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The importance of quality in optical glass for filters

When it comes to photographic filters, whether they are square or circular, the quality of the materials used for in their production is critical. As photographers we will spend hundreds, and often thousands, of pounds on our cameras and lenses with the aim of producing the highest quality images we can.

However, when it comes to filters, we often choose a low-cost solution without considering that no matter how good our lens is, it can only process the light that reaches it.

So whilst putting anything in front of the lens will, by its nature, affect the image, it is critical that you minimise the unwanted effects of low quality or cheap products.

In the following article, we explore what makes a great filter and by omission what makes a bad one.

Why use quality photographic filters?

The photographic filter is, in effect, another lens element: once mounted, the light must pass through it to reach your sensor. So if you have a poor quality filter with low transmittance, your image is never going to be as clear and sharp as it has the potential to be. To put it another way; the quality of the shot will be defined by the quality of the weakest optical element. Since photographic lenses are all precision optical instruments, we will have to ensure that the filters we mount on them are of at least equal or superior quality.

The importance of quality in optical glass for filters

Resin or Optical Glass?

At one time resin filters were readily available on the market due to the fact that producing a resin filter was relatively inexpensive, and the range of filters on the market did not justify the use of other materials.

Unfortunately, the cost-effectiveness of resin filters is the only real advantage, as their optical behaviour has several disadvantages, including:

  • Poor optical quality
  • Optical density is never uniform, resulting in loss or uneven sharpness
  • Can slightly shift the focusing plane unevenly
  • Irregular densities. A 10 stop filter will never really be 10 stops
  • Easy to scratch

There is a reason that lenses and glasses are not made of resin: optical quality does not accept compromises. To ensure quality, NiSi Filters has chosen to use only lens grade optical glass for its products, then coating it with the latest innovations in the field of nano-coating. Like any glass object, the only real disadvantage of optical glass filters is its fragility. But even a resin filter, if subject to falls, can deform irreparably or scratch heavily: even if not smashed it would be unusable.

When we think of an optical glass filter as any precision optical object and treat it accordingly (would you ever throw your precious lens on the table or would you manipulate your glasses with your hands covered with sand?), We are left to consider only the advantages:

  • Very high optical quality, equal to the best photographic lenses
  • Possibility of applying hydrophobic, oleophobic and IR nano-coatings
  • Uniform density
The importance of quality in optical glass for filters

Are all glass filters the same?

It is easy to understand that not all glass is the same (raise your hand if you have ever tried long exposure with glass from a welding mask!)

Even within what is commonly classified as “Optical Glass” there are substantial differences: in fact there are over 120 different types of optical glass according to their intended use.

After the introduction by NiSi Filters of the highest quality, lens grade optical glass filters, many manufacturers have tried to emulate our success but, not all optical glass is equal.

The Optical Glass chosen by NiSi

Unlike other filter manufacturers who have chosen multipurpose optical glass such as the SCHOTT B270 or the D263, NiSi uses glass intended for advanced optical applications, choosing the only one capable of meeting the requirements required based on the three main properties of an optical glass for photographic filters:

  • Refractive index: quantifies the decrease in the propagation speed of electromagnetic radiation when it passes through the filter.
  • Abbe number: which in our case quantifies the colour dispersion and chromatic aberration that will introduce the filter
  • Transmittance: which indicates the relationship between the intensity of the radiation transmitted within the filter and the intensity of the radiation incident on it
The importance of quality in optical glass for filters

The choice of lens grade optical glass ensures that those who choose NiSi filters have the same material in their hands as used in the construction of astronomical telescopes and precision measuring instruments. This particular type of glass is protected by several international patents and manufactured by only one factory in the world exclusively for NiSi.

NiSi thinks that photographic lenses do not deserve a trivial, multipurpose glass that isn’t even used in the cheapest lenses. The NiSi ND and GND filters use only the best optical glass on the market.

The same as used in the finest elements of the best optical lenses on the market. All treatments and coatings are of the highest quality and applied with cutting-edge machinery, so that the photographer can focus on what really matters: photography.

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