Re: More on filters and flare

[Jim Brick <jim@brick.org>]

At 07:21 PM 6/18/97 -0400, you wrote:
>>I believe that years ago, coating was an
>>expensive technique.
>
>
>Jim,
>
>Early coatings were soft and delicate, and could be easily damaged, even 
>by careful cleaning. This was another reason to leave the front element 
>uncoated.
>
>I read an interesting thing the other day, in a book written in the late 
>50s/early 60s. I had always thought of lens coatings as being primarily 
>for the purpose of controlling reflections and flare, but according to 
>this, the coatings also allow the manufacturer to control color casts. 
>According to the book, most optical glass absorbs some blue light, so a 
>normal, uncoated lens will yield slightly warm colors. According to the 
>book, most lens coatings appear blue or purple because they must 
>compensate for this warming. The absorbtion of blue light varies with the 
>composition of the glass and the number of elements, so a careful 
>manufacturer varies the color of the coating for each lens.
>
>There is a good expanation of exactly how lens coatings work on the 
>Contax website:
>
>http://www.contaxcameras.com
>
>
>- Paul

Thanks Paul,

I also read about the color of coatings and read that different colored
coatings were used on different elements of the same lens, with the total
color balance coming out neutral. Or skewed warm or cool depending upon
what the manufacturer wants.

Jim