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Re: [OM] Filters

Subject: Re: [OM] Filters
From: Moose <olymoose@xxxxxxxxxxxxx>
Date: Wed, 18 Jun 2003 15:52:35 -0700
No sound advice, I'm afraid. I thought we did light advice and left sound advice to audio lists. :-D

A bit more about 'daily protection' filters.

1. If you go this route, test them before relying on them. Take pictures with and without them and make sure they don't degrade image quality. Look at the "50mm f/1.4 Zuiko (multi-coated), OM-2000 with mirror and diaphragm prefire; lens with >1,100,000 test on Gary Reese's lens test site <http://members.aol.com/olympusom/lenstests/default.htm>. Notice that the filter looked good to the naked eye and what it did to lens performance. We also had the case a while ago of lots of posts about a Zuiko that was taking unsharp pictures until it was suggested that any filter on the lens be removed - bad filter.

2. If you just want protection, UV or plain are designed for that.

3. Many films have blue layers that are sensitive to light above the visible spectrum into lower UV range. Spectral sensitivity varies with film and UV transmission varies between lenses. Thus, there are many situations, high altitude, shooting up into the sky, etc. where there is enough UV to result in bluish images, or areas of images, but with no effect on sharpness

4. The atmosphere in general and areas with airborne dust and/or pollutants scatters the blue end of the visible spectrum more than the rest (viz, blue sky). This doesn't just apply to urban air pollution. The Great Smoky mountains in the SE US were so named because of the 'air pollution' from the trees which gives them a hazy, smoky look in the hot months. Again the result is bluish tinted images, but also with reduced contrast and sharpness. This is most apparent through long expanses of air, as with longer focal lengths and broad panoramas.

There are probably special, very expensive filters with sharp cut-off frequencies, but regular lens filters have a gradual slope between the frequencies they filter most and least. So there are a series of filters that filter progressively more UV and blue light, UV, 1A(Skylight), 81 series and 85 series. for some more info, look here <http://www.2filter.com/faq/warmfil.html>.

There are all kinds of uses of and opinions about these filters. One thing they will all do, to an extent depending on the UV and upper blue filtered out, is reduce the bluish tint resulting from 3. and 4. and help with the sharpness/contrast issues of 4. All of these issues are more obvious with slides, where the auto color balance of automated print machines can't compensate. If you are taking most of you images at relatively low elevations with nothing longer than modest tele lenses and not trying to get broad panoramas, a plain, UV or skylight filter should work well. Take the same gear up in the Rockies ,esp. on the Denver side, and you will get very blue pictures. You need something more like an 81C. Same thing in higher, unpolluted, areas around the world.

Unlike some color balance problems that can be easily adjusted in an image editing program, 3. and 4. can't be as easily compensated. Pulling out the 'blue' from UV, will also alter the color balance of any parts of the image unaffected by the UV, easily resulting of off color shadows. Loss of detail and contrast from scattered UV is also hard to compensate for.

I generally don't use 'daily protection' filters except for situations where there is blowing sand/dust, flying or falling water, etc.

Moose


John Hudson wrote:

----- Original Message -----
From: "James Royall" <james@xxxxxxxxxxxxx>
To: <olympus@xxxxxxxxxxxxxxx>
Sent: Wednesday, 18 June, 2003 10:49 AM
Subject: [OM] Filters


Hi,

I sent this before but it doesn't seem to have got through, so
apologies if this ends up a duplicate.

Does the om2n require a circular polariser?

Also, I am a bit unclear as to the differences in skylight and uv
filters. I'm looking for the general daily protection type - is it the
skylight 1a I should get? Would a uv be unsuitable? what are the
differences between them? I've had a look around at various sites, but
not found anything very specific.

Thanks for all the sound advice.

James


Jim Timpe answered the polarizer question. As for filter use / lens
protection I would suggest a 1A sunlight, or even perhaps a 1B sunlight
ahead of a UV filter. A 1A or 1B offers significant UV filtration as well as
having a certain warming effect, a la an 81A filter,  which can be important
when shooting colour slides.

jh

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