false colour in an 80ED ?

[Caveman]

How much false colour should be present in an ED telescope?

I have just acquired a brand new Skywatcher 80ED ota and was out last night trying it out.

The full moon had a very slight blue fringe around it, and Venus although very sharp had colour within it, (not around it strangely).

Is this normal or just due to the atmosphere?

Many thanks, Paul.

[johninderby]

I found the seeing atrocious last night even though it was very clear so it's likely that's the cause of the false colour.

The eyepiece can also have an effect. What eyepiece were you using and I'm assuming a decent diagonal not a cheap prism diagonal.

John

[Caveman]

I found the seeing atrocious last night even though it was very clear so it's likely that's the cause of the false colour.

The eyepiece can also have an effect. What eyepiece were you using and I'm assuming a decent diagonal not a cheap prism diagonal.

John

John, I was using a bst explorer 8mm and WO 1.25" diagonal.

[Caveman]

By the way, i'm in Suffolk and yes, the seeing was quite bad last night.

[johninderby]

Sounds like just the atmospheric conditions then.

John

[John]

I've owned a few ED80's and they have been pretty much CA-free at focus. On the brightest objects they did show a little CA either side of focus but that is not unusual for an ED doublet.

If you were seeing noticable CA at focus then it was probably caused by something other than the scope optics.

[Caveman]

I've owned a few ED80's and they have been pretty much CA-free at focus. On the brightest objects they did show a little CA either side of focus but that is not unusual for an ED doublet.

If you were seeing noticable CA at focus then it was probably caused by something other than the scope optics.

I've since found out that it's caused by atmospheric dispersion, and occurs when a bright object is low in the sky.

[John]

I've since found out that it's caused by atmospheric dispersion, and occurs when a bright object is low in the sky.

Yes that can do it. When I've seen that effect it seems to cause redness at the top of an object and blueness at the bottom edge.

Jupiter will be suffering from this at the moment as it's rather low now.