Bright stars = faint line across field of view

[kirkster501]

Hi, noticed that no matter what EP when i look at *bright* (Castor and brighter) stars I get a faint line of light across the field of view that passes through the star. Fainter stars don't do this. If I turn the diagonal on the visual back it turns with the diagonal - I think - need to investigate more.

This mean the diagonal is causing this? Worse with white stars like Rigel. Aldebaran and Betelguese not so bad.

Any ideas guys? Is this right? Not a show stopper but mildly annoying.

Thanks, Steve

[LukeSkywatcher]

Turn the EP inside the diagonal and see if the line moves. Then you will know if it is the EP or diagonal.

Cause of this?

Possibley a bit of grease or a smudge of some sort.

[kirkster501]

Turn the EP inside the diagonal and see if the line moves. Then you will know if it is the EP or diagonal.

Cause of this?

Possibley a bit of grease or a smudge of some sort.

Thanks Paul. I have tried turning the EP inside the diagonal. When I do that the line does not move. So cannot be the EP's (also happens with all EP's so its teh scope or the diagonal). Could it be a smudge on the corrector causing it (although i cannot see any such smudge.....)

[LukeSkywatcher]

If it was a smudge on the corrector then it would not move when you turn the diagonal. Sounds like it is on the diagonal. Even the smallest smudge (partial finger print etc) will cause "diffraction spikes".

[Peter Drew]

It shouldn't be possible to see such an effect from a Schmidt-Cassegrain scope. Try using the eyepiece in the visual back without the diagonal. If the diagonal was a roof prism type like the 45 degree ones, there would be a line through a bright star caused by diffraction from the roof.

[LukeSkywatcher]

Try using the eyepiece in the visual back without the diagonal.

I did that a couple of weeks ago by mistake with my SCT. I could not see a thing through the scope.

[kirkster501]

It shouldn't be possible to see such an effect from a Schmidt-Cassegrain scope. Try using the eyepiece in the visual back without the diagonal. If the diagonal was a roof prism type like the 45 degree ones, there would be a line through a bright star caused by diffraction from the roof.

Yes, that makes sense Peter - but what to do about it though ?

Rgds, Steve

[Peter Drew]

Steve. That quick test suggestion was to identify whether the fault was in the diagonal. If it is, then it must be a scratch or spider web or hair in it, the eyepiece will only show what it can focus on. If possible, try another diagonal for comparison.