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Does this primary mirror need washing?

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#1 wcoastsands

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Posted 14 October 2021 - 11:58 AM

I removed the primary mirror cell from my Explore Scientific N208CF yesterday to inspect it. Lots of dust and dew spots on the surface.

 

Used a bulb blower to remove some of the loose dust. Went over it again with a can of compressed air to see if it could do any better. This is the best I could do.

 

Is the surface dirty enough to justify washing it? If not, at what point should I consider washing it? Thanks in advance!

 

FBnZqepVEAQdaTV.jpg



#2 rgsalinger

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Posted 14 October 2021 - 12:00 PM

I would say that if you've already removed it, then wash it. You probably just need some de-ionized water and a couple of cotton balls and you'll be done in 5 minutes. 


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#3 Mike G.

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Posted 14 October 2021 - 12:35 PM

That poor baby needs a bath! 



#4 okiestarman56

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Posted 14 October 2021 - 12:49 PM

Don't use compressed air, you could blow more contamination from the can on to the mirror.


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#5 JaredLeeNewton

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Posted 14 October 2021 - 12:56 PM

"Bathe the Stiffmiester" - Steve Stiffler.



#6 BoldAxis1967

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Posted 14 October 2021 - 01:10 PM

Below is a link to the "fingertip" method that many, if not most seem to recommend here on CN. The video is from the co-owner (Cary?) of OWL (Optic Wave Laboratories).  I have used it several times and it is simple and effective.  I do give the mirror a final rinse with DI water. 

 

https://www.youtube....h?v=9Y8xFnXFVGQ

 

Others, more experienced than I will probably also comment on this method.  If you do a search here on CN you will find such discussions.

 

L.


Edited by BoldAxis1967, 14 October 2021 - 01:11 PM.

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#7 New-Old-Guy

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Posted 14 October 2021 - 01:28 PM

This Person/Link was very helpful when cleaning my 10".

 

 

 

Link:       https://www.youtube....h?v=z-vys30LThs

 

 

                           "Don't do that Or you will Cry"     best line of video  grin.gif



#8 Mike G.

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Posted 14 October 2021 - 02:33 PM

Below is a link to the "fingertip" method that many, if not most seem to recommend here on CN. The video is from the co-owner (Cary?) of OWL (Optic Wave Laboratories).  I have used it several times and it is simple and effective.  I do give the mirror a final rinse with DI water. 

 

https://www.youtube....h?v=9Y8xFnXFVGQ

 

Others, more experienced than I will probably also comment on this method.  If you do a search here on CN you will find such discussions.

 

L.

yup.  this is what I use as well for both my newts.  make sure your sink is clean first and wash your hands thoroughly before doing it, trying to get the flesh of your fingers as soft as possible.  then rinse with copious amounts of distilled water and let the mirror stand on edge to dry.  someplace safe


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#9 PETER DREW

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Posted 14 October 2021 - 05:37 PM

Hold the mirror up and look at the back against a bright light.  If you can see the light passing through where the spots are then that is due to oxidation of the aluminium film and washing won't remove them.


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#10 sixela

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Posted 15 October 2021 - 06:15 AM

Everybody ducked answering the question, even though the answer is "no, this mirror does not need a bath just yet". In fact, if it's less than 6 months old I would definitely not bathe it yet (sometimes the protective layer is not fully hard SiO2 yet, although I don't know about whether MgF2 overcoats suffer from the same thing).

 

On the other hand, you have to start to learn how to bathe your mirror one day, so there's no harm in cleaning it (carefully).


Edited by sixela, 15 October 2021 - 06:16 AM.

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#11 wcoastsands

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Posted 15 October 2021 - 06:55 AM

Thank you. It's getting to be about 3yrs old now. I haven't washed it yet. I like to keep my optics clean, but didn't want to be overzealous in my effort. From what I understand, a little bit of dust shouldn't affect the optical quality of the mirror, and should avoid washing as much as possible. Just wasn't sure how long I should let it go before washing.
 
FBnZqjNVkAQaTfs.jpg

 

I'm out imaging with it right now.

 

FBt_Mq6VcAQpPuy.jpg


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#12 Keith Rivich

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Posted 15 October 2021 - 11:07 AM

I clean my mirror twice a year. Right before my semi-annual star parties. 

 

Mirror.jpg

 

 

This is my 25" right after cleaning a few weeks ago. Original coatings. Over 20 years old!

 

 

 

 


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#13 sixela

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Posted 15 October 2021 - 03:04 PM

Ditto (I do it before I go to a long astro-weekend). After three years I'd indeed give it a bath. I do not subscribe to the maxim that you should clean as little as possible. But I wouldn't say it needs cleaning.


Edited by sixela, 15 October 2021 - 03:05 PM.


#14 SteveG

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Posted 15 October 2021 - 03:09 PM

Thank you. It's getting to be about 3yrs old now. I haven't washed it yet. I like to keep my optics clean, but didn't want to be overzealous in my effort. From what I understand, a little bit of dust shouldn't affect the optical quality of the mirror, and should avoid washing as much as possible. Just wasn't sure how long I should let it go before washing.
 
FBnZqjNVkAQaTfs.jpg

 

I'm out imaging with it right now.

 

FBt_Mq6VcAQpPuy.jpg

That doesn't look too bad. I clean mine about once per year, or more if needed.



#15 Bob4BVM

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Posted 16 October 2021 - 12:52 PM

3 years would be a long stretch for me.  That one looks good for going that long !

 

Dry dust is one thing, not that big a deal.

But if there are dew spots or any area where the the mirror saw moisture mixed with dust, pollen, bug poop, etc, you want that off .  Such organic concoctions do no good for a coating.

 

Use the fingertip method, no cotton balls etc.  Di-water rinse, blow or lightly dab (not rub!) the last water spots off surface,  Do not leave water spots to dry on surface, lift or blow them off.  


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#16 ButterFly

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Posted 16 October 2021 - 06:04 PM

Pollen season is the only time I even bother with soap.  A rinse takes off the dust just fine.  The distilled water rinse takes of the water crud just fine.  A rinse about every three months is good based on my observing frequency with a UC scope.  I can immediately see the difference in my autocollimator background with that dinky red flashlight.  The Moon is a lot brighter than that.  It's not the blocking of the light of the dust that is the issue, but rather the scatter.  Even galaxies benefit from a rinse.  The background is darker.

 

If the primary dews up in use or storage, keep an eye on that.  The difference between the blue and white spots may be spots in the coating rather than on it.  Rinsing off the crud could have avoided that.


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#17 sixela

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Posted 17 October 2021 - 04:48 PM

Knowing those coatings (assuming they are the same as on GSO mirrors), the blue spots could indeed be marks left by dew that is left on the mirror for ages. If left for to long tends to creep into the narrow tunnels between the SiO2 crystals and reacts with the Al. But they could also be organic stuff picked up by dew and left on the coating; I've also seen that.

 

One word of advice: if you take a scope inside with all covers on, then in the morning inspect the primary for dew. If dew has formed you really don't want to leave that on the mirror for days (a lesson I learned the hard way, after some dew formed a little pool of water in the centre of one of my mirrors.)


Edited by sixela, 17 October 2021 - 04:50 PM.


#18 scarubia

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Posted 17 October 2021 - 08:09 PM

Thank you. It's getting to be about 3yrs old now. I haven't washed it yet. I like to keep my optics clean, but didn't want to be overzealous in my effort. From what I understand, a little bit of dust shouldn't affect the optical quality of the mirror, and should avoid washing as much as possible. Just wasn't sure how long I should let it go before washing.
 
FBnZqjNVkAQaTfs.jpg

 

I'm out imaging with it right now.

 

FBt_Mq6VcAQpPuy.jpg

There should be a little space between the mirror clips and the mirror. Those mirror clips appear to be touching the mirror on the top and side surfaces. 



#19 wcoastsands

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Posted 18 October 2021 - 03:35 PM

Thanks for all the feedback folks. It’s helped to give me a better idea of when I should wash it. I think I’m most concerned about the residue left by dew, but the point about dust scattering light and reducing contrast is a good one, too. Thank you.

I keep the scopes in a dry room that stays at about 40% humidity, and has an air cleaner to minimize dust. I always remove the dust cap after bringing it in for the night to allow it to breath and dry out. I also keep desiccant packs in the case when scopes get put away.

The mirror clips on this one are touching the sides and edge of the primary. It’s actually pretty snug in its cell. I can rotate it with some effort, but haven’t been able to easily lift it out of the cell yet. There is enough play for the mirror to flop around though, which can throw it out of collimation if the clips are too loose. I’ve moved them outward as far as they’ll go to try and minimize the shadow they cast with bright stars. The screws for the clips are threaded in only until I feel them contact with the clips. Which I think is okay as is since star shapes are still round, both in focus and out of focus. When I first got the scope, the optics were pinched from the clips being tightened for shipping. I’ve adjusted them a few times since then.

Going to try removing the mirror and give it a wash. I’d like to replace the center spot while I’m at it. Measured it to be about 2mm off center. Also looks like the mirror may have been scratched when the center spot was added. Hopefully it’s just goo from the sticker smeared across the surface.
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#20 sixela

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Posted 18 October 2021 - 04:33 PM

A HotSpot placed 2mm off centre? shocked.gif

 

That would be really hard to do given they come with a template.


Edited by sixela, 18 October 2021 - 04:33 PM.


#21 wcoastsands

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Posted 19 October 2021 - 02:51 AM

I think quality control may have been an issue with this scope. I noticed the 2-color decals for Explore Scientific are also misaligned. Not critical issue, but one of those little fit-and-finish things that I tend to notice, and kinda bugs me every time I see it.

 

I've also had issues with the primary collimation screws since day one. There was one screw in particular that was always difficult to turn, and one of the others started to become the same more recently. I finally got around to checking them out when I had the primary mirror cell out this last time. Turns out that two of the threaded posts were rusting. Only one of them appeared to have grease on the threads, and that one was still clean and easy to adjust.

 

FBnbG9aUcAUvh8g.jpg

 

FBnbHAAVUAAYnk0.jpg

 

I'd like to replace the posts with stainless steel ones. And while I'm at it, replace the screws on the mirror clips with stainless steel ones as well, since those are also rusting.

 

Considering the conditions under which these scopes are used, stainless steel fasteners seem like they should have been a given. The black paint is also staring to flake off of the spider, likely due to the changes in temperature the scope sees, especially in winter when it drops below freezing. Maybe that's to be expected, though.

 

I'm also trying to figure out an issue with the secondary assembly. I haven't been able to properly collimate it because there isn't enough in-travel to center the secondary under the focuser. With the springs of the secondary collimation screws fully compressed, the secondary mirror is still positioned slightly off center away from the spider, toward the primary mirror, an issue which this video discusses a bit. I found some pictures of the assembly in this thread that have helped give me a better idea of what I'm working with. I understand now what he means by flipping the plate over so that the springs of the secondary can be recessed in order to allow for the additional travel needed to center the secondary. I can see how it would work, but it still doesn't seem right to have to do that. Feels like I'm overlooking another option.

 

Overall I think it's a good quality scope, but there are little things like this that I feel should have been considered during quality control.



#22 SteveG

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Posted 19 October 2021 - 03:24 PM

If those aluminum knobs thread on to the steel bolts, then this is no surprise. The steel zinc coatings on Chinese products is not of good quality. You will have the same problem with stainless, unless the coatings are better:

 

https://www.hunker.c...e-with-aluminum


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#23 sixela

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Posted 19 October 2021 - 04:24 PM

If the knobs are aliminium and the bolts are ungalvanized (or badly galvanized) steel or worse stainless steel, consider good ol' teflon tape on the bolt threads. And WD40, since it keeps humidity at bay (moisture is what mediates the reaction between e.g. stainless steel and aliminium -- add water and you've created a mini-battery with the bolt and the nut as two electrodes).


Edited by sixela, 19 October 2021 - 04:27 PM.

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#24 wcoastsands

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Posted 19 October 2021 - 05:38 PM

Aaaah… Thank you! I didn’t know aluminum was reactive when in contact with steel. That makes sense, though. Thanks for sharing the article.

I’ll wrap the posts with Teflon tape until I can figure out a better solution. I might reach out to Explore Scientific, too. After 3 years, they may have come up with a solution to this, if they’re even aware of it. I’ll raise the other issues as well.

I reached out to someone Explore Scientific had originally put me in touch with years ago to help me work through some of the issues I was having with this scope. He’s since moved on from this scope, opting for a 102mm refractor instead so he wouldn’t have to deal with collimation so much. He recommended adjusting the center screw on the secondary, but from what I understand it only adjusts rotation of the secondary.

I think the guy in the video is right: need to flip the tilt plate around so that the springs of the secondary collimation screws seat in the counterbored holes of the plate. Only way to free up enough travel to center the secondary mirror in the focuser.

#25 Starman1

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Posted 19 October 2021 - 06:08 PM

Aaaah… Thank you! I didn’t know aluminum was reactive when in contact with steel. That makes sense, though. Thanks for sharing the article.

I’ll wrap the posts with Teflon tape until I can figure out a better solution. I might reach out to Explore Scientific, too. After 3 years, they may have come up with a solution to this, if they’re even aware of it. I’ll raise the other issues as well.

I reached out to someone Explore Scientific had originally put me in touch with years ago to help me work through some of the issues I was having with this scope. He’s since moved on from this scope, opting for a 102mm refractor instead so he wouldn’t have to deal with collimation so much. He recommended adjusting the center screw on the secondary, but from what I understand it only adjusts rotation of the secondary.

I think the guy in the video is right: need to flip the tilt plate around so that the springs of the secondary collimation screws seat in the counterbored holes of the plate. Only way to free up enough travel to center the secondary mirror in the focuser.

You may be misunderstanding the nature of the push-pull screws in the secondary holder.

To move the secondary toward the spider, you loosen the collimation screws and tighten the center bolt.

To move the secondary away from the spider, you loosen the centerbolt and tighten the collimation screws.

 

But, if yours is the type with the small setscrews next to the main collimation knobs, then each of the 3 collimation screws becomes a push-pull arrangement, which makes moving the secondary up or down in the tube is a more complicated process.  It can still be accomplished, but it takes time to adjust 6 screws to do so.




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