Two Polarizers VND (Page 2): ` Light enters a CPL unpolarized, and then exits the CPL still unpolarized. Thaz why some cameras need a CPL. Light enters an LPL unpolarized but remains...

User ID

`

Light enters a CPL unpolarized, and then exits the CPL
still unpolarized. Thaz why some cameras need a CPL.

Light enters an LPL unpolarized but remains polarized
as it exits. So if you wanna lose 10EV of light, you can
see which way to stack them !

`

f8lee Loc: New Mexico

rgrenaderphoto wrote:

I think the mistake is thinking that adjusting 2 CPLs will knock back light reaching the sensor like a ND. Which won't work, since the function of a CPL is to bend light, and the function of a ND is to reduce the amount of light hitting the sensor, not bend it about.

In fact, a VND is a pair of stacked CPLs - and just as with ND or straight CPL filters the cheaper ones can impart a color cast.

As for the "Maltese cross" effect that has been alluded to above, this highly depends on the specific camera/imaging chip involved. My experience with a Singh-Ray VND was perfect with my film cameras as well as Nikon D200, ,D700 and D600 cameras. Then I got a Fuji X-T1 (and later X-T2) and discovered the issue; calling Singh-Ray is how I found out that they called it the "Maltese Cross". Right off the bat, that tells me that it's not the size of the sensor (the D200 and X-T1 are both cropped frame, nor the MP count (the D700 was 12MP, the X-T1 and D600 are 24MP). My guess is that it has to do with pixel pitch and destructive interference of the light waves after passing through the pair of CPLs (which would also be affected by the polarizing foils used in the CPL itself, so the Singh-Ray might differ from, say, a Hoya). But the point is, it does not always occur.

Largobob

Longshadow wrote:

Bultaco Loc: Aiken, SC

User ID wrote:

`

"In a pinch" ?

You mean you anticipate emergencies
requiring that you destroy up to 10EV
worth of light from the scene ?

Stack two CPLs. It might get amusing.
Report back with observations !

`

amfoto1 Loc: San Jose, Calif. USA

If you need the effects of a polarizer AND still need to further reduce the brightness of the light, it would make more sense to combine a C-Pol with an ND filter.... than come up with a "home-made" variable ND (which are notoriously problematic, anyway).

There are C-Pol/ND combination filters available.... I'm pretty sure Breakthrough Photography and Singh-Ray make them. Some others probably do, too... if you don't mind spending a small fortune on a pretty highly specialized filter.

tradio Loc: Oxford, Ohio

I had a variable ND filter that essentially two polarizers That left a dark "X" on some images. I guess it will work in a pinch.

Architect1776 Loc: In my mind

User ID wrote:

`

"In a pinch" ?

You mean you anticipate emergencies
requiring that you destroy up to 10EV
worth of light from the scene ?

Stack two CPLs. It might get amusing.
Report back with observations !

`

I have not but sounds like a great experiment if you have 2 CPLs of the same size. Otherwise get the Variable ND instead of duplicating the CPL.

RWR Loc: La Mesa, CA

User ID wrote:

Light enters a CPL unpolarized, and then exits the CPL still unpolarized.
Light enters an LPL unpolarized but remains polarized as it exits.

Non-polarized light that enters a Circular Polarizer remains non-polarized as it exits.
Non-polarized light that enters a Linear Polarizer remains non-polarized as it exits.

BebuLamar

Since I never care for ND filter I never use them in such a fashion. However, I did try to use 2 polarizers as a variable light attenuation. I was hoping to be able to dim the light (which I use as light source to test light meter) without changing the color temperature (because reducing voltage to light bulb would dim it but also decrease the color temp). I found that they do work and the linear ones work better than the circular ones for this application. However, the light get a bluish cast so I abandon this project.

BBurns Loc: South Bay, California

About 20 years ago, George Lepp did an article and demo of using dual PLs.
In his tests he had one on the camera and the other on the flash.
Yes, it eats up a lot of light but the results were impressive.

I have a friend who is a professional product photographer. He uses this technique in the studio occasionally as well.

User ID

`

f8lee wrote:

In fact, a VND is a pair of stacked CPLs - ........

Note for "home brew" or DIY types ...

Above has a small operational glitch.
Two CPLs will NOT create a VND. At
least one of them MUST be a LPL.

Unless you're trying to build your own,
that error is just a "slip of the tongue".
But it appears that some here ARE of
a DIY bent, and thaz where it matters.

`

BebuLamar

User ID wrote:

`

Note for "home brew" or DIY types ...

Above has a small operational glitch.
Two CPLs will not create a VND. At
least one of them must be a LPL.

Unless you're trying to build your own,
that error is a sorta "slip of the tongue"
butit appears that some here ARE of a
DIY bent ... and thaz where it matters.

`

Yup! I found the CPL doesn't work well or may be doesn't work at all. I then used 2 linear ones and they worked but somehow I got the blue cast.

rcarol

BBurns wrote:

About 20 years ago, George Lepp did an article and demo of using dual PLs.
In his tests he had one on the camera and the other on the flash.
Yes, it eats up a lot of light but the results were impressive.

I have a friend who is a professional product photographer. He uses this technique in the studio occasionally as well.

This is a very interesting lighting technique but the effect of using a polarizer on the light source combined with a polarizer on the lens produces an entirely different result than stacking 2 polarizers together on the lens.

BebuLamar

rcarol wrote:

This is a very interesting lighting technique but the effect of using a polarizer on the light source combined with a polarizer on the lens produces an entirely different result than stacking 2 polarizers together on the lens.

Using the polarizer on the light source and on the light both doesn't really work as VND although they do eat up a lot of light. I do that when copying shinny flat arts, they reduce the reflection of the light source very well.

BBurns Loc: South Bay, California

rcarol wrote:

This is a very interesting lighting technique but ...

You are quite correct. The subject reminded me of it.
I never want to inhibit anyone's imagination. Experimentation is the greatest learning tool.