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is polarizing filter neutral density filter?
Are they the same thing? is there any degree of light they block?..

Comments (29)

You can use you PL as a ND filter. I think it reduces around 2 stops. If you want to reduce more than 2 stops then you will have to choose a ND 3 or ND 4..

The PL will also reduce reflection off any surfaces except metal. It is also handy when shooting through glass or water and it will also give you the saturated blue sky when shooting landscape..

New_type wrote:.

Are they the same thing? is there any degree of light they block?..

Comment #1

Can be used as a neutral density filter but sometimes alter the picture because of it's polarizer effect...

Comment #2

A polarizing filter removes that very subtle glare from a photo that your mind doesn't even recognize as glare. As a result the colors are deeper and more saturated with the white glare removed..

It also tends to act as an ND filter, but that is a side benefit/problem (depending on your needs)STOP Global Stasis! Change is good!.

Now that you've judged the quality of my typing, take a look at my photos..http://www.photo.net/photos/GlenBarrington..

Comment #3

Tocar wrote:.

Can be used as a neutral density filter but sometimes alter thepicture because of it's polarizer effect...

Comment #4

If it reduce the light by 2 stops, can you actually change the aperture or shutter speed to achieve the same result?..

Comment #5

STOP Global Stasis! Change is good!.

Now that you've judged the quality of my typing, take a look at my photos..http://www.photo.net/photos/GlenBarrington..

Comment #6

Yes..

Also, "crossing" 2 linear polarizers can be used to get almost any degree of "Neutral Density" you may want, up to almost total light cut-off..

You have to be careful to avoid "polarizing" effects that one or the other may introduce if you don't want those effects: ie, if you are taking "silky water" pictures and want some reflections from the surface to show..

-E.

Image control:Zoom outZoom 100%Zoom inExpand AllOpen in new window..

Comment #7

New_type wrote:.

If it reduce the light by 2 stops, can you actually change theaperture or shutter speed to achieve the same result?.

ND filters are for use when you don't want to or can't use a narrower aperture or faster shutter speed and the photo will be overexposed without a filter. For example, the soft look of a waterfall that requires an exposure of a few seconds, a shutter speed that is far too slow for most daytime photos. Or if you want to create blur of a moving object in good light without having the background overexposed..

I have heard that a polarizing filter reduces the light by only one stop, perhaps it depends on the filter. (I haven't actually tested mine) So you could use it at least as a 1 stop grad and also adjust it to give a polarizing effect (or not). But 1 stop is quite limited for photography that requires grad filters...

Comment #8

Lanef wrote:.

The PL will also reduce reflection off any surfaces except metal. Itis also handy when shooting through glass or water and it will alsogive you the saturated blue sky when shooting landscape..

Just to add about shooting landscapes with a polarizing filter, it may cause the sky to streak if you shoot really wide. I think if you shoot at 16-18 on a crop sensor DSLR, then you're OK. However, I'd avoid shooting at 12 mm or something if you're using a circular polarizer..

Comment #9

Http://www.lensmateonline.com/newsite/polarizer.html.

The sky after using filter is more blue, less light but how come the grass after the filter looks more bright, the rocks and the mountains as well?.

If it's suppose block light, wouldn't the whole picture looks darker?..

Comment #10

Wmsson wrote:.

New_type wrote:.

If it reduce the light by 2 stops, can you actually change theaperture or shutter speed to achieve the same result?.

ND filters are for use when you don't want to or can't use a narroweraperture or faster shutter speed and the photo will be overexposedwithout a filter. For example, the soft look of a waterfall thatrequires an exposure of a few seconds, a shutter speed that is fartoo slow for most daytime photos. Or if you want to create blur of amoving object in good light without having the background overexposed..

I have heard that a polarizing filter reduces the light by only onestop, perhaps it depends on the filter. (I haven't actually testedmine) So you could use it at least as a 1 stop grad and also adjustit to give a polarizing effect (or not). But 1 stop is quite limitedfor photography that requires grad filters..

I have tested mine with an incident meter, it does reduce by 2 stops, but I am not sure if it is standard...

Comment #11

Nawknai wrote:.

Lanef wrote:.

The PL will also reduce reflection off any surfaces except metal. Itis also handy when shooting through glass or water and it will alsogive you the saturated blue sky when shooting landscape..

Just to add about shooting landscapes with a polarizing filter, itmay cause the sky to streak if you shoot really wide. I think if youshoot at 16-18 on a crop sensor DSLR, then you're OK. However, I'davoid shooting at 12 mm or something if you're using a circularpolarizer.

You are right there, if you use PL with very wide angle lenses, you tend to get what is sometimes termed as the bowl effect...

Comment #12

New_type wrote:.

Http://www.lensmateonline.com/newsite/polarizer.html.

The sky after using filter is more blue, less light but how come thegrass after the filter looks more bright, the rocks and themountains as well?.

If it's suppose block light, wouldn't the whole picture looks darker?.

No, just your shutter speed or fstop will change. If your picture looks darker, it is more an exposure problem. When you loose 2 fstops, the camera will compensate by changing your shutter speed, two stops slower or it can be vice versa, it depends which exposre mode you are using...

Comment #13

Lanef wrote:.

New_type wrote:.

Http://www.lensmateonline.com/newsite/polarizer.html.

The sky after using filter is more blue, less light but how come thegrass after the filter looks more bright, the rocks and themountains as well?.

If it's suppose block light, wouldn't the whole picture looks darker?.

No, just your shutter speed or fstop will change. If your picturelooks darker, it is more an exposure problem. When you loose 2fstops, the camera will compensate by changing your shutter speed,two stops slower or it can be vice versa, it depends which exposremode you are using..

I mean if the filter block light, wouldn't it change the whole picture uniformly?..

Comment #14

New_type wrote:.

Lanef wrote:.

New_type wrote:.

Http://www.lensmateonline.com/newsite/polarizer.html.

The sky after using filter is more blue, less light but how come thegrass after the filter looks more bright, the rocks and themountains as well?.

If it's suppose block light, wouldn't the whole picture looks darker?.

No, just your shutter speed or fstop will change. If your picturelooks darker, it is more an exposure problem. When you loose 2fstops, the camera will compensate by changing your shutter speed,two stops slower or it can be vice versa, it depends which exposremode you are using..

I mean if the filter block light, wouldn't it change the wholepicture uniformly?.

It will change the exposure tandem SP/FS only...

Comment #15

New_type wrote:.

Lanef wrote:.

New_type wrote:.

Http://www.lensmateonline.com/newsite/polarizer.html.

The sky after using filter is more blue, less light but how come thegrass after the filter looks more bright, the rocks and themountains as well?.

If it's suppose block light, wouldn't the whole picture looks darker?.

No, just your shutter speed or fstop will change. If your picturelooks darker, it is more an exposure problem. When you loose 2fstops, the camera will compensate by changing your shutter speed,two stops slower or it can be vice versa, it depends which exposremode you are using..

I mean if the filter block light, wouldn't it change the wholepicture uniformly?.

I think I understand your question..

The CP filter blocks out polarized light. It doesn't affect non-polarized light. Light from the sky is non-polarized, while light reflected from a surface is polarized. Now, realize that some of the light from the sky actually IS polarized because light is reflected off air particles, vapour, clouds and other particles in the atmosphere and air. Because this haze no longer exists, your sky looks more blue..

The details in the mountains and rocks is greater; they aren't actually "brighter", but just more detailed and a higher contrast in these areas..

To answer your question about the grass in the front of the image, I'm going to take an educated guess. You're right about the CP filter. If the CP filter was blocking light, it would block out light uniformly. It does. But think about these 2 ways of thinking about the situation:.

(i) Your way of thinking about it:.

The CP filter is on the front of the lens, and it blocks 1 EV (ie: 1 stop) worth of light. You need 2x more light to get the same exposure as you would without a CP filter on. Why? Because the CP filter blocks out 1 stop worth of light..

(ii) The CP filter is on the front of the lens, and it blocks 1 EV (ie: 1 stop) worth of light. That's how much light the glass blocks. The filter is also filtering out the polarized light, and so the TOTAL amount of light lost is due to both the glass of the filter + the loss of the polarized light, which was filtered out..

Let's say that the exposure of the image decreased by 1 EV due to the glass filter, and lets say 2/3 EV due to the loss of polarized light. The camera's light meter will show that there's a -1 2/3 EV change in the light, and the camera's meter will recommend that you expose +1 2/3 EV more. This is to keep the same "overall" exposure..

So why is the grass lighter than before? Well, I think that while the loss of polarized light caused an "overall" (ie: average) exposure change of -1 2/3 EV, different parts of the image will experience a different amount of exposure change. After all, each part of the image produced a different amount of polarized light. For parts of the photo where polarized light was a large component of the light (eg: the sky), the loss of light may be as high as -2 1/3 EV. In other areas of the image, no light was lost due to the filtering because there wasn't much polarized light (ie: only a -1 EV decrease in light was seen because no polarized light was lost)..

Maybe the grass was the source of NO polarized light, so when the exposure was increased by +1 2/3 EV to compensate for the overall/average loss of light in the photo, the grass ended up with a greater exposure. Only a +1 EV increase in exposure was needed for the grass to have the same exposure, while a +2 1/3 EV increase in exposure was needed for the grass to have the same exposure. Since that's not possible, the grass was exposed properly, while the sky was less exposed and obviously darker..

This is also how ND gradient filters work, except in a much less obvious way...

Comment #16

Nawknai wrote:Only a +1 EV increase in exposure was needed for.

The grass to have the same exposure, while a +2 1/3 EV increase inexposure was needed for the **grass to have the same exposure. Sincethat's not possible, the grass was should be exposed properly, while the skywas less exposed and obviously darker..

**Change to "sky", and it'll hopefully make sense...

Comment #17

New_type wrote:.

Http://www.lensmateonline.com/newsite/polarizer.html.

The sky after using filter is more blue, less light but how come thegrass after the filter looks more bright, the rocks and themountains as well?.

If it's suppose block light, wouldn't the whole picture looks darker?.

First an answer to your original question ... No they are not the "same"..

It is true that a polarizer reduces light by 1.5 stops; but the unique features of a polarizer can sometimes ruin the desired image that a ND is useful for..

An example is the flowing water effect mentioned earlier; that effect relies on the reflected highlights from the water; and a polarizer's main effect is to eliminate those "reflections"..

In answer to your question above; the sky is not more blue because it is "darker", but because the "glare" from the sky is gone. That is indeed one of the more common uses of a polarizer, to make the sky look more blue..

The grass also appears darker because the "glare" is also gone from the leaves..

So a polarizer can make all colors look more "saturated"; (possibly a more accurate word than "darker").

A polarizer can also eliminate the reflections from windows, and allow you to see "into" water by eliminating the surface reflections..

A word on the proper use of a polarizer ... the effect is ONLY (or most pronounced) at 90 degrees to the sun. So there is no-effect when shooting either directly into or away from the sun. IF it is NOON time on a sunny day AT THE EQUATOR on the right time of year, (sun at high azimuth); the effect works all around the horizon..

BUT if the sun is on an angle, the effect varies. This can be very evident with a wide-angle lens; where part of the sky is "bluer" than other parts..

Thanks for reading .... JoePhoto.

( Do You Ever STOP to THINK and FORGET to START Again ??? )..

Comment #18

A polarizer will reduce the light getting into your camera just as a neutral density filter will. The key word though is neutral. The polarizer is not neutral as it affects the picture in other ways as well, which you may not want.Laurie Strachan..

Comment #19

JoePhoto wrote:.

New_type wrote:.

Http://www.lensmateonline.com/newsite/polarizer.html.

The sky after using filter is more blue, less light but how come thegrass after the filter looks more bright, the rocks and themountains as well?.

If it's suppose block light, wouldn't the whole picture looks darker?.

First an answer to your original question ... No they are not the"same"..

It is true that a polarizer reduces light by 1.5 stops; but theunique features of a polarizer can sometimes ruin the desired imagethat a ND is useful for..

An example is the flowing water effect mentioned earlier; thateffect relies on the reflected highlights from the water; and apolarizer's main effect is to eliminate those "reflections"..

In answer to your question above; the sky is not more blue becauseit is "darker", but because the "glare" from the sky is gone. Thatis indeed one of the more common uses of a polarizer, to make the skylook more blue..

The grass also appears darker because the "glare" is also gone fromthe leaves..

So a polarizer can make all colors look more "saturated"; (possibly amore accurate word than "darker").

A polarizer can also eliminate the reflections from windows, andallow you to see "into" water by eliminating the surface reflections..

A word on the proper use of a polarizer ... the effect is ONLY (ormost pronounced) at 90 degrees to the sun. So there is no-effectwhen shooting either directly into or away from the sun. IF it isNOON time on a sunny day AT THE EQUATOR on the right time of year,(sun at high azimuth); the effect works all around the horizon..

BUT if the sun is on an angle, the effect varies. This can be veryevident with a wide-angle lens; where part of the sky is "bluer"than other parts..

Thanks for reading .... JoePhoto.

( Do You Ever STOP to THINK and FORGET to START Again ??? ).

This one is basically correct. The polarizer blocks polarized light - that's why you see the bluer sky and such..

Grass & rocks also reflect glare and the filter can remove that, too, making the grass appear greener..

Ther have been some strange answers, above - even involving "Circular Polarizers"..

Please - forget that. A "Circular Polarizer" is a regular, linear polarizer with another layer added to make it slightly less effective, so some SLR's metering systems aren't fooled by the filter..

Do yourself a HUGE favor: go to a good Photography textbook, or even Wikipedia, and find out what polarization is all about..

And quit worrying about "Circular Polarizers" which are basically a gimmick unless you have the sort of SLR which just happens to need them..

Easiiest: get a linear (it may not say "Linear - it just won't say "Circular", and will cost less) polarizer that fits your camera (or any one, but it may as well fit). Then leave the camera at home and walk around, looking through the filter at various things, sky, grass in sunlight, store windows, smooth pondwater, even puddles. Turn the filter and observe what happens. Turn it - that's why it has a twistable front section, so it can turn while attached to your lens. Try it at different angles to the sun, too..

In a very short time, you will understand it far better than words can describe. Then go back, get your camera & take some pictures with the filter turned so as to darken the sky, or cut through thr reflection in a window, seen through the camera's EVF or LCD screen, so you 'see what the camera sees'..

And, yes, the filter is a slight 'Neutral Density", just because of how it's made. If you have 2 filters you will see how turning one in front of the other can block almost all of the light. The camera will take care of this since it measures the light through the filter..

Observation is best for this - enjoy!.

-E.

Image control:Zoom outZoom 100%Zoom inExpand AllOpen in new window..

Comment #20

Nawknai wrote:.

The CP filter blocks out polarized light. It doesn't affectnon-polarized light..

It does affect non-polarised light - that's the 'neutral density' effect that others have been talking about. In theory it could be as little as one stop but practical polarising filters are less efficient and two stops is common. This effect is normally regarded as undesirable - for most purposes we don't want to lose light - but it is unavoidable..

It has a much greater effect on polarised light (assuming the polariser is rotated appropriately), in fact it blocks it almost completely. But it's a relative thing - it blocks much more reflected, polarised light than ambient, unpolarised light, but it does block some of both..

However, if the polariser is rotated to the 'wrong' angle, it can actually let through *more* polarised light than unpolarised - thus *increasing* glare. This effect is only noticeable in extreme cases..

[big snip].

So why is the grass lighter than before?.

Partly it is as you said - the balance between lighter and darker parts of the image changes, so it can happen that the sky is darker and the grass is brighter, relative to one another. But there is another effect which can be very important - leaves are shiny wet surfaces (to a greater or lesser extent) and light reflected from them is polarised. The filter can reduce the reflected glare from the grass (which is actually a reflection of the sky) leaving it greener and more saturated. Technically it is not 'brighter' but it seems that way. It's a richer more vibrant green...

Comment #21

Good post from Erik - just one thing I would quibble with....

Erik Ohlson wrote:.

Easiiest: get a linear (it may not say "Linear - it just won't say"Circular", and will cost less) polarizer that fits your camera (orany one, but it may as well fit). Then leave the camera at home andwalk around, looking through the filter at various things, sky, grassin sunlight, store windows, smooth pondwater, even puddles. Turn thefilter and observe what happens. Turn it - that's why it has atwistable front section, so it can turn while attached to your lens.Try it at different angles to the sun, too..

The effect is exactly the same regardless of whether you use a linear or circular polariser. So find out what your camera needs and buy the right one - then do as Erik suggests. Also, if it's a circular polariser, try using it the right way round and backwards, and observe the difference. Experimenting without the camera is a great idea..

You can also experiment with two filters as at least one previous poster suggested. But for that to work the front one must be linear, and the back one whichever your camera requires..

It can be very difficult to find out whether a given model can use a linear polariser, but the problem of incorrect metering and/or focusing could theoretically occur with any autofocus SLR (film or digital) so unless you're very sure, or willing to take a chance, you'll need to opt for circular...

Comment #22

When a neutral density filter is used the whole picture is affected evenly. It just decreases light coming into the camera. There are different gradients (shades) of filters, light to dark, depends on how much light you want to block. You can also combine two filters to achieve the desired exposure. Some actually have two or three #1 neutral density filters..

A polarizer is dark and can be used as a neutral density filter but it might ruin reflective shots if not used correctly. A polarizer is only one gradient.. usually a #2.

There's always manual exposure or Av or Tv mode if you don't have a neutral density filter...

Comment #23

New_type wrote:.

Learned something new.

OK .... exactly WHAT did you learn ???.

Tell us everything you know now about polarizers .......

Thanks for reading .... JoePhoto.

( Do You Ever STOP to THINK and FORGET to START Again ??? )..

Comment #24

Hahaha.. As long as I know how to use a polarizer I don't have to know the dynamics on what it does and how it does it...

Comment #25

At the risk of hijacking the thread, would a skylight filter darken th sky but not the rest?..

Comment #26

Njlarry wrote:.

At the risk of hijacking the thread, would a skylight filter darkenth sky but not the rest?.

Not really..

A yellow, orange or red will do that - darken sky, but why bother, the same effects can be made with post-processing "filtration"..

-E.

Image control:Zoom outZoom 100%Zoom inExpand AllOpen in new window..

Comment #27

Steve Balcombe wrote:.

Good post from Erik - just one thing I would quibble with....

Erik Ohlson wrote:.

Easiiest: get a linear (it may not say "Linear - it just won't say"Circular", and will cost less) polarizer that fits your camera (orany one, but it may as well fit). Then leave the camera at home andwalk around, looking through the filter at various things, sky, grassin sunlight, store windows, smooth pondwater, even puddles. Turn thefilter and observe what happens. Turn it - that's why it has atwistable front section, so it can turn while attached to your lens.Try it at different angles to the sun, too..

The effect is exactly the same regardless of whether you use a linearor circular polariser. So find out what your camera needs and buy theright one - then do as Erik suggests. Also, if it's a circularpolariser, try using it the right way round and backwards, andobserve the difference. Experimenting without the camera is a greatidea..

You can also experiment with two filters as at least one previousposter suggested. But for that to work the front one must be linear,and the back one whichever your camera requires..

It can be very difficult to find out whether a given model can use alinear polariser, but the problem of incorrect metering and/orfocusing could theoretically occur with any autofocus SLR (film ordigital) so unless you're very sure, or willing to take a chance,you'll need to opt for circular..

Thanks, actually, we were discussing regular Panasonic cameras, not the more exotic SLR's. The OP's question was very basic, and I'm trying to help by cutting out a good deal of the confusion (to be kind) which has entered the thread, above. You obviously understand the subject better than some..

CP's aren't QUITE as good (basically, a wash) & are a good deal more expensive - I'd opt for the linear unless I really NEEDED a CP, on a particular type of SLR, and with such expensive equipment one should know what's needed..

-E.

Image control:Zoom outZoom 100%Zoom inExpand AllOpen in new window..

Comment #28

Erik Ohlson wrote:.

Thanks, actually, we were discussing regular Panasonic cameras, notthe more exotic SLR's..

We were? I don't see any reference to Panasonic cameras, anywhere..

The OP's question was very basic, and I'mtrying to help by cutting out a good deal of the confusion (to bekind) which has entered the thread, above..

All I've done is to respond to the points you (and one other person) raised - I haven't introduced anything new...

Comment #29

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This question was taken from a support group/message board and re-posted here so others can learn from it.

 

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