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  1. #1
    LouP's Avatar
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    Default I think I just figured something out



    I ran into a little discovery last night. I was looking at my ep and noticed that some were dirty and my first thought was that I would grab a q-tip and get the dirt off after using a one of those bulb blowers used in photography. Then the alarm went off in my head, DON'T DO IT! Well I rationalized that if I was careful, everything would be fine. My Televues cleaned up great with no issues and then I got to my Q70 38 mm. I have not messed with this one much so I tried working on the edge first. There was a little smudge there and I am guessing it was from my eyes as my I tear really easily, especially in the cold. Well I was extra careful and put no more pressure than I did on the TVs and what appeared to be a scratch showed up . It was very small and the more I tried to see if it would clear or come off, the worse it seemed to get. I decided it was best to just leave it alone. I could not notice the area when I looked through the lens toward a light at all (don't even know if this is a valid test) but I was amazed at how rugged the TVs were compared to the Q70. I am not knocking the Q70 as the views are great through it on my scope but I think I just discovered how some of these ep are being sold so cheaply as compared to the TVs. Hmmmmm

    Going forward I may invest in the TVs as I need new eps, even if I have to wait a while to get them. I figure what good is a cheaper lens if it's not going to last.

    LouP

  2. #2
    AustinPSD's Avatar
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    All eyepieces are not created equal, nor are all lens elements, especially with respect to their coatings, or how they are applied.

    Many less expensive eyepieces use lens elements with either spin-coated, or chemical vapor deposition (CVD) coatings. Because of the way they are applied, the coatings are not very durable, and can be scratched, rubbed off, or eroded/dissolved by certain solvent-based cleaning agents. They can also oxidize over time, reducing transmissivity of the lens element.

    Higher quality optics use CVD and a dielectric process, or ion deposition coatings, which are hard and durable. They can be scratched, but are much more resistant to scratching, don't oxidize, and won't flake, chip, or dissolve by use of common solvents like isopropyl alcohol or deionized water.
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  3. #3
    LouP's Avatar
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    Default

    Thank you, Austin. Confirms my findings from last night. Thank goodness I stopped messing with the Q70. I still can't get over how easily the coating became damaged. It really is something to consider when purchasing eps. What may seem like the cheaper route may actually cost you more in the long run. I was planning on getting the 26mm Q70 down the road but this completely changes that idea.

    LouP

  4. #4
    AustinPSD's Avatar
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    Similar concerns apply to other components like star diagonals, focal reducer/correctors, and the surfaces of prime objective lens and primary/secondary mirrors.

    Higher end optics use dielectric coating methods or ion-deposition to improve their durability - low end stuff can be problematic. I've seen people disassemble and clean things like inexpensive star diagonals, only to rub off part of, or scratch the mirror coating....
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