Many aspiring photographers get intimidated by landscape photography because of their unfamiliarity to filters. While filters are not 100% essential to learning landscape, understanding this topic before making choices can lead you towards better gear decisions.
One of the most basic yet most common questions asked when talking about filters for landscape photography is whether to get screw-in circular filters or square format filters with a filter holder. The answer actually isn’t based on anything related to the output of the shot, nor is it related to any artistic intent aspect but is actually a simple logistic matter.
Every photographer’s first notion of filters are almost always circular ones. Probably because most entry-level camera kits come with a free circular UV filter. In actuality, circular filters are very handy especially for anyone who is just trying out ND filters and has not entirely committed to the genre. The only limitation of using circular filters is the fact that you can only stack about 2 or 3 at a time. Going beyond that would give you an unwanted vignette depending on the focal length of your lens.
Another disadvantage of stacking circular filters is the fact that most of them have a frame of about a half inch, the space between the glass layers of the stacked filters is a breeding ground for nasty flares. Flares come about whenever light bounces back and forth between two layers of glass. This becomes more intense when the filters involved have an IR coating because they reflect or rather, deflect infrared light. IRND filters, by that principle, should only be used on the outermost layer of the stack. However, circular filters are good when you want to keep a minimal setup and don’t intend to use more than two filters at a time.
Square filters are obviously more ergonomic than circular filters. This format comes in handy when you stack about 3 or 4 filters at a time. The general recommendation is to use as few layers as possible because any filter, no matter how good or expensive, decreases your overall image quality by a minute percentage. That minute percentage usually is barely evident but adding more layers to the stack exponentially increases that to a point where it might be noticeable.
Another simple reason to choose square filters is the intention to use Graduated Neutral Density (GND) filters. These filters very rarely come in circular form and having them in the rectangular shape gives you more control of its effect. GND filters have a graduated tint density for limiting light in order to balance the frame or simply decrease the brightness in one fraction of the frame. This comes in handy for situations wherein the sky is much brighter than the foreground, or the city lights are brighter than the night sky. Controlling the median point is done by sliding the filter up and down. This can only be done using square filters on a filter holder.
The last obvious reason to choose the square format is the fact that it’s easier to install and remove them once you have the filter holder in place. A filter holder has 2 main parts. An adapter ring that screws on to the front part of your lens, and the main holder which connects to the adapter ring. Most modern filter holders have a single screw-in slot on the filter holder (or sometimes the adapter ring) for a circular polarizing filter. This filter is probably the only filter that never comes in square format and that’s because of how it works.
On the main filter holder are slide-in slots for square filters. Most holders come with 2 to 3 slots. Going beyond 3 usually gives you a vignette which is due to the inner edges of the slots peeping into the sides of the frame. The biggest ergonomic benefit of this is not having to remove each layer by screwing in and out all components of the stack. Filters can be removed individually much faster and replaced much faster than with circulars. This might not be much of a major concern at first but in situations with dynamically changing light conditions, the additional 3 to 5 seconds of removing a single layer can make you miss your intended shot.
Making Your Choice
Your choice should be guided by whether or not you think you’ll be doing landscape photography long term, and whether you want to lessen the number of times you purchase individual filter. Getting square filters is obviously a bigger, but one-time investment. Usually, purchasing a filter kit gives you most of what you would need in the field and getting additional filters individually would be much easier because square filters are not lens size/diameter specific unlike circular filters.
Since circular filters are specific to the filter size or diameter, that would mean that if you eventually replace your lens with one with a different size, all of your existing circular filters would not be entirely compatible to that lens. Yes, you can use a step-up ring to make them fit, but the problem of a flare usually comes in. In comparison, changing lenses with the square system only requires you to get an additional adapter ring for that specific size and you’re good to go.
Starting to learn landscape photography should not be limited by the availability of lenses. Remember that the genre is a crucial game of composition and time of day. Having filters can help the photographer apply certain visual effects to better improve the composition and coherence of the elements. Knowing which filters to get before you spend out on them is recommended to avoid mistakenly spending on something that you don’t need or something that you won’t be using long term. With all of the sudden changes in standards for camera gear, having filters that you won’t have to replace for at least 5 years can be helpful.