Quite quickly I have become obsessively fearful about anything that links the action "cleaning" and telescope "objective" to the point I toss and turn in my sleep from memories of well intentioned yet misdirection swipes at objectives with cleaning tissues.
My reading indicates there is proportionately less fear in raising a cleaning cloth to an eyepiece than there is raising a cleaning cloth to an objective and that many premium eyepieces are formed from Lanthanum Glass
Why then when many good eyepieces are formed from Lanthanum Glass and that those La eyepieces generally tolerate quite harsh treatment and rigorous cleaning why not simply form objectives from La? allowing for misdirected and over enthusiastic cleaning. Is it a cost thing that prevents the use of La as an objective? Is it technically difficult to grind a large piece of La Glass?
Or..... is my belief that La eyepieces tolerate cleaning totally wrong?
Befuddled Cleaner...
Location: '34 South' Young Hilltops LGA, Australia
Posts: 1,435
Quote:
Originally Posted by Constant
Quite quickly I have become obsessively fearful about anything that links the action "cleaning" and telescope "objective" to the point I toss and turn in my sleep from memories of well intentioned yet misdirection swipes at objectives with cleaning tissues.
My reading indicates there is proportionately less fear in raising a cleaning cloth to an eyepiece than there is raising a cleaning cloth to an objective and that many premium eyepieces are formed from Lanthanum Glass
Why then when many good eyepieces are formed from Lanthanum Glass and that those La eyepieces generally tolerate quite harsh treatment and rigorous cleaning why not simply form objectives from La? allowing for misdirected and over enthusiastic cleaning. Is it a cost thing that prevents the use of La as an objective? Is it technically difficult to grind a large piece of La Glass?
Or..... is my belief that La eyepieces tolerate cleaning totally wrong?
Befuddled Cleaner...
The different refractive indices, suit different optical designs.
Lanthanum glass has a very high refractive index about 1.7, fluorite and other ED glasses & optical glasses are much closer to 1.5. The high refractive index is probably better suited to eyepiece design, the ED glasses to objective design.
OzEclipse, different refractive indices explains the variation in uses of glasses but.... are there harder objectives, materials that would make the cleaning process less fraught with fear? How conserned should I be when cleaning dust-stuff-pollen etc from the object? What the best way to determine, or assess damage caused by cleaning?
It is not actually the specific type of glass that is at risk when cleaning. I think all glass is hard enough too withstand tissue, hair brushes, etc.
However, the lenses have coatings to reduce light reflection & absorption and also increase light transmission. These coatings are at risk if cleaned with too much force or with wrong material/chemicals.
The coatings themselves are quite hardy and can well tolerate being cleaned with tissue, hair brushes, alcohol, windex, water (filtered/deminerlised will leave less residue). Just use common sense and be gentle (don't need to be obsessively gentle).
Last year I had to take the front glass (meniscus lens) off my 8" sct to clean a smudge on the inside (caused by mildew?). I had never done this before but after some reading online, I went ahead.
First I squirted lots of filtered water over the lense to remove any specs of dust. Then I sprayed the lense with windex and held the tissue in a loose ball whule wiping the lens with just enough pressure on the tissue ball to compress it about 1/4 - 1/2 it's size - not a lot but it was enough and the job was done.
I WAS worried when I started in case I did damage but with the assurance of what I had read online I accomplished the task with the feeling I was doing the right thing.
NOTE:
Common alcohols for cleaning are isopropyl & methanol, usually diluted formulations.
I would never use a tissue without fluid. A dry tissue has the potential to push a spec of sand (silicone) across the lense causing a scratch. A hair brush with puffer used dry is ok because it tends to lift the specs off the glass surface.
CSB, what your saying makes sense. The issue isnt with the hardness or lack of hardness of the respective glasses used to construct a lens, the issue is with the coatings.
Cleaning care requires care of the coatings, coating that would be measured in microns!
Many thanks
Constant
Having done quite a bit of reading over on the CN forums about cleaning mirrors, one of the suggestions has been that the finger is one of the best tools for cleaning. As long as you have removed the oils from your finger and using your finger in conjunction with a liquid, it is the perfect non-damaging abrasive surface.
Have I done it myself? Not on anything other than my glasses Just another suggestion to throw into the mix.
Astro Physics Cleaning Guide is amazingly useful and answers some questions I hadn't even thought to ask.... I have printed the sheet and will laminate it just in case the urge to clean arises again.
The article makes clear that most of the objective cleaning that is unhelpful if anything is to be cleaned it's the eye piece, not the objective.
Just another suggestion to throw into the mix.
