Arrggh what have I done?......

[Digz]

Hopefully nothing too detrimental to my scope?

I was removing my guidescope holder bracket from my OTA to see if I could connect it to my widefield setup, pulled the screws out and crash . There was a metal plate inside which I failed to notice, that crashed down the tube onto the mirror.

Serves me right for not having the scope horizontal like I normally do.

The question is, there are three marks on the mirror now, two look like smudges about 7mm in size and the third is a spider crack about 10mm in diameter - have I made a mess of my scope or in the grand scheme of things will I note notice anything? I have a SW250p DS which I use for imaging.

Im hoping things will be ok, but its rather put a dampener on going out tonight :(

[John]

Well it's not a good thing obviously but the scope will still be quite usable although you may well need to re-collimate it. A few small marks on the mirror won't affect the views too much for visual work - not sure about imaging ?.

You will have put a dent in it's 2nd hand value of course but we buy these things to use, not as investments, so I guess that's not the end of the world.

If the damage is to the coatings only then you can get the mirror re-coated but it sounds a little deeper than that.

[malc-c]

Ouch.... !

I'm no expert, and I guess it depends where the damage is, but would of thought that any damage to the main mirror would have an effect on the quality of the image produced.

[zcapp96]

I had a smudge on an 8" mirroe once and it made absolutely no difference whatsoever. A crack might be a different story though. If it is in the middle under the secondary you might get away with it.

[Doc]

In my experience a mirror can be really dirty and it doesn't effect the image but a scratch will. You do say it's only 10mm long and very fine so lets hope it's not that bad.

Only way is to test it.

Best of luck.

[Digz]

Im sooo annoyed with myself over this.

Attached is a photo of the damage, my god the mirror is really dusty.

Im kind of hoping the fact that the marks are no bigger than the centre dot and they are spaced apart it wont make any noticeable difference. But as you say Doc I need to try it out.

jahmanson - I know the second hand value has taken a dent (no pun intended!!!!) but as you say they are to be used and its not the end of the world, just really annoying!!!

[steppenwolf]

Im kind of hoping the fact that the marks are no bigger than the centre dot and they are spaced apart it wont make any noticeable difference.

The centre dot is out of the light cone (shaded by the secondary mirror) so unfortunately you can't count on your excellent logic for that one. Dust and many other marks do not seriously affect the view but that star crack could give you some strange diffraction artefacts - I hope not but the only way to find out is to try it in the field. I hope you have good news when you try it.

[Digz]

The centre dot is out of the light cone (shaded by the secondary mirror) so unfortunately you can't count on your excellent logic for that one. Dust and many other marks do not seriously affect the view but that star crack could give you some strange diffraction artefacts - I hope not but the only way to find out is to try it in the field. I hope you have good news when you try it.

Darn it. Thanks for the input Steve, much appreciated.

I guess that 80ED APO is calling sooner than I thought lol.

Ill guess Ill have to test out out and see what happens.

Thanks all

[Catanonia]

ouch nightmare...

Did the same ALMOST when plaing with my secondary on the MN190, but luckily I had the foresight to have the scope horizontal at the time.

Hope it is ok, but looks pretty bad to me

[Andrew*]

Always a good idea to have the tube horizontal when doing these things, but it's a bit late for that advice....

I doubt the marks will have much effect on the views, to be honest, but I've heard light scatter can be an issue with this kind of damage. If you get any flaring or an unusually bright background, it might be worth addressing the issue. Get a second opinion on this, but I've heard that blackening off the damaged areas with a black permanent marker can stop the light reflecting off the uneven surface and causing optical defects.

But don't let the accident stop you getting out tonight. The sooner you know how bad (or not) the effect is, the sooner you can relax! Just take a deep breath, and take care!

Andrew

[Andrew*]

By the way, those marks are pretty tiny actually. I seriously doubt you'll even notice a difference. And don't worry - your mirror's not too dusty. Photos show up dust a bit too well.....

[Hypernova]

I'd go with blackening the area around the spider crack, maybe with a permanent marker or a small black sticker of some sort.

I was told by OO last year that my mirror could be improved slightly by having the very edges blackened to around 3mm to cut out some warping caused by the clips.

[Digz]

Cheers Andrew, I think what Im really annoyed about is that I didnt even notice the metal plate inside the tube otherwise I would have put it horizontal :BangHead:

Hopefully I will not notice anything and thanks for the great tip about blackening off the damaged area.

As for the dust its quite funny because if I look down the tube it looks spotless, shine a torch and I can see shed loads of dust, unfortunately my arm isn't long enough to reach with a duster, lol.

Thanks again for all the advice

[Doc]

There shouldn't be a plate there haven't they heard of captive nuts.

[JamesC]

Tough luck Digz. Accidentally dropping something on the primary is every astronomer's nightmare. No experience with cracks thankfully. Blackening the crack sounds like a good idea to me.

[Shibby]

I feel your pain Digz, I really do. I did the same sort of thing myself, which left a chip about 8mm in diameter.

However, it hasn't made any difference to the visual performance that I can tell. Any imaging blemishes should be fixed by flats.

[spaceboy]

Very doubtful it will effect your views in anyway but I also remember reading something about blackening / covering cracks in the primary coatings. I'm sure if you Google it you will be able to find some thing about it. Try a small white or black sticker over the crack and forget about the smudges.

[umadog]

I dropped my secondary onto a nice David Hinds 9" primary. Damage was similar to what you show here. I couldn't notice the difference. It's true that you ought to cover the smudge with black marker. If not, it will reflect light at the wrong angles and decrease contrast. Once covered, it just means that you've lost a little light. It's no big deal.

From experience, I can tell you that such accidents loose you only 1% of the optical performance but they knock off about 85% of the re-sale value. I tried selling my 9" and received only very low offers. If I'd gone through with it, I'd have let a nice David Hinds primary go for 25 quid. In the end I decided to keep the scope. If I sold it, I'd be ripping myself off. I'll re-build it into a nice planetary scope. Remember that if you have get the itch to sell.

[sbooder]

I have not read all the posts, so someone might have already given this bit of advice. If the crack dose affect your image, it is better sometimes to put a piece of black tape over the crack, this will lower the light gathering of the mirror a little, not too much that you will notice, but it will get rid of any spiking from the crack.

What do others think?