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Shield bug, crossed polarized light

 
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Charles Krebs



Joined: 01 Aug 2006
Posts: 5805
Location: Issaquah, WA USA

PostPosted: Sun Oct 24, 2010 8:19 pm    Post subject: Shield bug, crossed polarized light Reply with quote

Thought I would post these in this section as they were really "test" shots.

This shield bug is very reflective. I have a 12" x 12" sheet of polarizer material. This was positioned over the subject (resting on top of a white "U" shaped frame). That was then covered with sheet of Lee diffusion material. A single flash was used above this. A polarizing filter was used on the Canon 65mm MPE.

These two shots were maximum "extinction". Actually for serious picture taking it probably would be better to allow a little more "glare" to show through... this gets a little too "flat" (you really want to retain some sense of the shiny surface), and the colors can actually get too intense (I had to tone down the red in the first shot). But there's no doubt that properly "set", polarization can be used with diffuse light to good effect.




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svalley



Joined: 03 Dec 2006
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Location: Albany, Oregon

PostPosted: Mon Oct 25, 2010 9:03 am    Post subject: Reply with quote

Charlie,

This is an interesting technique. Are you using it to only get rid of glare and blown highlights or also the "black hole" (reflection of lens)?

Was the polarizing filter used on the lens circular or linear?

Steve
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Craig Gerard



Joined: 01 May 2010
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Location: Australia

PostPosted: Mon Oct 25, 2010 5:06 pm    Post subject: Reply with quote

Thanks for sharing this Charlie. Smile

OK,
Who else is currently making "U" shaped sandwiches out of sheets of diffuser and polariser?

I confess

Craig
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AndrewC



Joined: 14 Feb 2008
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Location: Belgium

PostPosted: Sun Nov 07, 2010 3:40 pm    Post subject: Reply with quote

Craig Gerard wrote:
Thanks for sharing this Charlie. Smile

OK,
Who else is currently making "U" shaped sandwiches out of sheets of diffuser and polariser?

I confess

Craig


Been playing with it for ages, you can also get quite interesting results from rolling it into a tube with the polarizing plane orthogonal to the axis of the tube (despite our various optical experts' theoretical rebuttal). As I rely on flash illumination I have to go through trial and error to find the best extinction but it usually only takes few shots. If you don't have flexible polarizer sheet (I got mine from an eBay listing selling offcuts from car windows) it works quite well if you make a little "inverted V" shaped tunnel and direct a snooted strobe onto each face.

As a side note, if you want to figure out the polarizing axis for unmarked sheet material an easy trick is to use a pair of sunglasses as a reference - they normally have the axis vertical to minimise surface reflection from water (or so I believe)
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rjlittlefield
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Joined: 01 Aug 2006
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Location: Richland, Washington State, USA

PostPosted: Sun Nov 07, 2010 9:11 pm    Post subject: Reply with quote

AndrewC wrote:
you can also get quite interesting results from rolling it into a tube with the polarizing plane orthogonal to the axis of the tube (despite our various optical experts' theoretical rebuttal)

Hhmm... In searching the archives for cylind* AND polariz*, almost everything I found was in one thread started by AndrewC back in February, titled Polarized Light on Metallic Beetles. It contained a couple of images that were intriguing but also were ambiguous due to being shot from different angles as well as with different polarization. In carefully reading that thread, I don't see any rebuttal, just some questions and alternative possible explanations for what the images show. There was some discussion and a lot of suggestions about things to try, but I can't find any followup images or threads that would clarify what's going on. Did I overlook something?

In any case I would be very interested to see some more results. As I said in that earlier thread, I find it difficult to imagine the polarization angles in these setups. Having some solid experimental results would be very helpful.

--Rik
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AndrewC



Joined: 14 Feb 2008
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Location: Belgium

PostPosted: Mon Nov 08, 2010 6:23 am    Post subject: Reply with quote

rjlittlefield wrote:
.... Did I overlook something?

In any case I would be very interested to see some more results. ....

--Rik


Lot's and lot's of business travel Sad

Imagine two cases of cylindrical polarizer made out of linear polarizing film wrapped into a tube:

Case 1: pol. axis aligned to cylinder axis. In this case you have light polarized to arrive from every point of the clock from POV looking down the cylinder.

Case 2: pol. axis orthogonal to cylinder axis. In this case it is almost like having a set of focus planes stepping down the cylinder with each focal plane being a plane of polarized light. From POV looking down the cylinder all the light is polarized in the same axis.

Could well be I have a fundamental lack of understanding of polarization but try it and see and you get (well I got, and will post when I get a chance) markedly different results.

Myself, I find both approaches modify the light captured by a sensor and results are very subject dependent but can help to minimise or at least change the reflected light.

There is of course a Case 3: cut the linear polarizer sheet at a diagonal, but I'll leave that to your imagination !

Thinking about it (and checking my home email archive) it was actually some guy who emailed me offline who stated there was no way it could ever work despite my empirical evidence to the contrary Smile

I think where it gets even more challenging from a modelling point of view is where your polarizing film is reflective and close enough to the subject that you get a significant amount of internal reflection hitting the subject which will then start to mess up all planes of polarization. As stated above, I think it is very much a suck it and see approach.
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AndrewC



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PostPosted: Fri Nov 12, 2010 7:20 am    Post subject: Reply with quote

some examples:

http://www.photomacrography.net/forum/viewtopic.php?p=70919#70919
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