wdross Loc: Castle Rock, Colorado

Most of the time I agree with you. But you are not accurate this time. When I first got my Olympus OM-4ti, I only had linear polarizers. And in the manual, it said to use only circular polarizers. And with the linear polarizer, it caused visual variations in the viewfinder similar to morie patterns. As soon as I put on my new circular polarizer, those variations disappeared. And the manual also indicated the linear polarizer would not affect the actual metering although it would affect what one saw in the viewfinder. And this was caused by the mirror passing some of the light to a small mirror mounted to the underside of the main mirror. That small mirror reflected that small amount of light to the metering system. Everything was accurately stated and proven in actual usage.

The need for circular polarizers is normally caused by the mirror designs in DSLRs, not the meters themselves or the sensors. With no mirror, both linear or circular polarizers can be used.

selmslie Loc: Fernandina Beach, FL, USA

We can’t really argue with direct experience.

There were a number of different methods used to accomplish metering and autofocus in SLR and DSLR cameras where mirrors and linear polarizers were incompatible. But once the mirror moved out of the way, there was no issue with the film or sensor.

Mirrorless cameras eliminate those problems.

Longshadow Loc: Audubon, PA, United States

Some may, some (most?) don't.......
So to cover all bases, they simply say don't.

wdross Loc: Castle Rock, Colorado

It depends on the camera design and whether or not the mirror was also used for the light metering. Some camera designs had the metering in the viewfinder. The metering was cut off when the mirror flipped up, but this did not affect many images being taken unless there were a lot of flashes going off. Olympus initially had a black and white horizontal fabric shutter (I think OM-2) that as soon as the mirror flipped up, the exposure was being determined off the shutter and the actual film. But this also posed a problem when the mirror was down. The exposure metering was being blocked by the mirror. Because of the camera body size being so small, they eventually went to a small mirror mounted on the backside of the main mirror. And Olympus was not the only one to use this type of setup. So it comes down to mirror design as to whether or not a camera needed the circular polarizer or not. I can garenttee that if one used a linear polarizer where a circular was required, it was very difficult determining the correct polarization angle setting. Exposure still came out correct, but the polarization might not be maximized. I ordered my first circular polarizer very quickly after that.

DirtFarmer Loc: Escaped from the NYC area, back to MA

The problem with linear polarizers on cameras is not whether they are film or digital cameras. The problem arises from the fact that light reflected from a dielectric surface can be partially polarized (without using a polarizing filter). In fact early polarizers were just stacks of glass at angles that polarized the light.

Since light can be polarized on reflection, and since autofocus systems on cameras depended on light that was bounced around from mirrors and through various prisms to the autofocus sensor, the use of polarized light meant that the light that reached the autofocus system could be polarized in a different direction from unpolarized light that entered the camera. That could potentially cause errors in the autofocus system.

Using circularly polarized light mitigates this problem because circularly polarized light does not change polarization direction on reflection. That means that it acts like unpolarized light when it comes to the autofocus system. But since the outer half of a circular polarizer is a linear polarizer, it affects the light entering the camera just as a linear polarizer would. The second half of the circular polarizer is a quarter wave plate, which produces a quarter wave delay in one of the polarization components coming through the filter. This means the electric vector of the light wave is not constrained to one direction (as a linearly polarized wave would be) but has two components with a 90 degree phase difference, so the electric vector travels in a circular fashion. Hence the term 'circular polarization'. https://www.uglyhedgehog.com/user-page?upnum=3002

Autofocus systems were developed for film cameras late in the film era and digital cameras took them as a standard feature.

I suspect the effect on autofocus systems is small so that a linear polarizer will work on a modern camera. There is the possibility of focus errors, which I have not evaluated. I took a quick look a couple decades ago and didn't see any effect but it was not a real definitive study.

Note that a circularly polarizing filter will act as a linearly polarizing filter if it is reversed. The quarter wave plate will do nothing important to the light, leaving the linear polarizing component of the filter to do all the work.

Your Crown Graphic will work with either a circular or a linear polarizer (my old Speed Graphic did not have autofocus). Linear polarizers may be cheaper, but since circular polarizers are THE thing to use these days, linear polarizers may be in shorter supply (and therefore higher prices) than the circular polarizers.

PS: 'Disturbing patterns' probably refers to Moiré patterns, which arise from patterns in an image interfering with the square rectangular grid of sensors in a digital camera. They have nothing at all to do with polarizers. It is purely a geometric effect. It is not a problem with film because the film grain is arranged in a random pattern.

dbrugger25 Loc: Raleigh, NC

I posted the original question and appreciate the responses.

Tote1940 Loc: Dallas

I think you are correct
It is autofocus and metering, although early through the lens metering Cadmium disulfide in Mamiya Sekor worked well with simple polarizers
I think it has to do with how light reaches photosensor for exposure.
Quarter wave plates are used on microscopes to diagnose uric acid crystals ( gout) , we used a layer of scotch tape , same effect. Optics is fascinating

User ID

You just agreed with everything I wrote.

But as I predicted, Hawgsters seek to be contrarian even if it means contradicting themselves.

As I mentioned, the CPL is all about conveniences, not about necessities, as confirmed by your reported experience.

That is all.

Bill_de Loc: US

I doubt that!

---

Bultaco Loc: Aiken, SC

I've used both on a D500 and D850, can't tell the diff.

BurghByrd Loc: Pittsburgh

After reading these various responses I realized that I'd forgotten much of the detail so I looked it up again. The following links to a good article on the subject in Photography Life magazine. There is a section on "Types of Polarizers" that addresses the question.

https://photographylife.com/definition/polarizing-filter#types-of-polarizing-filters

Julian Loc: Sarasota, FL

Define ‘semi-obsolete’ please.

lamiaceae Loc: San Luis Obispo County, CA

Wow, no one seemed to a able to read your question. It is clearly to me about using a Circular Polarizer on a film camera. My guess it would make no difference but I have not tried using a Circular Polaringing filter on any of my film cameras since my first DSLR. I have rarely shot film since going Digital in 2010.

User ID

I think I know why you ask that.

DirtFarmer Loc: Escaped from the NYC area, back to MA

https://www.uglyhedgehog.com/t-805927-2.html#14592365
tl;dr
Next to last paragraph