I’ve read, that essentially there exist three types of reflections in Physics:

  1. Metallic
  2. Non-Metallic
  3. Total Internal Reflection (See Below)

Metallic reflections tend to preserve the polarization of the light, while non-metallic reflections tend to polarize the light. The latter are also the basis for “polarizing mirrors”.

Beam-splitters are essentially polarizing mirrors:

  • When randomly-polarized light hits them, the deflected beam will be plane-polarized in one direction, while the transmitted beam will contain, what the deflected beam does not contain.
  • When circularly-polarized light hits them, nothing really prevents them from splitting the beam.
  • When plane-polarized light hits them, depending on the angle of polarization, the amplitude of one emerging beam can become much lower, than that of the other. This is probably also why, linear polarizers can interfere with the physical auto-focus of a DSLR-camera.

From what I read, reflection, according to the particle depiction, takes place, because photons couple with plasmons, to form surface-polaritons.

From what I read, refraction takes place, according to the particle depiction, because photons couple with excitons, to form photon-excition polaritons.

(Updated 02/22/2018 : )

Continue reading Mirrors

I just ordered a linear polarizer.

IF the type of camera we own is a DSLR, then we are used to exchangeable lenses and lens-attachments. One type of attachment that has always been available since the days of SLRs, is a polarizing filter of some sort.

But a DSLR differs from the older, film-SLRs, also, in having an auto-focus system which is physical, and which fails to work with linearly-polarized light, aka plane-polarized light. And so where ‘in the old days’, we used to buy linear polarizers, these days, we’d buy circular polarizers, for use with DSLR cameras. In the pursuit of photography, they do everything a linear polarizer used to do, and never prevent the auto-focus from working.

This also has as practical consequence, that it will be difficult in most localities, to find a photographic retail store, that still sells linear polarizers. Usually, such stores only sell the so-called Cir-Pols. Yet, because the linear polarizer has always been technically easier to design and manufacture, than a cir-pol, it only stands to reason, that the linear variety can still be bought somewhere. It’s just that retail stores need to pay their rent, and frequently can’t make a profit out of stocking those.

One place where one can certainly still buy those is on-line, which is where I just ordered one. And I did so, because I wanted to test the hypothesis of This earlier posting. In other words, where I’ve run into a self-imposed question which I cannot find the answer to, just by thinking about it, I now intend to find the answer, using the Scientific Method.

(Updated 02/21/2018 : )

Continue reading I just ordered a linear polarizer.

Why some people might still want to put Polarizers on their Cameras

One concept which exists in digital photography, is that we can remove any need for special filters, just by using software to modify or rearrange the colors within a photo or video we have shot. And one problem with this claim is, the fact that software can only change the contents of an image, based on information already stored in its pixels. Hence, the color-vectors of resulting pixels, need to be derived from those of captured pixels.

Thus, if we have taken a photo of a gray, hazy day scene, and if we wanted the sky to look more blue, and if we wanted features in the scene to look more yellow, then we could be creative in the coding of our software, so that it performs a per-channel gamma-correction, raising the blue channel to an exponent greater than one, while raising the red and green channels to an exponent less than one. And we might find that regions within the image which were already more blue, will seem blue more-strongly, while regions which did not, will end up looking more yellow, as if sunlit.

(I suppose that while we are at it, we would also want to normalize each color-vector first, and store its original luminance in a separate register, so that our effect only influences coloration in ways not dependent on luminance, and so that the original luminance can be restored to the pixel afterward.

At that stage of the game, a linear correction could also be computed, with the intent that purely gray pixels should remain gray. )

The problem remains, that the entire image could have colorsĀ  washed out, so that the sky looks gray, and the subject does as well. So then, our software would have nothing on which to base its differentiation.

But light that occurs naturally in scenes tends to be polarized. Hence, light that came from the sky will have an angle of plane-polarization to it, while light which has been scattered by the scene will have more-randomized polarization. Hence, if we have a DSLR camera, we can mount polarization filters which tend to absorb blue light more, if it is polarized along one plane, while absorbing yellow light more, which is polarized at right-angles to the same plane.

The idea is that the filter could be mounted on our camera-lens, in whatever position gives the sky a blue appearance, and we can hope that the entire landscape-photo also looks as if sunlit.

Then, the actual pixels of the camera will have captured information in a way influenced by polarization, which they would normally not do, any more than Human Eyes would normally do so.

(Updated 02/23/2018 : )

Continue reading Why some people might still want to put Polarizers on their Cameras