Strange mark on eyepiece

[Neil H]

Hi guy just been out looking at the moon if i use my 40mm omni eyepiece there is a strange hazey part in the lens bang in the middle  so i tried to clean it and its still there so i got out another 40 mm plossl and its the same there is a hazey mark in the middle of the view so i put in a 20mm and no mark so i dont think its on the mirror but i may be wrong 

So now down to you all what do you think is wrong

If you look at photo its the mark just right of the moon 

Edited April 4, 2020 by Neil H
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[John]

Are you using a newt Neil ?

Could be the secondary shadow.

[Captain Scarlet]

The secondary shadow will become more apparent at very low magnifications, such as you might get with a 40mm eyepiece, which is very long by eyepiece standards. At twice the mag, ie a 20mm, that logic would dictate the shadow disappears, which seems the case here. Short version: it’s just a property of the optical system.

Cheers, Magnus

[Neil H]

1 hour ago, John said:

Are you using a newt Neil ?

Could be the secondary shadow.

Yes OO VX8L

 

18 minutes ago, Captain Magenta said:

The secondary shadow will become more apparent at very low magnifications, such as you might get with a 40mm eyepiece, which is very long by eyepiece standards. At twice the mag, ie a 20mm, that logic would dictate the shadow disappears, which seems the case here. Short version: it’s just a property of the optical system.

Cheers, Magnus

It is only with the 40mm 

20mm or 15 mm does not show it 

[Captain Scarlet]

26 minutes ago, Neil H said:

Yes OO VX8L

 

It is only with the 40mm 

20mm or 15 mm does not show it 

Nothing to worry about, in that case...

[Neil H]

Thank you both for the reply 

Your life savers so glad I not got to clean the mirrors

[Louis D]

To confirm it's the secondary shadow, put the moon in the center and pull back from the eyepiece.  The black fuzzy patch should become a sharp, black circle.  If you move your head around relative to the eyepiece, the black shadow will move around the face of the moon following your head's motion.

[Neil H]

6 hours ago, Louis D said:

To confirm it's the secondary shadow, put the moon in the center and pull back from the eyepiece.  The black fuzzy patch should become a sharp, black circle.  If you move your head around relative to the eyepiece, the black shadow will move around the face of the moon following your head's motion.

Hi yes it does that's how I got the photo of the hazey patch at the side of the moon 

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