Variable ND filters on wide angle shots
5 months ago
I was looking to pick up a rather dark ND filter for shooting moving water and lower apertures in the daylight. When searching, I came across variable ND filters, which sound great since I could focus at a lower setting and then adjust to ~8 stops rather than having to take the filter on and off.
However, in reading this review of one of them, the reviewer mentions the following.
It offers a controllable range from two stops (ND4) to about nine stops (ND500) – this range is not exact and depends on the focal length of the lens in use and whether you are using a APS-C or full-frame sensor camera.
The information below shows the degree of light loss you can achieve at different focal lengths on a cropped sensor DSLR.
12mm: ND4 to ND8 3 stop operating range
15mm: ND4 to ND16 4 stop operating range
18mm: ND4 to ND32 5 stop operating range
24mm: ND4 to ND64 6 stop operating range
35mm: ND4 to ND125 7 stop operating range
40mm: ND4 to ND175 7.5 stop operating range
50mm: ND4 to ND250 8 stop operating range
70mm: ND4 to ND350 8.5 stop operating range
100mm: ND4 to ND500 9 stop operating range
The downside is that to enjoy its potential nine-stop operating range means you have to be shooting with a telephoto lens – at least a 100mm with a cropped sensor DSLR.
If you are a keen wide-angler and want to enjoy this filter with a 12-24mm zoom set to its widest setting, for example, your options are limited to a three stop operating range from ND4 (two stops) to ND8 (three stops). Zoom back to 24mm, however, and you have a six stop operating range and a ND64. That is getting there for long exposures, but still not the nine stops that is possible with the filter on a telephoto zoom.
Is this true? If I'm shooting at a wide focal length I can only get a maximum of 3 stops even on if the filter is set to 8 stops? It's not something that I'd heard of before. If it is true, would this be the same on a fixed ND filter? That is, would a 9-stop fixed filter really only be providing 3 stops at a wide focal length?
Most of my shots are landscape shots and fairly wide angle, so this would make a big difference to me.