Polarizer Filter

This really is a hoary old chestnut of a subject . The usual discussion is about circular and linear polarisers and, I think, we are all agreed from empirical evidence that it doesn't matter with Pentax auto focus systems which type we use. My filters, for digital, are now all SMC Pentax ones apart from one multi-coated Hoya polariser. I can think of several reasons for using a Uv or similar for 'protection' - salt water spray for example and I can just run the filter under a tap - and I want an SMC Pentax filter on my SMC Pentax lens!

Curiously, I just picked up on Ebay a Pentax 49mm circular polariser. Now that raises a question, why have Pentax produced a circular polariser?

Not sure if they still make them, I picked up mine many years ago long before digital SLRs.

I've only owned one SMC Pentax filter and I must have been unlucky as it developed problems with the coating and therefore hasn't been used since. I wasn't best pleased at the time though as it was a fairly large size (67mm) and therefore not cheap.

I'd moved to Cokin "P" by that point though so didn't buy many other screw-on filters after that (although I did add a 77mm screw-on circular polariser date as that fitted - and still fits - many of my most-used lenses).

The idea of describing a filter as "digital" seems to have caused a bit of a stir. I have a Jessops "Digital Pro Filter" (Circulat Polariser) in front of me now, and their rationale is as follows:

Digital Multi Coated - greatly reduce lens flare and ghosting caused by reflections

Black Almite Frame - a black matte aluminium satin finish frame for reducing reflections

Black Rimmed Glass - reduces light reflection around the filter edge

Low Profile Frame - ultra thin filter frames to help avoid vignetting on super wide angle lenses

Knurled Edge Frame - for easy attachment and removal

At £39.97 it is not the most expensive polariser. At the offer price of £2 it might be considered reasonable.

I must say the "digital" description doesn't offend me as it does others, I merely take that as an indication that it has had some effort put into the particular needs of digital imaging. It could of course be equally valid on a film camera, but at least the description indicates what it has been designed for.

I am interested to know whether you think the description given is valid or not, and whether or not you feel it is reasonable for the filters to be given the "digital" tag.

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But I fail to see how "Digital Multi Coating" can possibly equate to "the particular needs of digital imaging". As far as I'm concerned, there's no difference between film and digital until the light exits the last element of the lens, and the angle at which it does so, and the reflectiveness of the rear element, are the only factors that, I feel, can have a 'Digital' design.

Anything in front of the lens cannot change the way light behaves towards a digital sensor specifically.

By the way, that description of the Jessops filter sounds very much like that of the Hoya.

Dan

I agree it's a moot point and that it can be backwards applied to film cameras as well.

The only relevance is that when the lens is open the CCD, being highly reflective, is more susceptible to flare and attention to all the lens elements, including the filter as part of the optical train, will be beneficial to some degree. Especially the rear filter it is true, but imagine how poor it would be with a properly treated rear element and no coating anywhere else. This would be dreadful and shows that it's not only the rear element that is rrelevant to digital performance.

It was the need for greater attention to flare reduction that motivated the production of improved filters, and why not? I'm very happy if the filters are better in the ways that have been described, both for digital and film.

my objection is mainly that I would like them to say what they mean.

All of the above listed features are clearly desirable in a high quality filter, whether it's for film, digital or an optical tele/microscope, but as far as I can see none of them is inherently "digital". The term is meaningless in this context, and is simply tagged onto things in much the same way "automatic" once was, to make the product sound high tech.

Since the term in relation to filters is at best poorly defined, I ignore it. Perhaps I am being overly cynical, but there's nothing on that list which couldn't have been done 5 or even 10 years ago.

The only thing which may have changed is the exact composition of the multi-coating, and I would still be willing to bet that a Pentax SMC filter from 10 years ago has better coating than a Jessops Digital filter today.

That's fair enough, but it is important to differentiate between a supposition like that and a fact, because we don't know that that is correct, and it might be quite wrong.

One thing is certain and that is that ten years ago there were not many multicoated polarisers around. Many were even uncoated, including quite good ones. Improved technology has made better polarisers possible.

Agreed, improved manufacturing techniques have made multi-coating a lot cheaper and easier to do, and I didn't mean it to be taken as a fact, just a strong hunch.

Well i must say it's been very interesting reading all of your points of view on this issue, and i too think that the digital filter is a load of hype. Therefore i have purchased a none digital hoya polorizer for £20 off e-bay.