10 replies to this topic

[LordNewton]

Last night I was observing the moon. When the moon was completely out of focus I could see these dots on the lit up area. But when the moon was in focus there was nothing and the image was clear (except for atmospheric haze).

 

The same happened when I moved the scope to Saturn and it was out of focus. Bringing it into focus and the image was clear and when it was out of focus I could see these dots. 

 

Do I need to clean some part of the optics?

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[happylimpet]

Do I need to clean some part of the optics?

Yup.

[LordNewton]

Yup.

What is this? and where is it? primary, secondary or eyepiece?

[Illinois]

When you see dots and turn your eyepiece and look at dots at the same time. If dots turns is eyepiece is dirty.  If dots is not turns then mirror or second mirror is dirty.  I think dots is eyepiece. 

[CrazyPanda]

When you see dots and turn your eyepiece and look at dots at the same time. If dots turns is eyepiece is dirty.  If dots is not turns then mirror or second mirror is dirty.  I think dots is eyepiece. 

This is definitely the eyepiece. The pronounced diffraction around these specks and their large size relative to the field stop indicates they are on the eyepiece - most likely the field lens.

 

These would have to be huge if they were on the objective.

Edited by CrazyPanda, 19 September 2023 - 06:39 AM.

[ngc7319_20]

Which eyepiece is this?  It is somewhere near the bottom of the eyepiece. Try rotating  the eyepiece --- see if the pattern rotates with the eyepiece.  Get a magnifying glass -- hold the eyepiece up to a bright light and look in the bottom with the magnifying glass.

[Barlowbill]

It's alive!  It's alive!

[LordNewton]

Which eyepiece is this?  It is somewhere near the bottom of the eyepiece. Try rotating  the eyepiece --- see if the pattern rotates with the eyepiece.  Get a magnifying glass -- hold the eyepiece up to a bright light and look in the bottom with the magnifying glass.

This was using the 9mm Plossl. I was too tired to investigate last night.

 

I will try my other eypeice and see if I can pinpoint the issue.

[TayM57]

Looks like the EP is dirty. Like a poster said, rotate the EP to see if its the EP thats dirty.

 

Dust on the primary almost never shows up like that. It's got to be the EP.

[LordNewton]

So I took the eyepiece out and aimed it at a street light in the dark. Turns out it is dirty.

How do I clean it?

[ngc7319_20]

How do I clean it?

 

Here's a good discussion of eyepiece cleaning...

https://www.televue....n=Advice&id=103

Edited by ngc7319_20, 21 September 2023 - 01:12 AM.