Whoops! finger prints on my secondary

[JulianB]

Hi all,

With the secondary being very exposed on my truss tube 250px dobsonian I accidently touched the secondary and on examination I see 3 finger prints + some other patches. I can see these patches in the background whilst viewing

I have read up on cleaning the secondary and it sounds like a bit of an involved process e.g. removing the mirror, bathing it in water etc. but as a photographer, if this happenend to one of my lenses I would simply blow any particles off first and then lightly breath on the glass and wipe away the residue with a lens wipe, but is this method likley to cause any damage to my mirror coatings?

It also struck me that the secondary dews up regulalry as it is so exposed and that if I lightly wipe it while its wet that might do the job too, Im concerned about removing the mirror as it seems like a major job especially being as I can access the mirror easily for a minor wipe given the truss arrangement.

What do people think?

Cheers and Happy New Year to all

Julian

[barkis]

There is always a risk of minute scratches if you wipe the surface.

If you must, then use a natural cotton wool, not a man made synthetic, which may impart minute scratches to the aluminium coat.

Baader Fluid is a useful cleaning agent, or an Isopropyl Alcohol dilution.

Ron.

If you do it in situ, then place the scope in a slightly depressed horizontal position to preven possible drips onto the main mirror.

[Doc]

Try your hardest to not touch the mirrors as they can scratch, Ron is correct use medical cotton wool if you do clean them in situ, but it is best to remove and bathe them in warm water then pour some IPA over them to remove water streaks.

[johninderby]

Very easy to clean. Get some Baader Optical Wonder cleaning fluid with one of their microfibre cloths. It won't damage the mirror at all. I've used it to clean SCT correctors, refractor lenses and dob primary mirrors, eyepiece lenses etc. The Baader microfibre cloth is ten times finer than the camera lens cloth or wipe so only use the fluid with the proper cloth.

John

[Capricorn]

I would clean it as finger prints will have amino acids from the fingers associated with them. These could start to eat into the coating. As the secondary is relatively small any imperfections the size of 3 finger prints could be significant over time.

A camera lens will have an antireflection coating and generally this is fairly robust, so cleaning those isn't so critical.

Guess that a cleaning fluid and cleaning it on the scope is fine and saves to problem of removing, reassembly and resetting.

[glowjet]

I would agree with Capricorn, get the mirror cleaned as quickly as possible, acid from fingers can do untold damage, I had a small black material strip in my camera which protected my changeable view screen, although I tried not to touch it when changing screens, contact was inevitable, it was no surprise to find it rotting away after a short period of time, I used surgical gloves after that.

[Astro_Baby]

I always use cotton gloves when messing about with optics. You can get them from Boots for about £1

I was told by someone with lots of mirror know how never to ise Isoprop on mirrors as their coatings can be damaged by it. Lenses usually have a tougher coating so arent so much affected. Dont know whether thats true but decided as they have been around a lot longer than me with optical assemblies I'd go with that.

I'd go with de-assembly and bathe the mirror but then collimation/taking scopes to bits isnt very scary to me. If I really wanted to keep the mirror in situ I'd go with the Baader stuff or there some new stuff out (forget its name) that you spary on and it forms a hard film on the mirror which you then just peel off.

I'd defo get thaose those fingerprints off the mirror cos the acid in sweat will start to damage it if not dealt with.

[johninderby]

Modern dobs from SkyWatcher etc. have a protective coating over the aluminium coating on both the primary and secondary mirrors and are surprisingly scratch resistant. Mirrors that have only a plain aluminium coating (typically an older scope or if you've had a mirror re-coated) are easy to damage and do need extra care when cleaning.

John