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Collimation... help please!

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#1 Mister Falcon

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Posted 04 July 2020 - 07:54 PM

Orion Starblast 4.5 Reflector here.

 

I followed the Orion collimating (“How to collimating a telescope”) tutorial with an Allen wrench and a philips head along with the collimation cap... and now, I the most I can see is the bottom 1/3rd of the secondary mirror. I turn the philips head one way and it goes out of view, turn it all the way opposite, and I just see the bottom 1/3rd.

 

What did I do wrong?



#2 ButterFly

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Posted 04 July 2020 - 08:03 PM

Take a picture through the focuser while pointing the scope at something bright like a wall or the sky.  Try to get the camera as centered as possible.

 

It sounds like the secondary is too high up the tube, but a picture is worth a thousand words.



#3 Mister Falcon

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Posted 04 July 2020 - 08:15 PM

Edited. The picture didn't upload right. Trying again.

 

Edit: Got it! let me know.

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Edited by Mister Falcon, 04 July 2020 - 08:18 PM.


#4 Mister Falcon

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Posted 04 July 2020 - 08:48 PM

Update. I had to hold the mirror and get it right, the hex screws were all loose. I got it much closer, but now I have this.

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#5 Philler

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Posted 04 July 2020 - 09:10 PM

I would get some Bob's Knobs that will fit over the Allen screws on your secondary mirror adjustment and make it a lot easier and safer from dropping an Allen wrench or Phillips head driver on your mirror. 

I would also get a good lazar collimator.  On a budget, an Orion lazar collimator, or you can spend more like a Howie Glator.  There are some videos online for collimating your scope and the collimator maker should provide instructions.  But I suggest with a lazar collimator you first collimate your secondary mirror centering the red lazar dot as much as possible either with the Allen screws, or better and easier with Bob's knobs as you look directly down the front of your scope tube.  The red lazar dot then should appear in the collimator window and you should be able to center it in the collimator window to collimate it using the rear collimation adjustments on the rear of you primary mirror.  Then do a final check looking through your focuser or with a collimating eyepiece.  Your last pic above looks like you are getting close to having the dot centered and right.


Edited by Philler, 04 July 2020 - 09:28 PM.


#6 Mister Falcon

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Posted 04 July 2020 - 09:19 PM

I think I got it. But I don't think I did it the right way. The Allen wrench seemed to do side to side (I just tightened the screws to where it matched up), the Phillips head did up and down. And I just turned the knobs at the bottom and got it. I hope I didn't break anything. I did it horizontally, no drops. 

 

Is this how it's done? THIS IS A PAIN.

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#7 Philler

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Posted 05 July 2020 - 01:31 AM

Falcon, what some of the scope makers provide with their scopes in the way of instructions, collimation tools, and hard to adjust screws make it not only a pain, but a confusing pain.  


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#8 spereira

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Posted 05 July 2020 - 07:04 AM

Moving to Reflectors, for a better fit.

 

smp



#9 sixela

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Posted 05 July 2020 - 07:27 AM

You first seem to have loosened the three tilt screws so much that you had completely misrotated the secondary, and then tried to compensate with tilt (which works for axial collimation, but given you a funny looking slightly elliptical and skewed secondary.

 

You apparently fixed it. But if tightening the Allen screws now make your secondary's tilt go all over the place, you probably overtightened and created dimples in the secondary holder, which also tend to prevent setting the rotation completely optimally (but no worries, small errors there are completely irrelevant).

 

There has to be some system tension (the centre bolt pulls, the tilt screws push) but if there's too much it isn't healthy either. That's why once it's tight enough (i.e. the secondary stays put and it's impossible to rotate it by hand) you use balanced adjustments: if you tighten one screw, your next adjustment should be loosening another, etc. If you only tighten, you make dimples in the secondary holder. If you only loosen the tilt screws, the secondary will come loose and rotate around the centre bolt.

 

The last picture looks OK as far as setting primary tilt, but really, we need a picture where we see the inside edge of the focuser to see whether your secondary is well placed and well tilted. You can't see the third clip, which means that either the secondary is tilted too much towards the focuser or it's a bit too close to the front of the scope. We can only tell which if we see if the primary's centre mark is well centred under the focuser...and the last image is so blurry we can't even see the centre mark.

 

But for visual observation, give yourself some rest: as long as the primary's centre mark is concentric with the little black hole in the reflection of the collimation cap, remains so if you rack the focuser in and out, and if you can see the whole primary from the focal plane (i.e. with the cap, and the focuser set as when you're using the eyepices provided with the scope), enjoy the views and only obsess about collimation when you have better tools (i.e. a sight tube and Cheshire combination) or if you really want to tackle it once more (since even with a collimation cap you have all the visual cues you need, it's just a little harder).


Edited by sixela, 05 July 2020 - 07:32 AM.

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#10 Vic Menard

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Posted 05 July 2020 - 08:22 AM

There's not much to work with in the image you provided--I pushed the exposure and shadow detail and was able to get what I believe is a close approximation of your alignment. I used the primary mirror clips to reference the reflected edge of the primary mirror, and from that I annotated the approximate (concentric) location of the primary mirror center marker, and from there, the (concentric) bottom edge of the focuser.

 

Even if my approximations are slightly off, I agree with sixela--leave it where you have it and see what your scope can do under the stars. (Next time you post a collimation image, put a white piece of paper behind the secondary mirror against the inside of the tube opposite the focuser--that will make the bottom edge of the focuser and the actual edge of the secondary mirror stand out clearly.)

 

 

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#11 dusty99

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Posted 05 July 2020 - 08:39 AM

Those cheap Synta reflectors take some fiddling.  As you discovered, you have to position and hold the secondary with your other hand while tightening everything down (and on my 130ST I then have to see how far and in which direction that final tightening will move it and loosen a bit and compensate for that...).  For the price the optics on these can be decent, but the mechanics are primitive.  The good news it that once you get the secondary correctly positioned and tightened it should stay, and adjusting the primary is easier.  You can get it close with your collimating cap, then take it outside with the back cover still off and finish collimating on a star.


Edited by dusty99, 05 July 2020 - 08:41 AM.


#12 Asbytec

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Posted 05 July 2020 - 10:26 AM

"THIS IS A PAIN."

Hang in there, the learning curve can be steep. Many of us endure it. It will click. Please be assured collimation will become so much easier. It's actually pretty simple, explaining it is more difficult. Once you arrive, you'll be collimating your scope in a few minutes and getting great results and images. Believe it or not, you'll actually enjoy doing it.
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