Which Polarizer?

I have a Canon XT with a Sigma DC 18-200mm 1:3.5-6.3 lens, so obviously
I'm not a Pro!
However I'm trying to decide on a circular polarizer filter for enhancing
sky colors and minimizing reflections.
I hear that circular filters can knock 2 f-stops off a lens. Since I
already have a slow lens, would a more expensive filter take less of a
toll than a cheap one? What are the considerations? Any recommendations?

Roger

Roger wrote:

I have a Canon XT with a Sigma DC 18-200mm 1:3.5-6.3 lens, so obviously
I'm not a Pro!
However I'm trying to decide on a circular polarizer filter for enhancing
sky colors and minimizing reflections.
I hear that circular filters can knock 2 f-stops off a lens. Since I
already have a slow lens, would a more expensive filter take less of a
toll than a cheap one? What are the considerations? Any recommendations?

Roger


Polarizers do take about 2 stops compensation. Light from the subject
is randomly polarized, and the filter passes only the light that happens
to be in the same polarization plane as the filter, so about 75% of the
light from the subject is rejected. There is also a small further
transmission loss from the polarizing medium iself, so there's your 2
stops. There can be variations due to the 'tightness' of the
polarization, and the transmission characteristics, and with cheaper
filters there can be some color shift as well. Get the best you can
afford.

Colin D.

--
Posted via a free Usenet account from http://www.teranews.com

I always shoot at ISO200 when using a polarizer (and long telephotos)
and have never had a problem. Most of the time they are used in scenics
where a fast shutter speed is not really necessary. I find them great
when I travel and want to photograph through a car windshield or window
and have only had one serious problem -- over polarizing at high
altitudes.


Roger wrote:
I have a Canon XT with a Sigma DC 18-200mm 1:3.5-6.3 lens, so obviously
I'm not a Pro!
However I'm trying to decide on a circular polarizer filter for enhancing
sky colors and minimizing reflections.
I hear that circular filters can knock 2 f-stops off a lens. Since I
already have a slow lens, would a more expensive filter take less of a
toll than a cheap one? What are the considerations? Any recommendations?

Roger

In article , ColinD
writes


Roger wrote:

I have a Canon XT with a Sigma DC 18-200mm 1:3.5-6.3 lens, so obviously
I'm not a Pro!
However I'm trying to decide on a circular polarizer filter for enhancing
sky colors and minimizing reflections.
I hear that circular filters can knock 2 f-stops off a lens. Since I
already have a slow lens, would a more expensive filter take less of a
toll than a cheap one? What are the considerations? Any recommendations?

Roger


Polarizers do take about 2 stops compensation. Light from the subject
is randomly polarized, and the filter passes only the light that happens
to be in the same polarization plane as the filter, so about 75% of the
light from the subject is rejected. There is also a small further
transmission loss from the polarizing medium iself, so there's your 2
stops. There can be variations due to the 'tightness' of the
polarization, and the transmission characteristics, and with cheaper
filters there can be some color shift as well. Get the best you can
afford.

Not quite - a theoretically perfect polariser would only take 50% of the
light (1 stop). Deviations from perfection in the polariser material do
indeed show up, and absorb a little more light, so the typical metered
attenuation is about 1.5 stops. As you say, the more expensive ones tend
to use better polarising material - or perhaps I should say that the
ones using better materials tend to be more expensive (the old adage
"you get what you pay for" should IMO be more accurately re-written "you
don't get what you don't pay for"). They may thus have slightly better
transmission and less colour shift.

However, this 1.5 stops (+/-) is for light that has no polarisation
whatever - i.e. is totally randomly polarised. In reality, light from
the sky or reflected from non-metallic surfaces (i.e. most surfaces,
including water and glass) has some component of polarisation. Thus the
observed attenuation may be greater or less than 1.5 stops, depending on
the orientation of the filter with respect to the predominant
polarisation of the light.

David
--
David Littlewood

In article , ColinD
wrote:

Polarizers do take about 2 stops compensation. Light from the subject
is randomly polarized, and the filter passes only the light that happens
to be in the same polarization plane as the filter, so about 75% of the
light from the subject is rejected. There is also a small further
transmission loss from the polarizing medium iself, so there's your 2
stops.

OK, this makes sense, but I still have a stupid question: doesn't the
camera meter notice this reduction in the amount of light entering the
lens and compensate accordingly? Or is the meter not operating through
the lens?
--
-Take out Ron to reply-
My random photostream: http://www.flickr.com/photos/boggissimo/

In article , Dr.
Boggis writes
In article , ColinD
wrote:

Polarizers do take about 2 stops compensation. Light from the subject
is randomly polarized, and the filter passes only the light that happens
to be in the same polarization plane as the filter, so about 75% of the
light from the subject is rejected. There is also a small further
transmission loss from the polarizing medium iself, so there's your 2
stops.

OK, this makes sense, but I still have a stupid question: doesn't the
camera meter notice this reduction in the amount of light entering the
lens and compensate accordingly? Or is the meter not operating through
the lens?

Yes, the meter is operating through the lens in your Rebel XT. The meter
will notice the reduction in light levels and approximately compensate.
However, it may not get it quite right. For example, if you want to
increase the saturation of a blue sky, and use a polariser, you actually
want the photo to be a little darker, but the meter might increase the
exposure too much in order to raise the overall illumination level back
to what it was.

Clearly a little trial and error may be required to get exactly the
effect you want - and clearly there is a great advantage in using a DSLR
that you can review the results (though only rather crudely) on the
screen straight away. For most occasions the reduction given by the
meter will be reasonably OK. The purists in film days advised: meter
without filter, fit filter, and apply compensation of +1.5 stops (or
slight variant of this according to taste, determined by trial and
error). This approach will still work; it is more time-consuming than
the simpler approach of sticking on the filter and letting the meter do
its thing, but perhaps slightly more reliable.

David
--
David Littlewood

On Wed, 26 Jul 2006 02:30:51 GMT, Roger
wrote:

I have a Canon XT with a Sigma DC 18-200mm 1:3.5-6.3 lens, so obviously
I'm not a Pro!
However I'm trying to decide on a circular polarizer filter for enhancing
sky colors and minimizing reflections.
I hear that circular filters can knock 2 f-stops off a lens. Since I
already have a slow lens, would a more expensive filter take less of a
toll than a cheap one? What are the considerations? Any recommendations?

Roger


The cam will adjust, so will you. Get a cheep hoya for $40 and
see if you like it. If ya move up - sell it with the lens.

cheers
Ken

AaronW wrote:
Roger wrote:
I have a Canon XT with a Sigma DC 18-200mm 1:3.5-6.3 lens, so obviously
I'm not a Pro!
However I'm trying to decide on a circular polarizer filter

A linear polarizer is better.

Unfortunately, it'll mess up metering and AF with a lot of cameras,
so 'better' is ... a rather relative term.

http://www.luminous-landscape.com/tu...larizers.shtml
http://www.photofilter.com/cir_lin.html
http://www.mat.uc.pt/~rps/photos/filters_uv_pol/#polq2

-Wolfgang

"AaronW" wrote in message
oups.com...
Roger wrote:
I have a Canon XT with a Sigma DC 18-200mm 1:3.5-6.3 lens, so obviously
I'm not a Pro!
However I'm trying to decide on a circular polarizer filter

A linear polarizer is better.

for enhancing sky colors and minimizing reflections.

What I like most about polarizer is to enhance the color of grass,
flowers, and trees, ...

I hear that circular filters can knock 2 f-stops off a lens. Since I
already have a slow lens,

This can be a problem.

would a more expensive filter take less of a
toll than a cheap one?

No.

What are the considerations? Any recommendations?

Just get a cheap polarizer, to see whether you like the effect. If you
want a better one later, maybe with a better lens, get a multicoated
linear polarizer.

http://digitcamera.tripod.com/#slr

Anyone else posted to say that a linear polariser is a bad idea with an
autofocus / TTL metering body?

AFAIK, such bodies use beam splitters and so have to be used with circular
polarisers.
To cope with the loss of light, load the camera with a faster film than
usual (or set a higher ISO than usual if you're using a difital body).

Note also that the effect of the filter will depend on the relative position
of sun, camera and subject. I found, taking the "classic" photo of boats in
a small harbour on a sunny day, that in one position the filter had very
little effect whereas in another position the effect was mich more
noticeable.


Regards, Ian.

Fred Anonymous wrote:
"AaronW" wrote in message
oups.com...
Roger wrote:
I have a Canon XT with a Sigma DC 18-200mm 1:3.5-6.3 lens, so obviously
I'm not a Pro!
However I'm trying to decide on a circular polarizer filter

A linear polarizer is better.

for enhancing sky colors and minimizing reflections.

What I like most about polarizer is to enhance the color of grass,
flowers, and trees, ...

I hear that circular filters can knock 2 f-stops off a lens. Since I
already have a slow lens,

This can be a problem.

would a more expensive filter take less of a
toll than a cheap one?

No.

What are the considerations? Any recommendations?

Just get a cheap polarizer, to see whether you like the effect. If you
want a better one later, maybe with a better lens, get a multicoated
linear polarizer.

Anyone else posted to say that a linear polariser is a bad idea with an
autofocus / TTL metering body?

AFAIK, such bodies use beam splitters and so have to be used with circular
polarisers.

The beam splitter is partially polarizing. That's why a linear
polarizer might interfere. But the AE metering is affected at most
about 1 stop. Since the meter is not perfect anyway, I might want that
1 stop exposure bracketing. And under certain circumstances (color,
angle, ...), circular polarizer will have exact the same AE problem as
linear polarizer.

For AF, the differences between circular and linear polarizer is very
little.

And because of the partially polarizing beam splitter, with a circular
polarizer, sometimes the color effect I see in the viewfinder is
different from that the sensor records when the mirror gets out of the
way. I noticed this problem with circular polarizer and switched to
linear polarizer.

http://digitcamera.tripod.com/#slr