Refractor focus

[+Stu]

Hi folks. When focusing the scopos TL805, if I'm out one way the I get a yellow halo round stars, if I'm out the other way it's orangey blue. Getting it in between is pretty tricky. Is this normal or is it just the limitations of this particular scope? 

[Speed]

not had this issue     so unable to offer advice    sorry 

[+Stu]

Just a bit of CA I suppose?

[+Bino-viewer]

You'd expect it to be fairly well controlled as a triplet F7 but its maybe a bit of that ?

What does it look like on Vega ?  I believe thats the 'acid test'.

 

But it could be a touch out of collimation ?

Or maybe thermal if its not reached ambient, or perhaps a bit of atmospheric if you are looking fairly low down.

 

 

[+Stu]

@Bino-viewerI was focusing with Arcturus the other night, I'll have a look at Vega on the next opportunity. I've not had a chance to go through the images yet so I'll see what they're like. 

[philjay]

If the out of focus stars either side are concentric discs, e.g. not lop sided then collimation is fine.

The colour is probably ca. Not all ed glass is perfect and one will always get some ca. The more expensive the glass the better also the longer the focal length the better.

Thats why I like f15 🙂

 

[+Stu]

They don't look too bad, I think.

There is a slight wobble on the focuser when it's loaded up. There was some discussion on CN about the type of glass used on its release, and the cemented lenses.