removing the miror from a Meade 8"

[mcolbert]

DIY II

I want to check the forum wisdom on how to remove the mirror from my SCT.

From what I have seen on other sites the three things to remember are;
1. DON'T DO IT!
2. DON'T DO IT!
3. DON'T DO IT!

The reason for removal is that I wish to have it recoated with gold to use as a dedicated IR scope. (I know, humour me;). )

So, are there any recommended links for this process either on other fora sites or Youtube / Vimeo?

Any words of wisdom??

Thanks

[Lady Fraktor]

Quite the undertaking!
Have you considered going the gold diagonal route?
Vernonscope used to make a 2” gold coated for imaging and visual and I believe there may be one or two places that can do it as well.

I know Meade released some SCTs in the 1980s with gold mirrors for imaging but I have never seen one before.

[mcolbert]

Lady Fraktor, that would certainly be a cheaper option, and I'll check with the place / people that are going to do the job and look if there are any advantages in doing it that way.
I'll chase up Vernonscope as well.

Re the Meades, that is the first time I have heard that they did that, never even seen one advertised on the second hand market. Thanks for the heads up.

I intend to have the mirror coated for use between 1000 - 1800 nm and it seems doable. The tricky thing with this DIY is removal of the mirror safely.

[Lady Fraktor]

I checked my faulty recollection and it seems they were made for optimizing laser communications but they do work for IR imaging.
The estimates I found were between 40-50 8” were made but not sure which company did the recoating.

[Lady Fraktor]

The big thing with taking everything apart is to make sure you maintain the orientation of the plate and mirrors.
There are quite a few YouTube videos on how to strip them down.

Here is something I just found about the Meade telescopes: https://www.cloudynights.com/topic/4925 ... de-10-sct/

[mcolbert]

LadyFraktor thanks for the link. I'm glad that it had input from someone at Meade. I have seen others on CN and they aren't as detailed - certainly not as clear as John was. Copy made for reference. The confidence (or is that foolhardiness?) is there to remove the mirror once I get the go ahead from the coating people that they are ready to go as well. They have a 16" being done at the moment apparently.

[Lady Fraktor]

look forward to hearing about the results, it should be quite interesting when viewing I imagine and create some unique images.

[mcolbert]

that's part of the idea, as well as some minor research possibilities.

[OleCuss]

I once asked one of the SCT makers just how critical the orientation of the corrector plate really is. The response I got was that if you were within a few degrees you were fine. It is still good to try to keep the orientation the same but I'd not be afraid about that.

It gets more interesting with the mirror, I think. IIRC there is an arm which comes off the mirror and is then used along with the focuser? I think that when they do the coating that they first remove the arm and you can thus totally lose the orientation of the mirror. I'd thus use something sharp to scribe the position onto the back of the mirror so that it will be re-attached in the right position.

It appears that getting the shimming done properly (the same) may be more critical? But I'm not entirely sure about that.

I've an 11" I need to take apart at some time. The shimming worries me most.

Oh, and I think OSI/Farpoint may still do gold coating?

[Richard]

I have only removed the front lens on my SCT as it needed cleaning , that was quite a simple job , but I have removed the primary mirror from a ETX 90 and it was not too difficult , the hard part is to know how it was put together so that one does not break anything. the ETX was filled with insect debris so had to come apart but all went well
Re coating the mirror I have no Idea but out of interest what is the advantage of gold?

[Lady Fraktor]

The gold coating improves IR viewing/ imaging dropping the blue/ green part of the spectrum.
From what I have read for visual you would have a yellow halo instead of violet as in a achromatic.
Supposedly it really enhances planetary detail as well.

Vernonscope made a 2" planetary diagonal that was gold coated for a short time.

[mcolbert]

I once asked one of the SCT makers just how critical the orientation of the corrector plate really is. The response I got was that if you were within a few degrees you were fine. It is still good to try to keep the orientation the same but I'd not be afraid about that.

It gets more interesting with the mirror, I think. IIRC there is an arm which comes off the mirror and is then used along with the focuser? I think that when they do the coating that they first remove the arm and you can thus totally lose the orientation of the mirror. I'd thus use something sharp to scribe the position onto the back of the mirror so that it will be re-attached in the right position.

It appears that getting the shimming done properly (the same) may be more critical? But I'm not entirely sure about that.

I've an 11" I need to take apart at some time. The shimming worries me most.

Oh, and I think OSI/Farpoint may still do gold coating?

OleCuss thanks for the info re Farpoint, they have been bookmarked. I am looking at a local service a few hundred kilometres away, but it's good to know of others to send future mirrors to.

You raise my concerns with orientation and making the small marks are the way to go, I'll ensure that is one of the first things that is done.

Re the shimming I plan on taking a continual series of images on the process - tricky as I can't be in two places at once but the movie function then comes into its own with the D3300.

Thanks for the tips.

[mcolbert]

I have only removed the front lens on my SCT as it needed cleaning , that was quite a simple job , but I have removed the primary mirror from a ETX 90 and it was not too difficult , the hard part is to know how it was put together so that one does not break anything. the ETX was filled with insect debris so had to come apart but all went well
Re coating the mirror I have no Idea but out of interest what is the advantage of gold?

you're giving me confidence - always good.

LadyFractor has covered the advantages in her response but I am keeping open to 'messing around' with it as well.

[mcolbert]

The gold coating improves IR viewing/ imaging dropping the blue/ green part of the spectrum.
From what I have read for visual you would have a yellow halo instead of violet as in a achromatic.
Supposedly it really enhances planetary detail as well.

Vernonscope made a 2" planetary diagonal that was gold coated for a short time.

Just out of curiosity I'll see if I can track down one of those diagonals. (email sent to Vernonscope)

Thanks!

[mcolbert]

I'll chase up the coatings people and see how their schedule is and with any luck I can do 'the deed' on Friday our time.

[mcolbert]

just received an email from Liz, apparently the diagonals were made by one Don Yeier, and they are no longer being produced, not even on special order.

[Lady Fraktor]

They were ridiculously expensive as well.
The regular Vernonscope 2” diagonal is $720USD and seemed like a bargain in comparison!

[mcolbert]

and what with the price of gold currently....

I will also check if they can do the diagonal as well.

Thanks

[mcolbert]

to report, the mirror has been removed - it was a pain free operation, no anaesthetic required for either mirror or operator.

Now to box and wait to send for coating.

On the Meade it appears to be a simple operation as shown in several threads elsewhere on other fora. I must say though that I haven't removed the secondary and will await confirmation as to whether this is required by the coating service.

Now, on to the next little project....

[Hartsville SkyGazer]

Interesting Thread. Keep us posted on updates! Be great if you could share a few images of this journey!