12" Dobsonian ... its a Revelation !

[Stu1smartcookie]

So, i collected a 12" dob , on Saturday ... It had stood in storage for many years and the primary needed some TLC . Took the mirror off and cleaned it as best as i could , but unfortunately the mirror will need a re-coat . This was not a surprise and was understood at the point of purchase . So after cleaning the mirror as best i could i used the scope for the first time last night . I have to say , i had no right to expect the view that i had ... just viewing bright stars , such as Arcturus and Vega as well as the lovely Albireo and its blue companion . The stars were all bright and if anything , although i think the mirror degradation has meant a little lack of contrast they seemed to show colour very well . The scope is well out of collimation ( i thought i had done a reasonable job after putting the primary back but a star test soon told me otherwise) . But as i didn't have a collimating device it was a shot to nothing and something that will be addressed this evening . I was shocked how a mirror, when in poor condition , can "work" so well . Now i realise that mirrors should only be cleaned when absolutely necessary ! I will get the primary sorted , but , i am really pleased with this scope . What i need now is a week of decent nights to explore what it can do ( hmmmm.. wishing for clear nights might be pushing it a bit  ) 

If anyone has had experience of having a mirror re-coated and a favoured place or company to use , i would be grateful for the tips . 

Stu

 

[CraigT82]

Congrats on the new scope... bargain of the year IMO! Even factoring in the cost of a recoat. 

I recently had a 12" mirror recoated by OOUK and it was freshly coated with hilux and back with me 6 days after sending it off. 

This was the mirror to beging with... full of pits in the coating. The views through the scope were actually really good with the mirror in this state.

[russ]

Its quite a surprise jumping up to 12" aperture after a smaller scope. I had the Revelation 12" dob which i also bought in the knowledge the coatings had gone. Took the mirror to Orion Optics and had their Hilux coatings applied. It wasn't cheap though. I paid as much for the recoat as the entire scope. It was worth it though. The Veil Nebula with an OIII filter and this scope from a darkish site was amazing. 

Enjoy the scope, hope you get some clear skies soon.

[Stu1smartcookie]

Thank you guys , Craig , my mirror is if anything worse lol ... but i have looked on the OO site and they seem to be the favourite , although i have noticed there is a company in Essex ( near to me ) who specialise in re-coatings as well . I'm heartened by your and Russ comments above .  

 

[NGC 1502]

I live in Southend and for convenience have used Galvoptics (Image Optics) at Basildon several times, always a reliable service. The big advantage (for me) is I didn’t have to pack the mirror to withstand the earthquake wind and fire of a postal service or pay for it. I delivered and collected myself. A phone call to say when you’re coming. Then just find a piece of hardboard or ply, cover with kitchen roll, then tape the mirror face down. Mark clearly the service required (strip/recoat/overcoat) and contact details, say you’ll collect when done.

On collection my mirrors have been taped to my hardboard and acid free tissue has been used in place of my kitchen roll.

Good job, recommended. Prices available online.

Ed.

[John]

I'm glad you are impressed by your 12 inch dob - once I moved to that aperture, there was no going back but I did need to find the lightest 12 inch that I could to ensure that it got used often, hence my Orion Optics 12 in F/5.3.

I had the 8 inch version of the Revelation (my 1st dob in fact) and had a similar issue with the mirror coatings. The mirrors are decent quality (GSO made) but the over-coatings for the 1st generation Revelations were either thin or skimped so a need to re-coat these is not unusual at all.

My current OO 12 was re-coated and hi-luxed (by OO) 11 years ago and the coatings are still immaculate.

There are other coating options than OO though, as I'm sure you will find out.

 

 

 

[Stu1smartcookie]

Hi Ed & John ... Ed the place in Basildon appeals to me as i would also take the mirror to them rather than risk the postal butchers .

The bulk rather than the weight is the only issue , John,  but hey , i knew that before i bought it . Everything about the scope was A1 ( apart from the mirror of course ) .. even has a dual speed crayford focuser , which is great . 

Stu

[NGC 1502]

Galvoptics at Basildon are a family run business and great to deal with. Their turn round times do vary according to what work they have, but they’ve always given a lead time when asked, and either kept within that or were quicker.

My local club’s 16” Dob had its mirrors coated there in 2003 and are still fine after several washes. They also coated a member’s own 20”.

Ed.

[Stu1smartcookie]

Been in touch with Galvoptics ( thanks Ed ) .. very polite and informative and to be honest a lot more reasonable on price than i thought . Now i have a question ...,

when i took the mirror cell from the scope i could not free the mirror from the cell. ( i cleaned it the best i could with it in the cell .. bearing in mind the mirror does need recoating anyway so i was ok doing this ) .. so , i now need to remove the mirror from the cell in order to take it to Galvoptics . Is the mirror fixed in the cell ? Or is it the case that it hasn't been removed for many years and is kind of stuck ? Or do i need to remove all the collimation screws /springs and locking screws . I presume the "floating "triangular pieces with the pads on just sit under the mirror without any fixing .

Any Guidance gratefully accepted here , as this is the first ( and only , hopefully) time i will need to do this . 

Stu

 

[John]

I found the same when I tried to remove the mirror from my 12 inch Meade Lightbridge, which used the same primary mirror and cell as the Revelation 12.

The mirror was fixed on to the cell by a number of small double sided sticky pads which need to be soaked with white spirit to loosen them and / or cut with fishing line or dental floss, so that the mirror can be removed from the cell. It's a bit of a chore to be honest but it can be done.

 

 

Edited August 10, 2021 by John

[John]

I found this on another forum about this issue:

https://www.cloudynights.com/topic/396951-12-gso-mirror-removal-and-re-mounting/

[Stu1smartcookie]

14 minutes ago, John said:

I found the same when I tried to remove the mirror from my 12 inch Meade Lightbridge, which used the same primary mirror and cell as the Revelation 12.

The mirror was fixed on to the cell by a number of small double sided sticky pads which need to be soaked with white spirit to loosen them and / or cut with fishing line or dental floss, so that the mirror can be removed from the cell. It's a bit of a chore to be honest but it can be done.

 

 

Thanks John, so ( apologies for wanting everything spelled out here ) , the mirror cell has to be taken apart ie all the screws out which i presume will just leave the triangles stuck on with the pads ?... what did you replace the pads with when you replaced the mirror ?... Just read the cloudy nights post , John ...thanks for the link . 

Will look at this tonight , unless its clear outside lol 

 

Edited August 10, 2021 by Stu1smartcookie

[John]

I took the primary mirror cell off the end of the scope tube. I then turned the whole thing upside down with the mirror face protected and facing downwards, removed any clips and screws holding the mirror in  the cell, applied a drop or two of white spirit to each sticky pad and allowed it to soak though, After some time (a couple of hours) I was able lift the whole mirror cell off the primary mirror. Some times the pads might need a bit of easing or even cutting which is where the fishing line / dental floss comes in.

When I put the mirror back I used small cork pads instead of the sticky ones and did not stick the mirror back in, relying on the mirror clips and gravity to stop it moving around.

It's important not to tighten the mirror clips down onto the mirror - there should be a very slight gap (playing card thickness) between the clips and the mirror surface.

Sorry that it's a bit of a faff. I don't think the primary cell design has changed in the past 20 years with these.

Another tip is not to use the locking screws once you have collimated. The mirror cell is quite thin and the locking screws seemed to cause flex when tightened  which moved the collimation out again !

 

 

[NGC 1502]

Great you found Galvoptics helpful, that’s exactly what I’ve experienced on several occasions.

When replacing the mirror of course it must never be clamped in place. But the mirror clips need just a tiny clearance from the optical surface. Paper thickness is fine. A large gap allows the mirror to shift and loss of collimation more likely.

Go carefully and you’ll be fine.

Ed.

[Stu1smartcookie]

31 minutes ago, John said:

Another tip is not to use the locking screws once you have collimated. The mirror cell is quite thin and the locking screws seemed to cause flex when tightened  which moved the collimation out again !

That's really interesting , John ... and something i will bear in mind ... after the tube will never go past horizontal so the mirror wont fall out !

So the cork pads would be glued to the triangles and just left to press on the mirror ?

 

[John]

4 hours ago, Stu1smartcookie said:

That's really interesting , John ... and something i will bear in mind ... after the tube will never go past horizontal so the mirror wont fall out !

So the cork pads would be glued to the triangles and just left to press on the mirror ?

 

The mirror clips would stop the mirror from falling forward from the cell but should not be pressing hard against it.

Yes, the cork pads were stuck to the triangles and the back of the mirror just rested against them.

 

[Stu1smartcookie]

15 hours ago, John said:

The mirror clips would stop the mirror from falling forward from the cell but should not be pressing hard against it.

Yes, the cork pads were stuck to the triangles and the back of the mirror just rested against them.

 

Thanks John , i released the mirror clips a little last night as two of them were a bit tight ... Have to say , the Cygnus region looked fantastic last night ... and i'm sure will look even better when the mirror is remedied .

 

[Stu1smartcookie]

UPDATE **** Last night i successfully removed the Mirror from its cell .... it was actually quite easy in the end ... the mirror gets taken to Galvoptics tomorrow for its "treatment " a bit like a spa week for Mirrors

Bobs Knobs ordered from Rother Valley ... cork pads ordered from Amazon ... just trying to decide what shape i want the centre spot ... any suggestions ? 

 

[CraigT82]

1 minute ago, Stu1smartcookie said:

UPDATE **** Last night i successfully removed the Mirror from its cell .... it was actually quite easy in the end ... the mirror gets taken to Galvoptics tomorrow for its "treatment " a bit like a spa week for Mirrors

Bobs Knobs ordered from Rother Valley ... cork pads ordered from Amazon ... just trying to decide what shape i want the centre spot ... any suggestions ? 

 

I find the triangle centre spots useful (can get them from FLO - along with a centering template).  If you orientate the mirror so that each corner of the triangle points to a collimation bolt, the primary collimation with a cheshire becomes really quick and easy.

Especially if you have a little note on the tube that reads "tightening bolt pushes dot away" or something like that, the dot being the reflection of the Cheshire's peephole.

Then just by looking through the Cheshire you can immediately judge which bolt to turn and which way to turn it.

[Stu1smartcookie]

1 minute ago, CraigT82 said:

I find the triangle centre spots useful (can get them from FLO - along with a centering template).  If you orientate the mirror so that each corner of the triangle points to a collimation bolt, the primary collimation with a cheshire becomes really quick and easy.

Especially if you have a little note on the tube that reads "tightening bolt pushes dot away" or something like that, the dot being the reflection of the Cheshire's peephole.

Then just by looking through the Cheshire you can immediately judge which bolt to turn and which way to turn it.

Thats a really good tip , Craig regarding the triangular centre spot . Thank you  

 

[callisto]

16 minutes ago, Stu1smartcookie said:

UPDATE **** Last night i successfully removed the Mirror from its cell .... it was actually quite easy in the end ... the mirror gets taken to Galvoptics tomorrow for its "treatment " a bit like a spa week for Mirrors

Bobs Knobs ordered from Rother Valley ... cork pads ordered from Amazon ... just trying to decide what shape i want the centre spot ... any suggestions ? 

 

If you don't mind me asking, how much do they charge for re-coating the Mirror?

 

Mark

[Stu1smartcookie]

14 minutes ago, callisto said:

If you don't mind me asking, how much do they charge for re-coating the Mirror?

I don't mind at all , Mark ..£160 .

[callisto]

7 minutes ago, Stu1smartcookie said:

I don't mind at all , Mark ..£160 .

Cheers, thanks for that 

[wookie1965]

13 minutes ago, Stu1smartcookie said:

I don't mind at all , Mark ..£160 .

Wow that's a good price I was looking into this when I had my 8" reflector, when I picked it up the front cover had been left off and the mirror was coated in allsorts  luckily a good clean and it was perfect. I respotted it with a hole reinforcer wish I had done what Craig did. I also wish I had never have sold it but cannot change the past. Good luck on the rebuild cannot wait to see the mirror back coated.

[Stu1smartcookie]

7 minutes ago, wookie1965 said:

Wow that's a good price I was looking into this when I had my 8" reflector, when I picked it up the front cover had been left off and the mirror was coated in allsorts  luckily a good clean and it was perfect. I respotted it with a hole reinforcer wish I had done what Craig did. I also wish I had never have sold it but cannot change the past. Good luck on the rebuild cannot wait to see the mirror back coated.

I was very surprised when i read their price list , i think OO have similar prices too .

https://www.galvoptics.co.uk/optical-components/telescope-products-andamp-services/telescope-mirror-coating---primary/