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Thread: What are the colors of eyepiece coatings?

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    Default What are the colors of eyepiece coatings?



    Help! I have forgotten the different colors of eyepieces to determine the quality of the coating. Thank You.
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    Default Re: What are the colors of eyepiece coatings?

    Looking at a slight angle, the color of a reflection from a light bulb tells something about the lenses, but the different colors of lens coatings generally are not significant.
    Fully multi-coated optics may reveal faint purple, green, or red-hued reflections.
    Eyepieces typically show several reflections, and a properly coated optic may show a variety of colors.
    This is because different types of glass are often used in the lens stack, and these glasses each need specific coatings in order for their performance to be optimized.
    Last edited by Gabby76; 01-13-2017 at 05:05 PM.
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    Default Re: What are the colors of eyepiece coatings?

    A bit more clarification:
    A lens coating actually is colorless. It is a perfectly clear material in the visible spectrum. The only two things that make it appear coloured is the refractive index of the coating and the actual thickness of the coating.
    The different coatings thickness will reflect a different part of the visible spectrum.
    j.gardavsky, DeanD, Leveye and 3 others like this.
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    The weakest link in the optical chain is the large nut located directly behind the
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    Default Re: What are the colors of eyepiece coatings?

    I have seen single coatings give off a light blue appearance and more modern multi coatings more greenish. Just to my eyes anyways. Both work well with my scopes.
    Last edited by Leveye; 01-13-2017 at 05:39 PM.
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    Default Re: What are the colors of eyepiece coatings?

    This is where single coated, fully coated and multi-coated come into play also. Magnesium fluoride (MgF2) is the most common coating and will reflect back blue, green and purple depending on how many layers are applied.
    A white reflection usually indicates a uncoated surface. All this only tells you that the lens is actually coated.
    A well coated lens when looking through it should show no colour or dimming at all.
    Refractors: Antares 105 f/15, Celestron 150 f/8, Stellarvue NHNG 80 f/6.9, TAL 100RS f/10, TS 102 f/11, UR 70 f/10, Vixen SD115s f/7.7
    Mounts: Celestron SLT w/ pier mod & EQ-3 tripod, Celestron hypertuned CG-5 w/ tracking motor & Argo Navis, Manfrotto 028B w/ Stellarvue M2C, Manfrotto 055PRO w/ 128RC, TAL-1 HD EQ, Vixen SXP w/ HAL-130 SXG & half pier
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    Default Re: What are the colors of eyepiece coatings?

    Thanks Gabby76 for clarifying (no pun!) the properties of lens coating.
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    Default Re: What are the colors of eyepiece coatings?

    Hello all,

    the antireflection coatings (multicoatings) on the lenses have a dual purpose:
    1. To minimize the light loss due to the air-to-lens surface reflections (hence the name 'antireflection coatings')
    2. To balance the color rendition of the optics system into a fairly flat spectral characteristic - no bluish or yellowish teint, as sometimes found in the budget products.

    When you look on the doublet objective from a side, you may often notice, that one of the lenses reflects blue, and the other reflects green.
    The first coated lens reflects away some percentage of the stray bluish/violet rays (skylight), which when passed, would reduce the contrast of the view.
    The second coated lens reflects away some surplus green passed through the first lens.
    the both antireflection coatings arts are matched to offer a fairly good color neutral rendition
    The high-end designs use also the amber multicoatings, like the Zeiss T*.

    The situation is more tricky in the eyepieces, which require a sophisticated design of the multicoatings choice on the high number of the individual lens surfaces to obtain a high contrast, high light throughput, and a strictly neutral color rendition, as in the wide and ultrawide eyepieces
    Even the eyepieces within one series of the focal lengths may require different multicoatings, when different glass materials are used. This explains, why different eyepieces may reflect different colors.
    It has nothing to do with the quality variation within the production batch, as wrongly claimed in one of the discussions on CN.

    The situation is much more tricky in the eyepieces, which require a sophisticated design of the multicoatings choices on the high number of the individual lens surfaces, as in the wide and ultrawide eyepieces.

    On the simple eyepiece designs, like the Plössls and orthos, you will see the bluish and greenish (eventually amber) reflections just close to the rims of the lenses, which otherwise look crystal clear. Herewith the simple eyepiece designs, when properly multicoated, achieve very high contrast and very high transmission of light with a well balanced color rendition.

    Best,

    JG
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