Re: Pentax's sudden infatuation with ED glass.

[Ronald Arvidsson]

Hi Joe,

 Re: Pentax's sudden infatuation with ED glass.
Joseph Tainter
Tue, 05 Apr 2005 09:37:07 -0700
David asked:
* ED glass has suddenly become cheap enough to use in a broader range 
of lenses.
* ED glass has become necessary to produce acceptible results with 
DSLR's.
* ED glass has become enough of a recognized feature that using it 
pays dividends in improved lens sales.
* Pentax has become committed to producing better zooms than ever 
before, possibly to try to close the door on 3rd party lenses (much 
like SMC does).

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I have wondered if ED glass is now less expensive to produce. 
Mentioning its presence is certainly an advertising point.
-----

Yes I believe so too. There are a number of new glasses. Just go into 
your opricians shop and ask for "thin"glasses - that will give a few ED 
glasses to choose from.

Then Fra wrote:
Today, IMNSHO, "ED" glass is quite a meaningless term. It doesn't say
anything about the good or bad of the lens, nor about its aberrations.
It doesn't mean the lens is Apochromatic. It doesn't even hint at it.
Same with "APO". Also, I have never saw any manufacturer actually
disclose what actual index does they mean by e.g. "ED" designation,
and how much "extreme" it is compared to "normal" glass.
-----
This is right. Some third-party zooms with ED (or SD or LD) and/or 
"apochromatic" designs are rather poor performers.
-----

And Ronald wrote:
However, AL and ED designs are important to make more compact and 
sometimes sharper optics, of course just the name is not worth 
anything but with modern computer technology the mix of different 
lenses with different refraction indexes make it much easier to make 
better and more compact optics with minimal input in the design. The 
best and sharpest optics is however a combination of good design and 
minute exactness.

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I am relatively unknowledgeable about optical design. But I have begun 
to suspect that ED and AL glass mainly allow for more compact 
designs/fewer elements. The FA 20 contains neither, yet it seems to be 
a better 20/2.8 than the offerings from Nikon, Canon, or Minolta. It 
is also a sharper lens than the DA 14 ED. The FA 20-35 contains no ED 
elements, yet at 20 mm. it performs slightly better on the D than the 
DA 16-45 does. (Of course, it also has a more conservative zoom range. 
I consider them essentially equivalent in their performance.)

Well it can help lenses become sharp not only in the center but also in 
the edges - have you ever had AL glasses - I mean those on your nose. 
Who knows exactly what optical glasses the FA20 and 20-35 contains?

Yes zooms become either sharper or more compact. Making it too compact 
with expensive glass will make it harder to produce a good lens than a 
somewhat larger zoom with good glasses. It is however as someone earlier 
in this post said not only ED and AL but the whole design together with 
the other glasses that makes the lens - nevertheless ED and AL makes it 
easier to produce sharp optics zoom or prime. How sharp the lenses need 
to be is a decision of how many and for what prize they can sell. I 
would be very interested though to know how expensive for the 
manufacturers the glass in reality is or is it the exactness of the 
design that costs money???? Even so I guess that recently industrial 
robots do a lot of the work - how good are these for a reasonable price??

Maybe someone who knows more could chime in on these last observations.
We know that third-party manufacturers can produce very fine lenses 
when they want to. But they need to undercut the first-party 
manufacturers on price, so often their lenses come up just a bit short.

Joe

Cheers,
Ronald