Linear Polarizer damages DSLRs? How?

I'm familiar with the circular Vs. Linear polarizers & the need for circular ones in many digital cameras but I recently discovered this little snippet about them:

 

"Do not purchase a linear polarizer to use with a DSLR. These are used for manual focus film cameras and, while they can polarize light more dramatically than a circular polarizer, they can damage your camera's electronics."

 

I understand linear won't work in any system using an internal polarizer, but has anyone heard of electronic damage? Can anyone explain this?

No damage, it just will mean the AF system (which relies on phase differences and polarized light) to be unreliable in most DSLRs. The contrast detection system should be unaffected I would have thought. You can still a linear polarizer via MF, or presumably also in AF if you have a dual pixel focusing system in live view as seen in the latest Canon DSLRs.

As said, I don't see how it could possibly cause problems. I'd say the "strength" or effectiveness of a polarizer is dependent more I think on the quality of the filter than on the technology itself. After all, to sort of wave my hands, a circular polarizer is really just a linear polarizer with an add-on to unpolarize the light. The danger of using a linear polarizer is that if you have some optical component that either has its own polarizer or act as one(i.e. a beam splitter/semi-silvered mirror) you can end up feeding light into the polarizer that's 90º out of phase and both will black out. Most AF systems use semi-silvered patches on the mirror.

 

With that said, the whole AF/MF distinction isn't necessarily true either. Linear polarizers can cause metering issues with a significant number of Canon cameras going back to the 1960s as they use a semi-silvered spot in the middle of the focusing screen to meter. That in and of itself acts as a polarizer. Offhand, I think some other models meter through semi-silvered patches in the mirror, which again can cause issues with a linear polarizer. My Pellix can completely black out(both through the find and on the film) with a linear polarizer in the correct orientation(or incorrect, as the case may be) orientation.

"Do not purchase a linear polarizer to use with a DSLR. These are used for manual focus film cameras and, while they can polarize light more dramatically than a circular polarizer, they can damage your camera's electronics."

 

Sheer nonsense! Wrong in almost every respect! The sort of crap that gets kicked around the internet and inflated into mythical status. The original author needs a good talking to! Or at least asking on what authority they have their information - with a baseball bat if necessary.

 

My experience is that linear polarizers cause almost no issue with AF systems, and IMO the introduction of AF was seen as a marketing opportunity to get the world to buy new polarising filters. Advertisers prey on fear and ignorance. It's their stock in trade.

 

Having said that; many DSLRs now have an LCD display overlaid on the focusing screen, and use of a linear polarizer can cause undue dimming and colour shifts through the viewfinder. The captured image isn't affected in such a way of course. And the idea that the camera electronics can be damaged is totally laughable.

Thanks. I've heard of the exposure & auto-focus problems, in fact that was a test for the usability of a linear back then, you rotated it while watching the exposure, if it changed it wasn't compatible. I just couldn't figure out how (or if) it could actually "Damage electronics".

There should be a change in (metered) exposure when rotating any polarizer. Otherwise it's not doing its job of blocking polarised light. That, or the subject simply doesn't have sufficient polarised content to warrant the use of a polarising filter.

 

Variable ND filters are a supreme example of the exposure change caused when polarised light is passed through a rotated polarising filter. Whether linear or circular makes no difference.

My experience is that linear polarizers cause almost no issue with AF systems, and IMO the introduction of AF was seen as a marketing opportunity to get the world to buy new polarising filters. Advertisers prey on fear and ignorance. It's their stock in trade.

 

I smell a conspiracy theory ;) Evil corporations preying on the ignorance of their customers. That is a strategy best employed by politicians.

 

A linear polarizer interferes with any process in the camera which relies on a semi-reflective surface, including phase detector focusing. Most DSLRs will revert to contrast focusing if phase detection is not functioning. My Nikon D3 (and I presume other models) no longer use a semi-reflective section in the mirror, rather a set of micro-perforations in the reflective coating, so auto exposure is not affected. The same is true in my Hasselblad bodies, which use linear polarizers without restrictions. Circular polarizers can be used equally well for any camera.

 

I find it hard to set a polarizer angle on my Sony A7xx cameras. The viewfinder compensates for exposure and (apparently) contrast, so there is very little difference as the polarizer is rotated. I slavishly buy polarizers, but seldom use them. I get a similar effect on blue sky using stacked HDR or tone-mapping, even with haze or light overcast, and no banding with wide angle lenses..

Blue® skies are the least use for a polariser IMO. The colours of foliage can be made to pop by taking the shine off leaves and petals using a pol filter. It also controls contrast. That can't be done in post. Neither can controlling the appearance of water.

 

The circular v linear argument is almost entirely academic these days anyway, since almost no company supplies linear pols any more. The main benefit of "updating" to circular pols is that many of them are now multicoated, which is of far more benefit than any difference between linear and circular IMHO.

 

"I smell a conspiracy theory ;) Evil corporations preying on the ignorance of their customers. That is a strategy best employed by politicians."

- Don't be naive Ed. Advertisers use fear and ignorance all the time. Why else would people have body-image issues or buy "nourishing" shampoo containing foodstuffs? Hair is dead, it can't eat or taste anything!

There should be a change in (metered) exposure when rotating any polarizer. Otherwise it's not doing its job of blocking polarised light. That, or the subject simply doesn't have sufficient polarised content to warrant the use of a polarising filter.

 

Variable ND filters are a supreme example of the exposure change caused when polarised light is passed through a rotated polarising filter. Whether linear or circular makes no difference.

I think you're missing the point. Yes there is a change because of polarization, but there's a much bigger change when you accidentally get cross polarization from internal features of the camera. (Like blacking out the meter if it also uses a beam splitter or polarizer as well. THIS is what you're looking for, not the routine 1.5~2 stops of normal polarization.

Like blacking out the meter if it also uses a beam splitter or polarizer as well.

 

Like I said, you can black out the entire optical path of my 1960s Pellix with a linear polarizer, and it's far from the only camera to use a beam splitter in place of a retracting mirror.

 

If you're a Canon user, you've probably needed to buy circular polarizes since the 1960s.

Me naive? I agree about the best use of a polarizer - reducing reflections from foliage and rocks, increasing saturation. It works on water too, but should only be used if the water is very clear. If the water is at all murky, it looks very ugly behind a polarizer. Polarizers make skin look unhealthy too, another caveat.

 

At least reflections give swamp water some life. In high country, a polarizer renders blue sky deep purple. Again, moderation is the key. In an electronic viewfinder, the same features that make it hard to judge the effect on sky render the sun as a bright patch rather than a disk, and obscure reflections from the landscape. I look for smooth, non-metallic surfaces (glass, cars, etc) to set the filter, usually at 45 degrees so it has the same effect in both landscape and portrait mode.

 

There are sound technical reasons to use a circular polarizer on some cameras. B+W (Schneider) is actually neutral on the subject, not at all pushing a product just because it is more expensive. I buy B+W "Kaesemann" filters (sealed edges) because I know what happens when other polarizers get wet.

FWIW I used an existing linear I had on a digital Fuji & it de-saturated the image! I'm hoping the new (circular) will not do that. Not sure how but it was a fall foliage shot & the color was decidedly weaker than the same shot without! I have no idea why, but it was hard to see the polarizers effect with it not being a mirrored SLR.

http://i60.photobucket.com/albums/h29/moosp/photography/DSCF0515_zpsuz6zsb5n.jpg

 

http://i60.photobucket.com/albums/h29/moosp/photography/DSCF0516_zpstorofz30.jpg

Edited May 5, 2017 by chazfenn

Very strange Chaz! I've seen no such effect on conventional Bayer filtered sensors.

 

FWIW, a circular polarizer uses exactly the same type of polarizing material as a linear pol. The difference being that in "circular" polarizers the polarising membrane is followed by a 1/4 wave plate that effectively scrambles the polarised light again. So unless the Fuji sensor itself has some polarising properties I wouldn't expect to see any difference in the effect between a linear and circular filter.

 

Polarizers do vary quite a bit in their colour neutrality though. Some having quite a noticeable blue or green tint. Especially true of budget brands.

I have an insanely large collection of polarizing filters, many of them linear. The problem with the latter on modern cameras is potential inaccuracy of the light metering.

In practice, depending on the camera, it often doesn't make any difference at all, however. I find it difficult to understand how it would "damage" the camera, a very different thing from simply not metering correctly. Mine seem to work well enough with most EOS Canon cameras.

 

My special favorites are the old Spiratone® Colorflow™ filters (LINK).

 

I just realised an explanation for the strange leaf shot above.

 

I'm guessing that the leaves were backlit against the sky, and filtering the sky reduced the amount of backlighting. Probably also altering the sky colour to reduce its red content. That could be a possible explanation. It would also mean that using a circular polarizer would give much the same result.

 

If you left the camera on Auto White Balance, that could also account for some of the blue colour shift.

 

You get similarly distorted colours using crossed polarizers through a microscope with "dark ground" images.

Edited May 6, 2017 by rodeo_joe|1

I don't think polarization from the sky would make that much difference. You see the same effect where there is a cloud in the background. I suspect the polarized image was grossly under exposed, then restored. Not all polarizers are neutral either, which is one reason the good ones are expensive.

 

You get odd colors between crossed polarizers due to a property called "dichroism," typically in crystals, transparent objects subject to strain, and organized colloids. I would not expect to find it in leaves.

The image was about the same exposure as the unfiltered one. The only change was the exposure being dropped to compensate for the ND effect of the pola.

Its a mystery to me as well, but checking further the linear seems to function with that particular camera because it doesn't use beam splitters or anything in the operation its all taken directly from the CCD. My only thought is its something to do with the plate in front of the odd Fuji double matrix sensor?

Well there is an obvious strong blue cast to the lin pol shot.

 

If you shot RAW you could try raising the CT to see if you can get the lost red back.

 

Trying to correct a jpeg will likely result in some posterisation and not be entirely successful.

 

That doesn't explain why the colour was shifted so drastically I know, but if the effect can be attributed to a colour shift alone it goes some way to solving the mystery.

Its a .JPG & I was able to resurrect the accurate color by simply adding to the saturation in an editing program.

I like the backlit blue sky explanation, but the greens seem desturated too?

Well I went out with the new (to me) Finepix S9100 & the old S7000. The 7000 takes 55mm filters & the 9100 takes 58's so I was able, with a little fudging, to try both on the 9100.

Guess what, both worked flawlessly!

As expected the circular was less dramatic then the linear, but there were no focus or exposure issues with the camera left on Program.

I think I may just exchange the 58 circular for a linear:D

Other than normal variations (e.g., between brands), both linear and circular polarizers have the foil, hence same effect on incident light. Circular polarizers have a second foil, called a "quarter wave plate," on the lens side of the polarizer which "scrambles" the polarization (shifts the magnetic vector relative to the electric vector).

 

Program mode? I thought the P was for "Professional." ;) Where DOF is an issue, you should take charge of the aperture, even if it means using a tripod (or auto-ISO).

Auto ISO!

Arghhh! Sacrilege!

"P" is for "Press here Dummy" mode.

(which I admit I've used quite a bit since they brought out "program shift" & "Exposure Compensation")

:)

I used to scoff at auto-ISO, but no longer. It wasn't a practical option for my succession of Nikon cameras, from D1 to D3. Over that span the improvements in ISO noise were relatively modest, with the D3 peaking at about 3200. The Sony A7Rii, on the other hand, is very useable at ISO 25,600, and the noise granularity is very fine due to the high resolution. The menu allows you to set limits on how high the ISO can go (e.g., 25,600, 104,000 maximum) and how slow the shutter can be (default = 1/FL). Call it "lazy" on my part, but I use auto-ISO most of the time, reverting to fixed settings for astronomical photography, portraits and closeups. I use aperture-priority or manual mode almost exclusively. With image stabilization, I can shoot as slow as 1/8 second with a 50 mm lens.

Although I don't use it that often, modern "P" modes that let you cycle through shutter/aperture combinations don't really bother me that much.

 

 

As much as I love the F4, I don't use the P modes on it since you only get "P" and "Ph". I've also never used it on my A-1(and I've never owned an AE-1P). I have, however, used it on the T90 which allows you to scroll through the combos. On my bottom of the barrel DRebel, I can do the same so I have used P mode. The(uncoupled) meter prism on my RB67 just has a dial that you spin to center the needle and it just gives you all the combinations that match its meter reading.

 

 

The one mode which I avoid is "green box" mode, as it gives you no control. The various specialty modes are okay for what they do, but I'll still take complete control.

 

 

I had an interesting conversation with someone at work the other day. She has a consumer level Nikon DSLR(nothing wrong with that-as I said I use a Rebel XS, the cheapest you could get when I got it) and I was walking around with a Nikon F Photomic. She was asking me about manual exposure as she wants to "learn how to use it", and I launched into an explanation about how the Photomic really isn't that great of a meter and you have to use your own judgement about whether or not it's right and also know how to compensate for filters. Her face glazed over, and after realizing that I'd gone into "ramble" mode and apologized I found out that "manual" to her is getting out of "green box" mode(or whatever the Nikon equivalent is).

In reality its a phase shift in how you think.

The old metered manual went:

Speed (is it a priority?)

Aperture (is it a priority?)

Exposure (normal)

Exposure modification.

set.

Shoot!

 

With controllable automation, which I was introduced to in the Maxxum 9000 with its program shifts, its a different thought process, but a similar flow & result:

Exposure compensation.

look at speed & aperture set.

Decide on a speed or aperture you want.

Shift

shoot.