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Filter classes

Hoya is the worlds largest and leading optical manufacturer. If your are reading this web pages with spectacles or contact lenses, chances are that high that you are reading through Hoya optical glass.
Obviously no two pieces of optics are the same. Not when you compare between manufacturers, nor between classes of the Hoya brand itself. On our web pages we try to explain the factors that make the difference. In the menu you can choose the filter class you want to learn about.

True differences

Quality is a rather vague term. A 'container' concept. The problem is: a difference in quality between one piece of glass and another might be totally invisible to the naked eye. The difference might appear clearly in a photograph. But to be able to compare, you would need to make two fully identical pictures, so the only difference would be that you did or did not use a filter in front (ceteris paribus). When comparing between similar classes of two different brands some visible differences are bound to emerge. Especially  when comparing two UV filters of two different brands.
So assessing the quality difference between two filters is difficult and complex. Every now and then professional magazines perform independent comparative tests between filters classes and brands. We tend to believe those comparisons and we advice you to do also, since the researchers are the professionals.
In the last national test, performed by the retail magazine Fotovisie, the majority of the branded filters that are offered in the Benelux have been compared. The journalist did not bother to test the numerous brand-less and cheap filters, similar previous tests (two years earlier) proved that most of them are not made of optical glass, nor are they polished and they perform appalling.
But amongst the tested (branded) filters, Hoya always appears in the top ranks, both as a result of the high resolution (pure optical glass, polished surfaces) and their spectral  quality (transparency, transmission, spectral composition. And there are more product attributes a Hoya filter distinguishes itself with, like thickness of the ring, number of coating layers, scratch resistance, resiliency and more. Hoya filters always come out on top. Surely we cannot always be the best in every attribute. Fair enough. But you can rest assure that with a Hoya filter you're always in the top ranks if not at the summit.


Obviously Hoya is very conscious when it comes to product quality and so do we as the official importer. In our headquarters in Almere we house a unique multi-instrument equipment that enables us to thoroughly examine photographic filters. We call it the HOTFA: Hoya Optical Testing Facility Almere.
With this equipment we not only perform tests on our own filters periodically as to affirm the quality levels, but we also very regularly test the other brands. That way we know that we offer the best there is to get.


A photographic filter is composed of a delicate piece of optical glass, that induces a certain filtering effect. Optical glass is totally different from normal window panes. Optical glass contains different elements to make it better suited to transmit light rays. As a result, optical glass is far more difficult to manufacture and consequently it is more expensive. So how do you know it you filter glass is made of true optical glass? Well, when you have no HOTFA and you don't do a ceteris paribus comparison, you will make photographs of less quality than necessary. But the good news is: you never have to doubt a Hoya filter. They are always composed of optical glass. And Hoya filters are always polished on both sides. So the glass surfaces are always totally plane. They need to be, since tiny, even microscopical irregularities in the glass or on the surface will induce a visible loss of sharpness in the detail of your images.
Again: Hoya explicitly distinguishes itself from the unknown cheap brands (or no-brands).


There are great differences in optical coating. Can you see it? No, not with the naked eye. Yes, when you do a test of compare images taken with different filters.
Thanks to our HOTFA we see everything. And so we learned that there are many other filter brands offer UV filters that are not UV filters at all. They are made of ordinary glass and they induce no effect in the UV spectrum (360-390nm). At the same time we measure unequal result in other regions of the light spectrum. Some other brands show a diminished transparency in red visible light. Or green.
Filters without a proper coating absorb and reflect light over the full spectrum. So they act as if they were some kind of neutral density filter. And some others just induce a color cast.
With Hoya filters this is not the case, since they are always coated. Depending of the filter class there's one, four of eight layers on both sides of the pane. Hoya filters do what they are expected to do. They induce a filtering effect.


Another important quality aspect of a filter is its mount. To start with the best: our HD-class filter is incomparable in its kind. The filter glass is directly locked inside the ring. There is no spring or screw ring. The glass sits clamped into the aluminium ring. This enables a very thin ring, which makes this filter class exceptionally well suited for (ultra) wide lenses.
All Hoya filter mounts are made of pristine aluminium, finished smoothly and sprayed black
inside and out to absorb unwanted reflections.


Hoya filter mounts are always composed of high grade aluminium alloy. Without a doubt this is the best material for a filter mount. Aluminium is very durable and weather resistant. But most important: aluminium alloy has a limited resilience. This will bring you advantage when you bump into something with your filter (and lens). The aluminium will absorb part of the energy and prevent further damage to filter glass or even your lens.
Now some other brands use very severe and unbending material. That will pass down all energy to your lens. And it might ruin the screw-thread of you lens too. Since many lenses nowadays are made of plastics.

Locked filter?

Some say that aluminium filter mounts are sometimes difficult to screw off. Well, that's true. Due to the suppleness of the aluminium a person might minimally deform the perfect circle and doing so, lock the thread into each other. It's just a matter of friction. And it's just a matter of doing things right.
When you mount or unmount a filter, don't pinch with your fingers, but alway put you hand flatly on top. The rim finishing will give you grip to the ring and the filter will willingly move inside the thread.

By the way, did you know that one of the brands that used to boast that their rigid iron mounts were better, recently started producing filters with aluminium rings themselves. It seems they start to see the light.