polarizers

[bob*donna]

What is the difference between circular and linear? I know linear is used for manual focus while circular is used with either auto or manual. Is there any other difference? Also, is there a polarizer that does not spin? If so I'd love to know where to get one!

 

[Overread]

Far as I know linear will work on any camera; but will mess up auto-focus on digital cameras and any film camera which had autofocus features in it. Circular, however, retains all the auto-focusing features.


AS for one that doesn't spin why would you want one like that? Most of the time the spin is tight neough that they won't "flop" around spinning on their own; and the scenes and lighting angles are such that being able to vary the angle of polarization is important.

 

[Alexr25]

In auto focus cameras beam splitters are used direct portion of the incoming light to the autofocus module. A side effect of using a beam splitter is that they polarise light so if you were to use a linear polariser on the lens you could end up with the lens polariser and the beam splitter cross polarised and no light going through to the auto focus module.

Using a circular polariser prevents this from happening.

A circular polariser is simply a linear polariser backed by a 1/4 wave plate, which converts linear polarisation to circular polarisation. In use the linear polariser section of the filter cut reflections, darkens sky and does everything else that a normal linear polariser does then the 1/4 wave plate converts the light to circular polarisation which the beam spitter passes as it would normal un-polarised light so that that auto focus module can do its work.

 

[bob*donna]

"AS for one that doesn't spin why would you want one like that? Most of the time the spin is tight neough that they won't "flop" around ....."

well Overread I'll tell you why.....

I would want one for shooting at water only or sky only or a photo that is shot thru glass and these items take up the WHOLE frame!!!! Why would I want to shoot a photo where the sky takes up the WHOLE frame using a circular polarizer?? In my opinion it would look pretty stupid if the sky was half polarized and half not. Don't you agree?

 

[480sparky]

"AS for one that doesn't spin why would you want one like that? Most of the time the spin is tight neough that they won't "flop" around ....."

well Overread I'll tell you why.....

I would want one for shooting at water only or sky only or a photo that is shot thru glass and these items take up the WHOLE frame!!!! Why would I want to shoot a photo where the sky takes up the WHOLE frame using a circular polarizer?? In my opinion it would look pretty stupid if the sky was half polarized and half not. Don't you agree?

But........... one needs to spin the filter in order to orient it correctly so it will actually have the desired effect on the image. Polarizers aren't just grey-looking filters that work no matter how they're placed on the lens. Rotating them is essential in making them work.

 

[fjrabon]

"AS for one that doesn't spin why would you want one like that? Most of the time the spin is tight neough that they won't "flop" around ....."

well Overread I'll tell you why.....

I would want one for shooting at water only or sky only or a photo that is shot thru glass and these items take up the WHOLE frame!!!! Why would I want to shoot a photo where the sky takes up the WHOLE frame using a circular polarizer?? In my opinion it would look pretty stupid if the sky was half polarized and half not. Don't you agree?

wait, what do you think a circular polarizer does?

 

[Overread]

Bob from what you say I think you've possibly mixed up polarizers with Neutral Density Filters (and possibly Variable Neutral Density Filters).

Now its true that a polarizer, as well as stopping reflections from non-metallic surfaces, will also stop around 1 to 2 stops of light (varies somewhat and 1.5 is normally a good rough ballpark for most). They are not the same.

Neutral Density filters will block a set amount of light in stops (depending on the power of the filter you get); they also come in variable versions where you get a variation on the filter. This variation comes in soft and hard gradients; the soft being a gradual increase in light blocking whilst the hard is a sudden shift (typically over the middle of the filter).

For what you say you might want to look into something like Lee Filters. These are square (or rectangular) shaped filters that go into a filter holder which holds the filter infront of the lens. The idea being that this allows you to vary the position of the filter independent of the lens.
With a screw in circular filter something like the variable version would have the dividing line always in the middle of the frame; but you might want a shot with 3/4 sea and 1/4 sky. The filter holder setup allows you to do this since you can lift the filter up or down in the holder so that its only blocking light from part of the frame. Most holders also let you put several different filters into the holder at once (sometimes requires an expansion upgrade to the holder). Thus meaning you can add-up different filters to increase the light blocking

 

[Derrel]

"AS for one that doesn't spin why would you want one like that? Most of the time the spin is tight neough that they won't "flop" around ....."

well Overread I'll tell you why.....

I would want one for shooting at water only or sky only or a photo that is shot thru glass and these items take up the WHOLE frame!!!! Why would I want to shoot a photo where the sky takes up the WHOLE frame using a circular polarizer?? In my opinion it would look pretty stupid if the sky was half polarized and half not. Don't you agree?

I don't agree with this, but then again, I own a bunch of polarizing filters...

Anywayyyyyyyyyy. Be aware that polarizing of blue sky tones looks a bit uneven on wider-angle shots. If you want to make shots where the sky looks half-polarized and half-not, shoot at really short focal lengths!

And look into graduated neutral density filters for landscape work. There are some good articles on the web discussing use of hard-edged and soft-edge neutral density filters.

 

[D-B-J]

Neutral Density Filters and Why You Need Them for Landscape Photography Red Skies Photography

As some have mentioned, the leefilters system is likely the most versatile system out there. I've recently added their circular polarizer to my kit and haven't yet updated that blog post to include that filter (as I wanted to properly run it through its paces before reviewing it. Check out that article for a pretty comprehensive overview of the Lee system.

Jake


Sent from my iPhone using Tapatalk

 

[bob*donna]

Overread Thanks for the writeup and telling me about the Lee filters. Unfortunately I cannot afford such luxuries! And no I am not confusing ND filters with polarizers. I work with ND filters a lot with waterfalls.

 

[480sparky]

..... And no I am not confusing ND filters with polarizers......

Then what would be the advantage to a polarizer that doesn't rotate?

 

[petrochemist]

..... And no I am not confusing ND filters with polarizers......

Then what would be the advantage to a polarizer that doesn't rotate?

There isn't one.

 

[bob*donna]

There would be an advantage!! I love to take photos of clouds with nothing in the photo but clouds and blue sky. Why would I want half the sky dull and the other half a beautiful blue?

 

[astroNikon]

Keep in mind. If you had a polarizer that did not rotate then when you screwed it onto your lens the horizon of the filter would be solely dependent upon where it ended up screwed on to the lens. And some lenses rotate and other do not when you zoom/focus so it could go round and round as you zoomed in/out. So you'd be stuck unless you screw it on/off to rotate it sans it falling off.

Otherwise, a rotating polarizer is a good thing as the base is solidly on the lens and you rotate the outer part of the polarizer.

 

[petrochemist]

"AS for one that doesn't spin why would you want one like that? Most of the time the spin is tight neough that they won't "flop" around ....."

well Overread I'll tell you why.....

I would want one for shooting at water only or sky only or a photo that is shot thru glass and these items take up the WHOLE frame!!!! Why would I want to shoot a photo where the sky takes up the WHOLE frame using a circular polarizer?? In my opinion it would look pretty stupid if the sky was half polarized and half not. Don't you agree?

It would look odd. that's why most people avoid using a polarizer on UWA shots. As some parts of the light are coming from very different angles this gives different degrees of polarization.
The filter behaves the same across the WHOLE frame, which is just how they are normally wanted.
There may be rare occasions where you might want to polarize different parts of your image in different directions (the sky one way & reflections the other) if so I don't know of any system that can do it without combining multiple shots in post.