Polarizer Question

[Vertabreaker]

So whenever im using my polarizer around a bright light source I get a green spot in the shot. Can anyone tell me what im doing wrong.

thx

[hmhm]

Can you post a sample?

Maybe lens flare?
-harry

[Vertabreaker]

This isnt the greatest example of what happens but since im at work this will have to do. On the righthand side you can see the spectrim, that is from the full moon. I also took a few of the moon(when i get home ill see if i still have any) and i would get a green spot in the shot. I have also had the same problem when I try to put the sun in my shots with the polarizer. Like I said if you need better examples I will look for some when I get home later.

http://www.vertabroken.com/Landscape/Small/sLandscape%2008.jpg

[robertwgross]

I see what seems to be lens flare on the right. Then some other spots might be either lens flare or else dust on the sensor.

---Bob Gross---

[Vertabreaker]

Is the what lens hoods are use for, to cut down flare?

[Malaxos1]

Wht brand filter are you using? Is it multicoated?

[RichardtheSane]

Vertabreaker wrote:
Is the what lens hoods are use for, to cut down flare?
Basically yes.
Hoods are there to stop any unwanted light from entering the lens, and flare is caused by unwanted light.

[Vertabreaker]

Malaxos1 I have no idea.

Thanks for the help guys Ill look into getting a hood.

[Malaxos1]

Multi coating is a must, as is getting a good quality filter. The camera is only as good as the glass in front of it is. You could get a gret $1500+ lens and ruin your photos buy using a cheap filter. I would get a hood if you don't have one, but if you are using cheap glass it woun't help with the problem...Dean

[rdenney]

Vertabreaker wrote:
Is the what lens hoods are use for, to cut down flare?

Yes.

The objective of a lens hood is to make sure that a strong light source (such as the sun) doesn't shine on the front lens surface. When it does, then it refracts in all sorts of visible ways, and it also illuminates any dust or film that's on that surface.

Note that when you use a polarizer, you have replaced a relatively small front element with a much larger one, and also it is right on the very front edge of the lens. So, a lens with a polarizer is harder to shade than a lens without one. The shade is therefore even more important.

But I'm wondering something else about your image. Look at the filter very carefully, and see if there is any sort of a chip in the glass along the edge. If so, it will do all sorts of unhappy things like what you are seeing.

I have used a polarizer intended for large medium-format cameras (it's 95mm) on my 10D lenses. I've just hand-held the filter in front of the camera. The trick is to make sure it's turned the right way, of course, and to also make sure it is effectively shaded. You can shade it with your hand if necessary--sometimes the hood isn't enough.

Canon hoods are nice in that they fit over screw-in polarizers, allowing you to turn the polarizer without messing with the hood.

Rick "a strong proponent of effective lens shades" Denney

[Vertabreaker]

Please dont yell still very much the noob.

Turn the polarizer? I noticed that the front moved but I dont know why. My guess now its an adjustment of somekind.

[vvizard]

Yes it's an adjustment. Here's a secret tip I've learned. Get another one, and screw it on in front of the one you already have ;) If your pictures turn out .. uhm.. black, try to turn a bit on them. This will probably give you a good clue of what the polarizer does.

And to save you from buying another one, I will try to give you my newbie-facts on what it does. It blocks off light coming from direction-X. So when you turn it, you change the angle that it will block light from. Put two in front, turn them in the right position, and the second will block out the angles the first one let's through, giving you a nice pitch-black picture :)

At least that's the impression I have gotten on how they work. They might not be correct, so hopefully some more enlightend souls here, will tell us what you don't know, and correct me on what I think I know :) Discussion-forums are great :) Can't possible understand how I survived my first year of photo without "hanging" in one. All the things I could have learned that year :/

[DAMphyne]

Mike,
vvirzd is right, the polarizer blocks light coming from a particular direction, the physicist could explain it better.
Try this, focus on a window during the daytime(outside), then turn the filter, you will see the reflections get less prominant. That is what the polarizar is for, to change the light entering the lens.
If you use the polarizar when shooting landscapes, it can help make the colors more vibrant looking, because it changes the light going to the lens.
You'll be suprised how much haze and reflection can be removed from your photo. Even leaves cast a reflection, you may have to adjust it for each shot.

[robertwgross]

damphyne wrote:
vvirzd is right, the polarizer blocks light coming from a particular direction, the physicist could explain it better.


It would be better to say that it can block all or part of the light with one polarization, not direction.

The easy way to think about it is this:
Imagine a bright light straight ahead of you, pointed your way. Now suppose that some of the light is composed of some light waves that are wiggling up and down as they approach. Now suppose that some other of the light is composed of light waves that are wiggling right and left as they approach. Got that?

The polarizer has an alignment, so it will let all the waves pass that are aligned with the polarizer, either the right-left light, or the up-down light. By turning the polarizing filter on the front of the lens, you can block the light of one polarization and pass the light of the other. Sunlight that reflects off something shiny gets a new polarization angle, so reflections can be blocked with the polarizer if you turn it just right.

---Bob Gross---

[Webster]

It blocks off light coming from direction-X. So when you turn it, you change the angle that it will block light from.


Not so. A polarizer allows light in from every direction. It's the direction each light wave is "wiggling" that's important. That's obviously a gross simplification, but it gives the basic idea. Light waves (when light is waves and not particles, that is) vibrate in a limited number of ways, called polarities. Light coming from a light source has waves of all polarities. Light that is reflected has waves consisting of a limited number of polarities. The reflecting object absorbs most. A polarizer eliminates waves of certain polarity, and allows all others to pass. When that "all others" is rich in polarities, the effect is negligible. But when the light is polarity poor - as is light reflected from certain objects, eliminating any at all has a great effect. Light reflected from air is highly polarized, so the more light in the sky is reflected (as in the further it is away from the sun) the greater the effect of a polarizer. Other objects reflect light with varying degrees of polarization, and are affected to a corresponding degree by the polarizer.

[robertwgross]

Webster, I think that it is at this point that we need to stop the physics discussion. If we go into wave theory versus particle theory, then all of the eyeballs will glaze over.

---Bob Gross---