Illumination Suggestions Wanted

[BugEZ]

I have a Dobsonfly that was given to me last summer to photograph. I have discovered that the eyes are quite different from most insects and I am having a difficult time lighting them for a good photo.

The basic issue is that the glossy covering over the compound eyes lacks the texture typical of flies and wasps. With this critter it is like photographing a glass sphere. My normal lighting techniques are producing excessive glare. It is worse than with insects with shiny bodies as I am trying to see through the clear covering into the eyes.

Here is my most recent effort. Suggestions?

Keith

[Joseph S. Wisniewski]

Put polarizers on your lights, and polarizers at 90 degrees to that angle on your lens.

Start with just one light, and rotate the lens polarizer until your glare is gone. Then add a second light, if desired, and rotate the polarizer on that light until whatever glare it adds is gone.

[canonian]

I can only think of one thing to try: using polarizing filters.
Last year I did an experiment with the glasses my son came home with after a visit to a 3D movie.
I removed the lenses from the 3Dglasses and taped them in front of my Jansjo LED lamps.
In front of the objective I put a circular polarizing filter, which --when turned-- dimmed the specular reflections in the eyes.

My 2 cents and in your case probably worth trying...

[BugEZ]

Thanks canonian and Joseph S. Wisniewski for the suggestion of using polarizers. I think I have a pair of glasses left over from watching Avitar several years ago. It will be interesting to see if it works!

Keith

[Chris S.]

Keith,

I use cross-polarization (aka "X-pol)--the approach recommended by Joseph and Fred--often. To my mind, it ought to be part of nearly any photomacrographer's bag of tricks. If experiments using your old 3-D glass don't give good results (though they may), I would suggest you not give up on the approach, but try other (probably higher quality) polarizing materials. In my work, the Edmund Optics Techspec laminated polarizing film (for the lights) and Edmund Optics Techspec unmounted linear glass polarizers behind the lenses) have been excellent performers. Sadly they are not cheap--but have been worth the cost.

--Chris

[Yann]

Another cheap alternative is to dismantle an old phone screen, there is a polarizing film behind the glass screen. You can ask to a local phone repairer to get one old phone.
YAnn

[canonian]

... I think I have a pair of glasses left over from watching Avitar several years ago.Keith

That's were my pol-lenses comes from too, visiting a 3Dmovie.
It's a cheap way to get aquainted with polarizing light.
Not the best however, there seems to be a lot of difference in quality.
I remember a fellow forum member did a test once which might also be useful for you.

[BugEZ]

Thanks Yann and Chris S. l for the tips and suggestions. I followed canonian's link to some very interesting discussions on polarized light. Good Stuff!

I need to get some polarizing film. Some plastic film would be ideal for placing in front of my lights.

I have two linear polarizing filters. One was purchased to fit on my 50mm Pentax macro lens (49mm thread). The other is a bit larger and I'll have to scavenge my old camera drawer to find it.
My dad purchased some polarizing film from Edmond Scientific in the 60's. I played with it quite a bit as a teen. My favorite “trick” was to use the filter to hide the alternately polarized reflections (Birefringence) inside a calcite crystal. It is a very neat trick.
Keith

[ray_parkhurst]

I just tried using two polarizers, one on the lens and one on the light, to see if I could eliminate direct specular glare from a coin photo. But rotating the polarizers 90-deg from each other literally turned the light off. Seems everything reflecting from the surface maintained the original polarization without any scattering. What am I doing wrong? ...Ray

[naturephoto1]

I just tried using two polarizers, one on the lens and one on the light, to see if I could eliminate direct specular glare from a coin photo. But rotating the polarizers 90-deg from each other literally turned the light off. Seems everything reflecting from the surface maintained the original polarization without any scattering. What am I doing wrong? ...Ray

Hi Ray,

By rotating the polarizer on the lens perpendicular to the one on the light source (flash) you have total extinction. Try backing off one of the polarizers. perhaps the one on the lens to let some light through and test again.

Rich

[ray_parkhurst]

I tried it rotated at all angles. At 0-deg there is minimum attenuation, while at 90-deg there is 100%. Between 0 and 90 I see a continuously-variable (sinusoidally...) attenuation but no change in the character of the overall lighting or the specular glare...Ray

[Chris S.]

Seems everything reflecting from the surface maintained the original polarization without any scattering.

Unfortunately, metallic surfaces don't polarize light that reflects off of them. This can be demonstrated by looking through a polarizer at an automobile on a sunny day. By rotating the polarizer, reflections on the windows of the car may visibly diminish--but the reflections off the metallic surfaces of the car will be unchanged.

So it sounds to me as if you aren't doing anything wrong--it's just that coins are not subjects likely to benefit from x-pol.

Cheers,

--Chris

[Pau]

To avoid specular reflections cross polalizers is the way to go. It eats a lot of light, of course, because it only allows to pass some difussed (ramdomized) reflected light.

You can see some pictures I posted all with X pol and no difussers:

http://www.photomacrography.net/forum/v ... 1001#91001

http://www.photomacrography.net/forum/v ... 7632#67632

http://www.photomacrography.net/forum/v ... 2059#82059

http://www.photomacrography.net/forum/v ... 2971#62971

http://www.photomacrography.net/forum/v ... 6730#56730

[naturephoto1]

To avoid specular reflections cross polalizers is the way to go. It eats a lot of light, of course, because it only allows to pass some difussed (ramdomized) reflected light.

You can see some pictures I posted all with X pol and no difussers:

http://www.photomacrography.net/forum/v ... 1001#91001

http://www.photomacrography.net/forum/v ... 7632#67632

http://www.photomacrography.net/forum/v ... 2059#82059

http://www.photomacrography.net/forum/v ... 2971#62971

http://www.photomacrography.net/forum/v ... 6730#56730

Seems everything reflecting from the surface maintained the original polarization without any scattering.

Unfortunately, metallic surfaces don't polarize light that reflects off of them. This can be demonstrated by looking through a polarizer at an automobile on a sunny day. By rotating the polarizer, reflections on the windows of the car may visibly diminish--but the reflections off the metallic surfaces of the car will be unchanged.

So it sounds to me as if you aren't doing anything wrong--it's just that coins are not subjects likely to benefit from x-pol.

Cheers,

--Chris

Using polarizers and cross polarizers are much more effective with living things; things containing water including living things and the atmosphere. As Chris has indicated it will reduce reflections on metals (but not totally eliminate them). I believe that should also apply to reflections off of glass, many mineral crystals, and often water surfaces.

Rich

[rjlittlefield]

Seems everything reflecting from the surface maintained the original polarization without any scattering.

Exactly right. Metal surfaces retain whatever polarization the illumination has. So does the specular component of reflection from any other surface. That latter aspect is what makes cross-polarization work: specular reflections retain polarization of the source so that those reflections can be blocked by the crossed polarizer on the camera. Unfortunately it makes metal go black also. Organic materials typically randomize the polarization of non-specular reflections, so x-pol works great with them to kill specular reflections. A few organic surfaces do retain the polarization, however. I once experimented with x-pol on a jewel wasp like the one shown HERE, and the whole thing went black just like a piece of metal would.

--Rik