Does anyone use polarized lighting?

[tweatherred]

I am currently reading Light: Science and Magic (http://strobist.blogspot.com/2006/08/strobist-reader-favorite-light-science.html) and am really impressed. Definitely one of the better photography books I have come across. Anyway, one technique they mention is using a polarizing filter over the light source to control unwanted reflections; this causes all reflected light from that source to be polarized, so a polarizer on the camera will control all reflections, not just glare. It struck me as interesting, but even the authors say it is sort of a technique for last resort when other things aren't practical. Anyway, I wondered if anyone out there actually does this, or if it is one of those things that looks good in a textbook but does not tranlate well into the real world.

[PhotosGuy]

I've done it a few times in the past for very special situations, but found that I usually don't need or want to. Have fun with it.

[FlashZebra]

Polarized light sources are used in a great variety of scientific, technical, and specialized product photograph.

In addition, I think it is the underlying principal in some forms of 3D photography.

So, in a big picture it is used in general photography when needed.

I suspect that most on this list that want nice pics of their cat, their crazy uncle Marvin, their bride and groom clients, those ducks in the pond, or the hunk or babe down the street, polarized light sources hold little upside.

I suspect that it does "translate well into the real world". If it is used in a manner that leverages its positive attributes. But, if just used where these positive attributes provide no upside, why bother.

There are thousands of situations like this in photography. So why bother if it does not matter is very popular.

But, to directly answer you question, I have personally never used a polarized light source for photographing anything. But, I am aware of the potential and I think there I have some rolled up polarized sheet stock lurking somewhere in the house that I could press into service if necessary.

I also have many hand tools about that I have never used; my larger diameter pipe thread cutting dies come to mind. But who knows, possibly tomorrow I may need to cut a pipe thread on a larger diameter piece of pipe.

But, I am with the previous post.

"Have fun with it".

Knowledge is worth harvesting even if it is never used directly, or not used for a very long time.

Enjoy! Lon

[MaxZoom]

I understood polarising on the lens worked because non polarised light became partially polarised by a reflecting surface, less reflective surfaces polarised less so we can reduce the light from highly reflective surfaces a lot while only reducing the light from less reflective surfaces by a small amount. Did I get it wrong?

I've used pairs of polarisers to look at stress patterns in glass and clear plastics, there you polarise the light through the first polariser, the subject being examined twists the polarity differently in the stressed areas and when you observe this through a second polariser you get lovely coloured patterns which change in the stress areas as you apply more or less stress.

I'm not a physics guy and have not stayed in a Holiday Inn in years so this might all be nonesense :lol:

[tweatherred]

I understood polarising on the lens worked because non polarised light became partially polarised by a reflecting surface, less reflective surfaces polarised less so we can reduce the light from highly reflective surfaces a lot while only reducing the light from less reflective surfaces by a small amount. Did I get it wrong?

I've used pairs of polarisers to look at stress patterns in glass and clear plastics, there you polarise the light through the first polariser, the subject being examined twists the polarity differently in the stressed areas and when you observe this through a second polariser you get lovely coloured patterns which change in the stress areas as you apply more or less stress.

I'm not a physics guy and have not stayed in a Holiday Inn in years so this might all be nonesense :lol:

You've got the role of polarizers partially right; the book I cited goes on to add that not all reflections are polarized (for example those from mirrors or metals) and many reflections are a mixture of polarized and nonppolarized light. If you want to minimize non-polarized reflections on an object but due to physical contstraints (such as the room is too small or ceiling too low) you are unable to position your lights to avoid reflections, you can polarize the light source which will them polarize the reflections, allowing them to be controlled with a polarizing filter on the camera. I thought it sounded interesting and wondered if anyone actually used the technique. It is also worth noting that there is a significant loss of light.

As far a more specialized uses of polarized light, yes, there are some beautiful scientific photographs out there using those sort of techniques; crystals and soap bubbles/films come to mind. I have learned the hard way about polarizers and plastics. On a recent trip to the Atlanta Aquarium I took a bunch of pictures, but most of the ones taken through the acrylic walls of the tanks had an annoying iridescent sheen. I was using a polarizer based on some old advice for avoiding reflections in glass aquariums, but it didn't work so well for plastic.

[tweatherred]

Another related question; does anyone know if the polarizer on the light source should be a circular polarizer to preserve AF function?

[chtgrubbs]

I have used polarized lighting for copying paintings. Oil or acrylic paintings that have alot of surface texture will get reflective highlights on them. Cross polarization will allow you to remove all the highlihts and will increase the color saturation. I have also used it to photograph small reflective objects when I wanted to show all the color and detail without getting any highlight reflections. You don'[t need CP for the light source.

[FlashZebra]

Another related question; does anyone know if the polarizer on the light source should be a circular polarizer to preserve AF function?
With many modern cameras, including all of the Canon DSLRs, the need for a circular polarizer is not because of autofocus.

But, to work properly on Canon DSLR cameras (and many other cameras) the light metering system does require a circular polarizer.

I strongly suspect that part of the metering system is behind a partially silvered mirror that creates this need (light through a partially silvered mirror is polarized after it is transmitted). Others on the list are likely to know the exact dynamics of the metering system attributes.

So, in a Canon DSLR it is typically the metering system feature, not the autofocus feature that requires the use of a circular polarizer for proper function.

I have found that relating the need for circular polarizers to autofocus very pervasive, but typically incorrect.

There may be a few cameras where the dynamics of the autofocus require a circular polarizer, but I am not aware of any, and I suspect that they are not very common.

But, cameras that require a circular polarizer due to the attributes of the metering system are extremely common.

Enjoy! Lon

[tweatherred]

With many modern cameras, including all of the Canon DSLRs, the need for a circular polarizer is not because of autofocus.




Thanks for correcting my misconception. I knew it was one or the other but guessed wrong.

Thanks everyone else for some interesting replies, too.

[MaxZoom]

Thanks everyone. Most informative, I just love this forum we all know something and when we share it its awsome. :D

[Jon]

With many modern cameras, including all of the Canon DSLRs, the need for a circular polarizer is not because of autofocus.

But, to work properly on Canon DSLR cameras (and many other cameras) the light metering system does require a circular polarizer.

I strongly suspect that part of the metering system is behind a partially silvered mirror that creates this need (light through a partially silvered mirror is polarized after it is transmitted). Others on the list are likely to know the exact dynamics of the metering system attributes.

So, in a Canon DSLR it is typically the metering system feature, not the autofocus feature that requires the use of a circular polarizer for proper function.

I have found that relating the need for circular polarizers to autofocus very pervasive, but typically incorrect.

There may be a few cameras where the dynamics of the autofocus require a circular polarizer, but I am not aware of any, and I suspect that they are not very common.

But, cameras that require a circular polarizer due to the attributes of the metering system are extremely common.

Enjoy! Lon
Actually, the AF mechanism, in the bottom of the mirror box, is behind the partially-silvered main mirror in EOS SLRs. In the classic FD Canons (F-1, FTb, FT) the meter received its light from a partially-reflective mirror in the focussing screen, and Canon recommended circular polarizers there. Current Canon exposure metering relies on direct readings of the focussing screen by strategically placed photosensors; it's possible that they're behind partially-silvvered areas of the pentaprism, but typically they've been positioned around the viewfinder eyepiece and haven't been behind any of the reflective areas.

Attached clipping from Canon's D60 parts list shows the location of the SPC metering cells (CG1-3798) relative to the eyepiece (CG1-3797). CG1-3795 is the AF assembly.