Using two linear polarizers? - DPChallenge Forums

Nikon AF Nikkor 50mm f/1.8

08/30/2006 08:31:11 PM · #1

Has anybody tried using two linear polarizers together to effectively give you a ND filter with a variable amount of stops that could be dialed in from 2 to infinity? Seems like it would work, but I don't know why I haven't heard of anybody doing it.

Sure the AF would be screwed up, but I would do this in landscapes and the focus can be set prior or you can manually focus.

Anybody with experience?

Sinky

Nikon D300

08/30/2006 08:39:20 PM · #2

Very clever and novel idea. I cant see why it wouldnt work.

wavelength

Nikon D300

Nikon AF Nikkor 50mm f/1.8D

08/30/2006 08:41:49 PM · #3

No direct experience but I found THIS on Google, seems like it's do-able, but a little twitchy and the suggested method was a linear in front and a CPL in the rear.

kirbic

Canon EOS R5

Canon RF 24-70mm f/2.8 L IS

08/30/2006 08:43:56 PM · #4

It does work. It can, of course cause vignetting on wide lenses, and there's the possibility of significant internal reflections (ghosting) due to multiple glass layers, so if you're doing this I'd try to use multi-coated polarizers. But it does work. Minimum ND value is about 2-3 stops total, depending on the polarizers, and maximum is ???

Edit: Yes! Linear in front, circular in rear. Why? Because a "circular" polarizer is just a linear polarizer followed by a "quarter-wave plate" that rotates polarization on half the light by 90 degrees. End result is that the second circular polarizer will cancel a maximum of 50% of the light from the first one. A linear polarizer does not have the "depolarizing" quarter-wave plate, so the second polarizer can cancel almost all the light coming through the first, at the right rotation.
Now, why not a linear in the rear as well? Answer: it doesn't matter, unless you want to retain AF, in which case you need the quarter wave "depolarizing" effect on the rear polarizer.

Message edited by author 2006-08-30 20:49:18.

Bear_Music

Samsung Galaxy S24, S24+, S24 Ultra

Sony 24-70mm f/4 Vario-Tessar T* FE OSS

08/30/2006 08:56:29 PM · #5

Originally posted by kirbic:

This is where I say "Oh, that makes it perfectly clear, you GEEK you!" :-)

R.

Canon RF 24-70mm f/2.8 L IS

08/30/2006 08:57:37 PM · #6

Well, that's even better as the only problem I was considering was how to mount two linear polarizers (which I assumed were more in the cokin form than round).

Put the circular on then attach your cokin holder to that polarizer and use a linear. You can spin the cokin any way you want and it would hold it in place. Sweet! I'm guessing a linear cokin filter wouldn't be too expensive.

I'll be unstoppable!

kirbic

Canon EOS R5

08/30/2006 09:09:31 PM · #7

Originally posted by DrAchoo:

I'll be unstoppable!

Or would that be "multi-stoppable?" ;-)

Originally posted by Row_Bear:

This is where I say "Oh, that makes it perfectly clear, you GEEK you!" :-)

R.

Guilty as charged!

eschelar

Canon EOS-7D

Canon EF-S 17-55mm f/2.8 IS USM

09/04/2006 01:51:52 AM · #8

I own both specifically for this purpose. I was a bit disappointed as it seems that the light reduction effect is NOT SMOOTHLY DISTRUBITED across the frame.

Indeed, it seems that there is a 'spot' that moves around throughout the frame as well as you rotate the filters.

Mine also gave a rather strong purple cast to the image. So strong that it might be difficult to remove, even when shooting in RAW.

I don't have my equipment with me right now as I'm still in transition, but I'll post some examples later if you like. PM me if you want.

My tests were done at 30 seconds shooting a white sheet of paper.

Tamron 70-180mm F/2.8 Di III VXD

09/04/2006 02:08:25 AM · #9

Interesting news Keiren. I'd love to see some test pictures before I go out and spend some money.

MadMan2k

Sony Alpha a6400

09/04/2006 02:47:14 AM · #10

I saw some sample pictures and heard from a guy who was able to get some really funky stuff going on with green foliage when he used two polarizers at once... it totally shifted the hue, almost like an IR filter but not quite. I don't remember if they were circular or linear, and he's not online now so I can't ask... here's the link:

//turbogfx.homelinux.org/gallery/v/experimental/bipolarization/

eschelar

Canon EOS-7D

Canon EF-S 17-55mm f/2.8 IS USM

09/04/2006 03:05:43 AM · #11

That's weird looking at those examples. I wonder if the purple cast would have anything to do with it. I didn't get a chance to try any real-world examples. I had a subject in mind, but never had time to put it together.

my gear is all sitting at a friend's house right now. I need to make a safe box for my apartment before I bring it over. I just moved into a roof top apartment which is pretty low in security.

the laptop is there too. I just have my little PDA at my house.

I will put it at the top of my priority list once I get moved in properly though. Expect it this weekend and if you don't get a PM, please PM to remind me.

my circular polarizer is very high quality and my linear polarizer is a bit cheaper, around 80 bucks for it.

Message edited by author 2006-09-04 03:06:24.

mobster

Canon EOS-400D Rebel XTi

Canon EF 50mm f/1.8 II

09/12/2007 12:56:39 AM · #12

Sorry to drag up this old thread but....

I've been wanting to do some long exposer shots (1-2 mintunes in bright daylight) so I was looking at buy some ND filters. And I also really need to buy a polarizer, but I can only afford to buy one or the other right now.

I could buy a linear polarizer and a circular polarizer for about the same price as that many ND filters. And if this would work then I could use the dual polarizers until I could afford to buy some real ND filters, and I would have a circular polarizer for those times that I need one.

So, I guess my question is will it work properly? and, how many stops will it block?

Thanks,
Matt

Canon 12x IS USM (S3 IS built-in Lens) -- 36-432mm (35mm EQ)

09/12/2007 01:38:05 AM · #13

Originally posted by mobster:

We never came up with the answer, but I'll tell you that for 1-2 minutes in daylight you are going to need probably more than 8 stops. Let's say you can get the exposure down to 1/30th of a second by stopping the aperture down and using ISO 100 or ISO 50. You are still 11 stops from 1 minute.

So my suggestion is go for it with the linear and circular (perhaps you could bring the linear back if it doesn't work), or look into a ND filter used for eclipse photos which is 15-stops or so.

GeneralE

Canon PowerShot S3 IS

09/12/2007 01:39:53 AM · #14

It might work, but you might also get interference patterns or moirÃ©.

If they anything like ordinary polarized glass, two linear polarizers could block nearly 100% of the light when at right angles, probably 1-2 stops when parallel, and variable amounts when at intermediate angles.

You can experiment with some polarized sunglasses.

GeneralE

Canon PowerShot S3 IS

Canon 12x IS USM (S3 IS built-in Lens) -- 36-432mm (35mm EQ)

09/12/2007 01:43:44 AM · #15

Originally posted by DrAchoo:

... or look into a ND filter used for eclipse photos which is 15-stops or so.

At our shop we have some high-contrast graphic arts film with a density of 3.8-4.2 (log scale), which is supposed to be enough to safely observe the sun during an eclipse. I'll have to play around with that ...

mobster

Canon EOS-400D Rebel XTi

Canon EF 50mm f/1.8 II

09/12/2007 12:51:36 PM · #16

Thanks for the help guys!

I think I'll give it a go... the worse that will happen is I'll have to return the linear polarizer.

As far as ND filter goes I know that B+W makes both a 10 stop and a 17 stop filter, I think when I get around to buying some ND filters I'm going to get a 10 stop, 6 stop and a 3 stop filter... that should give me plenty of blocking power.

Thanks again!
Matt

Olympus 12-45mm f/4.0 Pro

09/12/2007 01:06:09 PM · #17

Originally posted by mobster:

Man, if you do PLEASE report the results. I've had this at the back of my mind for a while now as a variable ND setup would be really useful for things like waterfalls and wave action.

mobster

Canon EOS-400D Rebel XTi

Canon EF 50mm f/1.8 II

09/12/2007 04:27:22 PM · #18

Originally posted by DrAchoo:

Man, if you do PLEASE report the results. I've had this at the back of my mind for a while now as a variable ND setup would be really useful for things like waterfalls and wave action.

Will do.

OdysseyF22

Panasonic DC-G9

09/12/2007 05:27:26 PM · #19

Don't they sell one that does this? It's been in ads in Outdoor Photographer, I think built by Sing-Ray, and as you twist the filter, it darkens the ND effect. I think I recall reading somewhere that this happened because they used polarizers.

Edit: Yes, here's the link to the Vari-D on Singh-Ray's website. It can go from 2 stops to 8 stops of ND. And at the bottom of the page, under the "Please Note" section, it states that it cannot be used with polarizers - because doing so would cancel out the remaining light, like

kirbic described in an earlier post?

Although at $340 and up, I don't see it fitting a lot of budgets...

Message edited by author 2007-09-12 17:31:36.

soup

Canon EOS-30D

Canon EF 17-40mm f/4.0L USM

09/12/2007 05:37:24 PM · #20

well for the cost of a couple decent polarizers i don't see the vari-d as being that out of line cost wise.
i have a mediocre 77mm CPL that ran a little over $100.00.

Canon EF 17-40mm f/4.0L USM

09/12/2007 06:27:07 PM · #21

Originally posted by soup:

well for the cost of a couple decent polarizers i don't see the vari-d as being that out of line cost wise.
i have a mediocre 77mm CPL that ran a little over $100.00.

WHAT? I have a perfectly decent 77mm CPL that ran $35.

soup

Canon EOS-30D

09/12/2007 06:29:40 PM · #22

decent in what sense? is it thin?

i dunno - i didn't shop around, and bought local, but the 55mm crappy one was $35.00. it works, but i'm not happy with the threading.

Sigma 30mm f/1.4 EX DC HSM for Nikon

09/12/2007 06:50:33 PM · #23

Originally posted by soup:

decent in what sense? is it thin?

i dunno - i didn't shop around, and bought local, but the 55mm crappy one was $35.00. it works, but i'm not happy with the threading.

No, it's not thin. It's a Hoya with their multi-coating. Thin will cost you extra, I suppose.

jdannels

Nikon D300s

09/12/2007 07:11:08 PM · #24

Originally posted by DrAchoo:

Originally posted by soup:
decent in what sense? is it thin?

i dunno - i didn't shop around, and bought local, but the 55mm crappy one was $35.00. it works, but i'm not happy with the threading.

No, it's not thin. It's a Hoya with their multi-coating. Thin will cost you extra, I suppose.

Where'd did you find it for 35 bucks? I got the $85 dollar multi-coated variety.