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Vari ND with a polarizer?

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Rich Sims
Vari ND with a polarizer?
on Nov 21, 2010 at 8:54:07 pm

Hello,

Normally when we're shooting outside we invariably end up using a polarizing filer to deepen the sky, clouds etc.

Recently everyone seems to be extolling the benefits of using a variable ND filters as opposed to the normal NDs, this seems especially true when talking about DSLR setups.

Since the variable NDs are comprised of two polarizers spinning counter to each other to darken or lighten the density of the ND, I am wondering if the addition of a third polarizer, (the one to deepen the sky and clouds etc) will add any ill effects to the image, or end up further changing the degree of the ND achieved with the vari ND to begin with.

I'm going to be trying to run some experiments this week if time permits but wanted to put this out to the masses to get a greater understanding of what people have been running into.

Thanks,
Rich Sims


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Bill Davis
Re: Vari ND with a polarizer?
on Nov 22, 2010 at 5:57:04 pm

I'd be careful.

Even with the double polarizers like the Fader - you can find settings where you get "blotchy" results due to the alignment of dual polarizer elements. Adding a third might be more problematic than helpful - but by all means experiment away.

I think the primary reason that so many of us use them is that DSLR chips are so much more SENSITIVE than traditional 3 chip cameras with exceptional light gathering capabilities, so being able to reduce light at the lens is a big advantage - particularly in places like here in the southwest deserts where instead of cooling forrest greens and blues we have a lot of highly reflective desert scenics and city concrete to contend with.

But let us know how it works out when you try.



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Michael Sacci
Re: Vari ND with a polarizer?
on Nov 23, 2010 at 7:27:21 pm

While they let in more light you just cannot film outside without ND filters, all pro-level video cameras have them built in. So ND is a must for outside, always has been.

The reason they are really needed on a DLSR is that most people are trying to get shallow DOF so that is taking away the main way we limit light. With video you are locked into only a couple of useful shutter speeds unless you want "Gladiator" motion. So if we cannot change the shutter speed and we don't want to give up the wide open aperture for DoF we have to cut the light coming in.

Using single ND filters would be better than Faders but Faders offer a quickness and in the end are a bit cheaper than buying a set. I use a Fader and love it. I put a rubber hood on it and use it like I do the iris control, with a figure I can open up or close down, to adjust exposure, even within a shot.

Now if you want a ND and Pol, I would recommend get a fixed ND and a Pol. If you have a Fader and a Pol, even if it didn't cause you some funky patterns it would be a bear to adjust.

Just my 2 cents.


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Tony Connoly
Re: Vari ND with a polarizer?
on Nov 24, 2010 at 2:17:10 am

I see people refering to Fader as if it's a brand. Is Fader a brand? I got a Genus Fader from B&H and was annoyed that it has no threads for a lens hood. But I had read that Faders have threads.


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