Neutral Grad interfering with polarizer ?

[JeanChristopheChouillet]

Hello all,

I have noticed that my resin  grad filters (bought on ebay, supposedly branded Kood) affect polarized light in a strange way. Here are pictures of two filters against LCD screen (polarized) taken through a CPL filter in different positions.
minimum and maximum polarization :


Would this have a strong negative effect on my pictures when stacking CPL and grad ? (I haven't really noticed myself, but...)
And do more expensive grads behave better ?

(I have already asked about this in a different forum, but was only told it was due to tensions in the resin)

thanks

[wittsend2]

Could be interference fringes due to the gel filters not being perfectly flat.

[dsp]

Would this have a strong negative effect on my pictures when stacking CPL and grad ? (I haven't really noticed myself, but...)
And do more expensive grads behave better ?

(I have already asked about this in a different forum, but was only told it was due to tensions in the resin)

thanks

Hello,

Most plastics have poor polarization properties, and alter the polarization of transmitted light.  As reported in the other forum, it usually has do do with different amounts of strain in the material.  Not sure about cost, but any glass ND should be better for polarization.  That said, if you stick your circular polarizer in front of the ND, the polarizer will still do its job perfectly.  For some cameras, like dSLRs, it is possible that the screwed up polarization coming through the filter could affect the metering or autofocus, as in many cases, the mirrors that bounce the light to the sensors have (linear) polarization sensitivity, but I would only worry about that if you see these affects.

best regards, Darcy

[Michael Bailey]

I believe dsp is right. It's best to shoot with the polarizer at the top of the stack, farthest from the camera. That way you're not asking it to polarize the plastic in the ND filter. I can't swear this will fix the problem but I'm pretty sure the alternative is disastrous.

[JeanChristopheChouillet]

Aha, I hadn't thought of that. Placing the polarizer on top of stack does indeed solve the issue, thanks for the idea.
Pity that my filter holder (Cokin P) has the polarizer slot at the bottom, or that it isn't convenient to handhold the polarizer.

I know there are many landscape photographers who stack CPL and grads. How do they deal with this ? (perhaps they just buy Lee grads)

[Davidlu]

Hi Jean-Christophe,
Which Polarizer do you use and which grads?
I had never problems using a Polarizer with my Hitech grads.
The image quality is certainly inferior as if i would take photos without filters,
but they aren't really noticeable.

[Outback Shooter]

as an FYI, I always use filters purchased from Singh-Ray, except for 1 of my polarizers.  Here's my list of ND filters & polarizers:
1.  Singh-Ray Vari-ND, thin mount.
2.  Singh-Ray LB Color Combo:  LB Warming Polarizer & LB Color Intensifier in 1 filter.
3.  Galen Rowell Graduated ND filters:  2 & 3 soft step in 4x6 size that I 'wave' over my lenses while shooting.  Sometimes I stack them, depending on the light.
4.  Nikon circular polarizer, thin [yes, a Nikon polarizer mounted on a Canon camera!]

Tony Sweet recommended these filters to me personally and I've been very happy with the investment.

Best wishes in your shooting!