Birefringence basics

In one of my previous posts I mentioned birefringence. Here are some more details.

Polarizers set up the direction of light polarization. If you apply two filters at the same time you can get  complete light blocking, complete transparency or something in between. This is how some adjustable Neural Density filters work. 

Some materials change the polarization of the light. If such object is place between two polarizing filters set to maximum blocking, the only thing one can get in the picture is the light disturbed by such material.

In order to try birefringence photography following are needed:
source of polarized light  - LCD screen/tv/monitor/tablet works perfectly. 
object made of material that disturbs polarization - cheap plastic is perfect, hi-quality glass is useless.
polarizing filter attached to your camera.

Place object in front of the polarized light source, rotate the filter so the source looks black and shoot.

Depending on orientation of the object polarization changes, so try moving object around.

As example I used plastic bag/pocket. First two pictures are without setting the polarizing filter to full black to show how the orientation affects color.





And now with polarizing set up to black



The thicker material the more interesting patterns you can see. 

The color of the light (or image displayed on the screen) affects the result. First I used blue droplets background (filter not set to full black).



Now with filter set to black:



The same setup, but with green/yellow background displayed on the screen:



The more complex shapes add more patterns to the polarization and in effect more interesting result





Hope you will enjoy your birefringence project. Please add comments or questions. I'm feeling quite alone in this blog ;).

Bookeh shapes

Not to anyone's surprise there are two characteristics of the hole - shape and size.

Common advice is that cutout size has to be smaller then the real apperture - so for 50mm lens and f/2 it has to be smaller than 25mm

Cutting tiny shapes is not my thing (I'm not great at DIY) and the results were far from pleasing. In most cases edges were jagged and you could spot it in the final pictures.






And another example with skull and bones.



Even that I put a lot of effort to do it correctly you can see that it is not something I can be proud of.

I decided to go digital. I have used laser printer to print on transparent media (transparent foil used for presentations). I'm not sure if it is related to the toner or set-up of the printer, but the results were quite bleak.



I used permanent marker to blacken surrounding area.



The advantage of this method is that I can use extremely complex shapes.




The disadvantage is that foil is not crystal-clear and it adds soft focus effect (like pantyhose over lens). This is even worse when shape is complex and have some dark elements in the middle.



If the shape has a lot of empty space in the middle it gets slightly better.




Another test I did was based on the fact that cutout adds shape to the lights, but it can also add some color. I used the same foil, cut the shape of the heart (ok... shape of something vaguely similar to heart) and marked edges using red marker.



The effect:



It can be improved, but it suffice as proof of concept.

I have already planned some more tests:

• using laser cut shapes - it will take time as it require some preparation.
• using combination of color foils to get multi-color bokeh.

Have fun.

Blur Bokeh

While working with custom shaped bokeh I initially tried the standard heart and star shaped ones and then moved to some complex shapes. In some cases it worked perfectly in some effects where not visible or not worth the effort.

I will write another blog entry related to custom shaped bokeh and tests I made (hopefully quite soon). 

One of the shapes that I tried lead to interesting effect. It is the bokeh in the shape of the slit.

At first I tried to do it using my typical bokeh models (very patient, lot of personality and great at standing still) and my normal setup with some lights in the back.

Lights were not that interesting, but I noticed that the other elements of background looked blurred horizontally as well. 

In most tutorials you will find tips suggesting to have distinct lights far in the back. However bokeh works also in full light outdoor conditions - custom shapes are just not as easy to notice. Even better! So my next attempts were concentrated on shooting slit bokeh during the day. 

Both camera position and photographed object did not move during shooting following pictures:

Conclusion is that slit shaped cutout makes bokeh effect similar to motion blur (direction depends on angle of the slit). It is not exactly the same blur effect you get when panning picture aiming at fast moving object, but close. 

I'm not great at panning - high percentage of my panned pictures have main object blurred as well - this method had additional benefit for me. The object/model does not have to move at all. Having said that there are differences that many can dislike. For example picture of the car that is done with this motion blur bokeh will have wheels not blurred, while the one done with panning will have them blurred due to spinning. I will update this entry once I have photo good examples.

Update (18-02-2016): I tried to use it with landing plane. As the plane was far enough, the effect was almost not visible. So the motion blur bokeh method is better for objects that are really close. I will try with macro photography.

Tools needed:

• Lens with big aperture (mine is 50mm 1.4)
• Piece of cardboard/this paper.
• Scissors
• Way of attaching the shape in front of lens

Process:

• Cut the shape of the slit (few mm wide) in cardboard.
• Attach in front of the lens so the slit is positioned centrally.
• Set to aperture priority and open as wide as possible.
• Shoot object that is quite close with background far back.

Things to try next:

• Different widths of the slit.
• Slits in not linear shapes (waves, long ovals, zig-zags).

As previously, I would appreciate any comments/questions/suggestions.