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04-10-2018, 03:03 AM - 2 Likes   #46
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Even if we stipulate that AF is now arbitrarily sensitive such that with linear polarization there is always enough signal with any real polarizer, there are still the potential issues of P-TTL acccuracy and focal plane array sensitivity uniformity to be measured, or demonstrated to be negligible. So any testing of LP vs CP needs to be wider ranged than just proving AF is unaffected.

04-10-2018, 03:59 PM   #47
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My manual focus film camera have no problem with linear polarizers.
I choose them for their more pronounced effect.

In a pinch a linear polarizer can be useful when you don't have a neutral density filter.
I don't suppose a circular polarizer would be much use for this purpose.

Chris
04-10-2018, 05:31 PM   #48
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QuoteOriginally posted by ChrisPlatt Quote
In a pinch a linear polarizer can be useful when you don't have a neutral density filter.
I don't suppose a circular polarizer would be much use for this purpose.
One thing are linear or circular polarizers, another is Neutral Density, Neutral density is basically made up of two linear polarizing filters assembled,
which when rotating, progressively decrease the light which passes through the lens and is received by the sensor.
I have some that go from ND1.8x or (x64) to ND3x or ND1000x and also (ND2000x) they serve in all the circumstances in which you want to lengthen the times of exposure
and/or to create particular effects in proximity of water sources or with the clouds of the sky etc.
04-10-2018, 05:55 PM   #49
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QuoteOriginally posted by ChrisPlatt Quote
My manual focus film camera have no problem with linear polarizers.
I choose them for their more pronounced effect.

In a pinch a linear polarizer can be useful when you don't have a neutral density filter.
I don't suppose a circular polarizer would be much use for this purpose.

Chris
You can stack two linear polarizers or stack a linear polarizer in front of a circular one to create a variable ND filter. You can stack two circular ones but the front one must be reversed for it to work.

The results are extremely sensitive to the quality of BOTH filters and usually there's a nasty color cast.

If you have a bunch of polarizers of unknown quality, you try various paired stacks (rotated to maximum darkness) to work out which are decent and which are lower quality. The darkest pair are your best two polarizers. It's a bit of a logic puzzle because if a pair can't produce a dark color-free filtering, you don't know whether the front or back polarizer is the cause unless other pairings prove one of them to be good.

Another quick test is to look through the polarizer at a high-quality LCD panel such as are found on laptops, monitors, and smartphones. To get good blacks on an LCD, the screen needs a very high quality polarizer. Rotating a good photographic polarizer will make the screen go to almost black whereas a bad polarizer will let more light through or have a color cast.

04-10-2018, 07:38 PM   #50
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QuoteOriginally posted by photoptimist Quote
You can stack two linear polarizers or stack a linear polarizer in front of a circular one to create a variable ND filter
Hi photoptimist, ChrisPlatt, kaseki ....!

Since the discussion between circular and linear filters is always alive, I would ask (Let's assume that I don't know).
What can happen if you put 2 linear polarizing filters crossed at 90, and if you put even 3?
04-10-2018, 08:02 PM   #51
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QuoteOriginally posted by maw Quote
Hi photoptimist, ChrisPlatt, kaseki ....!

Since the discussion between circular and linear filters is always alive, I would ask (Let's assume that I don't know).
What can happen if you put 2 linear polarizing filters crossed at 90, and if you put even 3?
In theory, two crossed polarizers would let no light through at all.

In practice, polarizers aren't perfect and crossed polarizers let some light through. Moreover, most polarizers are not perfectly color-neutral so the crossed polarizers often have a strong color (usually blue in my experience).

Three cross polarizers would let even less light through but the color effects would be even stronger.
04-10-2018, 08:53 PM   #52
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QuoteOriginally posted by photoptimist Quote
Three cross polarizers would let even less light through but the color effects would be even stronger.
I like your way of thinking, for three linear polarizers crossed it would take at least three hands (you can do it with two) or a friend who helps you in the experiment, or by deduction.
I say nothing... You can see the result through the movie, even if it is not of good quality.

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