Does stacking multiple lens filters reduce image quality more than using one?
Asked 10/15/2015
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I’m considering ND filters and wondering whether it’s better to buy several fixed-strength filters and stack them when needed, or avoid stacking whenever possible. If vignetting isn’t an issue, does using multiple filters reduce image quality more than using a single filter? Does it depend on the filter type, such as UV, ND, or circular polarizer? Are some combinations more problematic than others? Also, does the mounting style (screw-in vs square/rectangular holder systems) affect image quality, or is filter quality and coating the main factor?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
10y ago
2 Answers
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As you know, an optical filter must be optically flat, both sides. Making an optical flat is in many ways just as default as making a lens. Translated, that means you get what you pay for. Additionally lenses and filters are polished glass or plastic. Light plays on the front surface and about 5% is reflected away, 95% attempts to transverse. The filter, depending on its coloration, absorbs this transversing light energy and converts it into heat energy.
The 5% that is reflected away does no harm however; the light that exits the filter encounters a polished glass element. Again about 5% is reflected away. The re-reflected light from this second encounter echoes backwards encountering the back side of the filter which is polished. What happens is, about 5% of this light traces a route back towards the camera. Worse, the camera lens likely contains 6 or more polished elements. As a results the light total light loss can the 50% or more.
What you need to know is all this reflected stray light reverberates within the camera’s optical ray path and some will bath the film or imaging chip. This is the stuff of flare and ghosting. This stuff can be devastating. A tip of the hat to Harold Dennis Taylor (English 1862-1942 Optician). Taylor published in 1894 that old lenses of the same design passed more light than new ones. He deduced that the older lenses accumulated a tarnish due to atmospheric pollution from coal burning and the like. Investigation showed that older lenses with this "bloom", passed 2% or more light than ones freshly polished. Taylor experimented with suphuretted hydrogen and other chemical to artificially age lenses and was granted patent 29,561/04.
Today’s fine filters are coated or multi-coated. A single coat mitigates just one color of light. A super quality lens or filter can have many coats 3 with handle the light primaries, some will have as many as 12 coats.
What is the danger of stacking besides the vignette? Added flare – added distortion due to poor figure i.e. not being optically flat.
More gobbledygook from Alan Marcus
Originally by user44949. Source · Licensed CC BY-SA 4.0
user44949
10y ago
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Generated from our catalog & community — verify before relying on it.
Yes—stacking filters generally degrades image quality more than using a single filter, but how much depends mostly on filter quality. Each added glass surface can introduce extra reflections, flare/ghosting, reduced contrast, and slight light loss. Good optical flatness and multi-coating reduce these effects, so high-quality filters tend to stack better than cheap ones.
The main issue is usually not whether a filter is UV, ND, or CPL, but the fact that each filter adds more reflective surfaces. Some combinations can be more troublesome simply because you’re adding more glass and air-to-glass interfaces. A UV filter plus another filter is often considered unnecessary unless you specifically need the UV/protection filter.
If vignetting is controlled, mount style itself is usually less important than the quality of the filter material, flatness, and coatings. Screw-in and square systems can both work well.
Practical takeaway: use the fewest filters needed, buy good-quality coated filters, and stack only when necessary. For NDs, many photographers use a small set of fixed NDs and sometimes stack them, but image quality is usually best with a single high-quality filter of the required strength.
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AI10y ago
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