Replacing secondary mirror??

[MadamCaptain]

I've got a Meade Lightbridge 10 inch scope, which I've had for around 7 or 8 years now. I noticed recently that the secondary mirror was looking a bit corroded around the edges and not in great condition. It still does the job and there are no problems with viewing (it doesn't distort the view or anything) but I decided to buy a new mirror for it anyway. I did some research online and found the right size and ordered it from ebay. I tried to replace it but I realised that I couldn't get the secondary mirror out of its holder. It was pretty easy to unscrew the holder so I could take it out. I didn't want to break the mirror holder so I screwed it all back in, I guess I will just have to keep on using that secondary mirror, even though I would love to replace it.

I did some more research online about replacing the secondary but I couldn't find much info, apart from a few people saying the whole thing (holder with mirror in it and the spider) needs to be replaced. 

So my question is: 

Is there any way I can take the secondary mirror out myself and put the new one in?? I couldn't seem to find any way to get the mirror out of its holder, no clips or anything holding it in place or screws or anything. I think its glued in place. Surely there must be a way to get the mirror out because I was able to unscrew the holder and take it out of the spider. Or do I need to send the secondary to somewhere to get it re coated?

I live in a small city so there are no astronomy shops around, the last one we had here closed down a while ago. So I can't just take it somewhere to get it re coated or anything. Which is why I bought the new secondary mirror online.

Can anyone help??

[faulksy]

as far as i no, most mirrors are bonded on to the holder, usually silicon sealant or similar, can you remove the mirror and holder and use a small blade and cut between the mirror and holder?

[MadamCaptain]

I tried to do that but I was scared it would do more damage to the mirror and/or the holder. Plus there's a deep sky night on tomorrow night and I didn't want to turn up with a broken telescope!! 

There probably is a way to get the mirror out but I don't want to have no telescope - a camp is coming up in October (a whole weekend of astronomy) and I don't want to miss out on that either. The secondary will be okay for a while I think and it still works perfectly but it just looks a bit corroded. I guess it will have to do.

[Moonshane]

faulksy is correct, but so are you. don't miss out on observing opportunities for minor enhancements to the views. this includes fiddling with collimation while the stars are out and you can be too.

[astronymonkey]

I removed the secondary in my lightbridge and it was siliconed in place as far as I remember. It sounds like you have the newer enclosure for it which has a small clip held on by a screw , this needs to be removed and the mirror very gently prised out .

It does seriously mess up collimation though so be prepared to spend an hour realigning the secondary .

It took about 10 mins to remove and I took the whole of the spider out to do it. If the mirror is identical in size I dont see why the holder cant be reused though.

Cheers

[MadamCaptain]

You are correct, I have the mirror holder with the clip and screw on it, holding the mirror in place. When I unscrewed it, it didn't make any difference to the mirror though and I couldn't find any way to prise it out, gently or otherwise. Plus when I screwed it all back in and attached it back to the spider, one of the screws started splintering and little bits of metal shards came out of it as I screwed it back in. I managed to get it screwed mostly in but its sticking out slightly more than the other two screws. Its screwed in tightly enough though but I doubt it will unscrew again, without using a drill or something similar. I tried all my screwdrivers to get it back in all the way but the last little bit wouldn't budge. 

I've never unscrewed the mirror holder before. I've had this scope for about 7 or 8 years now. I was surprised that the secondary didn't stay in perfect condition because I've always been very careful about covering it up when not in use. The primary mirror is still perfect and I've never had to clean it. I know it will take a while to collimate the scope tomorrow because I've fiddled around with the mirror. I find that whenever I use the scope, I have to collimate it. Sometimes, it holds its collimation and other times, its way out!

Yes, the mirror is identical in size. Now if only I could get the other secondary out. But even if I did mange to get it out, without damaging the holder, would I need to glue the new mirror in??? What type of glue would I use?? I'm reluctant to try removing it again, unless someone on here has already done it themselves and can honestly tell me it can be done easily. Why would secondary mirrors be available to buy then?? Or are the sold like that, just a plain mirror, without the holder for people who build their own scopes??? 

[astronymonkey]

Hi,

The trick is to just remove the four silver adjusters from the outside of the tube which connect the spider vanes to the outer tube, you can then remove the whole spider assembly which is much easier. You then remove the small clip and screw from the secondary holder and you can insert a blunt flat metal object under the edge of the mirror , near the clip and gently and slowly leaver the mirror out. You need to be very careful and not apply too much force as the silicone glue holding it in will slowly stretch and give in a non-elastic way as the force is applied. I think I used the end of a teaspoon handle but dont apply any force to the mirror edge, just to the side of it.

So if you do it I cant take any blame but I managed and it took about 2 mins to slowly prise it from the holder.

The glue was black sticky mastic stuff and when I fitted the kendrick secondary heater, which was the reason for removing the mirrior in the first place, I realised that the mirror was a snug fit so only needed the metal clamp fitting to hold it in place.

For the secondary adjusters, it sounds like you may have cross threaded them , although on mine they are pretty stiff too.

Mine also gets collimated at each viewing session, I tend to set everything up using a cheshire but for a quick colimation when in the dark i tend to opt for a laser then a star test then just get on with viewing. Only if Im setting up in the daylight do I bother with a cheshire as a laser is quicker and I dont want to spend all night fiddling rather than observing.

Cheers

[MadamCaptain]

How did you remove the adjusters on the outside of the tube, to remove the whole spider?? I couldn't work out how to take the whole spider out, which is why I just took the mirror holder out.  In regards to the secondary mirror holder screws, I think they are cheap screws and thats why one of them started shedding metal shards. The other two screws were okay though. The mirror holder is well and truly screwed in place and shouldn't move.

I will try again to take the whole spider out and see if I can get the mirror out of the holder again. I might wait a while though because deep sky night in on tomorrow night and then a weekend of astronomy in about a month's time. I would love to be able to replace the mirror myself because the new one I bought looks so much better!! 

Thanks for the info, its good to know that someone has managed to replace their secondary themselves. I don't really know anyone else who has a Meade Lightbridge. Most of the members in my astronomy club have gotos and only a handful of us have dobs but I've only ever seen one other Lightbridge  and that was years ago (but I don't think that person is a member anymore)

[astronymonkey]

If you unscrew the four silver side bolts and the whole spider should wriggle free and lift out. Do I with just the top cage on the kitchen table to stop anyrhing falling anywhere.

Cheers

[MadamCaptain]

I had another go at removing the secondary mirror from the holder - and I got it out this time!! Woohoo!! I used a spoon to go inbetween the mirror holder and the mirror and it lifted out easily, almost straight away, no mucking around either.  I was able to unscrew the clip and small screw holding the mirror in place, without having to remove the entire spider. Then I pushed the new mirror in, it went in easily and I screwed the clip back on - no messing around with that either and nothing got damaged! And I didn't need to glue it in, it seems to fit snugly enough in the holder that is doesn't need to be also glued in. So now I have a nice new shiny secondary mirror and a deep sky night tonight so I'm hoping for some good observing. The weather here is great today, no rain or clouds in sight anywhere,  clear skies and warm temperatures. 

Now I will have to collimate again which I'm not looking forward to but I will probably set up my scope at home and collimate it before going out tonight. Then I will most likely have to collimate it again at the deep sky night but hopefully it will hold and won't be out too much. All I need now is some of those expensive eyepieces (Ethos) or there is a cheaper version too so I can get some really good views of Saturn and Jupiter. It will take me a while to save up for those.......

[MadamCaptain]

Sorry about the double post but I managed to collimate my scope in well under an hour - more like 10-15 minutes with my red dot collimator.

I did notice though, after my last post that the new secondary mirror is slightly thicker than the old one so I did have to glue in it after all, I didn't have any silicone glue so I just used a bit of super glue and it did the trick. I also noticed that the clip left a tiny scratch on the edge of the new mirror, after I screwed it back in. I don't think it will distort images though because its right on the edge. Its only about half a centimetre long but I'm a bit annoyed about that. I didn't realise the new mirror was thicker, which is why the clip has left a scratch. I managed to adjust the clip so its still holding the mirror in place but not scratching the mirror any further. 

I ordered myself another secondary mirror, just in cast the scratch does cause any problems. They are relatively cheap, under $100 so I'm not too annoyed about that. At least I will have a replacement mirror now. I'm also thinking that with scratches on mirrors, wouldn't it be worse if they were on the primary mirror, because its the main mirror?? Plus its such a tiny scratch and its not like its right in the middle of the secondary or anything like that. Nevertheless, I will find out tonight if it distorts any images. I'm hoping all will be good though. 

[astronymonkey]

Hi,

I found I needed to move the secondary holder back up the tube a bit as when I fitted the heater as this added about 3mm to the thickness and that was the fiddliest bit. Do the collimating when at home first so only small adjustments are needed in the field.... I made the mistake of not doing this and ended up messing on in the dark trying to sort out a collimmation mess.

Cheers

[MadamCaptain]

I ended up having to tighten the mirror holder because somehow, it was very loose. That was a bit fiddly and I had to play around with the screws a bit before I got the mirror holder to sit properly (and not move around) Then I had to collimate again, it was so far out of alignment that the red dot wasn't even shining anywhere in the tube!! But I managed to get it properly aligned again and it only took 10 minutes. When I went to the deep sky night last night, I had to collimate again slightly but it wasn't bad at all, just needed a little tweaking. I did notice a difference in the image quality too, having that new secondary mirror in. It was much clearer than before and I found that my collimation was a lot better than before too - perfect in fact!! So I'm glad I mucked around with the secondary!! 

I hadn't really taken much notice of how the secondary was positioned before, I had never really looked at it that way before. I also noticed, after looking at a friend's scope from the club, at last night's deep sky, that the secondary on her scope didn't have a holder. It was just a naked mirror attached to the spider. She has a Sky watcher 10 inch, very similar to my scope but its collapsible set up, whereas mine has truss poles. We got some viewing in but then it got cloudy around 8.30 so we gave up after that. 

[astronymonkey]

The older lightbridges used a directly connected secondary mirror too, but I find the neweer enclosed design easier to mess around with. Glad you got it sorted

[MadamCaptain]

When you say 'older' lightbridges, do you mean the model I've got? I bought mine new around 2007 but I'm guessing there is a new model out now. Or was there an older model that came out before 2007? I'm not sure what people do who have scopes with a naked secondary attached to the spider. How in the heck do you replace those ones??! I'm just glad I was able to sort mine out relatively easily. 

[astronymonkey]

over time meade has replaced the bare stalk with he plastic holder, but may have done this at different times with different models so itsnot easy to say which year the new holder was introduced, wither way it sounds like you have a current version of the secondary holder. For the open stalk versions the mirror is bonded to the stalk plate with silicone which can be cut to remove the mirror and then resiliconed to re-attach it.

Meades most recent version of the scope has black poles and this is the most recent change as far as Im aware.