Circular ND Versus Square ND Filters
Obviously Breakthrough Filters produce both square filters and circular. So for the sake of simplicity as the square filters are all made out of the same German Schott Superwhite B270® optical glass as our X4 series circular filters (with the exception of the Night Sky filter) and we know the glass has market leading sharpness and colour neutrality then light transmission and colour caste are not problems for either.
There are two key differences between the two types of filter. One creative and one practical.
GND Square filters
For those that know all about GNDs (Graduated Neutral Density) then you can skip this bit....
To shoot a great landscape shot you often have an exposure issue, bright sky like a sunset and at that time of day a darker area of foreground. Calculating your exposure from either will leave the other over or under exposed. So if you expose according to the darker land area your sky will be burnt out. Correspondingly if you expose according to the sky your land area will be underexposed. Taking a middle ground will give you a middle exposure where the ground is a little dark and the sky is a little too bright.
A GND filter enables you to slow down the exposure of the brighter segment of your composition so that both areas are optimally exposed.
Expand Your Dynamic Range
Outdoor photographers frequently struggle with dynamic range, as the human eye has a dynamic range of over 20-stops and a mid-day outdoor scene may range between 15-18 stops. Most camera systems range between 12-14 stops.
So if a sunset scene has a total of 17-stops between the sky and the foreground and the camera has 13 stops of in-camera dynamic range, a 2-stop soft GND and a 3-stop hard reverse GND would cover the exposure gap (12+2+3=17)
Correction could be done in post-processing (see HDR) but you can lose the long exposure component that is often so central in the best sunset scenes.
When you spend a lot of time doing photography your workflow becomes important to you. It's not just how much time you can save. More importantly is how your equipment helps or hinders your creativity. There are pros and cons to both square and circular NDs when it comes to workflow. When it comes to landscape photography squares have it for workflow. For almost anything else, including video then circulars have it.......
When shooting street photography you are less likely to change lenses, certainly don't want to be changing filters too often. You are more likely to have made your lens and filter choices before shooting and less likely to change compared to landscape.
With landscape however, changing lenses is very common so having a filter set that can be easily and quickly moved to another lens is important for workflow. A square filter holder can be taken off, with filters still attached, swap the adaptor ring and attach the holder onto the new lens.
Also when using NDs , especially the 10 stop or 15 stop, they are so dark the camera will have difficulty focussing. With square filters you can simply slide the filter up or out, check the focus, take a meter reading, adjust for the number of stops the ND is and then slide down again.
Pros for Circular
- Simple to use - just screw on the lens
- No additional adaptor rings or holders
- Less expensive
- Best choice for most genres of photography except landscape
Pros for Squares
- Only option for ultra wide angle lenses
- No mechanical vignetting even when stacking filters using a full frame sensor camera
- Faster when using multiple lenses
- Square GNDs are rotatable
- Best option for landscape photography