You might recall a
thread
not too long ago where I was experimenting with stacking polarizing filters. I know that if you use two polarizing filters you can effectively reduce the amount of light coming through the filters by rotating them in relation to each other. The idea was to use two filters as a sort of adjustable neutral density filter. I discovered there is such a filter already on the market but it is rather costly. Here is some of my discoveries.
The CPL filter (circular polarizing filter) is different from a PL filter (linear polarizing filter). Apparently this improved CPL filter was needed for the new technology used in digital cameras. It is very popular because it is a needed improvement. My first experiment involved using two of these CPL filters stacked. When I changed the relationship the amount of light varied but there was a significant color shift towards the red and alternatively towards the blue. I was able to get around this undesirable effect by mounting first the CPL and then the PL filters. Having the PL filter on first results in similar problems with color shifts.
Here is my base shot with no filters on my lens.
Shutter speed value 1/256 s
Aperture value f/6.4
ISO speed ratings ISO 2000
Next I measured using just the CPL. Note: rotating the CPL had no effect on the exposure in this example but it did increase the shutter speed as well as change the aperture from 6.4 to 5.7
Shutter speed value 1/166 s
Aperture value f/5.7
ISO speed ratings ISO 2000
I added the PL (linear) filter and then adjusted it so there was minimum attenuation to the light coming in. Shutter speed increased to 1/128s.
Shutter speed value 1/128 s
Aperture value f/5.7
ISO speed ratings ISO 2000
I adjusted the PL filter until there was some difference noted in the exposure. The shutter speed increased as expected and there was no color shift noted - so far so good.
Shutter speed value 1/83 s
Aperture value f/5.7
ISO speed ratings ISO 2000
A few more degrees of adjustment gave me this image. I notice a small color shift here and again the shutter speed increased accordingly.
Shutter speed value 1/6 s
Aperture value f/5.7
ISO speed ratings ISO 2000
The next setting gave me a very noticeable color shift. And another increase to shutter speed.
Shutter speed value 1/3 s
Aperture value f/5.7
ISO speed ratings ISO 2000
I adjusted to what seemed to the maximum effect from these two filters. Note that auto focus no longer has enough light to focus. The color shift has approached what I believe is the color of Papa Smurf. The shutter speed is now increased to 1 sec.
Shutter speed value 1/1 s
Aperture value f/5.7
ISO speed ratings ISO 2000
Conclusion... I need a drink. I'm not sure the cost savings in buying two polarizing filters instead of a set of ND filters is worth it but the razzle-dazzle-ooo-ahh effect on anybody watching might make the whole project worth while. I thought a few of you might find this interesting. I appreciate any comments, questions or other conversation about this. I'll post some follow up shots when I field test this technique on our local fountain.
“Amateurs worry about equipment, professionals worry about money, masters worry about light, I just make pictures… ” ~ Vernon Trent
Interesting results...Not worth the time & trouble though...I'd join you in the drink department
I have an older "Spiratone" DAD (dial a density) variable ND filter that gives from 3X to 8X factor, but I don't use it too often..Got it on eBay for $3.51 plus shipping...I knew what it was, when I saw the DAD listing (I'm sure many people just passed it by not knowing any better)
I experiment, I just don't get that scientific. I'm not familiar w/that type filter Scott, but discovered Spiratone not long ago - maybe Spira was a bit of a mad scientist himself, they seem to have made some unusual lenses and filters etc
My Spiratone Variable is 55mm . Since I use a lot of older MF & AF Nikkors that have a 52mm filter thread I just use a 55 to 52mm step down ring & can't beat the price I paid unless someone gives one to you...
When the last candle has been blown out
and the last glass of champagne has been drunk
All that you are left with are the memories and the images-David Cooke.
chasrich wrote: I'm wondering if that shift to blue is because blue has a shorter wavelength or simply because my two filters are from different manufacturers...
Can someone please calculate the f-stops I achieved from 1/256s to 1s. I'm getting 8 stops plus the change in the aperture.
I think the prof is right about chopping off the shorter wavelengths.
Thanks. I did a little follow up on this. I took some shots going for the fastest and slowest shutter speeds I could attain. The fountain I used as a subject didn't give me the effect I had hoped for but the shutter speeds ranged from 1/8000s to 16s using the ISO settings and the two filters.
Nice to know I have that kind of range to play with in daylight.
“Amateurs worry about equipment, professionals worry about money, masters worry about light, I just make pictures… ” ~ Vernon Trent
Thanks. I did a little follow up on this. I took some shots going for the fastest and slowest shutter speeds I could attain. The fountain I used as a subject didn't give me the effect I had hoped for but the shutter speeds ranged from 1/8000s to 16s using the ISO settings and the two filters.
Nice to know I have that kind of range to play with in daylight.
Big difference, I wonder how many stops that would be equal to?
SWM into chainsaws and hockey masks seeks like-minded SWF. No weirdos, please
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Nice test!
Great thread Chas!
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