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Skywatcher 200p Primary Mirror Problem?

markryan

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markryan

markryan

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Hi Folks,

I've been having a brilliant time with my new Skywatcher 8" Flextube Dob. Today I spent my lunchtime planning some purchases, looking at new EPs, filters etc

However I took it out tonight (it's stored in my shed, all caps on, tube upright, EPs out etc) set it up and pointed at the moon and couldn't focus on it at all with either a 32mm or 12mm EP. Just a bright, washed out blur from one end of focussing to the other.

Eventually I took the EPs out and looked down the focusser and with the bright moon for light could see a mark on the primary mirror. Looking down the OTA I could see a "splodge" about 5mm in circumference about halfway out from centre at 5 O'Clock that then appears to have trickled out to the edge of the mirror :icon_salut:

At first I couldn't tell whether it was a mark or a crack so I reached in and gave it a gentle waft with a lens brush and it looks like it has smeared a little (a very little compared to the mark, a few brush marks but enough to make me stop!).

So... a greasy drip on the mirror and no focus, I've just come in gutted.

Could I ask, would a mark like that on the primary cause complete loss of viewing? It's cold tonight and although the Dob would have been at or near external temperature I'm now thinking that maybe it could have been something to do the lenses coming out from the warm house and I'm putting 2 & 2 together and coming up with 5.

If it does sound like a primary mirror problem where could gunk have come from? Although I'm storing with the OTA vertical, I store it in a dry garden shed I'm very careful storing it (I've only had it a few weeks and treat it with kid gloves).

More importantly is it salvageable or ruined?

Thanks,

Mark.

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Moonshane

Moonshane

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don't panic, a small mark on the primary will have no affect at all.

have you left in the 2" piece in the focuser which should not be used for 1.25" eyepieces? this is a common error. are the extenders fully extended?

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Tribal-Wolf

Tribal-Wolf

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It is possible that it got there before you packed up last time, either way it will have to come off if you can't use your scope because of it. I think you may have to look at some of the tutorials around for cleaning mirrors. I have the same scope and store mine the same way, upright in my shed, the only problem I noticed was a little spider had moved into the side of the primary so I blew it out and now have a shower cap to put over the mirror end.

I would see what it's like when it's drier in the daytime and decide what to do from there. I feel for you on this I really do, I think with the flextube you see the mirror sort of closer up and worry about it more anyway as a result. Best thing is not to panic and see what can be done. It may be that it's nothing to do with your focus and it could be condensation.

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markryan

markryan

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Thanks for the replies gents...

Tribal Wolf - I'm hoping I've seen this blob, overreacted and it won't come to that. Better a blob than a crack though I suppose - which is what I first thought it was...

Moonshane - Thanks for the calming advice... What I think I'll do is revisit it tomorrow with a bit of early evening light, set it up and check everything out. To be honest I think I set it up as I have done every other (successful) night but I'm now doubting myself - perhaps I missed something obvious when setting up in the dark, so I'll go through it again tomorrow calmly and see where that gets me and I'll post back... One thing I have learned is it's hard to diagnose stuff in the dark with a headtorch (another is not to get to cocky when you've only has your scope a few weeks!).

Cheers,

Mark.

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markryan

markryan

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Don't panic, sounds more likely not fully extended or both EP mounts attatched.

Post us a picture of the mirror and the focuser

Good luck

I'm hoping it's something like that knobby. As I say I'll try setting up tomorrow earlier and in a more structured way. I'll make sure it's properly extended and that the EP mount is correct. If it still stays the same I'll post some photos back here... Either way I'll report back.

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jimmyjamjoejoe

jimmyjamjoejoe

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You can cover the mirror with your hand and still get a semblance of a focused image, i very much doubt the mark is worth worrying about, as others suggested, its probably a water mark. The lack of focus has got to be something else out of whack. Either you didnt set up right, got both ep adapters in, or collimation got knocked way out somehow. Nothing that cant be fixed though, so dont lose any sleep over it.

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knobby

knobby

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I'm hoping it's something like that knobby. As I say I'll try setting up tomorrow earlier and in a more structured way. I'll make sure it's properly extended and that the EP mount is correct. If it still stays the same I'll post some photos back here... Either way I'll report back.

Best of luck :icon_salut:

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Carbon Brush

Carbon Brush

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Mirrors have to be really really really dirty to give any significant image degradation. Yes I really mean 3x really.

Inability to focus is probably due to putting the eyepiece at the wrong distance as advised by others.

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markryan

markryan

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You did have it fully extended I assume lol

To be honest I'm hoping I didn't, or that I've done something else stupid - I'd like to get up and running again tonight and get back to planning purchases of goodies not working out how to remediate my scope.

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markryan

markryan

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How you getting on Mark

we're all worrying about you!

Don't worry! I had an impromptu visit from the in-laws tonight so couldn't get out and set up... I'll be out tomorrow and let you know, although now I know about a Texan Dob with a bullet hole through it I feel confident it is a neck and neck race between collimation and stupidity. Quite happy with either tbh!

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markryan

markryan

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Okay Folks,

I've just brought the scope in to check it. I put a 42mm in and pointed it at an object a few miles away and it brings it into focus fine. I'm hoping that that means my troubles are over and due to my stupidity when setting it up the other night...?

I'm not really sure what happened - as I said initially, could using warm EPs straight from the house on a cold night cause the image to be totally blurred?

On the plus side, I've now lined up my spotting scope accurately and am about to work out how I'm going to mount my telrad on a flextube (not very much real-estate). I also made a collimation cap to check collimation, it doesn't look too shabby to my eye (based on The Backyard Astronomer's Guide).

I've included some images of the infamous blob. Still not sure about its origins.

I'll stick a last update in once I've been out with the scope again.

Thanks for all the support,

Mark.

post-34131-133877759439_thumb.png

post-34131-133877759463_thumb.png

post-34131-133877759485_thumb.png

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Tribal-Wolf

Tribal-Wolf

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It certainly shouldn't stop you focussing but I think I would clean it too in case there is anything corrosive in it.

Incidentally I looked at my scope to see where any 'grease' could have came from but I can't see anywhere. Did you smear it or was it like that?

Check for insects and mice.

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pajr777

pajr777

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could using warm EPs straight from the house on a cold night cause the image to be totally blurred?

No, condensation usually occurs taking a cold object into a warm environment. Mirrors get condensation during observing because they cool more quickly than the surrounding air and eventually get colder than the surrounding air.

One tip I have read re Telrad - mount it temporarily using cable ties, when you are happy then mount it permanently using the adhesive strips or screws.

Looks like snail trail, but could possibly be bird poo? As others have said, probably worth cleaning just in case it's acidic. If it were dust etc I would leave as I doubt that would cause any visible difference at the eye piece.

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