Camera Filters Coatings and Multi-coatings, the quality difference.
Hoya manufactures a full line of camera filters in
both standard and Hoya multi-coated. The difference between Hoyas standard line and
that of other manufacturers is that Hoya standard filters have one layer of
anti-reflective coating applied to each surface of the glass. Many other manufacturers
standard filters are bare glass, and bare glass can reflect as much as 9% of the light
hitting it. This greatly increases the risks of flare and ghosting.
This can be seen in a simple test. Take a bare glass filter
hold it so that light reflection off the surface can be seen. Then take a long very thin
object like a pin or the tip of a pen and hold it over the filter so that its reflection
can be seen. There will actually be two reflections of the pin on the surface, one a
little more pronounced than the other. The more pronounced reflection is from the front
surface and the lighter one is from light reflecting off the rear surface.
Hoyas single layer coating decreases light reflection
off the surface from approx. 9% to an average of 4-5%.
To provide photographers with a higher quality
professionals require, Hoya created the Multi-coated line of filters. These camera filters
have a 3 layer coating system that further reduces light reflections off the surfaces of
the glass, the average is only 1-2%. This means that 98-99% of the light striking the
filter is going through it, and depending on the type of filter, into the camera lens and
onto the film. These layers of anti-reflective coating are bonded to the surface of the
glass in a furnace at a temperature of up to 800 degrees F.
You should beware! Some other manufacturers claim to have coated camera
filters. But this coating is often only applied to the front side of the glass, not both
sides like Hoya filters. Also, the coating on many filters is painted on or
applied as a cold spray that wears off easily.
Best of the Best
In 1996 Hoya introduced the line of Super Multi-coated
camera filters. Consisting of a Skylight, 1B, UV (0), ND 2X, ND4X, and a low profile
circular polarizer, this line of filters has a 5+1 layering system on each side of the
glass: 5 layers of anti-reflective coating and a transparent easy-clean top coat. This
reduces light reflections off the filter surface to an average of just 0.3%. This is the
lowest reflective rate on the market, from any camera filter manufacturer.
Lastly, how is the glass itself made? How do filters get
their color? Some manufacturers simply take two thin sheets of regular glass and sandwich
a colored gel or glue in between, as shown in the previous diagram. This process is called
lamination. It is a very cost-effective process but not a high quality one. Remember, the
disadvantage of this process is that over time the different materials can separate,
causing bubbling or pealing (referred to as de-lamination,) rendering the filter useless.
Also the thin gel used can shift its color so that the
filter does not yield the same color rendition over time. The last drawback of this
process is that all 6 surfaces of the three layers have to be perfectly flat and parallel.
If they are not, the filter will have a lens effect which can greatly reduce
To insure consistency in glass manufacturing, Hoya uses a
furnace called an Automatic V blender to mix the different materials at a highly
controlled rate. This process creates glass that is pigmented all the way through. With
pigmented glass there is no chance shifting over time. There is also no chance of
delamination. Also, the two surfaces of the glass are ground and polished for perfect
The only exceptions are Polarizer and Circular Polarizer
filters. No matter the brand or quality, they all are made of a polarizing film, or a
polarizing film and quarter wave plate in the case of the Circular Polarizer, sandwiched
between two layers of glass.
Hoya believes the filter frame is an extremely important
part of the filter as well. Hoya uses machined aluminum frames to hold their high quality
glass. They prefer aluminum to other materials because it is strong enough to hold up to
years of use. Some say that brass is the best material to use, however, Hoya doesnt
hold that view and here is why; brass is a far more rigid material than either aluminum or
the polycarbonates that are being use in todays lens barrels. This means that,
should the front of the lens get hit, the rigid brass filter ring will transfer almost all
the force of the shock to the lens barrels and mechanics. An aluminum filter frame will
absorb some of the shock by bending and at a certain point the glass will chip or break,
which is what the filter is supposed to do, protect the lens. Replacing a filter is always
preferable to getting a lens repaired.
The Value in a Hoya Multi-coated Camera filter
The wide aperture lenses of today are very expensive and
all photographers want to get the most speed, optical performance, and dollar performance
from their investment.
Say a customer pays $500.00 for a 28-70mm f/2.8 lens. Then,
to protect this investment the customer buys a cheap bare glass filter, which has a light
reflection rate of 9%. This filter is literally slowing the lens down by 9%, or
effectively turning a $500.00 f/2.8 lens into the equivalent of a slower f/3.0 lens worth
$455.00. The value of the lens drops 9% when you put the cheap filter on it. The cost savings
of the less expensive filter do not off set the loss of lens speed.
Also, this does not address the loss of sharpness or focus
shift, which can have a noticeable detrimental impact on picture quality. For these
reasons, Hoya multi-coated camera filters present the best value on the market today.
How to Clean Your
Hoya Filter Factors