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EA2007

Primary mirror indentation

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the secondary mirror of my Schmidt fell onto the primary...there is now an indentation as below:

Yfrog Image : yfrog.com/jnimg1424jj

will it affect performance much.

the optics need a good clean anyway so if i get them cleaned will it probably counteract the scratch?

I feel like an idiot

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ouch! sorry about the mishap. I suspect you are lucky it didn't shatter!

I'd just try it and see. I am not sure about your design of scope but I know that newt mirros can get seriously mucky before the performance is affected so you might be OK

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Your heart must have stopped when that happened!

I don't think it will be noticeable as it's far from the focal plane, but try it and see.

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tell me about it...i have done it before (well not dropped it obviously) and there was no problems. the secondary just fell out and i was like "what!", just stood there thinking "oh noo". I am thinking it should be okay.

reminds me of when my Olympus dSLR fell from my scope and hit the paviung slabs outside, eughhh

ideally all the optics need a good clean...any ideas?

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Bad luck on that one. It will have some effect - being near the edge doesn't make it any less problematic. But the effect may be one that you never notice visually. Just got to give it a go and see how it compares with what you're used to. It's a small mark and in terms of light loss has no effect - you can have a bit of muck that size and not notice anything. But as it's an indentation it will reflect and scatter light in unwanted directions: that's more of an issue, and cleaning won't solve it. Even so, it may turn out to be so minor that you can't see any difference.

Given your bad experience, I'd say leave off cleaning for now and just see how the scope is performing.

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If it's just a "plastic scrape" then no big deal - it looks worse than it really is. ( Yes.... you'll keep noticing it - a bit like a pimple of the end of the nose - more distracting than a real problem:rolleyes:)

If unfortunately it is a chip from the mirror then I'd cover it with a texta marker - the edges of a chip can cause ghost images near bright stars ( DON'T ask me how I know this!!!:):o)

Ken

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I'd be tempted to glue a bit of flocking material on it to make sure there is no focused light coming off it.

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yeah I might try and get some sort of filler thing for it.

anyway, went against common sense and decided to clean the optics myself.

not a bad job if I say so, the secondary never looked so clean, the primary is now 'blob' free and the lens is clear from any marks...although placing it back together resulted in a few smears on the lens but they are easily curable.

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You don't want filler on the mirror!

Just mask the damged area with a non reflective marker/ tape to prevent un wanted reflections. That's as good as it gets.

Ken

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I've got a couple of blobs of muck that size on my mirror and it does seem to affect it.

I think we are all agreed that covering the mark with something non-reflective is the best thing. You'd only be reducing the light recieved a tiny smidge but not affecting image quality.

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lol, i didn't mean filler filler....i meant something which you guys had already suggested!

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But as it's an indentation it will reflect and scatter light in unwanted directions: that's more of an issue

That's about the only problem i can envisage. Thankfully the primary didnt shatter.

Would a silver coloured marker (not the glittery kind) be good to use on it? It wouldnt show as much as a black marker or something similar.

Edited by LukeSkywatcher

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i'd have fallen over if the primary had broken.

good lesson though, I now know not to do it again. Once I had the scope open its surprisingly simple how it works, if one had the correct mirror / lens assemblies then you could make your own.

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i'd have fallen over if the primary had broken.

good lesson though, I now know not to do it again. Once I had the scope open its surprisingly simple how it works, if one had the correct mirror / lens assemblies then you could make your own.

Many people do make their own and do a great job. Some even grind their own mirrors.

If i was in ANY way technically minded i would make my own. Unfortunately i have to draw up a plan of action before even hitting a nail with a hammer.

Come to think of it..............i dont even own a hammer.

Or nails.

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Would a silver coloured marker (not the glittery kind) be good to use on it? It wouldnt show as much as a black marker or something similar.

No, you want it to be as unreflective as possible (hence suggestions of flocking paper etc). Issue is not what it looks like when you look down the tube, but what it looks like through the eyepiece. Aim would be to have that little bit of the mirror making zero contribution to the light that reaches the eyepiece.

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had a little peak through it this morning, made my own 'star' with a torch and a hole in cardboard to see if focusing was okay at a distance down the garden. it seems to be back together okay and there is no noticable changes in the view. the mirrors look shiny new in the daylight : )

if it stays clear tonight then i'll give it a proper go and see if its all in alignment etc.

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No, you want it to be as unreflective as possible (hence suggestions of flocking paper etc). Issue is not what it looks like when you look down the tube, but what it looks like through the eyepiece. Aim would be to have that little bit of the mirror making zero contribution to the light that reaches the eyepiece.

Yes, I was thinking either absorb as much as you can (and scatter the rest evenly at all angles) or, at the other extreme, reflect light away from the secondary with a tiny mirror at an angle to the primary's surface.

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Ah right, cheers forum friends.

I shall wait until tonight and see if the sky is clear, see what the results are of a nice observing session.

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Silly question - did you put the secondary and corrector plate back in the same orientation as it was originally? Sometimes during the manufacture of the scope, there is a bit of 'tuning' matching the secondary rotation and placement on the corrector to get the best collimation possible.

I did hear od a US-based astronomer who disassembled his SCT and spent about 3 months getting it re-collimated again.

Usually on the corrector plate there are index marks that match a mark on the side of the primary

See How do I align my Schmidt-Cassegrain telescope’s (SCT’s) corrector plate and secondary?

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