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Broadband coatings

Started by light trap, 04/07/2003 08:33PM
Posted 04/07/2003 08:33PM Opening Post
Is it true that broadband coatings scratch significantly easier, and are much more delicate than other coatings?
This was suggested by one of the more prominent importers of binox with these coatings. I'd like feedback from users and other marketers/importers. If true, at what level does this become a consideration? Is broadband as soft as the worst of the early multicoatings, that could practically be wiped off with a cotton cloth?

Mike Swaim
Posted 04/08/2003 11:18AM #1
I keep coming back here looking for any response to this question. I'm very interested to read any responses!

I think the Oberwerk (not sure about current models) claim to use the broadband multicoatings. I haven't had any problems with softness, But I sure am curious.

Posted 04/08/2003 03:56PM #2
There are too many factors to consider; a simple/pat answer may not be available. Aspects such depositional sequence, coating composition, method of deposition, preparation of substrate, presence or absence of a hardcoat, hardcoat *placement* (whether as overcoat or undercoat) -- all these will factor into how "hard" and/or scratch-resistant a series of AR coatings is. Heck, even the scratching agent and its interaction with the coating(s) can make a difference.

My understanding is that a well-applied MgFl film coating is harder than typical glass. Most oxide-based clear hardcoats are about as hard as (often harder than) quartz. However, "hardness" does not always strictly equate to scratch/abrasion resistance and/or deflection resistance. There's also the question of whether or not a given sleek or scratch actually exists on/within the coating(s) or *under* the coating(s) -- on/within the glass itself. Yes, it *is* possible for hard-coated glass to be scratched "despite" the coating itself (which may remain undamaged).

"Significantly" easier to scratch than a good MgFl coat? or a Pentax SMC?
No, not as long as sufficient care is taken. Most cleaning methods recommended for astronomical mirrors and lenses are safe and gentle enough for any/all readily available AR coating(s).

For what it's worth: I'm no more or less concerned about the AR coatings on my Sino-made 15x70s than about the coatings on my Fujinon 10x70s. I treat them equally gently and carefully.

Best wishes.
Posted 04/08/2003 07:49PM #3
Thanks for all the quick answers.

Kevin, I particularly appreciate your explanation of just what broadband coating is. I also like your very practical explanation comparing broadband to other coatings. I'm confused by the reference to bb and ebc showing smudges more readily, though. I guess I would have thought that smudges and fingerprints were basically univeral. It's weird to think that different coatings may affect how what amounts to oils deposited on the glass are perceived. Anyway, I won't dwell on that. I also really like that comprehensive binox comparo chart you've put up on your website. What's this I read about a 22x100? That would be cool.

Mike Swaim