Newcomer needing help please

[Squint]

I've been lurking around the site for a while & I've just got my first “real” telescope & I'm hoping that I haven't made a horrible mistake.

I've bought a secondhand Skywatcher Skyliner 200 Dobsonian (so far so good). I should have taken a lot more notice of what I was buying as I've found that the primary mirror needs a good cleaning. When I say this, I don't mean that it's dusty or misty, there's a couple of areas that actually look like they're covered in bird droppings!

I've read a couple of tutorials on cleaning the mirrors but I need to know what to expect when I dismantle the scope.

If I take out the screws at the bottom, what next?. Will the mirror just pull free? Are there any more screws/washers/springs/O-rings etc?

And will I be able to put it all back together without totally ruining the alignment?

Basically, how much trouble am I in??

Panic is setting in.......Can anyone help please?

[ronin]

Add a location of more then North of England.

That way there may be a club near you or even a person who could help.

If there are droppings on it then it needs cleaning as they will eat through the coatings eventually.

You could try a soft brush to see if they come away.

Just thinking of options that may not involve removing the mirror.

Which I think is not that much of a problem if done carefully. The screws at the bottom likely adjust the cell that the mirror sits in and not the mirror, I think there are 3 adjustable ones around the edge that actually do the holding. If you look down the tube you will I think see these as they will be just visible equally spaced round the mirror edge.

[happy-kat]

Could you share a photo?

[Coastliner]

Taking the mirror out will be an interesting project, but you need to assess whether or not it is worth it. If the dirt only covers a small area then it will not make a great deal of difference to the image. Alignment? Yes, it will completely mess it up, but getting it back into alignment is what collimation is all about, and I would guess that being second-hand it will need collimating anyway.

Neil.

[Squint]

Could you share a photo?

Please forgive me for being dim (no pun intended) but I can't see how to do that.  I've got a couple of photos on my commputer but I can't see how to insert them.  Do I have to upload them to a site & then provide a link?

I still think that the mirror will need to come out for cleaning.  If I remove the 6 x screws at the botom end, what will happen next?  Will the mirror assembly be free & what would I then have to do?

[xtreemchaos]

hi mate , if you have to take the mirror out make sure you have no distracsions, if its bird pupe you need to get it off as soon as poss. if your going to give it a full wash make sure you use real cotton wool and distilled water to rinse. clear skys charl       ps you need to remove the six screws on the bottom edge of the tube not the adjustment knobs on the bottom of the cell when you get the cell out there 3 mirror clips each with 2 screws remove clips to release mirror from cell.

[Coastliner]

To add a picture hit the "more reply options" next to the "post" button. You can then attach a file.

[Squint]

To add a picture hit the "more reply options" next to the "post" button. You can then attach a file.

Thanks again.  Pic now attached.

[Squint]

hi mate , if you have to take the mirror out make sure you have no distracsions, if its bird pupe you need to get it off as soon as poss. if your going to give it a full wash make sure you use real cotton wool and distilled water to rinse. clear skys charl       ps you need to remove the six screws on the bottom edge of the tube not the adjustment knobs on the bottom of the cell when you get the cell out there 3 mirror clips each with 2 screws remove clips to release mirror from cell.

Thank you.   So if I remove the 6 x phiilips screws from around the edge of the base the cell will come out?  Does it come out easily without any force or will it need gentle persuasion?  If I take the cell out as a whole unit, do I actually have to take off the mirror or could I do the cleaning with the cell intact?  Will I then need to realign the mirror?   Sorry for all the questions but I feel completely stupid at the moment!

[happy-kat]

You will need to realign the telescope afterwards, but you need to be able to do this anyway for regular use.

[happy-kat]

There are lots of threads which might help this is just one.

http://stargazerslounge.com/topic/243577-help-my-precious-mirror-is-in-danger/?fromsearch=1

Removing

http://stargazerslounge.com/topic/192901-removing-200p-primary/?fromsearch=1

Halfords for example sell distilled water.

Before taking anything apart.

Using your colimation tool take a look at how the mirrors look now, so you know what it was before hand and ideally give it a star test to see how well it is performing, so you have something to compare with afterwards.

[brantuk]

Before lifting the tube off the mirror cell - put a bit of tape across where the cell joins the tube. Slice with a thin sharp knice along the join and use that as a guide to where it was when you put it all back together. You can do a similar thing when you lift the mirror out of the mirror clamps. Getting it as close to how it was before taking to bits will mean less effort collimating.

When you reassemble - make sure you don't pinch the mirror - ensure the clamps are done up enough to hold it in place - and loose enough to not bend the mirror even slightly - it should only just hold the mirror in place. Otherwise you'll get distorted stars and recolimation will be impossible.

When you undo the six screws round the edge of the tube it will just lift off easy - be careful not to touch the mirror surface or the coatings will scratch. Hth

[xtreemchaos]

yer the mirror cell should come out easy i would get somebody to hold the cell when you undo the + screws to stop it falling,i would remove mirror from cell to wash make sure you wash in plastic boll to save damaging mirror.  charl.

[triton1]

As Brantuk says don,t tighten up the clips that hold the mirror in place I put a cigarette paper under mine and started to tighten each one while gently moving the paper as soon as you feel abit of drag on the paper that,s it job done.I also used tape to line up the cell with the tube.There are also plenty of threads on here about cleaning a primary mirror a valuable read,hope this helps.

[Squint]

Before lifting the tube off the mirror cell - put a bit of tape across where the cell joins the tube. Slice with a thin sharp knice along the join and use that as a guide to where it was when you put it all back together. You can do a similar thing when you lift the mirror out of the mirror clamps. Getting it as close to how it was before taking to bits will mean less effort collimating.

When you reassemble - make sure you don't pinch the mirror - ensure the clamps are done up enough to hold it in place - and loose enough to not bend the mirror even slightly - it should only just hold the mirror in place. Otherwise you'll get distorted stars and recolimation will be impossible.

When you undo the six screws round the edge of the tube it will just lift off easy - be careful not to touch the mirror surface or the coatings will scratch. Hth

OK guys, You've given me enough confidence to go for it....

I've got the cell out but I still a bit wary about removing the mirror from the clamps.   I've tried one of the clamp screws & it is very tight.   IE, to the point where the screwdriver is likely to slip off.   Is this likely to mean that someone has had it out before & has overdone it when refitting?  I've also noticed a couple of light scratches on the mirror (but too light to get a proper picture).    Is this a major problem?

[xtreemchaos]

squint- i find that holding the tip of the screwdriver between thumb and finger as close to the tip as poss helps also if worried about slip you could make a carboard cut out of mirror to lay on top to protect. scratches if you cannot see through eps i would not worry about them.  charl.

[Squint]

Thanks again Peeps.

I've done what I've done now so there's no going back.

I managed to remove the "organic matter" by disolving it with camera lens cleaner then flushing it with water.  The rest of the crud came off in ways that were done very gently but that you still probably wouldn't approve of but it looks much better (to the naked eye at least). With regards to the alignments, I've looked through the viewfinder without an eyepiece attached & I'm assuming that when the centre spot is directly in the crosshairs, the image should be central.  At the moment, it's slightly too high & too far left (but not by a lot).  I think  I'm going to have to do a quick learning curve at collumating the primary mirror but I'm going to leave that for another day.

I hope at the end of all this, I'm going to be able to look back at this thread & think "Boy, was I a wuss!!!"

[brantuk]

You could use an electronic screwdriver so you don't have  to apply pressure which might slip. I think they glue the screws in during manufacture/assembly - but I'm just guessing why they're so hard to get out. Mine unscrewed a long way before they came out. Triton's tip about the paper is good - that's how I judged how tight to go when I did mine.

Good luck and do come back with questions if you have trouble reassembling.

(Woops - post crossed with yours - well done! )

[xtreemchaos]

glad you have got it sorted mate.  clear skys. charl

[Charic]

Thanks again Peeps.

I've done what I've done now so there's no going back.

I managed to remove the "organic matter" by disolving it with camera lens cleaner then flushing it with water.  The rest of the crud came off in ways that were done very gently but that you still probably wouldn't approve of but it looks much better (to the naked eye at least). With regards to the alignments, I've looked through the viewfinder without an eyepiece attached & I'm assuming that when the centre spot is directly in the crosshairs, the image should be central.  At the moment, it's slightly too high & too far left (but not by a lot).  I think  I'm going to have to do a quick learning curve at collumating the primary mirror but I'm going to leave that for another day.

I hope at the end of all this, I'm going to be able to look back at this thread & think "Boy, was I a wuss!!!"

Hi Squint........There are no cross hairs as such,  What you are seeing are the 'Spider' vanes?

Since our chat, and in no particular order, here are some references to collimating your telescope. I was first introduced to the Astro Baby guide, which suited my needs. There are a multitude of references and guides on the web / you tube  for you to follow. My advice is to read them, understand their meanings, and visualise their intent before actually adjusting! Best bet is to carry out a Star test first, just to see if anything actually needs adjusting, but as you have removed the mirror, its possible some slight correction on the Mirrors will be required? Using coloured card also helps reduce confusing reflections when first starting out with the secondary?

I would recommend a Cheshire as the main tool for collimation, but dust caps can serve the same purpose until your fully equipped?

http://www.astro-baby.com/collimation/astro%20babys%20collimation%20guide.htm

http://stargazerslounge.com/topic/197640-collimation-and-star-hopping/

http://www.garyseronik.com/?q=node/169