My lens was covered in dew spots so decided to clean it according to the instructions on the Televue website. The spots are gone and it looks good, apart from a very light film that I can see at the right angle with sunlight on it. Could this have any impact on the optical performance? I don't want to do over wiping it, so should I just leave it alone?
Light smear/film on refractor objective lens after cleaning?
Posted 13 February 2020 - 05:46 PM
Edited by HARRISON SCOPES, 13 February 2020 - 05:47 PM.
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Posted 13 February 2020 - 06:47 PM
Here's what Roland Christen says (in part) in his cleaning instructions. This section deals with what you can expect after the lens cleaning:
"…When you are done with above steps, you will probably see swirling cleaning marks which look terrible, but which actually do zero harm to the image itself. These marks cause discoloration because they add a tiny thickness to the 1/4 wave anti-reflection coatings. You can eliminate these by one of two methods. The easiest is to breathe onto the surface and use the Lint-Free Professional Optical Cleaning Wipes in a final gentle rubbing action to get the surface clean. You can also wet the Lint-Free Wipe with clean acetone and wipe once around the aperture. Do not wet the wipe thoroughly, just barely damp to see the acetone evaporate almost instantly as you finish wiping. Do not get acetone onto the inner surface of any black painted retaining ring, since this will dissolve some of the black paint and deposit it onto the lens surface."
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Posted 13 February 2020 - 06:56 PM
And as you're already acquainted with, here are Al Nagler's instructions about the subject:
"If, after cleaning, any spots remain, try "fogging" the lens surface with your breath, then wiping it with a Q-tip or tissue moistened with alcohol. This method usually works with spots that are water-soluble. Because pure alcohol and pure acetone contain no water, without the moisture from your breath to help, neither can remove water-soluble spots.
IMPORTANT NOTE: Don't use acetone on binocular or camera lenses, only alcohol. Many of these lenses have painted surfaces surrounding the lenses; acetone will dissolve and smear this paint across the lens and may damage any parts made from plastic or other materials."
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Posted 13 February 2020 - 07:52 PM
When I had a Tak FCT 150 (not TOA) there was something between the lens. I had bought the scope used and being the third owner did not want to point fingers.
I sent the entire OTA to LandSeaSkyCo.com (was Texas Nautical Repair) for a thorough cleaning before I put it back on the market. This might be overkill for what your are experiencing, but if your cleaning involves removing the and disassembling the lens, then I would send it out to a professional service.
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Posted 13 February 2020 - 08:34 PM
Short answer, I agree, ignore it. More optics have been damaged trying to get 'that last bit' cleaned.
Usually someone pops in with a microfibers are bad' statement because people reuse them, apparently. But they are one of the best tools I've used for zero damage cleaning.
Microfiber loop-style towels are very effective with 'breath fogging'. I had a mak with oil smears that resisted all careful efforts to remove them (I ignored them until I needed to prep the scope for sale; any error was going to cost me), until I tried the micro fiber loop towel, new of course, and breath fog. No rubbing required, it wicked off the oil like magic.
Treat them as a moderately price throw away item. I would not wash and reuse them, particularly with whatever they put in detergents for odor, etc.
They have the unusual ability to absorb oils without any solvent other than breath fog, which probably just lubricates to avoid scratches.
I have used the automotive cleaning towels, grey, that are sold at Walmart, no issues. You get two or three, and they are huge, and easily cut up and put in bags for storage (cutting might increase the lint a bit).
The Harbor Freight ones work but are super linty.
NEVER use a paper or pulp based product. I seen name brand 'optical tissues' make observable microsleeks in coatings. Hey, I have a 20x dissecting microscope I use for watch repairs, can't let it go to waste. That testing was done iwth retired camera lenses.
Pec-pads (available on Amazon) are really great but totally non-absorbent. They are handy for lint removal and lens handling (I have classic refractors that needed cell repairs).
I found acetone, otherwise the recommended solvent in a pro setting, to evaporate too rapidly to remove oils, and it is so low viscosity it creeps into any space. It is also a fire hazard IIRC. While that makes it great as a base for a homemade bolt penetrant, it can be a nightmare on a scope. Besides, it eats plastics. I would avoid it for the average person.
Don't any purity level of any alcohol from the drugstore, only Everclear (booze, 180+ proof, food grade, no impurities to kill people beyond the alcohol itself) if you want ethanol, or lab grade undenatured alcohols. Isopopyl, lab grade I think, is the basis for many commercial cleaners. Lab grade undenatured methanol should work, but has subtly dangerous vapor issues and I would say to avoid it. Every year chem teachers started fires with common demos until most districts banned it after a well publicized student injury. You don't want an unknown denaturing agent or an impurity left behind on your lens.
That basically means you should buy a commercial lens cleaner. The Zeiss one is cheap and easy to get, about 5% propanol 95% distilled water. Baader's is good but not sold in the US, there are threads with other suggestions.
Edit: Just read MikiSJs post and agree completely. Leave it alone, send it to a well-reviewed optical repair, or, better, back to Chester NY and let Uncle Al do it.
Edited by markb, 13 February 2020 - 10:14 PM.
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Posted 13 February 2020 - 10:03 PM
Truthfully, all the answers given so far are good ones. Now there has been some talk about Takahashi lenses needing an even higher level of TLC when it comes to cleaning. Apparently, some of their lens coatings are very sensitive to certain liquids or cleaning agents. True or false? I'm not entirely sure. For the best advice there, a call to Texas Nautical should be in order. But the rule of thumb has always been don't clean unless it's really absolutely necessary.
Posted 13 February 2020 - 10:06 PM
If I recall, AL Nagler added, " no pepperoni pizza before *huffing* on the surface"
From a S.A.A. thread in 1997?
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