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When should you clean your SCT corrector plate?

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18 replies to this topic

#1 pyrasanth

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Posted 25 January 2019 - 04:34 PM

I make no secret of my C14 corrector plate is looking pretty grubby. There is an old school of thought that tells me that sometimes minimal cleaning is best and a bit of grime does no harm but my plate now looks really grubby. It's time to give it a clean. The question I'm asking is when should you clean the corrector plate and more importantly does it really matter if it is not pristine looking- is it going to affect anything. I understand that some substances could damage the coatings but then again so could careless cleaning so it's a bit of six of one and half a dozen of the other. Let me know your thoughts.


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#2 photoracer18

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Posted 25 January 2019 - 04:58 PM

If its just dusty leave it alone no matter how much. and don't shine a flashlight down the tube because it will look a lot worse than it really is. All that being said just remember taking it out will then require re-collimation of the entire system. How are you at doing that? You have to put the little shims that help center the corrector back in there original spots. Helps to have either a Glatter or Hotech holographic laser. I will assume from your equipment list that doing that is something you have experience at. As for cleaning there are three progressively aggressive cleaning compounds, distilled water, alcohol, and acetone. All need to be pure especially the acetone which needs to be regent grade (you can get a can at any DIY store). Be aware that while it won't harm optical coatings it will melt plastic. I use either new cotton balls or makeup cleaning pads, one swipe each only then toss. I have done Meade 16" SCT in the field a number of times. As for Celestrons just make sure you know where the alignment marks are on the secondary and corrector rim. Unless you have had a lot of outgassing I recommend you leave everything in place and only do the outside surface of the corrector and see how that looks Its usually the worst surface saves a lot of time and effort if you only do that. All bets are off if nature has leaked into the inside of the tube.

 

The real answer to your question is somewhere between seldom and never.


Edited by photoracer18, 25 January 2019 - 05:00 PM.

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#3 petert913

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Posted 25 January 2019 - 05:03 PM

I just cleaned my SCT corrector by following this video from Starizona.  Simple, and the results were great ! 

 

https://www.youtube....cMbivz-hrM&t=5s


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#4 ThermalSeeker

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Posted 25 January 2019 - 06:01 PM

First contact polymer cleaning kit may work fine without disturbing collimation. I wonder who has had experience cleaning with their products. They do have a video on YouTube of cleaning a corrector plate with the brush on polymer product.

#5 JoeR

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Posted 25 January 2019 - 06:29 PM

I usually dust my C14 corrector with a camel hair brush from an art supply store. If it's particularly grubby the Dr Sherrod cleaning solution works good. Even the Invisible Glass brand that you can get at any hardware store is safe to use. Really, it's not a really delicate process to clean corrector plates the coatings are pretty robust.



#6 barbarosa

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Posted 25 January 2019 - 06:32 PM

The FLASHLIGHT TEST-- Why you should not do it.

 

It is now accepted wisdom, widely and generally understood that you should not shine a flashlight down the tube.  If you are so bold or foolish as to do this, the photons will destroy the corrector, show Dust Dragons from the seventh circle. After that you won't sleep for days. 

 

On the other hand if you are careful  and with steady nerves you can see into the beast and there you might find not dust alone, but mold  or even dinosaur tracks.

 

I was bold, and I was foolish,  but my heart was pure. I gazed at the light(send the innocent from the room),  a partial print and a large  smear of oil or grease, a black spot  but not much dust. Celestron agreed that these were bad omens and all was made right.

 

Now in my dotage I clean the corrector when I think about it and when the pines are blooming, A little grunge hurts nothing.


Edited by barbarosa, 25 January 2019 - 06:33 PM.

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#7 Kokatha man

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Posted 25 January 2019 - 06:37 PM

"All the time!" lol.gif Not quite wink.gif but in the conditions ours is subjected to we probably clean it up to a dozen times a year.

 

Obviously if there is minimal effects from dust, pollen etc & the corrector stays relatively clean, the problem will arise infrequently or you might never have to bother.

 

It's also good to appreciate that looking at a dusty corrector from certain angles - or using a torch - exacerbates the appearance of crud & that these scopes work well despite seeming to appear quite dirty.

 

But if you are us we are not simply pernickety but we are always trying to extract the utmost efficiency from our planetary imaging...

 

I tilt the scope down at a very steep angle on the back lawn, sit on a low stool with all my cleaning gear at close hand & first give the entire corrector a good spray of distilled water via one of those cheap atomisers/garden spray bottles.

 

Leave it for a couple of minutes to loosen whatever might be on the glass before giving it a real flooding via the spray bottle, working from topmost position down flushing the loosened material off: if you were more OC than me you could even spray with an iso-alcoholic solution also but I've never found that necessary tbh.

 

Then using very light radial strokes of a single swab of clean cottonwool saturated in Dr Clay's solution (you can look up the recipe) clean the corrector...one stroke, one swab & discard is best if you find it difficult to turn the swab a couple of times using different swab surfaces to get several strokes from one swab...

 

Finish off with another complete flushing using plenty of the distilled water from the spray bottle.

 

If you use a tissue to very carefully dab dry the retainer ring & elsewhere that has water on, then the glass should dry free of water spots...but I use an air compressor with a nozzle gun - for this you must employ a high quality oil & water trap inline & I don't blast air while the compressor is pumping to ensure nothing but air is coming out the nozzle: this way you can quickly blow dry the corrector surface etc.

 

It's important to note that I have placed a thin neoprene gasket on the underside of the corrector which effectively seals the inside from water ingression for the aforesaid.

 

You can of course remove the corrector entirely (making sure of the orientation which is marked on both glass & ota support flange) to do the cleaning at which time I'd advise anyone to get a gasket made by taking the retainer ring to somewhere that they can have one made up while they wait - if they feel they wish to follow our own procedure for future possible cleaning...

 

If your Celestron isn't one of the Chinese-assembled units, then you might have to deal with the cardboard (yes, you read correctly!) spacers previously used to centre the corrector within its seating flange - later units have proper, adjustable nylon spigots that make corrector removal & installation much better although you do have to "pull" on the secondary assembly somewhat harder to remove the corrector from its seating with this arrangement.

 

My old C11's cardboard spacers would've got soggy with our current method, gasket or not! lol.gif

 

JoeR's comments about the robust nature of correctors is a very valid point for those who freak out about cleaning them btw..! wink.gif

 

 

 



#8 dusty99

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Posted 25 January 2019 - 06:41 PM

I blow the dust off my corrector when it accumulates, but have not hesitated to clean it with lens cleaner and a microfiber cloth if it gets spots from dried moisture droplets.  You're just talking about cleaning the outside, correct?  


Edited by dusty99, 25 January 2019 - 06:42 PM.


#9 whizbang

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Posted 26 January 2019 - 12:02 AM

Your post is ambiguous.  It is very easy to damage optical surfaces by cleaning.  The Starizona Youtube video is perfect example of what NOT to do.

 

The proper cleaning technique is daub, daub, daub.  There is a video on Youtube as well.

 

Mirrors and lenses can be quite dirty without compromising images.  If you want to clean the front face of the corrector plate, go ahead any time is bothers you.  If you want to remove the corrector plate and clean the back, well, wait until it id darn dirty.  Then wait some more.

 

Last month, I pulled the corrector off my C5 and got the haze and dirt off the back side.  The corrector is beautifully clean for the first time in a long time.  I am happy.   It was a very rewarding result.

 

Don't attempt any cleaning until you can do so without causing damage.


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#10 Kokatha man

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Posted 26 January 2019 - 02:18 AM

Your post is ambiguous.  It is very easy to damage optical surfaces by cleaning.  The Starizona Youtube video is perfect example of what NOT to do.

 

 

Well, not that I think whizzy was referring to my post, but it did induce me to look at the Starizona video & I have to concur - that demonstration is totally wrong!!!

 

I won't get pedantic about rotational cleaning strokes versus radial although many will agree with me about radial being the preferred approach...but hoping that canned air will prep your corrector by itself before Quote <"firmly pressing"> strokes with the soap & water on a Pec Pad approach is fraught with risks - anything the air hasn't removed (pollens & other sticky residues) that are not immediately water soluble might also contain small grit particles...result - a nice scratch in the coatings at the least! 

 

I could go on (btw the OP's C14's corrector plate surface is much greater than that of a small C8!) - Pec Pads are great for use with "Eclipse" or other preparations when cleaning camera sensors - but imho the presenter could have at least advised folks to wash their hands thoroughly before folding them like he did...at least using a saturated swab for only one stroke pretty well negates oily/dirty fingers etc - & I can assure people that swabs present a much softer "mop" than a Pec Pad in those circumstances.

 

For the initial stroke I actually only "drag" the saturated swab over the glass, turn it over a bit & then drag with the slightest of pressure... wink.gif

 

I'd also bet that after following all his procedures that you'll much more likely have "finishing smears" on the corrector glass that way - far better to finish off with another soap & water after the methanol etc then distilled water & canned air blow. (positioning a scrunched Kleenex unscented white tissue against the retainer ring where you are "pushing" any droplets via the air pressure so this blots them up, in the absence of my neoprene gasket...) 

 

Perhaps you will get away following that video advice without problems - & it is important to note that the optical surfaces are actually quite robust with a modicum of care & common sense - but I think the advice is overall poor! wink.gif



#11 rmollise

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Posted 26 January 2019 - 08:20 AM

I make no secret of my C14 corrector plate is looking pretty grubby. There is an old school of thought that tells me that sometimes minimal cleaning is best and a bit of grime does no harm but my plate now looks really grubby. It's time to give it a clean. The question I'm asking is when should you clean the corrector plate and more importantly does it really matter if it is not pristine looking- is it going to affect anything. I understand that some substances could damage the coatings but then again so could careless cleaning so it's a bit of six of one and half a dozen of the other. Let me know your thoughts.

 

You're on the right track. Clean it when it needs it. A little dust? No way. Pollen? Might want to get that off.

 

The thing is, many here have the impression that a corrector is delicate like a first surface mirror. It is not. It and its coatings are more like a camera lens. Relatively tough, that is. That doesn't mean you should undertake cleaning just because the corrector doesn't look pretty enough, of course.

 

How to clean? Forget alcohol and various witch's brews of chemicals. A corrector doesn't need that anymore than your camera's lens does. Blue Windex, un-lotioned Kleenex, and canned air will do the job--when the job is necessary. 

 

;)


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#12 barbarosa

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Posted 22 March 2019 - 01:46 PM

As a memory aid to the best practical cleaning method-

 

Dab, dab, dab the lens,
Use Kleenex for the sheen
Merrily, merrily, merrily, merrily,
Glass is Windex clean


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#13 gnowellsct

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Posted 22 March 2019 - 09:33 PM

I usually dust my C14 corrector with a camel hair brush from an art supply store. If it's particularly grubby the Dr Sherrod cleaning solution works good. Even the Invisible Glass brand that you can get at any hardware store is safe to use. Really, it's not a really delicate process to clean corrector plates the coatings are pretty robust.

You can do that but a blush brush from the ladies cosmetics section costs a lot less and is just as soft.


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#14 gnowellsct

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Posted 22 March 2019 - 10:35 PM

Oh.  And the time to clean it is when it's dirty.



#15 George N

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Posted 23 March 2019 - 10:33 AM

If its just dusty leave it alone no matter how much. and don't shine a flashlight down the tube because it will look a lot worse than it really is. All that being said just remember taking it out will then require re-collimation of the entire system. How are you at doing that? You have to put the little shims that help center the corrector back in there original spots. …..

 

The real answer to your question is somewhere between seldom and never.

Are there "little shims" on Meade SCTs? Any advice on re-assembly?

 

I know of a early 12" LX200 for sale for a good price: (fork mount's electronics are "fried", but everything else works). I would be keeping the tripod, and maybe some other stuff (electric focus, field de-rotator) and trashing the mount, or selling for mechanical parts.

 

The primary looks perfect, but there is some sort of white splotchy "deposit" on the corrector -- and it looks like it is both inside and outside. My guess - scope got left out too many nights covered in dew/frost that later dried, leaving behind what ever is in 'acid rain'. It looks pretty bad - bad enough that I would not want the scope not cleaned.

 

The owner is willing to let me test the scope - and see if the corrector can be cleaned - before sale. They (public observatory) got it as a "donation" -- and just want the thing 'gone' - making a few bucks of course.

 

However, I've never owned an SCT - and have no idea how to remove the corrector to clean.



#16 gnowellsct

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Posted 25 March 2019 - 01:07 AM

.

However, I've never owned an SCT - and have no idea how to remove the corrector to clean.


https://astromart.co...sct-childs-play

#17 Don W

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Posted 25 March 2019 - 10:27 AM

If you keep a plug of some kind in the eyepiece holder between uses, the inside of the corrector should stay clean. I've been using cats since 1980 and have never removed the corrector to clean it.



#18 coopman

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Posted 25 March 2019 - 10:58 AM

It would have to be very dirty for me to resort to that. 


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#19 elrico

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Posted 25 April 2019 - 02:02 PM

When I had my Evolution 9.25 SCT, I cleaned the Corrector with Tap Water & a single drop of Washing up liquid, Non perfumed Tissues, dip in water, squeeze off excess,  ,wipe gently from centre to outer,  throw tissue, get dry tissue and repeat, throw tissue,  then repeat the process all the way around the corrector back  to where you started.

Brilliant job, no damage at all/

I read up all kinds of advice on this topic and became frightened of touching the corrector as a result !!, until I read about the tissue/washing up liquid and decided to nervously give it a try, don't know what all the fuss was about.

Eric  


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