Debris on 8" mirror - ignore or attempt to clean?

[Girders]

Looking for advice please for debris on the primary of a Skyliner 200p Dob..  I know that I should largely just accept a bit of dirt and dust as inevitable - and that I'm generally more likely to do damage by cleaning, but this is a single bit of debris on an otherwise very clean less than a year old mirror.  Probably a bit of leaf or similar that's blown in but doesn't dislodge by tipping the scope downwards.  I know it won't affect views, but I'm concerned leaving it there may cause damage to the mirror.  Debris circled in red in the attached pic.  Any thoughts/comments/warnings/reassurance welcome.  Thanks!

[rl]

One man's search for optical perfection is another man's OCD....we all have our own standards on this one. Getting it off is not a big deal but sometimes unwarranted perfectionism causes these jobs to snowball..

Can you blow it out? Camera shops sell proper clean compressed air cans for this purpose. Could you get your hand inside the tube without knocking the secondary?

Do you feel happy removing the mirror / cell assembly? Once you get the mirror out, you often see a lot of stuff you can't see from the top, like water sleaks and dust, none of which really impact the view. But then you're into cleaning the mirror properly just to make the job worthwhile....not a big deal with a lint-free optical cloth, distilled water and a drop of washing up liquid. But it's still a risk. 

Do you feel happy recollimating after reassembly?

There is a good case for leaving it alone at the moment. If it is a bit of leaf I can't see it doing much harm long term provided it's dry. 

Personally I'm not in the camp that recommends cleaning a mirror one every 20 years whether it needs it or not, I like my mirrors fairly clean and probably take them out about once a year for this purpose. 

Not sure that helps much...

 

[pete_l]

28 minutes ago, Girders said:

I'm generally more likely to do damage by cleaning

You would have to be incredibly unlucky to cause damage removing that - unless the hammer slipped 😆

I've just used a photographers blower-brush to knock things like that off a mirror in-situ. Either that or a makeup brush or whatever other soft material you have to hand.

Edited August 13, 2021 by pete_l

[Barry Fitz-Gerald]

Whilst it will not affect the view as you say, it might affect the mirror coating as it decomposes - and it will also nag at you every time you look at it!

You could try and use something like a Rocket Air Blower held at arms length down the OTA to dislodge it - being careful not touch the mirror surface or the secondary - which might be the simple option, or you could just bite the bullet and remove the mirror cell (having first made a note of which screw in the OTA goes in which hole in the cell - mark the position with a bit of tape) and get to it that way.  Might have to tweak the collimation after, but it is a Newt, and you will have to collimate it anyway at some point.

Messing with newts can be a bit nerve-racking, but you end up learning how to tame them, just take your time and make a note of each step you take so you can reverse the process when you put it back together - if you choose that route.

If you are worried about messing with it, you could always just ignore it - I have stopped looking down my OTA because of the horrors it will reveal on the mirror surface - but the view through the eyepiece is the same as it always was.

 

 

 

Edited August 13, 2021 by Barry Fitz-Gerald

[Captain Scarlet]

If you can be sure it’s just a bit of dry leaf or debris, I’d ignore it until proper cleaning time. Try completely up-ending the ota if you can, to see if it’ll simply fall or slide off. If it’s a stuck-on “splodge” of something like sap or dew, I would remove the cell and give the whole thing a proper clean.

Cheers Magnus

[Girders]

Thanks for all the replies.  I'll sleep on it (the decision, not the telescope) and get someone to give me a hand tipping it vertical tomorrow and see if it dislodges.  Difficult to get a clear look at it, but can't think of anything else it could be.  We do get a fair bit of leaves blown around and it was fairly windy for the hour I was out tonight.    Will let you know if I decide to do anything.

[Mr Spock]

I'd suggest a blower brush. It should dislodge, unless it's sticky for some reason, fairly easily.

[Girders]

Thanks again everyone - I managed to dislodge it this morning by tipping it up and giving a very light tap. Mirror looks unaffected and hopefully collimation still ok.