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What's up with this mirror?

spark001uk

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spark001uk

spark001uk

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Skywatcher 130PM, only used it twice from brand new, and on bringing it back indoors i caught the light just right and noticed the main mirror:

11481_normal.jpeg

(click to enlarge)

I put a cotton ball on the end of a stick and very gently touched an area at the edge of the mirror, and it seemed to come off without any trouble. What should i do?

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Astro_Baby

Astro_Baby

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Hard to see from the pic - looks like condensation to me. Just let the scope warm up gently and it should go. Of course condenstaion will always leave a slight patina until the mirror is cleaned ( DONT clean it unless you really have to when its filthy ).

It may be the coatings on the mirror showing up as well - I had a similar thing with my Mak and apparently the mirror coatings can show up under certain types of light. They look as if the mirror has a thin film of oil on it - it isnst - just looks that way.

From the pic though I'd guess condensation. Dont panic - at Salisbury my 200 was like a bucket of water in the morning.

You say it gets worse outside - when - all the time or just after being taken out. If its going from a warm room to cold air it may well be condensation.

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Greg

Greg

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My SN10 mirror looks the same after a full nights session..Let it dry naturally in a shed or garage...

As Astro Baby has said don't clean it unless it's absolutely filthy as you can do more damage cleaning a mirror and it has to be in a worse state than yours to warrant a clean..

Just looks like some residue from condensation...

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Astronut

Astronut

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Is the mirror dry in that pic?

If not, it's condensation after bringing it indoors (warm) from outside (cold). The moisture in the indoors warm air rapidly condensates on cold surfaces.

Leave it exposed to the indoor air and as the mirror warms up to indoor temperature it should disappear. My mirror (and secondary mirror) looks like a block of ice within minutes of bringing it indoors after a session. You may have a few dry dew spot residues after it evaporates but don't worry about them.

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George

George

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Its condensation, give it a blast with an hairdryer to the BACK of the mirror and it will evaporate. It may leave a residue but that wont damage your optics or impair your views thru the scope.

You will always get this happening if your bringing a cold scope into a warm room, best to leave in an unheated area if possible.

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spark001uk

spark001uk

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I think it was slightly damp at the point i took the picture, however you can still faintly see the marks now its dry, altho only in a certain light.

Could do with a vessel with gradual temperature control couldn't we, like a decompression chamber but for temperature instead!! :)

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spark001uk

spark001uk

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Yes, my viewing is still good, altho i did notice when i look at something bright which is distant, for example Venus, at higher mags, i get a reasonably sharp image, but viewing it is marred a little by a slight streak coming from the object, much the same as you would if you look at a street lamp against a dark sky. Is this the same sort of thing, or is there a problem with the optics or the mirror?

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barkis

barkis

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Well it is unlikely unless it has been given a shock of some sort..

The scope is f5 which simply means the mirror diameter is 6 inches, and the focal length is 30 inches. If you divide 30 by 6 you have a focal ratio of f5. So conversely, if you know the diameter of a scopes mirror, and its f number, you can work out the focal length by multiplying the two numbers. Good Collimation is essential, especially in a short focal length scope.

You can check roughly your collimation by putting your 10mm eyepiece in the focuser, and find a bright star. Put the star in the centre of the field as accurately as you can, and defocus it until you see the shadow of your secondary mirror in the centre of the disc of light of the expanded star. Keep the the light central in the field, and make a mental note of how central the black portion is in the disc of light. If it is fairly central, then the collimation is not drastically off. You can then start to focus slowly watching the disc gradually get smaller until the black disc disappears altogether and you may see some concentric brighter rings. As you get close to perfect focus watch out for any sign of a flare on one side of the star. If you see that, it might mean that the scope needs collimation, which is something you will need to learn to do.

Ron.

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Astro_Baby

Astro_Baby

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Theres a whole load of stuff on collimation and what star testing with an EP will look like on my guide HERE - its pretty comprehensive. I only use a Cheshire and a collimation cap to do mine as I found lasers too much hassle. You spend half the time collimating the laser and mine - after a few goes broke down as well !!!

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ngc2403

ngc2403

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the mirror being dirty will not make lines form in ur images or an eye piece.

it will just remove alittle light from all of the FOV, i.e. it will be a little darker all over not a noticeable effect and if you want proof then just cover half your telescope aperture next time you look through it and tell me if you notice it getting darker?

ally

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Terry

Terry

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Hi I think you can get aerosol cans of compresed air for cleaning computer key boards etc(not sure where from but we had some at the last place I worked). Would you need to be careful though with the pressure these things put out?

Terry

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Whippy

Whippy

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Hi I think you can get aerosol cans of compresed air for cleaning computer key boards etc(not sure where from but we had some at the last place I worked). Would you need to be careful though with the pressure these things put out?

Terry

The problem with these are that they have a propellant that leaves marks on things like mirrors and glass :D. I read an atricle somewhere that said 'If your mirror is dirty, don't touch it. If your mirror is REALLY dirty, don't touch it. If your mirror is filthy, don't touch it'. I got the impression that it's best not to clean that mirror unless you absolutley have to :hello2:.

Tony..

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PhillyDee

PhillyDee

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Hi I think you can get aerosol cans of compresed air for cleaning computer key boards etc(not sure where from but we had some at the last place I worked). Would you need to be careful though with the pressure these things put out?

Terry

Yep, Don't.

Don't.

The propellant is corrosive. It can even eat silicon apparently.

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Terry

Terry

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The product I was refering to was just an aerosol can of compressed air with no solvent content.The product acted as the propellant. There certaily did not appear to be any residue left behind on the key board of the lap top when I used it. Working for a company that aerosoled materials we thought it was a great thing to be able to sell fresh air at an extortbitant price.

Terry

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