#10 Asbytec

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Posted 05 December 2020 - 03:58 PM

"If I focus in the other direction, the 4 o clock coma shrinks and a 6 o clock coma grows and replaces it. At no point were they both completely gone. It was a slight affect and didn't bother me too much, but it was enough for me to take note."

If you're moving the focuser to get better images at different points in the field, I'm wondering if you're seeing coma or a slight amount of defocus error. Maybe a little of both. When I insert my focal extender, it does wiggle a little in the focuser. So I can modify the quality of my collimated star images by adjusting the set screws. I ordered a parallizer to help reduce registration error when I'm operating at high magnification.

Defocus error depends on the tilt of the primary focal plane relative to the eyepiece, and that is a function of focuser axial alignment. Actually, it depends on the alignment of the eyepeice in the focuser. That is registration error likely caused be tightening the set screw holding the eyepeice. It can push the eyepeice out of alignment with the focuser. Sometimes it does not take much registration error to make a difference over the long focal length of the primary mirror. It may tilt out of focuser axial tolerance of 0.03D. This is why we say to register the eyepeice in the same way we register the collimation tool, so they both stay in the same alignment during collimation and use.

For coma, sometimes the thin un-Barlowed return beam can be problematic, but I'm not sure about the Barlowed laser return beam in your method. It may be fine. In the traditional Barlow method, the return to target image of the primary center mark does not budge with focuser registration error. It depends only on primary tilt. That's the beauty of the diffuse Barlow laser covering the primary center and the target at the Barlow aperture. But, your return beam is moving up the focuser to reach the target, so registration error may matter.

Edited by Asbytec, 05 December 2020 - 04:16 PM.


#11 bazookaman

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Posted 05 December 2020 - 06:21 PM

The coma is all the same direction (4 o clock or 6 o clock, or both, depending on the focus) and it is the same direction and same amount across the field.



#12 Asbytec

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Posted 05 December 2020 - 10:28 PM

The coma is all the same direction (4 o clock or 6 o clock, or both, depending on the focus) and it is the same direction and same amount across the field.

This does not sound like normal off axis coma. 

 

I just reread your OP and realize you are using a parallizer. Re reading your comment to see if I misunderstood anything. 

 

What I did notice last night was on dim stars, there appeared to be a small amount of coma across the entire field, even in the center. 

If it is coma across the field and in the center and it all points in the same direction (4 or 6 o'clock), then your primary alignment is way off. Sounds like the primary optical axis (and diffraction limited coma area) is outside the field of view (at 10 or 12 o'clock). If so, in the direction of the tail in the field away from the primary optical axis, coma should not be a small amount across the entire field. Coma increases exponentially with the field angle from the primary optical axis. 

 

So, it should not be the same small amount across the field, unless coma is seen is pointing in the other direction in the opposite side of the field. If the scope is collimated well enough, and it may be, then coma will not point in the same direction across the field because the primary optical axis is located somewhere close to the field center. 

 

If I focus on one side of the focal plane, the coma points to around 4 o clock. If I focus in the other direction, the 4 o clock coma shrinks and a 6 o clock coma grows and replaces it. 

 

Now, that does sound like coma being it will point in (what seems like) the same direction and will do so on both sides of focus. 

 

At no point were they both completely gone. It was a slight affect and didn't bother me too much, but it was enough for me to take note.

 

At no point was the defocused coma (pointing toward 4 o'clock then 6 o'clock) completely gone. Was is still visible in focus? Without a coma corrector, coma can be still seen in the defocused image somewhere in the field if we defocus the star. That's normal and the amount is small but noticeable, yet it's more difficult to see in focus. This is true if coma is diffraction limited and it may mean you are just seeing coma in the diffraction limited area around the well collimated primary axis.

 

At f/4.7 the diffraction limited coma "free" area is 0.022f^3 = 2.3mm and 57.3 * 2.3mm/FLscope = 0.11 degrees true field of view. At 205x, that is only 250 * 0.11 ~ 28 degrees AFOV, or about half the field of a 60 degree AFOV eyepiece giving 250x. If it doesn't bother you beyond that and closer to the edge, then you may not want or need a coma corrector.


Edited by Asbytec, 05 December 2020 - 10:37 PM.


#13 bazookaman

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Posted 05 December 2020 - 10:48 PM

But according to my pics and the responses, I'm fairly confident I'm collimating correctly. Perhaps it was just my contact lens giving me an issue. I didn't think to switch eyes. I'll play around with it on my next outing (possibly tomorrow) and see if I can get any more evidence/data. It's cloudy tonight. :(



#14 Asbytec

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Posted 05 December 2020 - 11:00 PM

It's cloudy tonight. frown.gif

Alas, isn't that often the case? lol.gif

 

Yea, sorry for being verbose, but I am trying to understand and think this through. I had a similar issue I mentioned above, it turned out to be related to defocus, focal plane tilt, and registration of my focal extender. I collimate using a 2" light pipe and register it in the 2" eyepiece adapter. I register the 1.25" adapter the exact same way, so it should be very close to being true to the 2" focuser axis. The problem is inserting the 1.25" focal extender then trying to register it to the focuser axis, too. It wiggles a tiny bit. 

 

Point being, I was fighting with something similar to what I thought you might be describing with focus. In focus, I could see what looked like both defocus and normal small amounts of defocused coma in one part of the field. I could fix the defocus part by working the out the registration error of the focal extender by adjusting the set screw to get it to align more or less with the focuser, too. (A poor man's parallizer smile.gif ). So, this sounded like what you might have been experiencing. 


Edited by Asbytec, 05 December 2020 - 11:04 PM.


#15 bazookaman

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Posted 06 December 2020 - 03:04 PM

One thing that might be causing the problem is I wasn't using the Parallizer properly... I was using both focuser screws to clamp it instead of one. I think it'll be clear tonight so I'll try again.

 

I performed another re-collimation. First I put the laser in the parallizer and tightened it enough where I could still rotate it. I had the beam centered in the primary and while rotating, there was virtually no change. I say virtually because there was still some wobble. But not enough to move it outside of the doughnut.

 

I only made minor adjustments to the secondary to get the laser centered. Then I adjusted the primary a bit to recenter the return beam.

 

After, I put the col cap on and took these pics:

 

 col_cap.jpg

 

And one without col cap:

 

focuser_noep.jpg

 

It still isn't aligned visually, even though the laser seems to be collimated and using the parallizer. Would it be better to align with the col cap instead and get everything concentric?


Edited by bazookaman, 06 December 2020 - 03:06 PM.


#16 MellonLake

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Posted 06 December 2020 - 04:04 PM

It is really hard visually photographing down the tube to see if you are actually on the focuser axis.  So the second picture is not that helpful, it really needs to be through the collimation cap or a combo tool.    

 

The collimation cap image looks great in terms of the secondary tilt and rotation!  I can't really see the pupil dot in the mirror marker but the if you do the barlowed laser for the primary I am sure it will be excellent.   

 

The only thing we can't see is the centering of the secondary.  In the collimation cap the secondary mirror should appear centred in the focuser drawtube (equal space around the secondary.  This is the only thing we can't see in the images.  Your collimation cap and the second image do suggest that the secondary is very close to right position or even in the right position but... I can't tell if it is exactly right.  Take the collimation cap picture again and:

 

1) Move the focuser draw tube way out so we can see the entire secondary and the inside of the drawtube.

2) Put a piece of paper on the far tube wall behind the secondary so we can see where the secondary is.  

3) Let a lot more light into the tube so we can see the walls of the focuser drawtube.

 

Below are my pictures of my secondary, annotated.  You can see the primary collimation is very slightly off because the dot is not in the middle (I did not collimate the primary).  The annotated image show the drawtube (blue circle). The distance from the drawtube to the secondary mirror (green bars of equal size).  Thus, my secondary is centred.  The red circle is the secondary (not this is a circle and not an elipse so it is "rounded".  When I draw diameters on the circle the diameters cross on the primary marker indicating my secondary is very well collimated. Note that there is a little triangle on the right in the image on secondary (this is a fold in the piece of paper I placed against the tube as it is not sitting flat against the wall)

 

Unannotated

Collimation Cap image small.jpg

 

Annotated

My Annotated Collimation small.jpg


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#17 Asbytec

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Posted 06 December 2020 - 06:36 PM

"One thing that might be causing the problem is I wasn't using the Parallizer properly... I was using both focuser screws to clamp it instead of one. I think it'll be clear tonight so I'll try again."

Interesting. Yes, see how that works.
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#18 bazookaman

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Posted 06 December 2020 - 07:18 PM

Took another pic... I found that I couldn't get my phone close enough to the col cap to get the whole thing with the Parallizer so I switched to the regular 2" - 1.25" adapter.

 

thumbnail_20201206_180150.jpg


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#19 MellonLake

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Posted 06 December 2020 - 07:49 PM

The secondary looks centered within a mm or so (pretty good, I would not change it).  In this image the collimation looks very far off compared to the earlier image (too far off). I am concerned the cheap adapater is tilting something!  Don't use the cheap adapter any more.  

 

Given the secondary looks well centred and your laser is well aligned.  I would go back with the Parallizer and:

 

1) Visually check with the collimation cap in that the secondary looks rounded (it is close but is off slightly).  

2) Use the laser (no barlow) in the Parallizer to tilt the secondary so the beam hits the centre of the mirror marker (on the mirror).

3) Centre the return beam on the laser target.

4) Put the barlow in and centre the image of the mirror marker on the laser (It may not need to be moved after step #3).

5) Do a star test.  This is the real test.

 

I am confident you will be well collimated after this!  

 

I would always use that Parallizer.   Hopefully it looks as good as the image in post #15 (if you want to check it with the collimation cap).  The secondary collimation in Post #15 looked really good.  

 

 

Rob 



#20 Vic Menard

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Posted 06 December 2020 - 10:29 PM

Took another pic... I found that I couldn't get my phone close enough to the col cap to get the whole thing with the Parallizer so I switched to the regular 2" - 1.25" adapter.

 

waytogo.gif It looks good to me. I see what might be a couple of tweaks, but you're already better than the high magnification error tolerances, so I would leave it "as is" and enjoy your well collimated scope. The annotated image shows optimal secondary mirror placement (green circle) and the "tweaked" focuser axis/secondary mirror tilt (red circle). 

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#21 Asbytec

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Posted 06 December 2020 - 11:07 PM

Once the well collimated laser is in the primary center donut, the reflection of the primary mirror is necessarily centered under the focuser. The primary reflection can then be used as a reference for centering the secondary. Once the focuser axis is aligned to the primary center, both the edge of the focuser and the edge of the primary reflection are concentric. That's two of the collimation signatures. Bringing the secondary centered on the primary reflection completes the third collimation signature. All three edges will be concentric when the focuser axis is collimated.

Given Vic's annotated image, it does look very good. The secondary position might use a tweak on a cloudy night, but it looks fine. Secondary position only deals with field illumination, axial alignments are responsible for image quality. So don't fret much over secondary position, as long as the primary reflection is fully visible in the secondary.

Edited by Asbytec, 06 December 2020 - 11:14 PM.

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#22 bazookaman

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Posted 06 December 2020 - 11:39 PM

The secondary looks centered within a mm or so (pretty good, I would not change it).  In this image the collimation looks very far off compared to the earlier image (too far off). I am concerned the cheap adapater is tilting something!  Don't use the cheap adapter any more.  

 

Given the secondary looks well centred and your laser is well aligned.  I would go back with the Parallizer and:

 

1) Visually check with the collimation cap in that the secondary looks rounded (it is close but is off slightly).  

2) Use the laser (no barlow) in the Parallizer to tilt the secondary so the beam hits the centre of the mirror marker (on the mirror).

3) Centre the return beam on the laser target.

4) Put the barlow in and centre the image of the mirror marker on the laser (It may not need to be moved after step #3).

5) Do a star test.  This is the real test.

 

I am confident you will be well collimated after this!  

 

I would always use that Parallizer.   Hopefully it looks as good as the image in post #15 (if you want to check it with the collimation cap).  The secondary collimation in Post #15 looked really good.  

 

 

Rob 

I didn't change anything since the first pic, the only difference is I took out the Parallizer and put in the cheap orion adapter because the Parallizer couldn't allow me to get the phone close enough to the col cap to take a good pic.  I made no adjustments to either mirror. It's in the garage so not much change in temperature, but probably a little.



#23 bazookaman

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Posted 07 December 2020 - 12:05 AM

So my concerns are... I'm just not totally confident the laser is collimated. I've tried the two sets of nails (or sheetrock screws in my case) in wood trick and it is just terrible. Rotating the laser, the thing is about as smooth as you can imagine metal on metal could be, until it catches on something and bounces around. I can't get 180 deg without the thing bouncing and jerking all over the place on a wall about 15 feet away. I need some bearings or something to roll it in smoothly. Any ideas? Even rotating it in the Parallizer isn't quite satisfying to me as it still bounces around a bit as it scrapes against the sides, although this was much better than the screws in a board trick.

 

Tonight, I again experienced the coma pointing down at what seemed to be the best focus. Of course, I get so caught up in the sights, that I forget to do a basic thing like try another lens. I mostly used the 30mm. Either the seeing was terrible, my mirror wasn't cooled, or my col was off because mars looked terrible at 7mm. It was just a blurry mess. The stars looked bad at 7mm also. I didn't even try a barlow.

 

I did notice that if I move my eye location down and look up into the ep, this moves the center field up toward the top of the field stop, and it also seems to neutralize this "coma" that I'm seeing. I did defocus with the 30mm on mars and.... well, there's just so much to remember, when I'm out there I can't even remember what I'm looking for. I defocused both ways and I can see the 4 vanes and the center shadow... it looked perfectly concentric one direction and maybe a bit off in the other. But just moving my eye around seemed to change the results so I don't really know what I'm doing.

 

I think tomorrow I'm going to try to collimate with just the col cap. I don't trust that laser.


Edited by bazookaman, 07 December 2020 - 12:06 AM.

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#24 Waynosworld

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Posted 07 December 2020 - 01:28 AM

This is what I made, I used 4 round headed screws so there would be no sharp edges, I put a end piece on so it would ride on a smooth area all the time, you have to fit the laser collimator to your laser, I had to take the end piece off to do the other laser.

Another trick was to only turn it half a turn back and forth, then I could see the "U" shape it made on the news paper I was using that was 19 inches away and I could see what letter it needed to be on to be centered, it took me over 20 minutes to get it done, but when I rolled it the rice shaped laser dot spun on the letter "C" that was center(the word was school), I was able to spin it smoothly 360 degrees when I was done as by that time I was used to spinning it.

You can see mine is clamped to my counter and that base does not move, yes it jumped around several times and I just started over, whenever the dot was centered at the bottom of the "U" I stopped and tightened up the top screw after loosening a quarter turn the other 2 screws, the closer I got the less I loosened the 2 screws the tighter I tightened the top screw.

 

The first time it took over a half hour and I stated that it was pure luck I got it as there was no rhyme or reason(pattern) on what the screws did, this second laser there was a process that made sense, make the "U" in the news print, find the center of the "U", center the laser dot in the bottom of the "U", tighten the top screw and watch the laser dot rise until centered, then lightly tighten the other 2 screws then see if it moved out of center, repeat until you get it.

 

Once you get it close, then if you want to take the chance do it the 15 feet you mentioned, but keep in mind that I regretted loosening the screw on the first laser I did that took over a half hour to collimate, at the time I thought it was not off enough to go thru all this and I wondered if I will ever get it back to where it was let alone centered, that was one of them cheap $25.00 Svbony lasers.

 

002.JPG   

 

003.JPG

 

It will not let me do a 3rd photo, see next post.


Edited by Waynosworld, 07 December 2020 - 01:32 AM.

  • bazookaman likes this

#25 Waynosworld

Waynosworld

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Posted 07 December 2020 - 01:28 AM


Edited by Waynosworld, 07 December 2020 - 01:29 AM.



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