CPL Question

Discussion in 'Photography Beginners' Forum' started by decado, Oct 24, 2009.

  1. decado

    decado TPF Noob!

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    I'm having a hard time seeing the change in the picture by turning the cpl, so I was wondering, can I just look at the histogram and turn the cpl until it shifts as far left as possible or what?
     
  2. Dao

    Dao No longer a newbie, moving up!

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    Look at the viewfinder while you are turning the CPL.

    Try it on your lcd monitor to see the effect first.
     
  3. decado

    decado TPF Noob!

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    I've tried both and I can't see any change, maybe my eyes just suck. I can definitely see change with the light meter though, which is why I was wondering if you want to turn the cpl until the meter is shifted furthest to the left.
     
  4. Stosh

    Stosh TPF Noob!

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    Just curious, why are you using the CPL? I ask because it's important to know what it's going to have an effect on so you can watch that in the viewfinder to see what's happening. If you're using it to darken a blue sky, you watch the sky. If you're using it to remove/reduce reflections from glass, water, or asphalt, then watch those areas to see when they're the darkest. If you're using it to get the richest fall foliage colors, watch the leaves - when they become their darkest the CPL is working the best. I'm not buying it that your eyes suck. If you can't see any difference, then the CPL probably isn't making a significant difference.

    To answer your question about watching the light meter, I don't know your camera or light meter, but generally yes, the darker, the more the CPL is working. But it's not that simple. You may be removing light from something other than what you're trying to remove it from (if that makes any sense). Seriously, I believe it's better to watch it live through your viewfinder. Every shot is different. Sometimes there's a huge difference depending on CPL orientation and sometimes there's zero difference. Go out on a clear day and point your camera somewhere at 90 degrees from the sun. Rotate the CPL quickly and watch the blue sky. You'll definitely see it.
     
  5. decado

    decado TPF Noob!

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    I was shooting plenty of times today at 90 degree angles to the sun with lots of water reflection, leaf reflection, and blue sky all at once, and I had a very hard time seeing change. I thought I saw very small changes but I couldn't really tell... It should be a fairly good cpl too, I have the hoya hmc cpl.
     
  6. Stosh

    Stosh TPF Noob!

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    Actually when you shoot a double whammy like you described (blue sky with water reflection) it's very possible that the CPL will work best on the sky in one position and work best on the water in another. Maybe this was messing you up? Other than that, all I can suggest is to turn the CPL quickly. This will make the changes more noticeable. You never mentioned anything about it, but don't use live view. It will compensate for the lower light and almost instantly adjust the exposure. Yes, there will be a change in contrast or reflections gone, but it's way easier to see it through the viewfinder.

    Just for silly - take your CPL off and take it outside and hold it in front of your eye. Then start twisting it and playing with different positions. It will have the same effect in front of your eye as it will through the viewfinder. Just don't let anyone see you doing it! Good luck.
     
  7. tirediron

    tirediron Watch the Birdy! Staff Member Supporting Member

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    Odd. I think the time of the day and conditions are important here. You say you were shooting at different times of the day. What times? A CPOL will have it's greatest effect when the sun is lower in the sky (early morning or evening) and almost zero around noon. If you have clouds or haze, they will lessen the effect as well.

    This image shows just how severe the effect of a CPOL can be when shot under ideal conditions.

    Go out early in the morning on a clear day, say an hour or less after sunrise, point your camera either at the southern or northern sky and slowly rotate the filter around. If you don't see anything then... you gotta problem.
     
  8. decado

    decado TPF Noob!

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    I was shooting all day from early morning on. According to Understanding Exposure midday is one of the best parts of the day to use a CPL because the suns always at a 90 degree angle to you. Clearly it's working, because as I watch the light meter the highlights get squished down and pushed to the left merging better with the darker light, I just can't physically see the change.
     
  9. Stosh

    Stosh TPF Noob!

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    Yes, that's correct. But in our northerly latitudes the sun is never straight up, but yes, the closer to straight up, the better for CPLs because everywhere on the horizon is 90 degrees to the sun.
     
  10. DennyCrane

    DennyCrane No longer a newbie, moving up!

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    Personally, I've found mid-morning and mid-afternoon best for a CPL. Pick a shoulder, put your arm straight out and rotate yourself until your arm is pointing at the Sun. This is the 90° they're talking about.
     
  11. Stosh

    Stosh TPF Noob!

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    That's a close approximation, but it's not totally correct. Think of a globe where the sun is directly above the north pole and you're also standing there (yes, I know this can't happen). 90 degrees is anywhere around the equator. Now move the sun to anywhere on the equator. Now 90 degrees from your perspective standing on the north pole is a half circle like a rainbow. If you did a cartwheel while looking at the sun on the horizon, your hands and legs would "draw" the 90 degree half circle. These situations are easy to picture. It gets a little more difficult to picture when the sun is at any other angle (like your mid morning or mid evening sun). If you used your 90 degree azimuth method, you're actually a little more than true 90 degrees from the sun. Again, 90 degrees is a full circle where every spot on that circle is 90 degrees from the sun. This is why when the sun is directly overhead, the 90 degree circle is the horizon.

    CPLs certainly work at positions other than 90, but they quickly loose any effectiveness when you go below 45 degrees (or past 135 degrees). Combine that with the fact that mid-morning and mid-evening light is much more pleasing and soft, you certainly can have great results at these times.
     

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