Cross-Polarization

and the - Completely - Lost Reflexions

(2011- 07- 01)

 

 

 

The principles for use of cross-polarazation to produce "natural" (:non-photoshopped) colour effects has been known for a long time.

 

Colour effects from cross-polarization: Without and with polarizing film placed behind the plastic lid.

 

Likewise well documented is the use of cross-polarization for reduction of reflexions from ordinary flashes. The idea presented below is essentially brutally stolen from the naturescapes site.

 

However, the question about reduction of reflextions from flashes is often asked, particularly in relation to macro photography, is often asked and the "standard recommendation" is the use of a polarizing filter on the lens.

 

However, in many cases, this does not suffice; hence this little illustrated presentation:

 

Everyone who has tried to fire a flash head-on into an oil painting will know the inevitable result:

 

Reflexions - and lots of them!

 

In a situation like this, a single pol-filter on one's lens will more often not have the adequate effect. No matter how much one rotates the filter forth and back, the reflections will still be there:

 

    

Minimum and maximum dampening of reflexions with polarizing filter on lens.

 

Here, cross-polarization comes to the rescue. Cut a sheet of liner polarizing filter in the shape of the front of your flash:

 

- here shown with a home made filter adapter to make things easier, but transparent tape may also do to keep the polarizing filter in place.

 

Now, use that in conjunction with an ordinary pol-filter on your lens and you will see things happen:

 

    

Minimum and maximum reduction of reflections with linear polarizing film in front of flash and ordinary polarizing filter mounted on lens.

 

Some may find that the resulting picture will look unnaturally flat and dead because ALL reflections are absent. But there are lots of details retained or even brought forward, as the following crops will show:

 

Further, one should note that the span between minimum and maximum dampening is now so great, that one may start controlling and using the reflexions in a creative manner.

 

The sample images above were shot with the flash head-on to the painting in order to make the reflexions as aggravating as possible. Any "depth" and structure in the brush strokes arises from the reflexions only as there is little or no shadows to work with. Normally I would not photograph a painting that way but rather use the flash - or natural, ambient light coming a bit from the side in order to have some shadows to provide the impression of depth in the brush stokes.

 

This is a bit like photographs of the full Moon where the sun rays fall more or less perpendicular on the surface of the Moon providing very little and/or extremely short shadows. As a result, pictures of the full Moon are usually rather dull and flat - with a few, scattered highlights from craters and mountain tops to break the monotony.

 

Anyway, flash was head-on and here a a couple more samples from my series as I move away from maximum dampening:

 

 

I believe that you will agree to my postulate above: That one can control and use the reflexions in a creative manner when one applies cross-polarization techniques.

 

Thus, the ideal set-up for "controlled flash use" in macro photography could be something like the image to the left: Flash mounted on a flexible arm (: homemade and very easy to do) with a mounting head that can be rotated. This, in combination with the cross-polarizing technique just described would allow ideal control over both shadows and reflexions.

 

     
A window pane, a fly and a flash (2011-07-07)
Yesterday there was a house fly wandering around, around and around in endless circles on my window pane. The poor beast seemed to have given up all aspirations of further flight in this life - and that gave me the chance to present another, rather "dramatic" demonstration of the effects of cross-polarization in conjunction with use of flash. Now, the fly was constantly moving so I had to take the following images hand held and with manual focus, but I have done my best to point my flash in the same, perpendicular manner to the window pane for the next three examples show.
 
A dark fly on a well-backlit, clear window, that requires some fill-in flash. But firing the flash directly into the window, however transparent, will give some considerable flares:
 

Flash without polarizing film; polarizer on lens

 

Again, mount the polarizing film on the flash, and you may vary the results by rotating the polarizing filter on your lens:

 

Polarizing filter on flash; polarizing filter on lens. Adjustment to near minimum dampening

 

Polarizing filter on flash; polarizing filter on lens. Adjustment to near maximum dampening

 

I trust, there's no arguing about the effect and potential levels of adjustment.

 

Finally, a more practical example:

 

Light from flash (with polarizing film on) comes in more from the side and polarizing filter is rotated a bit away from the maximum dampening position

 

Appendix 1: Sources of polarizing film and alternatives.

I had my pieces of polarizing film in a jumble box from around 1978 where I acquired some sheets to make a variable flash light. That was for astro purposes in those days long ago - very long ago - where we didn't have variable LED flashlights. I then have had those sheets lying around, believing that I should find some real useful application for them some day. And thanks to Wil Hershberger I have now found it!

 

Although not a very common everyday consumable, polarizing film is used in both industry and art work, and you should be able to find sources reasonably near to you if you google "Polarization Film" or "Polarisation Foil" or combinations hereof. Here are some sources that i found (July 2011) by such a quick search

Alternatively, linear polarizing filters for photography may often be found used at very reasonable prices - also the larger ones required here. If you go for that it should be easy for you to construct a simple adapter to your flash using paper, cardboard and glue. By the way, while circular polarisers are today's standard recommended for digital photography, I used an older linear polarizing photographic filter  for the the series shown here. Both types will work on your lens for this application.

 

Circular polarizing photographic filters should also work (I haven't tried it out yet) in front of the flash, provided that you mount the filter with the back-side pointing out from the flash (in order to make the orientations of polarization oppose each other on the flash-camera lens filters).

 

Finally, you may stumble upon an old pair of polarizing sunglasses, polarized goggles for 3-D motion pictures watching or there are - as far as I have been told - certain sun-blocking foils for windows that are based upon linear polarizing materials.

 

Surely, there will be some polarizing stuff that you may use nearer to you than you may think.........

 
Appendix 2: Equiment used for the above

Camera:

Pentax K200D

Lens:

Tamron SP 35-80 mm f/2.8 - 3.8 Model 01A (Adaptall-2 system)

Flash:

Metz Mecablitz 44 AF-1

Polarizing filter(s):

Run-of-the mill no-name 62 mm diameter linear polarizing filter. (Works fine with TTL and P-TTL on my Pentax). I also have and use a more modern Hoya Digital CIR-PL circular polarizing filter. There is effectively no difference for this application between the two.

Polarizing film:

Bought in a domestic graphics supplier shop. Cannot remember brand or any other details. See Appendix 1 above for today's sources.

 

 

 

 

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Copyright 2011 - Steen G. Bruun