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Collimation question


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I cant get all 3 mirror clips to appear in my secondary, I can see 2 of them but 1 is always just off to the side, just out of range - does this mean I need to mess about with it more, or do some telescopes looks like this??

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You don't see the 3 clips because your focuser axis is not aligned properly. You collimate this adjusting the 3 screws behind the secondary mirror holder. 

If you don't have done it already, I would suggest to replace those screws with Bob's knobs (FLO sells them), to make the focuser axial collimation much easier.

Once the 3 clips are visible, you can proceed with the primary mirror axial collimation.

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As far as I can see, your secondary mirror is titled and too low with respect to the focuser axis. 

As not all the primary mirror is reflected on the secondary mirror, there is also some aperture loss.

Coming back to your questions, yes, it is absolutely possible to see the three clips of the primary mirror (and you should see them!). Your collimation issue can be solved.

 

Could you take a photo of your secondary mirror holder from the front of the tube, please? 

Secondly, which tools do you use to collimate your telescope?

Edited by Piero
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I think that image I took with my camera phone makes it look worse than it is. Next time. Have the scope out to collimation I will take an image of the secondary.

i use everything to collimator! A colli cap, a laser, a Cheshire etc, just think I’m not very good at it, the secondary I’m finding impossible to get correct.

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Ive also been learning how to colimate over the last 2 weeks. Its interesting see other peoples efforts. Has anyone with perfect colimation taken a picture through their cap? Ive seen diagrams in the helpful guides but not a picture. 

Ive not yet had a clear night to try it out what ive done but im hoping!

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Andy, with the 130pds and mine 150pds the secondary mirror is offset  follow astrobaby's setup guide if you do get a laser collimator (Chinese equiv )cheap then verify it is true there are 3 grub screws under plastic covers to collimate the laser unless you spend money for a descent one. 

 

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On 15/12/2019 at 13:17, blinky said:

Nope - Still no better tonight!  After trying again with it on the mount this is the best I got.

 

 

stars.JPG

I'm curious- what do you collimate with for your astrophotography work with newts?

image.png.d6669ce8c9e06d238688314788cd786f.png

Edited by jetstream
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9 hours ago, Andrew Singleton said:

Ive also been learning how to colimate over the last 2 weeks. Its interesting see other peoples efforts. Has anyone with perfect colimation taken a picture through their cap? Ive seen diagrams in the helpful guides but not a picture. 

Ive not yet had a clear night to try it out what ive done but im hoping!

This is not perfect (e.g. there are asymmetries between the sight tube circle edge and secondary mirror edge as well as between the secondary mirror edge and primary mirror edge), but it works just fine, particularly because my secondary mirror is oversized. 

Thank you for asking! You reminded me that I need to redo this, now that I improved my primary mirror cell! :)

IMG_20190921_181447.thumb.jpg.deeff97fc9707477116f6bfdeb441f0f.jpg

Edited by Piero
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10 hours ago, Andrew Singleton said:

Has anyone with perfect colimation taken a picture through their cap?

LOL, no one would dare because there's sure to be someone come along and point out why it's not perfect! With that in mind, please see below my perfectly collimated reflector.

But seriously, it doesn't have to be perfect. The secondary mirror is simply a flat bit of glass; get it somewhere near and then leave it. But before you adjust anything, be sure to read the collimation myths. They'll clear much confusion and save you a lot of time.

HTH and clear skies.

IMG_20180325_132130_HDR.jpg.2fac7c9e0987e8ac036ee8c8802ecbcd.jpg

Edited by alacant
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Thanks for posting your very decent colimations! It helps a lot. A laser and a cheshire are on my list of future purchases. 

Im posting where i got mine too on Sunday. Im almost happy although it bothers me that the reflection of the secondary in the primary has visible curves between 6 oclock and 9 oclock and not between 4.30 and 7.30 opposite the focuser tube. It looked perfectly fine inside the telescope. ( i hope that made sense as its dificuly to describe!)

 

That said im not getting hung up on it. If, when the skies clear, this turns out to be still wrong then i'll try and correct it but if its ok then why change it! 

20191215_193157.jpg

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17 minutes ago, blinky said:

I was about to hit the buy button but then thought, is It just that I need to get the crosshairs of the Cheshire cantered on the primary mirror spot?

In theory yes, but for me at least the crosshairs are so out of focus there's lots of room for error. You also need to ensure the secondary appears circular by dividing the secondary into 4 equal "pie slices" using the (fuzzy) crosshairs.

Both tasks are much, much easier to do using the aforementioned Concenter: I have one and it makes it all so much easier. See this view of my secondary through the Concenter peephole:

IMG_6099.thumb.jpg.c2c3f8d3d2031a0f835a71dda2b0aa25.jpg

 

Cheers, Magnus

Edited by Captain Magenta
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