Cautionary note for Refractor owners...

[Merlin66 (Ken)]

I have bought and used many refractors over the years and still use a Genesis, ED80 and a TS102.
Recently I was asked to look at an older ED80 which seemed to give "odd" star images.
The out of focus disk instead of having the usual three dark "fingers" intruding from the edge (due to the excessive size of the spacers used on some air spaced objectives) this had four bright "ears" symmetrically spaced around the disk!
These in turn caused the star image distortions.....
The focuser was removed to check for any obstructions/ edges on the inside and the baffles. Nothing obvious.

Removing the dew cap exposed the problem....
The objective elements each had four small (really small!) collimating adjustment screws bearing on the outer edge of the lenses.
These were as tight as hell! I'm sure they were pinching the optics terribly..
Backing off all the screws and leaving the objective for a few days seems to have fixed the problem - I still have to check and re-collimate.

Moral of the story: If you don't know what you're doing - Don't!!!!

[Kunama]

Originally Posted by Merlin66

Moral of the story: If you don't know what you're doing - Don't!!!!

Great advice Ken !
I have looked at a few scopes over the past decade and had to walk away after seeing the collimation screws showing damage from being turned with gorilla grips or ill-fitting screwdrivers.....

[JimsShed (Jim)]

Good to know. Thanks for the advice Ken.

[Wavytone]

Almost worthy of writing a "how to" guide for noob refractor owners.

There are a few more "don'ts" that come to mind that well-meaning but unknowledgeable types are likely to commit that will damage or possibly ruin the optics.

[Atmos (Colin)]

I'd be too scared to touch the optics, focuser collimation yes but not the optics!

[skysurfer]

Originally Posted by Wavytone

Almost worthy of writing a "how to" guide for noob refractor owners.

There are a few more "don'ts" that come to mind that well-meaning but unknowledgeable types are likely to commit that will damage or possibly ruin the optics.

Well, a refractor is the most simple telescope type. No collimation needed (unlike Dobson and SCT) after it is pre-collimated by the manufacturer.

That means hands (and screwdrivers) off any set screws at the objective cell !

[glend (Glen)]

Originally Posted by Atmos

I'd be too scared to touch the optics, focuser collimation yes but not the optics!

Yes but if the previous owner screwed it up and then sold it, someone has to adjust it. Its not that hard if you have a push/pull cell. Anyone who has built a refractor knows how to do it.

[Merlin66 (Ken)]

Postscript:
I'm glad to say after a couple of days "relaxation" the objective lens elements are still good.
Fine adjustment now gives an excellent star image with no flare.
All's well that ends well.

[Wavytone]

Well,

A few of the don'ts for the noobs:

1. Don't use aerosol insect repellants anywhere near the scope - especially upwind of it - this stuff will permanently damage optical coatings. Same applies to your eyepieces.

2. Don't attempt to clean a fluorite objective with liquids starting with water, you'll probably wreck it.

3. Don't attempt to disassemble the objective to .. ahem.. "improve" it. You'll almost certainly make things worse.

4. Think carefully before you fiddle with crayford focusers, lost of fiddly bits to reassemble that probably won't work as well after you've messed with it.