A low-pass filter, also known as anti-aliasing or “blur” filter, is used by camera manufacturers to eliminate the problem of moiré by blurring what actually reaches the sensor. The low-pass filter blurs the image very slightly. While extreme details are lost in this process, the problem of moiré is completely resolved. Most cameras that are designed for day-to-day photography use a low-pass filter so that moiré is avoided, whereas higher-resolution cameras or smaller-sensor cameras sometimes do not have such a filter to maximize detail.
Table of Contents
How a Low-Pass Filter Works
A typical low-pass filter contains of 3 or more different layers, as shown on the top illustration below:
As light rays reach the first “horizontal low-pass filter”, they get split in two, horizontally. Next, they go through an infrared absorption filter (illustrated in green color). After that, the light rays go through the “second vertical low-pass filter”, which further splits the light rays vertically. This light ray conversion process essentially causes blurring of the details.
With the Nikon D800E DLSR model, Nikon took a different approach. The full low-pass filter cannot be completely removed, because it would cause the focal plane to move; plus, the camera still needs to be able to reflect infrared light rays. Instead of making a single filter with one layer, Nikon decided to still use three layers, but with two layers canceling each other out. As light rays get split into two with a vertical low-pass filter, then through the IR absorption filter, those same light rays get converged back when passing through a reversed vertical low-pass filter. Hence, instead of getting blurred details as in the first illustration, we get the full resolution:
Advantages of a Low-Pass Filter
The only benefit of a low-pass filter is that it ameliorates the effect of moiré. This problem is especially prevalent in shooting fine patters such as those present on clothing with fine lines or in the feathers of birds:
For photographers shooting many scenes with fine patterns, a camera with a low-pass filter is a great benefit.
Disadvantages of a Low-Pass Filter
Having a low-pass filter is a big blow on landscape photographers that never see moiré and yet end up with blurred details. Indeed, with any kind of photography that does not involve very fine patterns, a low-pass filter is only a detriment.
Even with bird photography, where moiré is occasionally present, it is usually better not to have a low-pass filter. That’s especially true since modern Raw developers have moiré reduction tools that work pretty well in the usually mild symptoms of moiré in bird photography.
Therefore, if you are very concerned about fine detail, it’s better to use a camera without a low-pass filter.
Should You Get a Camera with a Low-Pass Filter?
The truth is, these days, the choice between a low-pass filter and no low-pass filter comes down to resolution. Higher-resolution cameras like the Nikon Z7, Canon R5, and Sony A1 do not have a low-pass filter. Moiré is less of a problem on such cameras due to their higher resolution, an due to the situations where most people use them.
On the other hand, lower-resolution cameras like the Nikon Z6 do have a low-pass filter, especially as they are more susceptible to moiré. The truth is, in most practical scenarios, a low-pass filter will not be a massive detriment to your image quality, and it is far more important to choose the resolution you’ll need rather than worrying about a low-pass filter.
That being said, if you’re after extreme image quality, getting a high-resolution camera without a low-pass filter is ideal.
Conclusion
A low-pass filter is used mostly on lower-resolution cameras to prevent the moiré effect, whereas higher-resolution cameras typically omit the filter. The filter does affect the sharpness of your photo ever so slightly, but it is not something to worry about with most kinds of photography. Additionally it can save many photos from moiré, which is very hard to remove properly in post, especially if the effect is strong.
So is the answer to increase the sharpness in a D800, is it?
My camera is set to the D800 default, around mark 3. I have been told a lot of my shots look soft so should I up the sharpening to 8 or 9 for landscapes.
Would be grateful for your comments.
Great website, keep up the good work.
Mike
Sharpness is BULLSHIT it doesnnt EXIST !
Its just local contrast !
Yep, and you are a moron.
‘Anti-aliasing filter’ on Wikipedia is interesting, too.
en.wikipedia.org/wiki/…ing_filter
The birefringent crystal material mentioned there is Lithium Niobate – it expands and contracts in electric fields, which may be how the self-cleaning function works (Surface Acoustic Waves – also used in focussing !). Conversely, it also generates voltages from vibration or temperature changes, which might attract dust – so it probably has an outer conductive coating, too, to prevent this.
Amazing how much can be done in one component.