Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Coatings & Air to Glass Surfaces

This topic has been archived. This means that you cannot reply to this topic.
10 replies to this topic

#1 Diego

Diego

    Viking 1

  • -----
  • topic starter
  • Posts: 721
  • Joined: 29 Jul 2003

Posted 28 April 2004 - 09:14 AM

What do you folks understand by the spec "coated on all air to glass surfaces".

I think they mean every surface, including those not directly exposed to the outside air (i.e. in-between ep elements also).
I know some economic binoculars have coatings only on the outside surfaces of both objective and ep but not on those inside the optical tubes or on prisms. I wonder if this is also the case for eyepieces.

Diego

#2 erik

erik

    telescope surgeon

  • *****
  • Posts: 24,858
  • Joined: 30 Jan 2004

Posted 28 April 2004 - 09:37 AM

that's what it means. multi-coated means one or more surfaces have multiple-coatings, and fully-coated means each surface has a single layer of coating (usually magnesium fluoride) applied. and then there are still some eyepieces (like meade's cheap .965" ep's) that only have a single layer of magnesium fluoride on the outer element.

#3 Tim2723

Tim2723

    The Moon Guy

  • *****
  • Posts: 5,765
  • Joined: 19 Feb 2004

Posted 28 April 2004 - 09:47 AM

I believe it also means that for certain multi-lens elements, such as cemented doublet and triplets, only the two outside surfaces are coated, the coating being applied after the lenses are permenently cemented.

#4 Craig Simmons

Craig Simmons

    Surveyor 1

  • *****
  • Posts: 1,502
  • Joined: 10 Dec 2003

Posted 28 April 2004 - 09:48 AM

I've wondered about the "air-to-glass surfaces" description as to whether or not it means all surfaces. It seems to imply all surfaces.

#5 Diego

Diego

    Viking 1

  • -----
  • topic starter
  • Posts: 721
  • Joined: 29 Jul 2003

Posted 28 April 2004 - 09:49 AM

Thanks for the response. I know the difference between coated, fully coated, multi & fully multi coated. Maybe I wasn't clear but I was asking whether some of the surfaces have no coating at all, like for example in-between elements.

#6 erik

erik

    telescope surgeon

  • *****
  • Posts: 24,858
  • Joined: 30 Jan 2004

Posted 28 April 2004 - 09:51 AM

with the term "fully-multi coated", that's what it's supposed to mean, that ALL surfaces are multi-coated.

#7 erik

erik

    telescope surgeon

  • *****
  • Posts: 24,858
  • Joined: 30 Jan 2004

Posted 28 April 2004 - 09:52 AM

even "fully coated" ep's have at least one coating on every surface. it's ep's that are labled "coated" that are only coated on the outside elements...

#8 Diego

Diego

    Viking 1

  • -----
  • topic starter
  • Posts: 721
  • Joined: 29 Jul 2003

Posted 28 April 2004 - 09:58 AM

I think Tim's reply pretty much rounds it up.

Erik, thanks for clearing that up. "Coated" are the ones that have surfaces un-coated

Thanks,

Diego

#9 EdZ

EdZ

    Professor EdZ

  • *****
  • Posts: 18,849
  • Joined: 15 Feb 2002

Posted 28 April 2004 - 10:28 AM

Just last year, information was posted by a US binocular importer that Chinese meanings for these terms don't necessarily match what we think. In fact binoculars that were being produced and supplied to distributors as Fully Multi -coated were not FMC on all air to glass surfaces. This was a part of the enlightenment that all distibutors were not providing the same product to the consumer and only those distributors that paid for the premium FMC got true FMC.

Depending on the manufacturer, FMC may mean that one surface is FMC. It might be better to see documentation that says FMC all air to glass surfaces. That should mean only cemented faces are not coated. BTW, that does not address the issue that all lenses and prisms are surely glass, and none plastic. that shouldn't be in issue in eyepieces.

edz

#10 Mike Hosea

Mike Hosea

    Fly Me to the Moon

  • *****
  • Posts: 6,175
  • Joined: 24 Sep 2003

Posted 28 April 2004 - 11:27 AM

Note that you probably would not want to coat the surfaces at a cemented interface since the transmission is so high for cemented interfaces to begin with and the bond would only be as good then as the coating bond. Coatings are designed to reduce the much greater problems encountered with air-to-glass surfaces.

Pentax, on the other hand, has advertised something about a partial coating process used in the XW line, which is, of course, fully multi-coated on all air-to-glass surfaces as well. My impression upon reading it was that the partial coating business had something to do with the cemented interfaces, but I have no details, and my impression may be wrong.

#11 erik

erik

    telescope surgeon

  • *****
  • Posts: 24,858
  • Joined: 30 Jan 2004

Posted 28 April 2004 - 05:40 PM

ed, that's a good point you made about the chinese manufacturers idea of what constitutes an eyepiece being "fully-multi coated". a few years ago, orion advertised their ultrascopics as being "ultra-multi coated", with every surface multi-coated, which was supposed to be a higher standard than "fully-multi coated". (so what the hel did "fully multi coated" mean?) now they just call them "fully multi coated" and assure me that that's actually what it is. of course, the ultrascopics are made in japan, not china. but i would hope that now that only a couple of different manufacturers make probably 50% of the eyepieces for the different companies, that were actually getting what we pay for.... :question:


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics