On Sun, 25 Mar 2001, Frits J. Wüthrich wrote:
> Last Thursday my new lens arrived, bought it in a Dutch auction at eBay
> ($129.99 + $10.- for shipping), arrived direct from Moscow, the seller is in
> the USA. The custom forms, filled out in by the sender, noted it was a gift.
> I didn't have to pay import duties, perhaps because it was a gift? The
> packaging was simple though sufficient, and perhaps supporting the idea of a
> gift.
So, you were the other buyer. I got it in the same auction, and it
hasn't arrived yet. I presume from your btinternet.com domain that you
are in the UK?
> To make sure, I replaced the transparent filter (that is screwed into the
> rear of the lens, not very easy to do) and guess what? I can focus properly
> now. I did look at the filter before mounting it, and it is no lens, no
> magnification. I don't understand why, but it works. Also the focus
> confirmation works now.
A flat piece of glass *behind* the lens does affect the focus
plane. Light rays are refracted when they go into the glass, and when
they leave it they again bend so the incident angle is the same as the
exit angle, but the fact that the ray changed angles while inside the
glass will change the focusing distance.
Let me try some ascii art, you should look at the following with a
fixed-width font:
\ /
\ / <- light coming from the lens
\ /
------------------
| | <- flat filter
| |
------------------
\ /
\ /
\/
----------------- <- film
So if you take the flat glass out, the focus point will be in fron of
the film.
Looking forward to receiving mine,
j
--
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Juan J. Buhler | FX Animator @ PDI | http://www.crosswinds.net/~jbuhler
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