Does using multiple filters reduce the image quality more than just one filter? [duplicate]

Question

Context

With regards to filters, I notice that Neutral Density Filters can go from 1-10 stops and sometimes even more. For larger square/rectangle filters, some of the holders can hold three while others others can hold one, for wider angle lens.

I will get a Neutral Density Filter soon but I'm curious if some people, rather than buy a Variable Neutral Density, buy all Neutral Density Filters from 1-10 stops and select the one they want to use, or just stack them to get the correct value they desire.

Question

Assuming I had to put on a filter and don't get vignetting for it, if I put multiple filters on a camera, does that degrade image quality a lot more than just one filter? Is it effected by the filter type (UV, Neutral Density or Circular Polarizer) mounted? Are there combinations of filters that degrade image quality a lot more than others (ignoring cheap ones of course)? Is image quality effected by the filter mount type (e.g. screw-in v square/rectangle ones) or is it simply down to the price?

Reference

Screw in V Square Filter

Answer 1

There are several questions to unpack in your query, so I'll address them individually.

if I put multiple filters on a camera, does that degrade image quality a lot more than just one filter?

The link to Roger Cicala's blog post in Bart Arondson's comment sprang immediately to mind. Yes, stacking filters will cumulatively have an effect on image quality, but noticeably less so with good filters.

Is it effected by the filter type (UV, Neutral Density or Circular Polarizer) mounted?

Mostly the effect is mitigated by the quality multicoatings on better lenses, rather than by the type of filter (UV vs ND vs polarizer). I doubt you'll find anybody who recommends stacking a UV filter with any other filter. (UV filters are always a hot debate in any forum anyways). There are many cases where you might want to stack a polarizer with one or more ND filter.

Is image quality effected by the filter mount type (e.g. screw-in v square/rectangle ones) or is it simply down to the price?

In terms of light leaking between the filters, screw-in filters are better in this regard. With square filter holders, and especially with high-ND filters, you have to be careful to wrap or shade the portions of the filter outside the image circle to prevent "external" light bouncing in between the filters, or between the filter and front element. This is essentially not a problem with screw-in filters.

If you are going to stack multiple filters, vignetting becomes an issue with screw-in filters much faster than with square holders. Assuming you standardize the size of your screw-in filters, if you want to make sure you don't vignette on a particular lens, you would conservatively have to greatly oversize your filters much larger than you typically would choose for your lens/camera system.

If you choose to ever use ND grad filters, the only reasonable choice is to use square holders. There are screw-in ND grad filters, but you cannot shift their "horizon" line up or down, so screw-in ND grads completely remove the vertical axis from your choice in composition. Conversely, you can position your rectangular ND grad however high or low you desire in order to suit your composition's horizon. This is especially important if you cannot recompose if you are taking multiple shots of the same scene, where you need to change your filters during the shot sequence.

So indeed, there are important considerations other than price when it comes to choosing between screw-in and filter holder systems.

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In the Context section before your questions, you wondered,

but I'm curious if some people, rather than buy a Variable Neutral Density, buy all Neutral Density Filters from 1-10 stops and select the one they want to use, or just stack them to get the correct value they desire.

Variable NDs are okay for photography. Realize that a variable ND is essentially just 2 polarizers mounted in a common body, and they can rotate with respect to each other. Polarizers in general do not work well on wide angle lenses, because the polarization axis changes over the width of the scene with respect to the lighting in the scene. This usually results in variable color of the sky, or in the case of variable ND filters, an "X" pattern of changing ND amount. But, if you are using normal (or longer) focal length lenses, both of these problems are reduced.

Variable NDs, as well as a full range of ND filters, are often used when shooting video, as they give back to the videographer another factor of control in their compositions. Shutter speed is not under the cinematographer's control, so light control and ND filters are heavily used to control the exposure in scenes.

Personally, when it comes to ND filters in DSLR photography, I have never needed to have every single stop from 1-10 as an option. I can easily find an additional stop of reduction by combining, say, a 1/2-stop smaller aperture with 1/2 stop slower ISO. I use 1, 2, 6, 10, and 16-stop 100mm square ND filters. I have no problem with stacking two of them to get the effect I desire, and often put a 105mm circular polarizer in front of them as well.

Answer 2

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