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AT8RC Mirror cleaning

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#1 anismo

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Posted 16 May 2015 - 09:25 PM

I cleaned my AT8RC's mirror today and thought I will share my experiences since we have few folks with this scope.

 

My scope was bought last year and has been an excellent performer but the mirror  started to become quite dusty. I was planning to swap my steel tube to CF tube and  was thinking of using that opportunity to clean the primary mirror (but swap is on hold because the CF tube seems to be 1.5'' shorter than the steel tube). 

 

Things to have before cleaning:

1. Tray to hold primary mirror

2. Dish cleaning soap

3. Cotton balls

4. Distilled water

5. Hair dryer

6. Microfiber towel

7. star screw driver and Allen screw set (both SAE and MM sets)

 

Step 1: Removing the primary mirror cell: I took few photos before removing any screws, but it was quite easy. The two dovetails (The L and V ) have to be removed first because they are screwed to the mirror cell. There are two other screws that tie the steel tube to mirror cell. After that, that the cell comes out easily. 

 

iPhone-img_0265.jpg

 

Step 2: Remove the mirror from the cell: The Mirror was very dirty and I didnt think I can clean it leaving it in the cell. So the next step was to remove the mirror from cell .

There is a central tube that needs to be unscrewed first and then the locking nut in the center is secured by two allen screws. Remove those allen screws and keep it safe. The center locking nut can now be unscrewed releasing the mirror.

 

iPhone-img_0268_1.jpg

 

To be continued in next post

 



#2 anismo

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Posted 16 May 2015 - 09:26 PM

Step 3: Remove the mirror: With the locking collar removed. The mirror can be removed from the cell. There is a plastic (or some flexible) material between the mirror and the central tube, so it needs to be removed gently. I simply inverted it over a towel and it slid right off. The mirror definitely needed some cleaning :)

 

iPhone-img_0270_1.jpg

 

Step 4: Initial cleaning: Place the mirror in a tray and fill up tray with warm tap water. Add one drop of dish washing soap (apparently too much will leave cloudy residue so one drop should be enough). Without touching the mirror surface, tilt the tray back and forth for any loose dust to be dislodged.  Drain the water and and refill it. Drop two or three cotton balls on top of the mirror and again without touching mirror surface, tilt the tray back and forth for the cotton balls to move over the mirror on their own weight.  Discard the earlier cotton balls and a add fresh cotton ball and this time, drag the cotton ball  over the mirror without putting any pressure on it. After this step, the mirror should be fairly clean.

 

iPhone-img_0272.jpg

 

Step 5. Final cleaning and Drying: Rinse mirror with distilled water and immediately use a hair dryer to dry the mirror without allowing for water spots for form. For larger drops, use the tip of the microfiber cloth to absorb them. 

 

iPhone-img_0273_1.jpg

 

I could not get rid of couple of areas because I had scratched it up some time back trying to remove an insect :(


Edited by anismo, 16 May 2015 - 10:01 PM.


#3 anismo

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Posted 16 May 2015 - 09:26 PM

Step 6: Time to put it all back. Simply reverse the steps and it all falls into place quickly. Once I reassembled the scope, I did a quick collimation check using cheshire and It was very close. Couple of quick turns of secondary fixed it. I still need to do star test to recollimate.

 

iPhone-img_0274.jpg

 

Overall, I am pleased to see that it is fairly simple to clean it and it certainly is one of my favorite scopes. 


Edited by anismo, 16 May 2015 - 09:39 PM.


#4 rflinn68

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Posted 16 May 2015 - 09:57 PM

Nice thread Anis! Mirror looks much better now!  :waytogo:  As many RC owners as we have in here, we might need to put this in the "best of" section here after it runs its course. Please remind one us and we'll get it done. :)  



#5 David Ault

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Posted 16 May 2015 - 10:36 PM

Very informative Anis.  I'm curious if you see an actual difference in your data.

 

Regards,

David



#6 Lenbo

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Posted 17 May 2015 - 09:23 AM

I noticed recently while working on collimation that my mirror although not as dusty as yours sure doesn't look very clean. I was wondering if there is any way to accurately judge the need for cleaning or is it a judgment guesstimate thing? I have enough other projects going right now but might put it on my to do list. (One thing at a time!) Thanks for posting the process. Seems pretty straight forward. Mirror sure looks better now. Len

#7 anismo

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Posted 17 May 2015 - 09:41 AM

Thanks Richard, David and Lenbo

 

My mirror was pretty dusty  (and probably lot of sticky pollen as well) and I think it must have had impact in my images (May be one of the reason I was able to go 10 minutes or even 15 minutes on Lum filter :) ). I will definitely compare once I get a chance to image again (it is clouds/rain in forseeable future) . 



#8 rflinn68

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Posted 17 May 2015 - 11:47 AM

How was your secondary mirror? Mine is pretty bad...both mirrors need cleaning. It is from regular dust, but also from spiders, and lots of pollen.  :(



#9 pdfermat

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Posted 17 May 2015 - 12:21 PM

Thanks for posting this - it'll be nice to have as a reference.

#10 anismo

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Posted 17 May 2015 - 01:23 PM

Thanks Pat.

 

 

How was your secondary mirror? Mine is pretty bad...both mirrors need cleaning. It is from regular dust, but also from spiders, and lots of pollen.  :(

 

My secondary looked pretty good, so I didn't touch it..  I didn't want to push my luck :) . But I think it should be fairly easy to remove as well.



#11 josh smith

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Posted 17 May 2015 - 01:54 PM

Very nice examples here...  I am also quite curious how much of a difference it makes.  I suspect it is more mental than anything, but your before and after pictures will be a great reference if it does end up making a strong difference in the data.  My understanding is that the primary mirror acts very much like the primary lens on a refractor and it won't make very much difference.  However, we are always pushing for even a few percent better transmission, so that may be worth the cleaning alone.  If it is only that much, it would probably be hard to prove it was from the cleaning, but would still be nice to see :)



#12 rflinn68

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Posted 17 May 2015 - 02:11 PM

 

How was your secondary mirror? Mine is pretty bad...both mirrors need cleaning. It is from regular dust, but also from spiders, and lots of pollen.  :(

 

My secondary looked pretty good, so I didn't touch it..  I didn't want to push my luck :) . But I think it should be fairly easy to remove as well.

 

Mine will need it. My main problem was spiders...= very bad.   :(



#13 anismo

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Posted 17 May 2015 - 02:46 PM

Very nice examples here...  I am also quite curious how much of a difference it makes.  I suspect it is more mental than anything, but your before and after pictures will be a great reference if it does end up making a strong difference in the data.  My understanding is that the primary mirror acts very much like the primary lens on a refractor and it won't make very much difference.  However, we are always pushing for even a few percent better transmission, so that may be worth the cleaning alone.  If it is only that much, it would probably be hard to prove it was from the cleaning, but would still be nice to see :)

 

True.. It probably will not make much "real" difference. but every time I saw the mirror it  was always nagging me. It was almost like having permanent due on the mirror.   I will take 10 minute subs to compare but with the sky conditions changing, I don't think it will be of any usable value



#14 Jon Rista

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Posted 18 May 2015 - 12:47 AM

I too am very curious to see if there is a difference in the end results. If you do get better transmission, you should see a drop in exposure time. Too bad you did not take some pre-cleaning reference images, along with some accurate sky darkness readings, of a couple targets so you could more directly measure a change in exposure time, and correlate that change to sky darkness or mirror cleanliness.

 

My mirror has some spots on it, but it does not look as bad as yours did. Seems Josh took pretty good care of it overall (thanks man! :)) I doubt I would get near the benefit you might from cleaning my mirror, but who knows what it may look like a year or two from now. 



#15 anismo

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Posted 18 May 2015 - 10:31 AM

Jon, I dont have any hope of testing this thing anytime soon. We have a front parked right over us with no sign of moving.. At least we are getting some much needed rain. 

 

I think my main issue was the pollen.. It is pretty bad here .



#16 Jon Rista

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Posted 18 May 2015 - 11:00 AM

I hear ya about the weather. Outside of two clear nights that ended up being a bust because of miscollimation, I have had clouds at night since early/mid March. It's been quite rainy as well. That in and of itself isn't unusual, there used to be a saying about 4pm showers in Colorado...however lately, we have showers day and night, with short dry patches inbetween. That is less common.

I have been looking at my mirror a lot lately, and it is pretty clean relatively speaking. I don't think I am losing enough transmission to pop it out and clean it...so I'm just sticking with collimation right now.

I truly hope I get some clear sky soon here...I wonder if it's going to be a cloudy and rainy summer this year. Colorado was in need of water a couple years ago...however since that 2013 fall storm that flooded the front range, our water tables are full, and even the smallest amount of rain pushes reservoirs above their normal levels, and in some cases causes flooding. Cherry Creek, my birding and wildlife haunt, has been totally flooded and overflown for weeks now.

#17 David Ault

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Posted 18 May 2015 - 11:05 AM

I think this is one of those years that drives people away from the astronomy hobby.  Some of the members of my club were talking about a few years where only a handful of nights were any good for observing and a lot of people dropped out of the club and then eventually left the hobby entirely.  I think some of the stuff Shawn is doing with processing professional data is good for keeping moral up and at least keeping us in practice with image processing.  This post is also great.  Talking about what we can do in the downtime to maximize the little time we are getting when out under the stars is very useful and keeps us focused on the hobby.  I have to say, I really want to get out and test my camera though.

 

Regards,
David



#18 Jon Rista

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Posted 18 May 2015 - 11:39 AM

I still have a backlog of data to process. I've got M106 to finish, M101 to redo (with new techniques), Thor's Helmet, M78, and maybe one more. I hardly have time for that these days, as I am working on both my own web site design, TAICs web site, and now that stuff is growing, I gotta take care of my yard as well (the last snow storm broke branches all over the place, still chopping those up so I can dispose of them.)

I guess that's a good reason to build up and keep a backlog of data to work...so you have something to do through the dry months.

#19 anismo

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Posted 18 May 2015 - 12:02 PM

I certainly say that resource like CN goes a long way in keeping me engaged.  It is nice to be able do astronomy related stuff in spite of bad weather.  I want to catch up TAIC as well. I might have to do pass 2 of data.   I also ended up ordering a WS-8 cover and Nikon adapter so I use my nikon lenses for narrowband (and may even try some mikly way imaging).  



#20 rflinn68

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Posted 18 May 2015 - 11:22 PM

I added this one in our "Best of" threads before it gets away. :)



#21 rflinn68

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Posted 19 June 2015 - 12:57 PM

Just removed the rear cell and primary on mine. When I unscrewed the central baffle, everything came out together in one piece. No need to remove the two allen screws at the center of the primary.  :thinking:



#22 anismo

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Posted 19 June 2015 - 02:09 PM

Just removed the rear cell and primary on mine. When I unscrewed the central baffle, everything came out together in one piece. No need to remove the two allen screws at the center of the primary.  :thinking:

 

:) looks like multiple ways to skin this cat. so getting it all ready for the fall season?



#23 rflinn68

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Posted 19 June 2015 - 02:22 PM

Yep, figured I would be using my 107mm and Star71 a while so it was a good time to tackle it. Its still sitting here on my desk while I wait on the wife to bring home some distilled water, but I'll probably go ahead and get it soaking soon. I might just leave it in the cell, I dont think it will hurt anything, do you? Those two small screws under the central baffle stick out a little on the bottom (mirror) side, but if they didnt hurt anything coming out I dont suppose they will hurt anything going back in. I'll probably just keep it all in one piece.



#24 anismo

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Posted 19 June 2015 - 02:28 PM

I dont think those screws will affect anything. Just make sure to put it back the same way .. no need to add additional tilts to these things :)

 

I am not sure about letting it soak (though it shouldn't affect anything) but don't put any soap and let it sit for long .. just to avoid residue settling on the mirror.



#25 rflinn68

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Posted 19 June 2015 - 07:59 PM

Thanks for posting this thread Anis!  :D  Now my mirror is all clean too!  :whee:

 

Mirror1.jpg

 

 

 

 




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