collimation issue

[Ally8446]

When the focus tube is drawn all the way out ref astro baby's instructions I cannot see ANY of the primary mirror clips. If it's halfway I can see all three. How important is it to have the focused all the way out ?

Thanks in advance. Al

[andrew s]

It depends on the normal range of focus. If it well in or in the midrange then you don't need to come all the way out. I would withdraw the focuser as far as you can and still see all the clips.

If your normal focus position is well out then the focuser or secondary may be vignetting the light from the primary mirror.

Regards Andrew

[Moonshane]

the purpose of seeing all the clips is to get the secondary as central as possible in relation to the focuser drawtube. it's therefore irrelevent to a large extent where you position the drawtube. it's not always possible to see all (or any) of the clips through a cheshire (I cannot see them with my fast f4 newts) and aligning the secondary using the donut on the primary and the cross hairs on the cheshire has the same effect anyway so don't worry. some scopes don't even have mirror clips.

think logically, if the Cheshire is fixed in the focuser and the cross hairs are fixed in the cheshire then if you point the cross hairs at the donut on the primary (which is reflected in the secondary) then it must mean your secondary is aligned with the focuser drawtube. you must of course ensure that the secondary is centrally placed down the tube too but that's the stage before.

you then need to adjust the primary which is the easy bit.

[Jason D]

How important is it to have the focused all the way out ?

Not important at all. I suggest collimating your scope with the focuser drawtube racked approximately half-way.

[Jason D]

if you point the cross hairs at the donut on the primary (which is reflected in the secondary) then it must mean your secondary is aligned with the focuser drawtube.

It does not mean the secondary mirror is centered/rounded under the focuser. See attached animation. In each frame, the setup will pass the cross-hairs alignment test but as you can see the secondary mirror placement under the focuser is all over the place.

EDIT: You need to click on the attachment to see the animation.

[Moonshane]

sorry Jason, I badly worded what I meant to say, although I did add "you must of course ensure that the secondary is centrally placed down the tube too but that's the stage before". I do find describing collimation very difficult - it's so much easier to show someone.

[Lakewitch]

I found that the clips were in view at the half-way focus point... and then putting a sheet of card between the secondary and primary, along with a piece of coloured paper behind the secondary, made assessing the secondary mirror position much easier.

Guess that collimation gets easier the more you do it. (Hopefully).

Frank

[earth titan]

Are you looking through the hole in the end of a Cheshire or have you got a film cap with a hole in? I struggle to see the mirror clips through the very small hole in the end of the Cheshire. The film cap with hole in, is better.

[NGC 1502]

What a brill animation in post #5, thanks.

Regards, Ed.

[Jason D]

sorry Jason, I badly worded what I meant to say, although I did add "you must of course ensure that the secondary is centrally placed down the tube too but that's the stage before". I do find describing collimation very difficult - it's so much easier to show someone.

No worries... I sometimes run into the same situation when my typing fingers get out of sync with my brain

[Jason D]

What a brill animation in post #5, thanks.

Regards, Ed.

Thanks...

Jason

[Moonshane]

No worries... I sometimes run into the same situation when my typing fingers get out of sync with my brain

I think it's familiarity in me assuming that people know what I'm thinking

[Ally8446]

I used a colli cap to position the secondary then a Cheshire for the rest. I 'think' I'm happy with the outcome. I'll find out AS SOON AS THE CHUFFIN CLOUDS CLEAR. If I've got it right or got it wrong, I'm not fussed, I just love 'footering' (good Scottish word) with my scope. Clear skies

[8kids]

I've found it's the best way to learn is to footer about..........I think.

[earth titan]

If you strip the whole scope apart to flock the inside (eeeek) you learn an awful lot about collimation..... whether you want to or not.

Typed by me on my fone, using fumms... Excuse eny speling errurs.

[Jason D]

I think it's familiarity in me assuming that people know what I'm thinking

Hello Moonshane, had I noticed your username I would not have made my original post; however, you keep changing your avatar and I did not realize it was you until now

Jason