Filter question

[BostonBrother]

I have been looking for a polarizing filter for my 50mm lens and I have seen that there are a bunch of lenses for sale on ebay that average between 15 and 20 dollars for sets of three filters usually a uv, one for indoor lighting, and the polarized filter. I'm looking for opinions as to whether these filters are ok or just a waste of money.

 

[molsen]

probably cheap crap, honestly. you should plan to spend a pretty penny on a good polarized filter. I have a Hoya MC circular polarizer 52mm and 58mm neither was cheap but they're both great

i have http://www.adorama.com/HY52CPLM.html

http://www.adorama.com/HY58CPLM.html

 

[Rachelsne]

Mine wasnt to bad, I got it in Best Buy in the US, It was a sunpak circular polariser, it is $19.99 and is not bad for the price.

 

[molsen]

i would recommend getting multicoated filters. I used to think it wasn't necessary, but I found myself having to take the filters off anytime a light point was in the frame because of the ghosting. they're a little more expensive, but no ghosting with MC!

 

[kundalini]

Expect to pay $$$ for a good CPL. You are adding another piece of glass in front of your lens, why put a cheap one there?

Brands to have a look at are B+W & Hoya. Definitely get the multicoated.

 

[BostonBrother]

Thanks for the advice everyone. Your comments brought up another question however. I'll be using this filter on a 35mm SLR and now I am wondering if I should get the standard polarized filter or the circular.

 

[molsen]

for film, use a linear polarizer. for digital, use circular polarizer

 

[rmh159]

I'm fairly certain the circular will work best with the camera's metering. I know that's the rule of thumb for digital... not sure about film.

I did want to second the other posters as far as getting a good polarizer. The filter can be used (and probably should be used) for almost all outdoor shooting and it's affects can not be recreated in post processing.

I'd advise to go without a polarizer for awhile and save up the dough than to buy a cheaper one now.

 

[molsen]

keep in mind, however, most polarizers do filter out some light....usually 1/3 stop's worth or so

 

[Helen B]

There are very few reasons to choose a linear instead of a circular, so it is a safe bet to go for a circular polarizer. The type of sensitive medium does not matter, it is exposure and autofocus systems that may be affected by linear polarizers.

A perfect polarizer would lose one stop of light (ie one stop of randomly polarized light), real ones may lose a little more. I agree with the general advice to get a good one rather than a cheap one.

Best,
Helen

 

[Socrates]

for film, use a linear polarizer. for digital, use circular polarizer

Incorrect. Most late model film cameras must use circular polarizers. It has nothing to do with film vs. digital. It's related to the auto-exposure and auto-focus mechanism inside the camera.

 

[molsen]

Incorrect. Most late model film cameras must use circular polarizers. It has nothing to do with film vs. digital. It's related to the auto-exposure and auto-focus mechanism inside the camera.

i stand corrected, thanks

 

[Helen B]

i stand corrected, thanks

No problem. A lot of people find the circular vs linear thing confusing.

Best,
Helen

Edit: Maybe it's worth explaining the reason. Many SLR autofocus and TTL exposure systems are behind semi-silvered mirrors. The proportion of transmitted to reflected light depends on the polarization angle. They work properly with unpolarized light, but may not work with linearly polarized light, depending on what angle it is at. A circular polarizer gets round this by effectively depolarizing the light after it comes out of the linear polarizer* . The light isn't actually depolarized, it is circularly polarized, which is equivalent to an even distribution of polarization angles.

*a circular polarizer is a linear polarizer foil followed by a foil that turns linearly polarized light into circularly polarized light.

 

[BostonBrother]

Because I am using a manual focus camera, I think that I will get a linear polarized filter. However, I read on the specs for the Hoya filter that the filter factor changes as you rotate the filter changing the orientation of the lens to the light source. When using TTL metering I am assuming you wouldn't really need to give this much thought because the meter will be giving you a correct reading for a proper exposure. However, when you do not use the TTL metering is it very complicated to determine the correction that needs to be made for a correct exposure?

 

[Socrates]

Because I am using a manual focus camera, I think that I will get a linear polarized filter. However, I read on the specs for the Hoya filter that the filter factor changes as you rotate the filter changing the orientation of the lens to the light source. When using TTL metering I am assuming you wouldn't really need to give this much thought because the meter will be giving you a correct reading for a proper exposure. However, when you do not use the TTL metering is it very complicated to determine the correction that needs to be made for a correct exposure?

1. The filter exposure factor will change when rotating ANY polarizer. The very essence of a polarizer is that it blocks different amounts of light depending on it's position. There is no way around that. It's near impossible to figure out the correct exposure for any setting other than minimum and maximum.

2. As has been explained before, the problem is that most auto-focus AND auto-exposure mechanisms will not function properly with polarized light. That's why a circular polarizer is needed. A circular polarizer blocks the desired light and the remaining light is then "unpolarized" before hitting the camera's focus and exposure devices.

3. It's not a good idea to EVER buy a linear polarizer. Sure, you save a few dollars but I'll guarantee that next year you'll accidentally use it when you shouldn't.