Today’s Question: I will be heading to the Smokey Mountain National park in late October and wanted to find out more about Variable Neutral Density (ND) filters. Originally I was thinking of getting a big stopper but then thought a variable ND with polarizer might be a much better choice. It looks less cumbersome to use and will also allow me to keep a lens shade attached. What are your thoughts or preferences about this? Up until know most of my filter use has been confined to a Circular Polarizer and while I would like to keep things simple, I can really see the opportunities a strong variable ND filter can provide.
Tim’s Quick Answer: Variable neutral density filters offer considerable flexibility, and the option for a built-in circular polarizer filter only adds potential value. That said, my personal preference is to use a solid neutral density filter, because I find a solid rather than variable filters provide a more streamlined workflow. And I’m a huge fan of strong neutral density filters in terms of what they enable for creative effects.
More Detail: Due to the nature of variable neutral density filters, it can be a bit of a challenge to achieve a precise density value, which means it can be a bit of a challenge to find the right exposure settings. A little more trial-and-error tends to be required in order to find the right exposure settings based on the specific rotational position of the variable neutral density filter, and light angles play a role in this regard as well.
Because of this issue, as much as there is a tremendous potential benefit with variable neutral density filters, I prefer to use solid neutral density filters. When combined with an adjustment to the ISO setting on your camera, just one or two solid neutral density filters can provide great flexibility with a more streamlined workflow.
I discussed my specific approach to working with a solid neutral density filter in the July 2015 issue of Pixology magazine (http://www.pixologymag.com). The key is that with a solid neutral density filter you can simply establish your initial exposure settings, then add the filter and apply an adjustment to the exposure settings based on the density of the filter you’re using.
Even better, with a solid neutral density filter you can adjust ISO to improve your flexibility and reduce the number of filters you need to carry.
For example, I generally carry a ten-stop and a six-stop neutral density filter when photographing. I’ll also carry filters with a lower density value when shooting video, but that’s a different matter.
The ten-stop and six-stop filters are, of course, four stops apart in terms of density. If I am using the ten-stop filter but want to achieve the same results as would have been achieved with a six-stop filter without changing the shutter speed and aperture, I could raise the ISO setting to 1600 ISO. But, of course, that wouldn’t generally be necessary because I could simply switch to the six-stop filter or change my aperture or shutter speed values.
The point is, when using a solid neutral density filter you can adjust the ISO setting to create a result that is similar to what you might have achieved with a different neutral density filter or a variable ND filter. In my mind, being able to take this approach makes up for the lack of variability with a solid neutral density filter. And by using solid neutral density filters I’m able to avoid the trial-and-error issues that tend to be involved with the use of variable neutral density filters.
To be sure, there are some excellent variable neutral density filters available. I’m a big fan of the variable ND filters from Singh-Ray (http://www.singh-ray.com) for example. But my personal preference from a “workflow in the field” standpoint is to use solid neutral density filters rather than variable filters.