Strange collimation behaviour

[Steve Ward]

I found problems when I started playing with the collimation on my scope for the first time because the Cheshire tool was undersized by quite a way and always sat askew when even gently restrained , therefore was always pointing off target (same with my laser tool)

Cured with a single layer of packing tape on each to gain a nice snug but easy pushfit on both tools , no more problems after that (touchwood) always concentric in EP holder .

Once everything centred from focuser onwards it all just falls into place.

[LukeSkywatcher]

There is another person somewhere here who has the Heritage and is also having trouble with the spider arm. It seems to be a common problem. I'll try to find the thread and redirect them here.

I see Cis has discovered this thread already.

[Tribal-Wolf]

Collimation is a strange animal lol, I did a strange test today as I was doing a few 'mods' to the scope and focuser in particular. I have read so many times about cheap laser collimators being useless because they are often out of collimation themselves and as I have one and know it to be collimated very well I tried something. First I checked my collimation with a cheshire and set it up bang on, I then checked it with my laser and it was still good. I then deliberately knock the collimation out on my cheap laser and also uncollimated the scope. I didn't knock the laser far out but enough to make the dot move about 6mm when turning the laser and looking at the dot on the primary mirror. I then set up the scope collimation using the now 'out' laser. When everything was showing as collimated with the laser I checked it with my cheshire and it was once again bang on. This leads me to believe that even though the laser was not accurate it was still good enough to collimate the scope as good as a cheshire, which surprised the hell out of me tbh. Interesting though.

[AuntyCis]

Yes, I found it, thank you!

Interesting to see that others have experienced the loose spider problem and use of nail varnish to fix has been noted, will give it a try.

We had some clear sky last night and got both scopes out in the garden. While the views throu the Heritage were good, the views through the Explorer were better - sharper, so going to have another go at sorting out the Heritage.

Thanks for the comments/input, much appreciated.

Cis x

[Tim]

I The star test is satisfactory but can this test appear okay even if collimated incorrectly?

Not if you do the star test correctly

The star test is the ultimate test of the entire optical train, including your own eye.

[Albenn]

Tim, thanks for confirming star test is the yardstick.

[Moonshane]

I have never been able to do a proper star test as I cannot get seeing good enough to get the high enough magnifications to make it worthwhile (min 25x aperture in inches minimum and optimum maybe 40-50x - would mean clear views at 240x in two of my scopes and 640x in my big dob). personally, I'd sooner be observing than analysing my collimation and close is good enough. the mirror moves about a little as you point to different areas of the sky anyway so I only check the collimation again during a session when the seagulls start to return to the field of view - not often. it's usually when I inadvertently knock the scope. I always check the secondary and primary before every session on all my newts though.

[Albenn]

.. the mirror moves about a little as you point to different areas of the sky anyway...

Moonshane, glad you mentioned that. It would explain why the view is slightly off when looking up near the Zenith with my scope.

Just hope I haven't broken forum etiquette by replying with a partial quote..

[Moonshane]

not at all Alan. Many prefer that actually. bigger mirrors move more of course but they are all (or should be) loosely held in the cell so they all move a bit.

I should add that for someone who seems to be learning collimation as a new skill, you have rather quickly grasped the idea of what affects it - impressive. I wish more would adopt your approach of 1) not being scared to try things and 2) appreciating the effect of what you change. keep it up - this is an interesting and I am sure useful post to many with the same scope

[Albenn]

Moonshane, glad I haven't upset the powers that be re part quotes It just seemed to be wasting b/width by fully quoting. Thanks also for your encouragement. It's nice to know that my scribblings are actually making some kind of sense and may also be of some use to others.

[Moonshane]

no worries. to be honest we are pretty free and easy until it comes to people being not very nice, using bad language or blatantly flouting the current no buy/sell rules. to use a footy analogy I think everyone wants a free flowing game, without the refs putting their two-penneth in all the time