ED telescope and chromatic aberration in cold.

[Dai150PL]

I have a Skywatcher 100ED DS pro that for the past few cold nights has showed a rather large amount of chromatic aberration. I have owned the telescope for around eight months and tested the amount of chromatic aberration on the first few evenings out and found that there was very little, so little that you had to go looking for it. So my question is to any other owners of this type of telescope is does the cold affect it to this extent? The song "blue moon" comes to mind when talking about the levels. Would be grateful for any information please.

Thanks

[John]

Hi David,

I have an ED120 which has been out for long periods on some very cold nights recently and has shown no ill effects. Is there any chance that something in the optical train of yours has become mis-aligned ?.

The ED100 I used to have was practically colour free, as yours was when you got it.

If you have a cheshire eyepiece you can check the collimation of the scope following this method:

Refractor Collimation

[Dai150PL]

Thanks for the link John, will check and see if it is collimation. Have been lucky enough to have had some nights out with it lately so fingers crossed it just needs a tweak. Have you collimated one of these before, is it going to tricky.

Thanks

[John]

The Skywatcher ED refractors don't have collimation facilities built in unfortunately. You can tilt the focuser a little and that's about it.

Another trick is to fix the tube pointing upwards, remove the dew shield (it unscrews) then loosen the objective lens retaining ring and gently "slap" the sides of the objective lens cell to settle the objective lens elements. Re-tighten the lens retaining ring so it is just tight enough to retain the objective lens but no tighter - just pressing gently against the edges of the lens is enough.

Before all that though, see what the collimation test shows.

[Dai150PL]

There does appear to be mis-alignment when viewed through the cheshire. Its not easy with a cross and no marks to work against, will spend tomorrow working on it during the daylight as indoor lights and me do not get on. Thanks for all the info will work through it and get back to you. Really hope its a focuser issue as do not want to go anywhere near the lens cells if I can help it. Maybe the perfect excuse I have been looking for to get the Baader steeltrack from flo.

Thanks again John really appreciate your help.

[John]

No problem David - hope you get it sorted

[cs1cjc]

Check at a warmer temperature and see if the problem goes away. It may be that the cold is causing the cell to pinch.

[Dai150PL]

Thanks Chris will give it a try.

[ollypenrice]

I'd second extreme cold and a pinched cell. A dewstrip might be all you need...

Olly

[Dai150PL]

Its supposed to be clear later so will give the dew strip a try, thanks for the tip Olly.