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Taming The Moire Beast in DSLR's
by Bill Pryor
Editors note: Morire and aliasing are the most consistent criticisms leveled at DSLR's. Our resident video pro, Bill Pryor, shows you how to tame the beast on those difficult brick walls without sacrifising image quality. A must read for up and coming DSLR shooters.
Everybody in filmmaking knows by now that the images produced by the leading HDSLR cameras can rival 35mm motion picture film production.
and Canon 7D
have been used extensively in major production work during the past year. The well known last episode of the last season’s “House” was shot with three 5DMKIIs, and the cinematographer routinely intercuts the 5DMKII with 35mm film. Shane Hurlbut’s “The Final Three Minutes” and his work with the U.S. Navy Seals has eliminated any doubt whatsoever that the 5DMKII and 7D cameras can be used in big budget motion picture production. A number of other productions have intercut both the 5DMKII and 7D with the Sony F900.
For the $2500 price of a
body you are not going to get an Arri Alexa. You are going to get a camera with a huge sensor that is capable, in the right hands, of producing quality footage that can be used in motion pictures and TV shows without any apology to anybody. There are shortcomings to shooting with the HDSLR. There’s no denying that. If I could afford an Arri Alexa would I make it my primary camera? Hell yes. Would I get rid of my 5DMIII? Hell no. Both cameras have their place, often in the same production.
The HDSLR revolution has been a spectacular thing, there’s no denying that. But
there are difficulties to be aware of when shooting video with a DSLR. And just for the record--let’s quit calling it video. It’s really digital film. HDSLR shooting is much closer to shooting motion picture film than it is video (a subject for another article).
For me, the biggest obstacle to overcome is the excessive moire that sometimes rears its ugly head in certain circumstances--for instance, a brick building in bright sun, strongly side lighted. That will almost always get you moire. Interestingly enough, it also can cause moire with still photos from the same camera, but moire is easier to deal with in still photography than video.
Behold the beast. Note the curved banding in the shingles of the roof. The tight pattern of the shingles plus strong side lighting make this a poster case for moire. This is a frame grab from a video tour of the home.
In most cases when I am shooting urban exteriors, I’m shooting subjects who happen to be in front of brick buildings. The subject is usually not the building. Here’s an example of a subject in front of a brick building in bright sunlight with no moire:
In this photo I wanted the building in the background to be soft enough to eliminate the moire
that almost always happens on a brick building under strong sidelight. Using an ND.9, I was
shooting at an f5.6 with a Zeiss 50mm ZE lens on the 5DMKII. This gave a depth of field
shallow enough so anything four or five feet behind the focal point would be a bit soft. I didn't
want the building to be blurred out--we wanted to see all the detail, including the mirror fragments
glued to the wall. The building doesn't look soft unless you zoom in to it quite a bit. But it is just
soft enough so the moire goes away. So, with a 5DMKII, it's pretty easy to avoid moire in a
situation such as this with a subject a few feet in front of a brick wall. With a cropped sensor
camera (7D) you'd have to shoot at about an f2.8-3.5 and would need a stronger ND filter to be
able to open up more. Of course, if I had wanted the building to be totally blurred out, I could have
stacked on another ND and opened up to about a 2.8 and then you wouldn't be able to tell that
the wall was brick.
The stills are from test shots for an upcoming short, no sound. The subject is sitting approximately 4 feet from the brick building, maybe a little less. Because of the “full frame” chip size of the 5DMKII, it’s easy to control depth of field so that even on the wide shot the building is slightly soft. A viewer watching the clip probably doesn’t see that the building is slightly soft. I could have totally blurred it out, but I wanted the viewer to see the pieces of mirror glued to the wall. So in this case I wanted a slightly shallow depth of field, but not the total “bokeh” the camera can do at will.
Using a Zeiss 50mm f1.4 ZE lens, I stacked on two ND filters--an ND .9 and ND .6 (both B+W filters), which allowed me to open up to about an f2.8. The .9 knocks off three stops and the .6 two more. The depth of field was shallow enough to eliminate the moire on the bricks. If I had focused on the bricks instead of the subject, you would see the moire.
The aperture was open to an f4 for this shot and the background is farther away and therefore
blurred out quite a bit. Notice the difference in the skin tones from this photo and the first. This
shot was with a flatter picture setup. The purpose of the shoot was to test different setups to see
which we wanted to use for the real production .
To do the same thing with a “cropped sensor” camera such as the 7D, the aperture probably would have had to been at least open to an f1.4, requiring a strong neutral density. An ND 1.8 loses six stops, so it’s a good one to have, and if you’re using a wide angle lens you could get some corner vignetting with too many filters (unless you use a matte box).
This is basically the same shot as above but with a different setup. In the video, the hot areas are
not overexposed. For some reason DVKitchen (my quick and easy way to make frame grabs
from video) seems to always drop the exposure down by about a stop, so all three of these
photos have had the exposure boosted a bit in iPhoto. I may have boosted this one a bit too much.
In the timeline, no tweaking is necessary.
The purpose of this article is to point out that controlling depth of field is a nice tool. It can be used to solve a problem--moire, or for a specific look. In this case it’s difficult to see that I even used it to get the shot. In the next shot (still photo or link), the shallow depth of field is obvious. In this case it’s used for a different purpose: to avoid recognizing people in the background. If I had wanted to identify something, say a specific person walking by or a car driving past, then I would have used less neutral density and stopped down more.
The bigger the chip, the easier it is to control depth of field. The smaller the chip, the faster your lenses need to be. And here's the final clip for you to judge for yourself:
Controlling depth of field in controlled lighting situations is easy because you can add or subtract light. Outdoors in bright sun, it requires ND filters. I have an ND .9 and have ordered a 1.8
. Some people would get a .9, .6 and .3, which gets you to the same place as a single 1.8, if you can stack three filters on your lens. All my filters are 77mm, and I use 77mm stepup rings on all my lenses. The rings stay on the lenses permanently, with 77mm threaded lens caps. Buying a stepup ring and new lens cap for every lens is a lot cheaper than buying a variety of filters of different sizes. It’s also more convenient.
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