Go Back   Steve's Digicams Forums > Post Your Photos > Biweekly Shoot Out

Reply
 
Thread Tools Search this Thread
Old Jun 13, 2011, 10:45 PM   #1
daz
Senior Member
 
daz's Avatar
 
Join Date: Apr 2005
Posts: 436
Default Polarizer – Crossed.

Mtngal in her detailed post on polarizers should what happens if you crossing them. As this is something that takes the right photo to show and I have not had time to set this up I had to go into my archives for this one.

I wanted to take a photo of this bridge with no cars or people on it in daylight. As this bridge just about always has car on it I need to use some tricks. First I took a photo with a lens to test what I wanted to do. I decided I needed a shutter speed of about 3 sec and I wanted the f-stop to be about 5.6. This works out to 4 stops. From the test lens the AOV worked out that I could use a 77mm lens. This is good as I only have 2 lenses that use the correct size polarizers and 77mm is one of them. (I also used 9 in camera blended photos but that is a different subject).

Most of the polarizers I have are circular but I have one older liner polarizer. To do this you need at least one liner polarizer. First you have to focus, as it will get to dark to do this later. Then you start by putting on the circular polarizer next to the lens. Turn it to get the effect you want (if any). Then (holding the first so it will not turn) put the liner polarizer in front of that. When you turn the liner polarizer (holding the circular polarizer so it will not turn) so that it is crossed to the other polarizer it will darken as shown by Mtngal. This is not perfect as you will get a color shift the farther you go and you will also get some loss of color and contrast. At about 4-6 it is usable and you can get about 9-10 stops but you will have a lot of color shifting to work with.

Why the circular polarizer and then the liner polarizer? Or for that matter why a circular polarizer at all? In modern digital camera we have come to like (depended upon?) auto focusing and metering. Some of the parts in the camera that do this may, depending on how they are designed, behave like a polarizer. If you use a liner polarizer and the sensor in the camera is sensitive to polarized light then if you turn the liner polarizer so it lines up you could get the sensor to read the light incorrectly. This is hard to know when you are doing this and it would look like an intermittent problem. Intermittent problems are the hardest to see and know what the problem is so most just recommend using a circular polarizer. How is a circular polarizer different? A circular polarizer is a liner polarizer in the front part. So you can get the effect of the liner polarizer but behind it is a layer that turns the polarized light back in to the random (circular) polarized light but the first part has already filtered the light so you still get the polarizing effect.

Now if you put the circular polarizer in front of the liner polarizer no matter how you turn it you won’t see much of anything because the circular polarizer has turn the light back into the random (circular) polarized light but if you put the liner polarizer in front you can cross them and block the light. You could also turn the circular polarizer around and do this (you can even do this with 2 circular polarizer) but there is no way to screw them together this way.

The first photo is the test photo (no polarizer) and the second the photo (crossed polarizers) with no cars.

DAZ
Attached Images
  
__________________
Painting is an additive art. The artist adds to the canvas until they stop with their version of reality. Digital photography is subtractive art. First we throw away 90 percent of reality then remove what is left bit by bit until we have only the reality we wish to show. Flickr is like fun. PPG is like work. A camera is a machine of light and time with the purpose of capturing a luminous moment. Like the eye it is a tool of the mind.
daz is offline   Reply With Quote
Sponsored Links
Old Jun 14, 2011, 8:29 AM   #2
Senior Member
 
mtngal's Avatar
 
Join Date: Nov 2005
Location: Frazier Park, CA
Posts: 16,044
Default

Arrrgh! You would have to bring up this brilliant idea that I hadn't thought of doing on a day when I don't have my tripod with me. This is definitely something I'd like to play around with (though the only two polarizers that I have the capability of putting on one lens are both linear, but that should be all right from what you wrote). I've recently been doing a fair amount of b&w conversions, so the color shift wouldn't matter at all.

Thanks for an absolutely wonderful idea, something I hadn't thought about at all.
mtngal is offline   Reply With Quote
Old Jun 14, 2011, 6:51 PM   #3
daz
Senior Member
 
daz's Avatar
 
Join Date: Apr 2005
Posts: 436
Default

Quote:
Originally Posted by mtngal View Post
Arrrgh! You would have to bring up this brilliant idea that I hadn't thought of doing on a day when I don't have my tripod with me. This is definitely something I'd like to play around with (though the only two polarizers that I have the capability of putting on one lens are both linear, but that should be all right from what you wrote). I've recently been doing a fair amount of b&w conversions, so the color shift wouldn't matter at all.

Thanks for an absolutely wonderful idea, something I hadn't thought about at all.
Thanks, but you took my wide idea so that make us even.

DAZ
__________________
Painting is an additive art. The artist adds to the canvas until they stop with their version of reality. Digital photography is subtractive art. First we throw away 90 percent of reality then remove what is left bit by bit until we have only the reality we wish to show. Flickr is like fun. PPG is like work. A camera is a machine of light and time with the purpose of capturing a luminous moment. Like the eye it is a tool of the mind.
daz is offline   Reply With Quote
Old Jun 14, 2011, 11:15 PM   #4
Moderator
 
selvin's Avatar
 
Join Date: Aug 2002
Posts: 7,204
Default

Daz,
Dazlling display of how polarizers work!
Couldn't help myself by the way...

Selvin
selvin is offline   Reply With Quote
 
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -5. The time now is 1:26 PM.