Primary Mirror Imperfections/Scratches?

[ChargingStag]

I was having a little inspection of my dob primary mirror the other day and came across something I'm looking for advice about.

While shining a light at it and looking at a certain angle, I could see lots of little specs on the mirror.  At first I thought it may be dust even though I always keep the tube cap on.  So I very gently pumped some air against it using a modified and clean bicycle pump but nothing cleared.

After that, all I can describe them as are either imperfections on the mirror, very tiny scratches or stubbornly settled dust.  What makes it particularly strange is when looking directly down at the mirror or at different angles they do not appear.  So I'm just wondering if anyone here knows what these marks are, and if they are completely normal or something to be worried about.

I couldn't get very good pictures but I have attached the best one highlighting the marks (even though they're not really identical...)

[acey]

If your scope has had any use outside then they're little dewspots left from moisture that has evaporated. Completely harmless, leave well alone. The fact that the spots are only visible from certain angles is not strange. Take any mirror in your house, tilt it in the light, and you'll see the same effect.

[Dave In Vermont]

Indeed. A perfectly clean and good mirror and/or lens will resembe a World War I battlefield when lit by a bright light - incandescent or from a torch/flashlight. Best advice is to ignore such. Otherwise you'll end up chasing ghosts and possibly damaging the optical-coatings trying to remove things that aren't really there.

"Who you gonna call?"

Dave

 

[brantuk]

Yup - dew spots. Nothing to worry about - had them on my dob for ages and it doesn't spoil the views nor do any harm to the mirror.

[laudropb]

These little spots are unavoidable and best left alone. They will not noticeably affect your views.

[todd8137]

I think the first time you shine a torch don a tube it's like ' what !'  I've been to star parties and seen scopes that you would think are so bad you would not think possible ,but they see just as good 

pat