So I have been told that a Variable ND filter is a must for recording video, especially in event situations (like weddings), or anytime your preference is a run-and-gun style of shooting; where you have no control over lighting. And since your shutter speed is usually fixed, your preference for aperture is generally set, leaving really only a small window with ISO - a variable ND filter just makes things so convenient. At least, more convenient than using set ND filters.

After using a variable ND filter, I definitely agree that they are a must have - though they do come with their drawbacks.

Currently I own the Polaroid Optics Variable ND Filter and the LightCraft Workshop Fader ND Mark 2. The former runs around $55, depending on what size, and the latter runs around $129, also depending on what size you get.

Here are some test shots with them to help point out the drawbacks.

Images using a Canon 5DmkIII, 70-200mm f2.8 at the 200mm range

(Click on images to open a lightbox to view better)

Notice the striations in the bokeh in the Polaroid VND image, especially in the yellow marigolds. Also, you can see how the contrast flattens with the VND filter in place, as compared with the original image.

Image without ND filter, enlarged for detail

Fader ND Mark 2, enlarged image for detail

Polaroid Variable ND filter, enlarged image

Here you can notice the lessening of detail when a VND is used, though this is more apparent when pushed to maximum zoom in zoom lenses. The plant images have been enlarged to show both the striation drawback and detail loss.

Images using the 24mm f1.4 with the 5DmkIII

Shot with Canon 5DmkIII and 24mm f1.4L, no VND

Using the LightCraft Workshop Fader ND Mark 2, set to "MAX" setting on the filter

Using the Polaroid Optics VND, set to "MAX" setting on the filter

Lastly, you notice a distinct, almost "X" pattern that developes near the maximum setting of the VND, as regards exposure. Instead of the clean exposure across the image, some areas are darkened more so. You can begin to see the "X" pattern starting around the mid range of the two filters.

However, once again, the LightCraft Workshop filter does a better job than the cheaper Polaroid Optics filter.

PLEASE NOTE that neither of the two VND's are weather-sealed. Meaning small, or fine, dust particles may enter between the two rotating glass elements. So if you are shooting in a desert, or a very dusty place, bear this in mind.

Overall, I still think the VND filter is a necessity for the videomaker, even a set of standard ND filters. It is as simple as having the tools necessary to shoot in various settings.

I'll revisit this when/if I get a more expensive VND filter.

For video comparisons, 90% of my videos currently use the filters. If you think a video comparison would help you out better than just the above image samples, let me know and I'll see what I can put together.

Got a question about what filters do, and what they are good for. So I thought I would post my response to him and the link I gave him; maybe it will be useful for you!

WHY DO I GET CRUSHED OUT COLORS IN THE SKY, AND WHEN I ADJUST FOR THAT, THE SUBJECT IS TOO DARK. DO I NEED A FILTER FOR THIS? IS A UV FILTER WHAT WILL WORK???

From my understanding, let's say there is a scale from 0 to 100, where zero is black and 100 is white, and the scale moves dependent on whatever is your brightest element. Just like if you are staring at the sun, you can't see everything else. The blow out on the highlights occurs because of your uneven lighting; which is what happens in natural light, during peak daylight (usually around noon-3 is the brightest). The brighter your brightest element, and the more focused you are on it, the less you'll see and get detail in elements that are darker. If you concentrate your image on the dark places, then the highlights will be blown out and there will be no detail in them.

SO, either shoot NOT during peak daylight, choose a time closer to dawn or dusk, to get more even lighting, or you enter the world of filters and (if you are still photographer you shoot RAW format or shoot multiple images of the same but at different exposures) post-production and processing.

This page has some good info that might help regarding filters. I did a cursory scan, and it seemed legit to me, and will save everyone posting a tid bit here and there.

cambridgeincolour.com/tutorials/camera-lens-filters.htm

Cheers.