I've made a home-made collimation cap and am trying to use the procedure linked to in another answer.

However, I've run into two issues right off the bat. In this picture from the linked page, it shows a "primary mirror donut". All I see is a black circle with nothing in between. I'm using a piece of bright white paper that I printed the alignment patterns on to attach to the eyepiece and I thought this would be bright enough to see, but apparently not.

The second issue is that this method seems to rely on there being four "spider vanes" which are holding the secondary mirror in place. However, my telescope only has one, making it seemingly impossible to line anything up.

Here is what it looks like through the cap: enter image description here

It looks like the dark circle in the middle it fairly well aligned, but I can't tell for sure if it needs any adjustment. And I'm not sure how to deal with the fact that there is nothing inside the circle to align with. I have tried taking an LED flashlight and shining it on the top of the paper while i look through the pinhole and if I focus the LED circle on the edge of the paper at 90 degree intervals it appears to be aligned, but I don't know if this is sufficient.

Incidentally, the halo around the outside seems to be the edge of part of the inside of the side tube, and it does not move when I adjust the collimation screws.


1 Answer 1


The Gary Seronik website that you cite is a good one - it's not leading you astray!

There are a couple of important things to look at:

  • Look straight down the main tube of your telescope at the primary (largest) mirror. Is there a small paper ring or another mark dead in the centre of that mirror? If so, good. If not, read through this webpage http://garyseronik.com/centre-dotting-your-scopes-primary-mirror/
  • What are the lighting conditions when you're performing this? The photo you included is helpful but seems to imply that you might be pointing the scope at a bright light. This will wash out all contrast and make the procedure difficult. I collimate my scope just using ambient light during the daytime

Don't worry about only having one support rather than four. The key will be to identify your centre dot (you can just see it on Seronik's webpage, first picture ) and to see how it is centred when you look through the collimation cap onto the secondary.

Maybe read this article: http://www.skyandtelescope.com/astronomy-resources/how-to-align-your-newtonian-reflector-telescope/

Or search for Newtonian Collimation on Youtube?

  • $\begingroup$ looks like i'm going to have to find the time to take my mirror out to do the marking... :-( as for the lighting, i did this inside during the day with the scope pointed towards a window. so, not a really bright light, but not dim either. likely it's overexposed due to trying to get my cell phone lined up with the small hole in the cap and hold it steady long enough to get the shot. :-) $\endgroup$
    – Michael
    Sep 16, 2017 at 21:45
  • $\begingroup$ Thanks for the update. Sorry about you're having to take the primary out. I've only had to do it once to clean things up, so I haven't got any experience in actually doing the primary spot installation. $\endgroup$
    – MartinV
    Sep 17, 2017 at 10:37

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