Yeah i am a bit nervious about opening her up.. But if i do i want to do it right and properly. Is there some particular textar or marker that should be used for centre spoting. i have head that using a ring type marker is better, but where do you get these.
undo the 4 or 5 screws on the side at the bottom of the outside of the tube.
lift the tube up and out of the way.
there are then three vertical screws that hold the mirror down via a little rubber angle. undo these and put to one side.
you can then lift the mirror out of the base and onto the carpet, face up!!!
i centre spotted mine with rulers, but the best i have heard of from this forum is to get a piece of paper that is bigger than the mirror. put it on the a hard surface, say a book on the carpet.
then place the mirror on it face up and then trace the circle around the mirror.
remove mirror and then cut out the circle.
fold circle in half and in half again and again and again.
unfold and you should have a very accurate indication of what is the centre of the circle.
place over the mirror and align edges
with a small marker, press down in the centre of the paper. this sould leave a mark on the mirror underneath.
Take paper away
either make spot bigger with marker or place the sticky ring binder around the mark.
I used the marker and made a spot. I do not see the spot at all, unless it is daytime and i am way out of focus.
Good luck
(mike i will try and put pictures to this one and submit as an article) can anyone else please proof read these words and comments for changes?
Someone write a how-to for centre-spotting, please! the question comes up often and would be great to have a local article to point them to.
Well, I center spot a little different than most, but I'm happy with the results.
This is how I do it with my Hardin (GSO). To start, place the tube on a table covered with a soft towel. Remove the mirror from your scope and from the mirror cell. This is easier than you'd think, just remove the 6 screws around the end of the scope and the whole rear mirror assembly comes off. The GSO's are rather a tight fit and, at least the first time, you may need to tap the lower ring off with a piece of wood and a mallet. I've found Synta's to be a little looser.
Once the rear assembly is off, remove the 3 mirror clips (details in the mirror clips forum - lol). Lift the mirror off and place it. face up, on a clean sheet of paper. Trace the mirror and cut out your pattern. Fold the circle in half, then in half again. Snip about 1mm off the point of the folded circle. Unfold it and you have a very small, perfectly centered hole. Lay it on your mirror and place a dot on the center with a fine point dry erase marker!
Remove the paper and draw 4 lines away from the center dot forming an 'X'. Be sure to leave about a 1mm gap bewteen the dot and your lines so the dot stands alone. Make the 'X' lines about 4mm long. If you make a mistake, just wipe it off with a damp Q-tip. That's the beauty of marking your mirror with a dry erase marker instead of a paper reinforcing ring. Fear not! The center of your mirror is behind the secondary and doesn't contribute to the image. If you prefer the paper reinforcing ring install it during this step instead of making the 'X'.
When re-installing the mirror, be careful not to over-tighten the clips. The slightest pressure applied by the mirror clips can change the shape of the mirror!! Some people say to leave enough room for a credit card between the mirror and the clip. I don't go that loose, but I'm careful that the clips do no more than barely touch the mirror. I've never seen any mirror distortion in star tests.
Before reinstalling the rear assembly, align your secondary!!! Use a chesire/sight tube. It's very easy to do with the mirror removed. No confusing reflected images. Rack the focuser in so you can see all of the opening at the rear of the tube. Just center the the rear end of the tube in the secondary. Don't forget to check the radial alignment of the secondary, too.
Now reinstall your primary and collimate normally, starting by double checking your secondary alignment with the mirror in place. I collimate with only the chesire/sight tube, but lasers still work with the dry erase marker mark on the center of the mirror. Rotate your chesire so that the cross-hairs are turned 45 degrees from your new 'X' lines. You'll get a very neat pattern to align to align by.
I remark the mirror after each cleaning, which for me is about twice a year.
I cleaned up a scope that was donated to our club the same way. That scope had been stored open in a garage for several years. Lots of dust, car exhaust and cat hair on the mirror. An hour of soaking in warm soapy water and a ton of cotton balls eventually brought it back to like new condition.
I have an idea and wonder if it will work. Use some freeware cad program, use it to draw a cross hair then draw 6", 8", 10" and 14" circles using the cross hair as the common center. Print this onto a Transperency Sheet, use a hobby knife to cut litle slits in the cross. This template can then be set ontop of the primary mirror taped to the edges, or taped to the little clamps. You then use a non-perminent text to draw the lines off the cross hair through the slits.
It should not be difficult to make slits for diffrent patterns, but i am guessing the cross is the best to align using a cheshire.
What do you guys think?? Could these be our DIY guide.
Anyone know where we can get exact dimensions (aprox would do) for the GS mirrors.
I remember seeing an site in the US that rebadged and sold GS who gave all the specs, anyone have a link to it as i dont have it anymore.
Anyone know where we can get exact dimensions (aprox would do) for the GS mirrors.
I remember seeing an site in the US that rebadged and sold GS who gave all the specs, anyone have a link to it as i dont have it anymore.
I don't know how much variance there is in GSO mirrors, but of the 2 - 6"ers I've measured, they varied by more than 1/16" in diameter. One was slightly under 6", the other was barely 5-7/8". Best just to trace or measure your own mirror, IMO.
Pegster, you are correct it is probably best to trace your own, but for a howto i think we can genralise a bit. What you could do for a custome size is trace it, use a ruler to make a cross and photocopy onto a transperency.
I did a quick Visio drawing and printed it to a PDF file, see attached. Please review.
By the way the idea is not mine i got it from a document i read on the net on
NW, sounds like you're well on your way to creating the how-to guide for the site - a combination of all the great pics and advice given in this thread would be a fantastic how-to guide.
I examined my scope today in preperation of the primary cell on either this or next weekend. I was mainly looking at the screws that would need to be removed at the base to pop the mirror cell out at the back. I noticed two things.
1. on the back of the mirror cell on there is a small hole in the outter ring of the cell. Is this normal? I also noted that it can be seen when looking down in the tube, at the edge of the mirror. I am guessing this is by design as it seems to be a machined hole.
2. I ran my hand over the tube as i was examning the back and noted a slight dent above the altitude bearing, i then examined the other side and it was smooth. I am thinking this is a defect. Looking into the tube i could note if positioned correctly with a torch that there is a slight dent there. I am not certain if this was there when i got the scope or something that has happned since due to my noob handling. I noted also that the plastic alt bearing on that side was a bit groved, now this was not there when i got it. I think perhaps the teflon on the rocker is groving it..
Does the dent pose any effect on my viewing? It does not protruede over the mirror so i am not sure it will have any effect. What do you guys think. I am more nervious no w about removing the mirror given the possible dent i may have inadvertenly caused. Will removing the mirror void warranty? Does warranty cover dents and groves?
1. on the back of the mirror cell on there is a small hole in the outter ring of the cell. Is this normal? I also noted that it can be seen when looking down in the tube, at the edge of the mirror. I am guessing this is by design as it seems to be a machined hole
Can you post a picture? If it's what I'm thinking, it helps you to align the mirror cell when putting it back in the OTA. That's normal.
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2. I ran my hand over the tube as i was examning the back and noted a slight dent above the altitude bearing, i then examined the other side and it was smooth. I am thinking this is a defect. Looking into the tube i could note if positioned correctly with a torch that there is a slight dent there. I am not certain if this was there when i got the scope or something that has happned since due to my noob handling. I noted also that the plastic alt bearing on that side was a bit groved, now this was not there when i got it. I think perhaps the teflon on the rocker is groving it..
Dings and dents are a normal part of handling a tube like that, you should see mine! It even has little bits of surface rust from neglect and very very (once!) irregular cleaning
And the alt bearing will get some grooves in it from the teflon pads, that's normal too. I guess you can just try to keep it clean from dust and grit to keep the alt motion as smooth as possible.
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Does the dent pose any effect on my viewing? It does not protruede over the mirror so i am not sure it will have any effect. What do you guys think.
There's quite a gap between the inside of the OTA and the mirror, about an inch on each side usually. So unless it's quite a severe dint that protrudes in an inch, you won't notice it and it will have zero effect on your viewing.
I have flocking on the inside of my tube that is peeling off in one spot and actually does protrude slightly into the light path, and I can see when I have a bright object defocussed all the way out - but when things are in focus, I can't see it at all.
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I am more nervious no w about removing the mirror given the possible dent i may have inadvertenly caused. Will removing the mirror void warranty? Does warranty cover dents and groves?
Don't be nervous - you've done nothing wrong. The small dent will cause no issues. I don't think removing the mirror will void the warranty, it's normal maintenance when you own a reflector. But I also don't know what you'd possibly claim warranty on unless the mirror suddenly cracked or the focuser snapped in two?
Warranty most certainly wouldn't cover dents - that's part of normal handling. They're not china dolls, they can take a bit of a bashing. Just be careful with the optics.
I noted also that the plastic alt bearing on that side was a bit groved, now this was not there when i got it. I think perhaps the teflon on the rocker is groving it..
Check the staples that hold down the nylon pads on the base that the plastic alt hub sit on. You might find the staples havent been punched down properly and are gouging the plastic.
the question comes up often and would be great to have a local article to point them to.
