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Controlling Specular Reflections

This is a daughter topic of Tom's ice pictures here. So we have many specular reflections to deal with. It could be on a framed picture with a lot of varnish or behind glass or a chromed, steel or bronze sculpture. Taming specular reflections is an issue we have to face in a variety of situations. Asher






Mark,

Only ambient light was used. The ice had different thicknesses, and this was the main reason for the subtle change in colors. I've found that flash can be very tricky to use due to specular highlights. Cross polarization might help with this, but have trouble thinking to experiment when standing on ice and the temperature is below zero Fahrenheit . This might be a great way of increasing contrast, however.

Tom
 
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Asher,

A circular polarizer alone with the available light would have only reduced the light through the lens by almost two stops. The available light was bouncing off the canyon walls, and by the time it refracted through and reflected from the ice, it essentially had no polarization.

On the other hand, if the light source were polarized - by placing polarized film in front of the flash output, for example - then the circular polarizer at the lens could be adjusted so that it was at right angles to that of the light source. This effectively reduces specular reflections. The degree of reduction depends upon the surface of the subject. It is tough to reduce specular reflection with ice and glass, for example, but it works amazingly well with dewy flowers.

I've got a couple examples illustrating this, if you're interested.

Tom
 

Asher Kelman

OPF Owner/Editor-in-Chief
On the other hand, if the light source were polarized - by placing polarized film in front of the flash output, for example - then the circular polarizer at the lens could be adjusted so that it was at right angles to that of the light source. This effectively reduces specular reflections. The degree of reduction depends upon the surface of the subject. It is tough to reduce specular reflection with ice and glass, for example, but it works amazingly well with dewy flowers.

I've got a couple examples illustrating this, if you're interested.
Tom,

This makes a great new thread. We'd love to have your examples!

Thanks,

Asher
 
Asher,

Every spring, in an out of the way location deep in the woods, a patch of yellow lady's slippers sprout up. They are tough subjects because their three dimensionality requires the use of a small aperture, and the smallest breeze makes them dance around. Additional complications include the lack of sunlight in this area of woods, and the small window of peak condition of the flower - it's always windy and cloudy in May.

All this adds up to the need for flash, in my experience. I prefer off shoe with a couple cords connected in series.

This version was taken with the flash positioned at the left side of the frame without polarization of any sort -



The most obvious reflection is from the waxy surface at the "nose" of the flower.

This second version was taken with the flash polarized at right angles to a circular polarizer mounted at the lens -



Which version is better depends on your objective. I think the reflections give the flower some sense of its surface texture, and prefer the first one taken with the usual setup. The version without reflections might be preferred if flower detail is important, as an illustration in a field guide, for example.

The concept of cross polarization is straightforward: light from the flash is positioned at right angles to the polarization at the lens. Polarized film can be obtained from Edmund Optics. I used a sharp knife to cut a piece that covers the output of the flash. A couple tabs left at each end of the film were bent at right angles, and then slipped under an elastic band around the head of the flash. This holds the film in place on the flash. One can use the depth of field preview button to strobe the flash, and then simply adjust either the tilt of the flash or the circular polarizer at the lens to minimize reflections while looking through the viewfinder.

The cross polarization technique takes time to set up when hand holding the flash, as I do. If a flash bracket is used, the cross polarization angles could be worked out in advance. This might be the best approach when shooting bugs and such.

Tom
 

Asher Kelman

OPF Owner/Editor-in-Chief
The difference, Tom, is spectacular. I wonder how it would be for B&W photography. There's such a different esthetic with and without the use of the filters. I might even want to use different degrees of filtration.

Thanks for sharing this particular rare sight. I have not seen the flower looking so pretty and soft. I would love to hear Ken's view as to how this might make a difference to the composition and balance of the picture. Certainly, it's a different dialogue altogether.

Asher
 

Asher Kelman

OPF Owner/Editor-in-Chief
Tom,

Coming back to this, I am feeling that the effect of using flash and the polarized light is to take away the dimensionality. Obviously here, it's the distribution of the light which is almost evenly lighting everything. The light should be used to bring out the texture and the form. Here it has given a more 2D look.

Of course, the actual file may have all the detail imaginable but I can't see it in this jpg.

So your view on this would be interesting.

Asher
 
Tom,

Coming back to this, I am feeling that the effect of using flash and the polarized light is to take away the dimensionality. Obviously here, it's the distribution of the light which is almost evenly lighting everything. The light should be used to bring out the texture and the form. Here it has given a more 2D look.
Correct, but then nobody forces us to fully extinguish the direct reflections. The polarization filter allows to dial in just enough control to eliminate the hot spot, yet retain surface structure.

Bart
 

Asher Kelman

OPF Owner/Editor-in-Chief
Bart,

Why does polarized light remove this detail or is it just that this occurred in this instance because of the position of the light. Maybe the detail is there in a fine B&W rendition at full size?

Asher
 
Bart,

Why does polarized light remove this detail or is it just that this occurred in this instance because of the position of the light. Maybe the detail is there in a fine B&W rendition at full size?
Light (polarized or otherwise) gives shape to objects. Object surfaces can be transparent, produce direct (specular) reflection, or produce diffuse reflection. It usually is a mix with diferent ratios between them.

The direct reflections can be polarized, not polarized, or be a mix. They are usually mostly polarized if the surface is smooth unless they come from a bare metal surface.

The waxy plant surfaces produce mostly polarized reflections. Therefore a polarization filter alone can already eliminate a lot of reflection. The remaining reflection can be removed by using a polarized lightsource. The polarized light is reflected as is, and can be totally removed by a crossed orientation polarization filter. The plant surface acts as a mirror, and we look at a 'black' lightsource. This effectively removes surface structure as well. The surface structure gives us visual clues about the surface shape (e.g. a small hotspot reflection suggests a curved surface, a bumpy surface produces many small hotspots). With crossed polarization axes, all that's left is overall light and shade, with a gradient between them that gives visual clues about the relative size/distance of the lightsource.

The human visual system interprets a total lack of direct reflections as a flat subject, therefore I suggest to leave part of the reflection in.

Bart
 
Asher, your observation is on the money, but as Bart pointed out, this was an example of maximum reduction of reflection. It was intended to serve as an illustration of the concept, and there are variations between the extremes.

I use cross polarization on rare occasions, but doing so while hand holding the flash takes an awful lot of time. I'd rather spend such time on composition and other aspects. Bugs might prove to be better suited to the lighting scheme than flowers, but cannot speak from experience.

On a rainy and windy day, about a month ago, I experimented with a mix of ambient and cross polarized light while photographing an RF power amplifier tube from ham radio days long ago -



Cross polarized light was from the left, and ambient incandescent was from the right. It took a lot of exposures to finally get an image I bothered to process and save. I don't mean to discourage anyone, but while the concept is simple, its execution is much less so.

Tom
 
On the other hand, if the light source were polarized - by placing polarized film in front of the flash output, for example - then the circular polarizer at the lens could be adjusted so that it was at right angles to that of the light source. This effectively reduces specular reflections. The degree of reduction depends upon the surface of the subject. It is tough to reduce specular reflection with ice and glass, for example, but it works amazingly well with dewy flowers.
Language is key here. I have not read the full thread (I lack time) but only one image shown has a subject capable of specular reflections.

A specular reflection shows the subject clearly. You can easily find a specular reflection by looking in a mirror or looking at a reflection of a scene in water..

The subject of this thread is eliminating specular highlights. Specular highlights are the tiny over-exposed/blown reflections off of objects. In the case of a flower, these objects are tiny shiny spots reflecting directly towards the lens.

Also consider using larger light sources (softbox, ...) as these soften specular hightlights. Reflectors used on shadows will also soften lighting.

Even the little 5cmx15cm velcro on softboxes for flashes make a huge difference in controlling specular highlights when shooting insects.

some thoughts,

Sean
 

Ken Tanaka

pro member
Light: Science and Magic by Hunter, Biver, and Fugua, 3rd Edition, 2007 Focal Press

Answers all such questions, as well as much more. Plus it helps to give the reader a grounding on the important accurate language of lighting (as Sean noted earlier), most of which has been around for hundreds of years.
 

Cem_Usakligil

Well-known member
Light: Science and Magic by Hunter, Biver, and Fugua, 3rd Edition, 2007 Focal Press

Answers all such questions, as well as much more. Plus it helps to give the reader a grounding on the important accurate language of lighting (as Sean noted earlier), most of which has been around for hundreds of years.
Since I have been hearing so many praises about this book, I have bought it last week from Amazon. It has arrived a few days ago and I could only skim through it so far. But from what I have seen, it really deserves all the credit it has been receiving. Highly recommended.

Cheers,
 
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