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Help! Mucky SCT corrector plate!


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Has anyone experienced what looks like a mist of very fine condensation on the front corrector plate of an SCT, that doesn't clear with time or with exposure heat? Is it just accumulated muck from the atmosphere, from lots of nights pointing up into the damp night air? I'm not planning on cleaning it, and the images through the eyepiece look fine, but I'm just a bit worried about what it is. I think it is on the outside of the plate, and not inside the OTA.

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Cleaning isn't scary or dangerous when done properly. All of the dust on the corrector plate probably got wet from humid air and created something like dirt stains ;) it can be cleaned using Baader clear wonder or other similar agent and a microfiber cloth.

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All I ever did to clean mine was to tip the 'scope down (so the water you wash the corrector with won't flow into the body of the SCT) and use a very, very (1 or 2 drops, no more) dilute window cleaner in tap water. Then dab the corrector with either a soft cloth or cotton wool. Don't rub or wipe as this could scratch abrasive particles across the front of the glass.

I never felt the need to use distilled or de-ionised water and it always came up clean afterwards. Though I never noticed any improvement in the views through the SCT, it just made me feel better to see it wasn't dirty.

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Not a scary operation if done carefully. Even if the muck is on the inside, removing the front plate doesn't take long. It's sometimes required when the scopes get mildew inside. Clean with Baader Wonder Fluid or similar and a soft lens cloth.

Typed by me on my fone, using fumms... Excuse eny speling errurs.

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another vote for the Baader fluid but as an additional note to Earth Tiatan's message:- If you are ever tempted to remove the corrector plate, please be sure to do your research and ensure you make lots of recognisable registration marks !! As the plate will have to go back in the same orientation ! Apart from that there's nowt to get up tight about :)

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Unless the front corrector is truly dirty (not just the "mist" you mention which is common after a few uses), leave it well alone. It makes no difference whatsoever.

Another tip is always to use dew control. It stops the dampness that forms on the corrector from collecting pollen etc that dirties up the corrector.

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Unless like me you get green fly resin/poo getting blown onto it from the nearby tree :) that's inspite of a lengthy dew shield .

Aha! You're a genius Karlo! I've just realised, after reading your post, that I've been setting up the scope in our garden next to a very large Sycamore tree!! So it probably is crud from the tree that's built up - I've got more dew prevention than I can poke a stick at so I think that's unlikely to be the issue. I think I'll take Kirkster's advice, though, and leave well alone. I was reading "Turn Left at Orion" this morning and there's similar advice in there too.

Thanks everyone for your help - I'm comforted to know it's not just my SCT, and so will observe worry-free tonight (assuming the clouds clear as forecasted)!

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TBH Andy if it is tree crud I'd get it off -quick ! once set it's like cement ! coatings on modern optics is better than one might realise and will certainly be able to withstand some gentle rubbing with a Baader cloth and some WonderFluid. Specs of dust fine leave 'em but tree resin is a no-no.

Your choice tho ;)

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Just clean the thing. The corrector plates at the front are cast in moulds and they are a quite substantial bit of glass.

Yes it is a big bit of Schott water clear glass, the coatings are more fragile than the glass but as long as don't go too mad it should be fine.

The corrector plates are actually vacuum formed onto a mould and not cast, you would never get the quality or tolerances from casting glass. it's quite a cool process, on a recent trip to Asia I witnessed a very similar glass vac forming process - amazing tolerances when you think what they are actually doing.

Sent from my iPad using Tapatalk

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All clean - and not as scary as I thought, as many of you said. Used a soft brush or a few specs of dust and then Baader Wonder fluid with their microfibre cloth. Looks as goos as new now! Also it's clear tonight, so finally I get to try out the 13mm Ethos...

Thanks for all the advice, guys! :icon_salut:

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