Optical Glass vs Resin Neutral Density Filters – Which Is Best?

When it comes to optical performance in photography, the quality of lenses and filters being used plays a huge role in the overall quality and sharpness of the images being produced. Quality camera lenses are finely tuned pieces of equipment containing multiple glass elements which are aligned to direct the path of light rays as accurately and efficiently as possible to the camera’s sensor. If light is not passing through the lens correctly, and points in the image are not being translated accurately between those glass elements, when that light hits the sensor optical aberrations occur. This will be noticeable in images through reduced sharpness, blurring of pixels, chromatic aberration (misalignment of colours), reduced tonal contrast and just an overall reduction of image quality.

When you are using lens filters of any kind such as neutral density filters, graduated neutral density filters, polarisers and even UV filters, you are adding an extra “element” (and sometimes multiple elements when stacking filters) onto the front of a lens. The camera sensor will receive information in the same way as it would without that filter – the light still needs to pass through the glass elements of the lens and onto the sensor in the most accurate and efficient way possible. Any changes to the path of the rays of lights will impact the performance of the camera.

When you consider that accurate light transmission is the key factor in photography, it makes complete sense that the optical quality of lens filters you use also needs to be of the highest standard to match the glass being used in lenses. If you take a precision piece of equipment like a camera lens and then use low quality filters which limit, shift or change the path of light in any way, chances are very high that the images you produce will not be highest quality possible from your chosen camera and lenses.

When it comes to lens filters there are two major manufacturing materials being used by different brands on the market – glass and resin. NiSi use only the highest quality optical glass in the manufacturing of our filters – the exact same quality of materials being used in deep space telescopes, scientific microscopes, medical imaging and other highly specialised fields of advanced optics that require the highest possible degree of precision. Optical glass has very little to no imperfections in it, and will not distort, or impact on light as it passes through.

Let’s take a look at the advantages and disadvantages of both optical glass and resin when being used for neutral density and other types of optical filters being used for photography.

Why choose Optical Glass filters?

 

Quite simply, optical glass provides the highest degree of accurate light transmission and colour reproduction for lens filters. The internal elements of modern, high quality camera lenses elements are made of optical glass and are aligned to maximise the accuracy of the paths of light being transmitted through them. As mentioned above, any variations to that path of light through the lens elements will cause optical aberrations. By using the same high quality glass found within lens elements to manufacture our filters, we are ensuring the highest possible chance for the accurate light transmission from the filter, through the lens and onto the camera sensor.

Optical glass filters in the NiSi product range have a uniform density across the entire filter, ensuring light transmission is consistent throughout the entire glass filter element. This ensures that no vignetting can occur, colour reproduction is at it’s best, and that corner to corner sharpness is maximised and not impacted on as light passes through the lens to the sensor.

Optical glass filters are able to be coated with our proprietary NiSi IR-Nano coating which allow filters to be cleaned and maintained easier. Water and other liquid will tend to “bead” rather than spreading and smearing across the filters. Our coating also adds a protective layer to help with scratch resistance to maximise the life of your filter. These types of coatings are not suitable for resin filters as they simply do not stick to them.

While optical glass is less prone to scratches than resin, just like with other glass items mishandling by dropping is more likely to cause breakages than resin. Care should be shown when handling optical glass filters just as you would a wine glass or other glass objects, and possibly even more so with a precision optical tool like a neutral density filter!

NiSi GND Filter Sharpness
NiSi GND Filter Sharpness
Resin GND FIlter Sharpness
Resin GND FIlter Sharpness

Advantages of Optical Glass for camera filters

 

Best possible light transmission – The properties of high quality optical glass allow for the most amount of light to be transmitted accurately through the lens to the camera sensor. Optical glass has very little to no imperfections in it, and will not distort, or impact on light as it passes through.

Maximum image quality potential – Why put a cheap piece of resin (or even low quality glass) on the front of your expensive lenses? By using quality optical glass filters you are increasing your chances of producing the best quality images possible.

Uniform density – Optical glass can be produced to ensure the exact same density of material is use throughout the entire filter, ensuring uniform light transmission throughout the entire filter.

No focus shifting – When shooting through optical glass, the focal plane does not shift in any way. This means you do not need to adjust your camera focus when compared to using no filters.

Less likely to scratch – Optical glass is a far denser, harder material than resin. The filters in our NiSi product range are far less likely to scratch than filters made from resin.

Water and scratch resistant coatings can be applied – Protective coatings that add an extra layer of durability and scratch resistance such as our NiSi IR-Nano coating can be applied to optical glass. Similar coatings just simply don’t stick to resin.

Optical glass filters can be stacked together – Using multiple neutral density filters at once will not impact on image sharpness when using optical glass filters in the NiSi product range.

Resin is much softer than glass and is much more prone to scratches.
Optical glass filters are less likely to scratch and can have a protective coating applied to them.

Disadvantages of optical glass for neutral density filters

 

More prone to breakages – While optical glass is less likely to scratch than resin filters, they are more likely to crack, chip or shatter through mishandling or droppages.

More expensive than resin filters – The complex process involved, and the cost of the materials being used to manufacture optical glass is far more expensive than producing resin. This can make the purchase price of optical glass filters more expensive when compared to resin.

The Nano coating on our NiSi filters allows water to bead and be easily wiped off allowing for easy cleaning when compared to resin filters.

Why choose resin filters?

 

For many years resin lens filters were the most commonly available on the market. There were not many manufacturers producing filters, so lack of competition and innovation in the industry just didn’t push brands to improve the quality of their products, or to invest into new materials and manufacturing processes. Resin is very cheap to manufacture compared to optical glass, but the trade off in image quality from lower quality light transmission is very easy to notice when comparing each material.

One benefit that resin filters have over glass filters is they tend to be more durable in certain situations. Resin does not shatter when dropped, and it is more flexible and able to handle slight bending. But the flip side to this is because resin is a softer material, filters made with resin are far more likely to get scratches, which can have a huge impact on an already degraded image quality.

Variations in density across different parts of an individual filter, or even when comparing two different filters of the same type are far more likely to occur with resin that with optical glass. Some filters such as graduated neutral density filters are quite often “dipped” into a dye solution which is absorbed into the resin to create the darker parts of the filter, and this process often creates inconsistencies in the end result.

Resin ND filters are very well known as not being truly “neutral” in their colour reproduction. This causes a shift in white balance throughout your images and tends to produce images with a blue or magenta cast, or images that have a brown or yellow colour cast depending on the brand of filter you are using.

If overall image quality is of primary concern to you, resin filters simply do not perform as well as optical glass filters. But when it comes to the initial purchase price, if you are happy to trade quality and performance for budget, resin filters may be an option for you. Just be prepared to replace them with a higher quality set of filters when the photography bug truly takes over and you realise what you have been missing out on!

Advantages of resin for neutral density filters

 

Cheaper to manufacture – Resin is far cheaper to produce than optical glass, which is why resin filters tend to be cheaper than optical glass filters.

Less likely to shatter when dropped – Resin is softer and more flexible than optical glass and is far less likely to shatter when dropped.

Resin filters bend very easily and cause the focal plane to shift, decreasing sharpness.
Glass filters do not bend and will maintain the correct focal plane, ensuring edge to edge sharpness.

Disadvantages of resin for neutral density filters

 

Lower light transmittance – Resin filters restrict the amount of light coming into a camera, even when they are clear. Due to unevenness in the density of the actual resin itself in different parts of filters, light cannot pass through them as efficiently and accurately as with optical glass

Reduced image sharpness – Due to the inaccuracies caused in the paths of light passing through resin filters, image sharpness can be negatively impacted.

Shifting focal plane – Resin filters cause a shift to occur in your focal plane. Think of it like looking through a plastic soft drink bottle. Not everything lines up exactly as it would without the filter. Quite often you need to refocus your camera if you attach any resin filters to your lens. You may also find that focus is uneven in different parts of an image due to the potential differences in uniformity of resin across a single filter.

Inconsistencies in light reduction – Resin filters often have inconsistencies in either the density of the material itself, or in the chemicals used to dye the filter to create the reduction of light for ND filters.

More likely to scratch – Resin filters are much softer and more flexible than optical glass. This means they are far more likely to get scratches on them.

More likely to cause vignetting – Because of the lack of uniformity in the density of the material, and due to the impact of reduced light transmittance when compared to optical glass, resin filters are far more likely to cause vignetting.

Film coatings cannot be applied to resin – Film coatings like our NiSi IR-Nano coating just simply won’t stay applied to resin. This means resin filters tend to lack the protective layer that allows dust and liquid to be cleaned off easily, and also lacks any scratch resistant layer over an already soft material.

Stacking filters can further reduce image quality – If a single filter can reduce sharpness and overall image quality, stacking multiple filters together is going to exponentially decrease image quality through those multiple layers, and this is quite often the case with resin filters.

Which is best – Glass or Resin ND Filters?

 

If image quality is of primary concern for you in your photography, then without a doubt optical glass filters will be the better choice when compared to resin. Optical glass produces the best quality light transmission, a far more uniform light distribution throughout the entire image, less chance of colour shifting, better sharpness and lack of optical aberrations. What is the point in impacting on your image quality by limiting, restricting , reducing or negatively impacting on the quality of light your camera sensor receives?

If budget is of your primary concern, resin filters can be a more attractive option to many due to their cheaper price. But consider this – on modern, high resolution digital cameras optical aberrations are far more noticeable than they were in years gone by. The higher the resolution, the more noticeable imperfections and image quality issues become. We spend a lot of money getting the best quality cameras and lenses we can. There is a saying that goes “buy cheap, buy twice!”. And this cannot be more true when it comes to investing into camera gear. Once the photography bug truly takes hold of you, you will be wanting more from your gear. And the quality of resin filters will not stand up to high quality optical glass.

Optical glass filters like those produced in our NiSi product range will help you to produce the best imagery possible. And image quality matters to any serious photographer.

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