SCT Corrector Plate Streaks and Cleaning Q's
Posted 04 April 2005 - 06:59 PM
During the winter I used my C-11 a lot. The corrector plate didn't dew up out in the field, but because of the temperature difference between outdoors and indoors it dewed up when I brought it in. I kept it covered so that dust could not settle on the plate.
I took the C-11 out during the day yesterday so that it was set up for viewing that night. I noticed in the daylight that a couple of small areas had streaking (such as water streaks). When looking at a particular angle I could see the slight rainbow reflection on the plate in two areas near the outer edge of the corrector plate. The obvious dust, etc. that collects on the plate were noticeable, but not horrible.
The streaks concern me. I studied the recommended corrector plate cleaning procedures including Celestron's recommended solution (>91% Isop. alcohol, distilled water, drop of biodegradable liquid dish soap). I bought some surgical quality cotton (no contaminents) and also some plain (unscented Kleenex wipes) as recommended by a couple of the sites linked to here in Cloudy Nights. I had a can of pure compressed air (no additives, etc.) and a high quality camel hair brush. I didn't shake the compressed air can and I kept it vertical and used a few short bursts on the small area (after testing a couple of shots away from the plate). I also gently bushed in one direction with the camel hair brush as recommended. Then I applied the cleaning solution by dipping a small pillow of surgical grade cotton in the solution as suggested, etc.
I experimented in one small area, being careful to follow the procedures to the tee.
It seems that the streaking may be on the inside of the corrector plate as the cleaning solution and plain distilled water applied (and gently wiping after applying as was recommended) did not remove the streaking. Either that or I'm being too gentle? I certainly did not want to apply any pressure and only gently brushed in a radial motion, in one direction. One source said to gently breathe on the glass and ever so slightly buff it in one direction in a radial motion from the center outward in a short stroke. I did not use reuse any application pillow or wiping pillow. I had several prepared and ready.
Does anyone else have some minor "streaking" like this? Does it have an impact on observing? I didn't seem to notice it when observing Saturn and Jupiter last night, but the seeing was below average.
Does bad dewing up leave a "film" in places?
Can anyone offer any advice?
Posted 04 April 2005 - 07:26 PM
TV102 / TV76
SolarMax 60 / BF-30
Posted 04 April 2005 - 09:15 PM
Thanks for that tip. I read the ASO website guide as part of my research.
I noticed that in one small area where I applied the high grade Isopropyl alcohol/distilled water solution and didn't get it asll gently wiped off, that a small streak formed. I'll check into the OPT stuff.
Posted 04 April 2005 - 09:47 PM
In the 11 years I owned my 8" LX200, I cleaned the corrector around 50 times, 5 of those on both sides.
I use very soft Kleenex, isopropyl alcohol, and I rub the entire corrector with circular motions until the alcohol begins to dry. Then i fold the Kleenex to a dry section and continue rubbing in circular motions until all the corrector is clean and streak-free. I then use an ear syringe to blow off the inevitable Kleenex dust that has accumulated.
Result? Scratch-free, streak-free, dust-free, looking like new.
I've gotten a drop or two on the corrector while in the field. I've breathed on the spot and wiped it off with a Kleenex.
The coating is harder than you think.
Dew forms on a dirty corrector faster than a clean one (probably because water droplets grow faster with a "seed").
My Mak is now 3 years old and has a like-new appearance.
The fogging up that inevitably happens will always "cement" dust particles to the corrector.
At the least, they'll need cleaning every 6-10 nights under the stars.
If you use a brush, use a brand-new one and throw it away after use. They're never as clean the second time as they are the first.
Never use a lens pen unless you are using it to apply a slight pressure to a Kleenex to get the very edge of the corrector. They WILL scratch the corrector.
TeleVue's recommendations for cleaning eyepieces works just fine on correctors (it's on the TV site).
Posted 04 April 2005 - 10:06 PM
Thanks for the info. I just looked over the corrector plate in the house. I have a good magnifying glass and glanced over the plate. It seems that some of the dew must have dripped and made slight streaks with dusty particles. In some places I can see where tiny rivulets where dripping dew must have carried some dust with it. If you look at an angle you can see these things in some areas.
I don't really want to clean the entire plate at this time but will get some high grade stuff and investigate it even more.
I did read on one site that the high percentage isop. alcohol can leave streaks if it isn't wiped quick and that rinsing might have to be necessary.
P.S. It always helps to share and get feedback from CNers. The first time you try to do something like cleaning, it can almost "freak you out." That's why I wanted to start in one small edge area and then get feedback.
Posted 04 April 2005 - 10:18 PM
Posted 04 April 2005 - 10:33 PM
There are some different techniques suggested depending on personal experience and preferences. At least two sites that I ran across (SCT experienced) recommended Radio Shack's "Velocity" compressed air (as it has no chemicals added and supposed less chance for propellant to come out). You don't shake it, you use short burst (test one or two on your hand first), keep the can vertical, and if the can starts getting cold, stop and let it warm up. You do this to get general dust off. Then you get a quality camel hair brush (soft, lots of bristles, and taper cut) to gently in one direction dust ever so lightly.
After that the solutions and techniques begin to vary. I can link some sites, but the one John Crilly refers has some good steps.
Here is the only CN post that I could find about cleaning the corrector plate:
[URL poster is not working now--email me for link until I can post a short cut link to site].
Here is the site John Crilly recommends:
And here is another site:
SCT corrector cleaning link
(note this last site's Celestron formula is off--Celestron recommends 40% Isopropyl alcohol (91% or higher) and 60% distilled water).
I'm sure others can suggest some more.
It is not recommended to do it often. I just don't want a couple of areas where the stuff formed more with dew to degrade my image (but I *bleep* well don't want to scratch the plate).
Read all those sites and maybe some more experience people can add their remarks.
Posted 04 April 2005 - 10:46 PM
Posted 04 April 2005 - 10:54 PM
The seeing was below average last night. I didn't see any noticeable effects from the "streaked areas." I even viewed a robin on a telephone line about a half mile away during the day. Filled the FOV and I didn't notice anything in the EP. It just caught my eye when looking at the corrector plate from the right angle in two places where water and some dust must have combined to slightly reflect. When I look straight on/into the OTA, I don't notice the streaks.
Posted 04 April 2005 - 11:17 PM
Posted 05 April 2005 - 10:24 AM
I blow off the dust first.
so you use just alcohol full strength when cleaning and wet the entire corrector and then wipe it off. do you blow the dust off first? if you've cleaned your corrector that many times and it comes out like new then thats the system i want to use. i did'nt relize you could clean it that often.
I get the kleenex wet with alcohol.
I rub in circles until I've gone all the way around.
The kleenex picks up the residual dust adhered to the plate.
I then use a dry, fresh, kleenex, and making circular motions and very little pressure, follow the path of the first Kleenex.
Sometimes the second kleenex gets dampened by the alcohol so I move to a third kleenex and repeat.
When done, a bright light on the corrector shows NO stains, NO dust, NO streaks, NO scratches, and only a dark blue coating reflecting cleaner than when I received it.
Now, you don't need to do this just because the bright light shows a little dust on the corrector. As a matter of fact, a lot of that dust is probably sticky pollen, and brushing it will smear it across the corrector, making the problem worse, so NEVER use a brush unless your very next step is to clean the entire corrector.
But my scope always seemed to fog when bringing it inside, and though I let it evaporate, after about 3 months (30+ hours of viewing), the surface of the corrector began to look hazy. About every 6-9 months I cleaned the inside (if cleaning the outside made it clear, I didn't) because a haze could be seen building up on the inside of the corrector.
This haze was exudate from the paint inside the tube, the grease on the baffles, pollen that got inside, etc.
Cleaning the inside is as easy as the outside:
Remove the corrector-holding ring, lift the corrector out by gripping the secondary, turn it around and replace the corrector backwards into the scope with the secondary facing up. Blow all the dust off the secondary (if any) and clean the inside of the corrector exactly as you'd do the outside.
When you replace the corrector, make certain the edge registration marks line up, replace the pressure ring (not too tight on the screws--just enough to hold the corrector),
and collimate (your collimation shouldn't be too far off, so you can wait for Polaris at night if you want).
I sold the scope to a friend after 11 years. The mirrors still looked good with no dust or spots (despite the use of a Lymax cooler), and the corrector was clean and unscratched. Perhaps had the corrector been really dirty when cleaned, the dirt could have scratched the plate. But I cleaned it when it got hazy, not filthy.
I think the coated surface is at least as hard as an eyepiece, and I clean them after EVERY outing. Some of my eyepieces date from the '80s and are still unscratched (under very bright light, angled to see the surface blemishes).
Never use lens tissue, as I think this has too many coarse fibers in it and will scratch the lens (I speak from experience). Use soft white kleenex (not the stiff, recycled kind) without any scent or lotions added. Use an ear syringe to blow off any dust from the kleenex--don't rub the dust around.
This pretty much echoes what Al Nagler says to do for eyepieces on the TeleVue website. Well, a corrector plate is just a big eyepiece, in a way--just coated glass.
Posted 05 April 2005 - 10:38 AM
In the '90s I was given some Opti-Clean Polymer to clean optical surfaces without rubbing. This is an expensive, but effective, way to clean a dirty surface.
You brush the polymer on, making the coat as thick as paint and making sure the whole surface is covered.
While the polymer is still wet, you stick a piece of paper they provide to the edge of the polymer surface. When the polymer is dry (an hour or a little more), you lift the edge and peel it off as if you were peeling off a saran-wrap cover. It takes off dirt, oils, and everything not chemically bonded to the glass or mirror. No residue, and clean down to the molecular level.
I never used this on my mirror because it was close to $100 to do a mirror once, though it might have been worth it if I had bought an old scope uncleaned for years.
I did use this on my eyepieces (not the little ones, because the lenses were too small), and I cleaned a secondary with this once.
It works, though the film tends to break in thin spots (so you learn to ladle it on thickly). You can add more, though, because it sticks to itself better than to any surface. It's just too expensive to use on a regular basis.
I will say that the secondary I cleaned with it looked like it had just been coated--a bright light showed NO dust at any angle--for a few seconds. I could watch dust specs in the air settling on the mirror as I watched. 2 weeks later a bright light showed some dust on the mirror. Sigh.
A once-a-year distilled water bath is far more cost effective, even if harder on the mirror's surface.
Posted 05 April 2005 - 11:05 AM
Posted 05 April 2005 - 01:39 PM
Alas, I have a dob now, but perhaps this website will help you see what's in play Flocking a C11.
the next time you remove a corrector for cleaning maybe you could take pictures and give step by step instructions. i know it would be a big help to a lot of people like myself who have never done it.
This person goes farther than you need to go:
cleaning the corrector plate inside
You won't remove the secondary mirror. I maintain it's easier to clean the corrector in the scope. That's why I recommend removing it (with the secondary attached), turning it around and reinstalling it backwards. Then, cleaning the inside is no more difficult than cleaning the outside.
If you get really ambitious, here is a site that itemizes how to completely dissemble and reassemble the OTA of a C11:
Last, you can collimate fairly well before you take it outside at night to use Polaris to collimate with:
daylight SCT collimation
I'd love to oblige with photos. Somewhere on the net there's a site with step-by-step photos. If I find it, I'll post it.
Posted 06 April 2005 - 07:08 AM
I haven't noticed any degrading in image quality, visual or in images, and I keep leaning toward the notion that less cleaning is better.
Maybe in a couple more weeks.
Dust on the corrector is about the only thing regarding CAT's I don't like, seems like it is simply unavoidable even when you're careful.
Posted 06 April 2005 - 09:28 AM
Dust is unavoidable and dewing up after viewing during the winter is also. I guess that's the nature of the beast.
Posted 06 April 2005 - 11:05 AM
I agree, but no pictures, which is contrary to the request for a step-by-step with Pix.
I'd love to oblige with photos. Somewhere on the net there's a site with step-by-step photos. If I find it, I'll post it.
THIS is one of the best step by step's out there for OTA disassembly.
I've seen step-by-step with pictures where the person re-machined the cell, added mirror locks with pistons, re-machined the baffle to contain bearings, and essentially turned his SCT into a machinists work of art. That is true dedication.
I could probably find that site, but it's not too relevant to merely removing a corrector plate, turning it around, and cleaning the other side.