Probably extremely newb question, but

Maestro

a few months back I purchased a Sigma 500mm that I pair with with my Wimberely set-up. Except for the weight I have been very happy with the results. However, there a quite a few times when I have tough time getting the exposure (and this may be more a camera setting than lens question). In reading the information provided by Sigma it states that the lens should be used with the polarizing filter that came with the lens. I had originally taken it out when I noticed my images were a bit underexposed and replaced with the clear UV filter that also came with the lens.

My question is this: The filter is a drop-in and rotatable. What does rotating the polarizing filter do? I have checked for info at Sigma's site and I came up empty handed. I have never worked with filters before so any info would be appreciated or just a link to info. Thanks in advance.

Maestro

Maestro wrote:

a few months back I purchased a Sigma 500mm that I pair with with my Wimberely set-up. Except for the weight I have been very happy with the results. However, there a quite a few times when I have tough time getting the exposure (and this may be more a camera setting than lens question). In reading the information provided by Sigma it states that the lens should be used with the polarizing filter that came with the lens. I had originally taken it out when I noticed my images were a bit underexposed and replaced with the clear UV filter that also came with the lens.

My question is this: The filter is a drop-in and rotatable. What does rotating the polarizing filter do? I have checked for info at Sigma's site and I came up empty handed. I have never worked with filters before so any info would be appreciated or just a link to info. Thanks in advance.

Here are some example pics. I did no processing. These are directly from the RAW file.

All were shot at F5.6 ISO 200.
The first one is with the filter orientated in the middle position.



Filter rotated 1/3 tick to right



Filter rotated 1/3 tick to left



Filter rotated 1/4 to right


Filter rotated 1/4 to left


It would seem that ticks to the right make the shot darker and ticks to the left make the shot brighter meaning that in harsh light I should move the filter to the right and in lower light I should move the filter to the left. Does this make sense with the assumption that I am using the filter correctly?

Maestro

I finally found an article.
Apparently depending on your orientation to the sun when taking the picture, the filter will have more effect on the picture. The article I found stated that when the sun is high, the filter will not filter much light but when it is low either in morning or evening, the photographer needs to try to place him or herself at somewhere between 0 and 90 degrees from the sun to take the picture to achieve maximum effect. I think I will forgo the triangulation and just play with rotation of the filter to see if I can find the desired outcome I want.

Any other advice would be appreciated.

Icebear

Forgive me
I don't mean to insult, but your question leads me to believe that you have no idea what a polarizing filter does. Rotation is EVERYTHING. If you Google for how a polarizing filter works, a lot of your puzzlement will become clear. The polarizer filters reflected light depending on the angle the light enters it. Don't take my explanation as anything more than a gross oversimplification, but a polarizing filter is like no othr filter you can put on your lense.

Maestro

Edit: Deleted long response; not worth it.

Pathfinder, the description of the forum says from beginner to advanced techniques. Apparently, I need to be knowledgeable before I ask a question, but if I were knowledgeable, I wouldn't need to ask. Anyhow, delete the thread or move it to the appropriate forum.

pathfinder

Stephen, your question was fine. You have posted enough here on dgrin that you are not a newbie. You just missed a small piece of information about how polarizers work.

The description of what a polarizer does is long and wordy, but pretty easy to see if you understand a little about how it works. Sunlight is polarized light - that is to say the vibrations of the photons are in a unique plane - a polarizer only allows light to pass that is vibrating in the plane the polarizer permits, thus a polarizer will make skies 90 degrees to the suns axis darker and deeper colored, and will decrease the glare of reflected light - like from water on vegetation.

Spend a little time looking through your lens with the polarizer as you rotate it and you will quickly see the effect. The cost is from 1/2 to about 1 2/3 stops of light. I rarely use a polarizer with a long telephot because the light cost is usually to high when shooting wildlife.

Go to Wikipedia to look up polarizers and you will learn much more.

Maestro, you and your questions are always welcome here.

wxwax

Hi Stephen, the other thing is that you don't want to leave the polarizing filter in all the time.

It's a specialty filter. Under certain conditions (i.e. with the sun at your back) it can enhance the vividness of colors when outdoors, and cut through haze and reflections.

But it's not an everyday filter. If the sun's not in the right position, you can end up with bizarre effects. Look at how inconsistent the sky is in this shot, for example.

pathfinder

Waxy's comments are very pertinent about the use of polarizers with wide angle lenses, which is due to the different angles to the sun across the field of view of a lens wider than about 28mm. You will NOT see this phenomenon with a 500mm lens and a polarizer.

The real use of a polarizing filter and a 500mm lens would be shooting surfers across the water or wildlife in the forest with wet leaves, with the sun at 90 degrees to the right or left of the axis of the lens.

henryp

Maestro wrote:

In reading the information provided by Sigma it states that the lens should be used with the polarizing filter that came with the lens. I had originally taken it out when I noticed my images were a bit underexposed and replaced with the clear UV filter that also came with the lens.

You may want to double check the instructions. Most long tele lenses which use rear drop-in filters want something there for the optical path and to keep the filter slot from becoming a portal for dust, but I doubt very much the instructions specify you should keep the pol filter in regularly.

My question is this: The filter is a drop-in and rotatable. What does rotating the polarizing filter do?

Pol filters reduce non-metallic reflections. The quantity of the effect you'll see depends a lot on the angle of the sun to your subject. They're often used to dramatize the blue sky against white clouds, but they can also be used to reduce the reflections on shiny leaves and the surface of water.

You can see the effect by holding the filter in front of your eye and rotating it and you should see substantially the same effect looking through the camera finder while rotating the filter in the lens.

My advice is to play with it, but I would NOT leave it in the lens all the time. As someone else said -- you use it when you want the pol effect.

Now, since you admit to being a filter newbie, here's some more confusion. You have a round filter. That refers to its physical shape. You have a rotating filter. That means you can rotate it to change the amount of the pol effect. You have a circular pol filter. This has nothing to do with shape or rotating ability, but refers to the method by which the filter polarizes light. In general modern auto-focus / auto-exposure cameras require a circular pol filter to operate correctly. Older cameras used linear (a/k/a "top") pol filters. Newer cameras have pol material in the light path and if you added a 2nd linear pol filter to the light path you could rotate it so all visible light is blocked. A circ pol filter lets you add the pol effect to your images w/out risk of the two filters (yours and the one permanently in the camera) to conflict.

All pol filters absorb between 1 & 2 stops of light which may be why your images are a bit underexposed, but your camera's light meter should be compensating for the filter. Then again it's worth remembering that digicams have about the same exposure latitude of slide film, which is much narrower and less forgiving than negative film, so exposure accuracy is important.