OVERVIEW:
Okay, let's agree first that using a filter doesn't actually change the dynamic range specifications of your camera's sensor. It is however, an optic that will affect the way light will hit the sensor, and THIS is what can change what I'll call the "perceptive dynamic range". So, I do agree that filters affect the image, but what if I told you there are times when using filters can sort of improve the dynamic range? So, before anybody gets too upset, let me emphasize that I think it works well with SOME lenses, but not with others. I explain a bit more, below.
ABOVE: A "filter purist" will say "The best filter is no filter" (as I used to) but can filters actually improve the "perceptive dynamic range"?
HOW CAN A FILTER "IMPROVE" DYNAMIC RANGE?
So, what's really happening is that we're controlling how the light strikes the sensor, by modifying the light first. We're kind of making the light jump through hoops as it were, by forcing it to travel through the piece of glass (and layers of coatings) known as a filter. It's kind of like making the light "run the gauntlet" or sending it through one of those fun houses at the fair, with all those mirrors. Whatever you call it, we're kind of pre-treating the light before it hits the sensor, reducing the contrast, sharpness and color...to constrain it into the limited dynamic range of whatever sensor you're using. If your camera has a highly capable sensor, it might be able to handle the extreme contrast of newer lenses, but if it's not (like most of the cameras I can afford) it might just prefer the lesser amount of contrast that's delivered through a filter...or perhaps a vintage lens (more on that, later).
ABOVE: For the longest time, I put off testing the Tiffen Black Pro Mist #ad filters, but after working with this one for a while (the 1/8 strength) my take is certain lenses like it.
AM I SAYING FILTERS ARE GOOD?
So, when people ask me this question, I answer "It depends on the lens". As I mentioned, with sharp and contrasty lenses, filters can sometimes improve the image (because they result in less "contrasty" or "sharp" light being sent to the image sensor). A lot of sensors can't handle the high contrast of "modern" lenses. An example of using filter on a newer lens to reduce contrast and improve the image, is the video above (and other videos on my YouTube channel). The video shows the use of a diffusion filter (the Tiffen Black Pro Mist #ad or others) which can lift the shadows and smooth the gradations between the "zones" (like the Ansel Adams Zone System). I use them to "protect" the details in the shadows and highlights, even though it's at the cost of reducing contrast and sharpness (things that were historically referred to as positive attributes of lenses). I do agree that some older lenses can have low contrast and sharpness that DOESN'T look good, while others have a "vintage look" that many seek. Diffusion filters can also create effects such as sunbursts and lens flare, which some people like and others don't.
ABOVE: Here's a comparison of this lens-sensor combination WITHOUT a filter, and while I think these CUSTOM SETTINGS help to make it look more realistic, it didn't come as close to a "REAL" look as the version WITH the Tiffen Black Pro Mist #ad filter did.
WHAT ABOUT "UV" FILTERS (FOR "PROTECTION")
"You need protection" said the thug...a high-pressure sales technique of "FOMO" (Fear of Missing Out) that has been used for thousands of years to influence people's decisions. Am I saying this is the reason camera salespeople always try to sell you a UV filter? No, part of the reason they do it is for the commission, but many of them really do care about protecting your lens. But do our lenses really need protection, or does this just degrade the image quality without reason? I think there can be good reasons for using filters (for protection) at times, but you might be surprised to discover that sometimes they can also keep the highlights from blowing out...which helps shadows retain their detail. So, it's not always a bad thing to use certain filters. Now, depending on the quality and/or type of filter, you're probably going to lose some SHARPNESS (and CONTRAST and COLOR) but what I've found (after hundreds of lens tests) is there are times where it's actually a good thing (as the lens had been sending TOO MUCH of those things to the sensor).
ABOVE: Should we be using filters? We've always been told by camera salespeople that we need to "protect" our lens, but do filters degrade image quality...or can they improve it?
I ACTUALLY USED A CLEAR PLASTIC CD CASE...
Here's an extreme example (when I tell people this part, they usually have some sort of a reaction sometimes good, sometimes bad). When I had my first DSLR (a Nikon D70) the dynamic range was SO BAD I actually used a plastic CD case over the lens TO REDUCE THE CONTRAST. Yep...that lens-sensor combination couldn't handle contrast, and it was so bad I couldn't shoot outdoors in sunlight. I could shoot in a studio with controlled lighting ratios, but that sort of thing isn't always possible on-location. The result was a lower contrast image that truly was less sharp, but it actually made the image look better. So, how does this translate to using filters? Well, to be sure, what we're talking about is using filters as a gate to control how light strikes the sensor, and this comes down to what I call the "lens-sensor relationship" (that was a PODCAST link).
CONCLUSION:
So, to answer the main question of "can filters improve image quality?" I think it comes down to the concept of lens-sensor relationships, as I think it really depends on the combination. What I tell people when they ask "What are the best settings to create cinematic-looking footage?" I always say that it depends on which lens-sensor combination you're using (and then figuring out the best settings for each combination) which was the reason I created this website.
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