[rollei_list] Re: Step Up Ring - uncoated filter
- From: "Gene Johnson" <genej2ster@xxxxxxxxx>
- To: rollei_list@xxxxxxxxxxxxx
- Date: Wed, 18 Apr 2007 20:47:50 -0400
I've done a lot of shooting with coated, uncoated, and multicoated
lenses, and there is definitely a noticeable difference in contrast
between all 3, especially in difficult light situations. How much a
coated filter makes vs an uncoated one? Dunno for sure, but it might
be more than you think. I'm pretty sure it ALL matters, if you're
after that modern high local contrast look. Not really my thing most
of the time, but I know it is for a lot of people. I don't own any
coated filters, but like I said, not really my thing:)
On 4/18/07, Richard Knoppow <dickburk@xxxxxxxxxxxxx> wrote:
----- Original Message -----
From: "Marc James Small" <marcsmall@xxxxxxxxxxx>
To: <rollei_list@xxxxxxxxxxxxx>
Sent: Wednesday, April 18, 2007 3:03 PM
Subject: [rollei_list] Re: Step Up Ring - uncoated filter
At 05:05 PM 4/18/2007, eroustom@xxxxxxxxxxx wrote:
>It shouldn't matter if the filter is coated should it? The
lens is coated.
>
Well, to be honest, the difference in performance
between a coated lens and an uncoated lens
with proper lens hood is minimal save under
direct countre jour shooting. Under a VERY few
conditions, coating on a filter might help but,
again, a lens hood is the best answer to eliminating flare.
For that matter, many night recon and security
lenses remain uncoated to this day as this
preserves detail while sacrificing some background darkness.
Marc
Every glass-air suface has reflection due to the mismatch
in index of refraction between the glass and air. The
coating acts as what would be called in RF technology a
matching section which eliminates at least some of the
reflection. The coating is effective on the surfaces to
which it is applied so a coated lens has no effect whatever
on a filter used on it. Because there are only two surfaces
to a filter the amount of reflection is not very great but
where a multi-coated lens with very low flare is used the
differenc may be detectable especially for color where flare
affects color purity.
Lens shades do not perform the same function as a lens
coating. The coating is effective in reducing multiple
reflections in the lens which wind up producing flare or
ghose images in the image light. A lens shade affects only
extra-image light. While this can conribute to flare in the
image it is the image light that produces most of the flare
and this is not controlled by a shade. For low flare one
should have good coatings, use a lens shade and the lens
must be properly baffled to prevent direct reflection of
light from its internal structure. Baffles in the camera
also help, but again, only with extra-image light.
A note, there is little flare from cemented surfaces
whether in a lens or a filter so the internal surfaces of
filter with a cemented gelatin or plastic filter do not need
to be coated although the index of Gelatin may be low enough
to cause some reflection.
For absolute minimum flare and optical effect on the
lens a thin gelatin filter should be used on the long
congugate side of the lens.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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