The extent to which a polarizing filter reduces the light that passes through it is measured by the amount of light that allows it to pass to be attenuated. That is, light already polarized in one direction is directed to a polarizer rotated to allow polarized light in that direction to pass. The measured difference between the brightness of the light before and after it passes through the polarizer is the amount of transmission loss.
When using a polarizer with light that is polarized in more than one direction, the amount of light that will be allowed to pass and the amount that will not be variable depends on the amount of total light that is polarized in the direction in which it is allowed. filter. Pass and how much is not.
Roger Cicala at lensrentals.com did a study of circular polarizing filters a while ago and wrote a blog post on this topic: My not nearly complete, but rather entertaining, circular polarizer filter article
He compared six different CPLs in a diameter of 77 mm with a price of $ 102 to $ 200 purchased from an important and recognized online seller (listed in alphabetical order).
- $ 102 – XS-Pro MRC-Nano High Transmission Circular B / W Circular Polarizer
- $ 200 – Heliopan Circular Polarizer
- $ 140 – Marumi EXUS Circular Polarizer Filter (EXUS is an acronym for a form of high transmission)
- $ 150 – Sigma water-repellent circular polarizer filter
- $ 103 – Tiffen Ultra Pol circular polarizing filter
- $ 180 – Zeiss T * Circular polarization filter
He found that all of them were at least 99.9% efficient in polarizing light. I could not say that none were more efficient because 99.9% was the limit of their measurement configuration.
He found that all of them were flat enough not to affect the IQ more than any of the others. In his words, "They all passed with great success."
Where they differed was in how much light they let pass when do not Polarizing light In other words, he already shone polarized light through them with the filter turned to allow the amount the filter could allow. A 50% reduction would be exactly one stop. Here are the results from least to most transmissive:
- 55% – Tiffen ($ 103)
- 58% – Heliopan ($ 200)
- 66% – Zeiss ($ 180)
- 68% – Sigma ($ 150)
- 88% – B / N ($ 102) (HT)
- 91% – Marumi ($ 140) (HT)
Note that the transmissive measurement is performed with light that is already polarized in the same direction as the filter allows. Any loss of transmission due to polarized light that is not allowed through will be Additionally A transmission loss measured in this test.
Roger noted that some shooters could actually want the ND effect of reduced transmission when using a polarizer, which is often used in bright sunlight. So it's not always necessarily true that more transmissive translate to best in terms of CPLs.
In terms of spectral response., the two high-transmission CPLs (B & W and Marumi) had almost identical graphics between 430-700nm, with a flat line of around 500-700nm and a drop in the blue end of things with a significant limitation of the wavelengths UV
The rest had curves similar to each other but different from the two high transmission filters. There was no UV cut or peel off in the blue sections, there was a slight increase through the green wavelengths, then a very modest decrease from green to red before a slight increase in infrared.
None of the types had individual differences between the colors when it was oriented to block the greater amount of light and when it was turned to block the least.
Roger's first conclusion:
If you are buying a circular polarizing filter because you want some circular polarization, it does not seem to matter much which one you choose; they all polarize as gang members. So today I saved you some money.
Then he went on to say:
The second point, one that I have been told before doing all these tests, is to set the white balance after placing the CP filter, not before. Because the CP filters will have a fused color. Or just shoot raw and repair it later, which is what we do most anyway.
The last important conclusion he drew was what he called "the painful one":
I did not want to try filters; I really did not do it. But people wanted me to do it. So I chewed up the budget of my test equipment to buy laser transmission material and an optical spectrometer, spent a few weeks doing everything calibrated and setting standards, and then a couple of days testing these CP filters. I did this in clear violation of Roger's Third Law: no good action goes unpunished.
Once I finished, I told Aaron that I had just documented that the CP filters had different percentages of light transmission and different colors. And those high-transmission filters had an aspect, and it was different from the normal CP filters, which were all really similar. Because I was proud that my investment in time and money would have been worth it.
Aaron took off the filters, put them on a piece of paper, took this picture with his cell phone and said: "Yes, you're right".
Later, Roger followed up with another publication in which he tested a couple of cheaper CPLS:
- $ 35 – Tiffen Circular Polarizer 77mm
- $ 45 – Hoya 77mm HRT UV Circular Polarizer (ostensibly a high transmission filter)
And measured the following:
- 38% – Tiffen CP with a spectrum very similar to the four non-HT filters above.
- 53% – Hoya HRT with a spectrum very similar to the two previous HT filters.
He noted that the lower transmission seemed to be related to the lack of antireflection coatings on the cheaper filters. They were also as flat as their test could measure, as were the first six filters.
Your final conclusion:
… There is not much doubt that, in terms of polarizing light, cheap CP filters do it very well. Also, as you would expect from uncoated or partially coated filters, they reflect A LOT more light. This is a major problem in a transparent or UV protection filter. Honestly, I'm not sure if it's a big problem for a polarizing filter.