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Archive 2012 · Variable Neutral Density Filters-- polarizer needed?
  
 
ericspicts
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p.1 #1 · Variable Neutral Density Filters-- polarizer needed?


I am considering the purchase of a variable neutral density filter and am looking at the expense for the best rated ones as opposed to just using single nd filters as I have been doing. Since most of the use will be for moving water shots, I would think that I would also want to be using a polarizer to cut down on glare off of rocks etc. So I am thinking that if I am going to plunk down the money for a variable ND, I mine as well get one that combines variable nd with a polarizer rather than stacking.

The singh-ray duo is the only filter I have seen that explicitly states that they have a polarizer combined with a variable neutral density filter.

But then as I read how a variable neutral density filter works, I find that all that is happening is that the manufacturer is placing a circular polarizer in front of a linear polarizer. So if this is the case, the variable ND is functioning as a polarizer correct?

So do peopel using variable ND's see the need for additional polarization?

Please let me know.



Aug 12, 2012 at 03:21 PM
Micky Bill
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p.1 #2 · Variable Neutral Density Filters-- polarizer needed?


From what i understand about my Fader ND it is 2 polarizers that act as both polarizers and ND. I don;t think adding a third would be much help...might make it even darker, more ND?


Aug 13, 2012 at 04:10 AM
aborr
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p.1 #3 · Variable Neutral Density Filters-- polarizer needed?


The 'variable' part of a variable ND is a circular polarizer on top of a linear polarizer.

You can use a polarizer in combination with a conventional (fixed) ND filter.

But, it makes no sense to put a polarizer on a variable ND, because that would give you three polarizing elements in the light path, one of which probably has its orientation fixed.



Aug 13, 2012 at 05:41 AM
 

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ericspicts
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p.1 #4 · Variable Neutral Density Filters-- polarizer needed?


Thanks. So from what I can tell, most variable nd's are a linear polarizer in front of a circular and there is little control as to how much polarization you are dialing in as you go.

I have read posts about making your own simply by putting your own linear polarizer in front of a circular, and it would seem that since both rotate, you then have control over both nd and polarization -- perhaps this is what singh-ray is doing to give control of polarization in their duo. I am thinking about just going this route with two polarizers but it is unclear to me how the focusing would work as I also read that a linear polarizer messes up auto focus, but then something must be possible for the vari nd's to work.

The reviews on vari nd's seem to be all over the place. Maybe the best best is to just find a shop with a good return policy and try a variable nd.



Aug 13, 2012 at 10:24 AM
aborr
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p.1 #5 · Variable Neutral Density Filters-- polarizer needed?


That seems reasonable. I tried the "do it yourself" route with a good quality CPL and a somewhat 'vintage' linear polarizer I had from my early film days. With my particular combination, I found I got a nasty color cast that I couldn't clean up in Photoshop when I went beyond about three stops of reduction.

I haven't tried any of the variable ND's from Singh-Ray or others. Some FM'ers have reported that they work pretty well.



Aug 13, 2012 at 11:07 AM
dsjtecserv
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p.1 #6 · Variable Neutral Density Filters-- polarizer needed?


This will work with two linear polarizers as well, but you would generally want to use a circular polarizer in the "innermost" position, for the same reasons as when using a polarizer alone. I experimented with this, using a standard threaded CP and a holder-mounted Lee 4 x 4 linear polarizer. The idea was to adjust the innermost polarizer for the degree and location of the polarization effect, and then adjust the outer polarizer (without moving the inner) for the degree of neutral density. This worked, but as others have reported, I got a blueish color cast and discernible pattern of uneven darkening (X-shaped) when the adjustment approached 5 stops. I returned the Lee linear polarizer and now just use standard ND filters, when needed, in conjunction with the threaded polarizer.

Dave



Aug 13, 2012 at 07:58 PM





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