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 03/02/2011 02:28:21 PM · #51
Originally posted by Bear_Music:
Originally posted by Citadel:
More related to the original post, I just happened to come across this:

//www.photorepublik.com/articles/20110202/all-one-cameron-mc-fader-nd-filter

You can adjust the ND effect from 1 to 8 stops. I know Singh-ray has something similar but its stupidly expensive. This one looks to be bit more reasonably priced.


This appears to be two polarizing layers co-axially mounted. That got me to thinking, I had an "AHA!" moment: I have a 77-67mm stepdown ring, and I have 67mm and 77mm polarizers, so this means I'm all set right?

NOT.

I think because mine are circular polarizers, the effect doesn't happen. I'm assuming the referenced variable ND Filter uses linear polarizers, which can cancel each other out? Anyone know?

R.


Exactly correct Bear... You need 2 linear polarizers set at 90 degrees for full extinction, which, incidentally, should be more than 8 stops, it should be completely black, but then, perhaps that's not true when talking about big scale stuff (I'm used to this stuff from mineralogy, we use polarizing scopes to look at rocks under crossed polarizers, incidentally, if you have something between the two polarizers, you can tell how much it bends light, very useful for identification of small minerals, and their different phases...)...

ETA: According to master kirbic, you only need one linear polarizer... The second can be either type apparently...

Message edited by author 2011-03-02 14:29:45.
 03/02/2011 02:42:02 PM · #52
Originally posted by coryboehne:
ETA: According to master kirbic, you only need one linear polarizer... The second can be either type apparently...

Should be able to test this with a CP filter and some (probably linear) polarized sunglasses.
 03/02/2011 02:55:18 PM · #53
Originally posted by GeneralE:
Originally posted by coryboehne:
ETA: According to master kirbic, you only need one linear polarizer... The second can be either type apparently...

Should be able to test this with a CP filter and some (probably linear) polarized sunglasses.


Yep, just make sure the CP is the one *closer* to your eye.
 03/27/2011 10:55:04 PM · #54
OK, I picked up a used linear polarizer for $8, and I can confirm that you can achieve almost total opacity by rotating the two in relation to each other; you can then further alter the color balance by rotating the two together.

Originally posted by kirbic:
... just make sure the CP is the one *closer* to your eye.

I did this, but why does it matter?

I was able to blur the water in these fountains with a 2-second exposure at f/8.0 and ISO 80. I was using a little table-top mini-tripod, so I think the BG has a little vibration-blur. Or, it may be a bit OOF because I let it use auto-focus instead of just setting it at infinity; focal length is 291.6mm (35mm EQ). I lightened it a bit with Curves.

This one is unedited, shot with a 4-second exposure.

Message edited by author 2011-03-27 23:06:40.
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