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Articles

2009-10-09
 

Polarizing filters test - supplement

1. Introduction

Originally posted 2009-04-27 on Optyczne.pl

After publishing our polarizing filters test new Hoya HD filters found their way to Polish shops, which, apart from a very catchy media name, were supposed to be mechanically resistant. We don’t pay special attention to that feature in our tests but, taking into account huge interest in these products, we decided to check their optical properties.

Polarizing filters test - supplement - Introduction
Hoya HD CIR-PL 72 mm

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What’s more, in the commentaries below some people were complaining, and not without a reason, that we omitted the Cokin system filters. That system is very popular among more demanding users because it allows them more freedom of action when working with filters (especially graduating filters). It is based on a universal filter thread, suitable for all SLR cameras, video cameras, medium and large format cameras. As a result you don’t need to buy a lot of filters with different diameters to fit particular lenses. We can use one set of filters with all the lenses and an appropriate holder.

Polarizing filters test - supplement - Introduction
Cokin filters system

Polarizing filters test - supplement - Introduction
Cokin CPL P164

The fact, that an ordinary filter can be simply put on and forgotten about and a filter with a holder must be put on and off constantly, can be considered a fault in the Cokin system. Maybe exactly because of this problem Cokin offers also an ordinary screw-on polarizing filter and we tested it, of course, as well.

Polarizing filters test - supplement - Introduction
Cokin Circ. Polarizer 72 mm

As a part of other updating of the test we added a Fomei WDG Circular Polarizer 72 mm filter and a King Digital Slim MC C-PL 72 mm.

Polarizing filters test - supplement - Introduction

The testing procedure and the assessment criteria, adopted by us, are similar to those used in the previous test and described more precisely on the following page. This way we were able to compare the results directly but you must take into account the fact that in the flares testing the frame lightning changed due to different season (snow).

Homogeneity was assessed compared to the reference image, which, due to difficulties of practical nature, was not ideal. In order to eliminate any doubts we should make it clear from the beginning: the visible artifacts don’t come from the tested filters but from the reference beam.

Polarizing filters test - supplement - Introduction
Reference image which was used during homogeneity test.

Filters’ homogeneity is tested by a parallel light beam. The best tool for obtaining such a beam is a laser but its usage entails some difficulties. Regardless of the sharpness surface position of used lenses every obstacle on the light’s way is clearly visible in the picture. The laser beam behaves as if it came from an infinite spot source. That’s why every obstacle casts a shadow with sharp edges (you must just take diffraction into account). The pollution, seen in the picture, consists in fact of just single specks of dust with dimensions in micron scale, which were made look bigger in the beam enlarger system. Of course you can obtain a “clear” beam in laboratories through space filtration and high standards of cleanliness of all the elements in the system but in practice a slight beam pollution is allowed. The same situation takes place in case of cleaning photographic lenses – sometimes it’s better to leave one speck of dust than to try to clean the lens again and bring several others inside

You should also be aware that, due to significant price rise in the last months it is difficult to compare the prices given here to the filter prices from the previous test. It was the reason why we decided not to publish the Econo- ranking of the tested products.

Seizing this opportunity we would like to thank warmly all the distributors who lent us filters for our tests:

Polarizing filters test - supplement - Introduction Polarizing filters test - supplement - Introduction

Polarizing filters test - supplement - Introduction Polarizing filters test - supplement - Introduction


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