Video camera choice for AP

When the Canon 5D Mark II was released in 2005 the independent film industry – and soon also the TV ditto – went wild. Over one night the pricey 35mm adapter systems got competition from a camera body that cost less than 2 500 € and could do exactly the same thing. Or could it? Let’s look at the features that have made the film shooting  DSLR:s so popular compared to the traditional broadcast video camera.

The depth of field

Since the birth of photography, using a shallow (short) depth of field (DOF) has been the number one way of making an image look more arty. Foreground and background becomes blurry while the main motive looks focused and crisp. An easy way to draw the attention to a certain object in the image, and to get a more dreamlike look.
The DOF is determined by three features in the camera system: The focal length of the lens, its aperture, and the size of the sensor. The larger the sensor, the shorter DOF. The DSLR sensor is significantly larger than the one in a conventional video camera. For documentary and ”on the go” filming, you usually want a greater depth of field. Otherwise some objects will end up out of focus in cases where the cameraman can’t control the situation. But, on the other hand, on occasions when you actually want a short DOF, for instance an interview in a fixed position, you’re stuck with your long DOF and either need to use a very long lens or attach an unwieldy 35mm adapter to make the background come loose from the interview object. But with a DSLR you just zoom in, crank the aperture up and BANG!, there’s your film looking arty shot. And that’s the kind of footage you see on Vimeo and go ”My next production has to be shot on a DSLR!”, charmed by the 100 year old trick of a short DOF.

The second advantage of a large sensor camera is the low light performance. A large sensor collects more light than a small one. Therefore the output voltage from a large sensor is greater, which in turn requires less amplification before the signal is digitized and stored. And less amplification means less noise in the image. Therefore a DSLR can give clean and crisp images from a candle light scenery, while a conventional video camera would mostly deliver noise.

So, with these two advantages, you would think a DSLR is the perfect camera to put on a radio controlled photo helicopter? Well…

Depth of field, again

First, let’s look at the DOF. In aerial photography, DOF is not an issue. Since the motive (the ground) is so far away, a short or long DOF won’t look any different since there is no foreground or background to become unfocused. This is why the most important feature of the DSLR becomes useless for camera flying.

Low light performance, again

Now let’s look at the second strength of the DSLR; the low light performance. Since 90% of the shots we make take place in full daylight, low light performance also becomes a non issue.

The disadvantages

This part might sting a little for you Vimeo freaks. We’ll start by comparing the video codecs between a Canon DSLR and the Panasonic SD-800.

Codecs

The Canon DSLR:s use the h.264 video codec, with an average bit rate of approximately 40 Mb/s. h.264 is widely used on the internet and in many recording and playback units, but it’s old (2003) and written for general purpose video and audio compression.
Modern consumer and semi professional camcorders use the AVCHD codec. This codec has been specially written for HD video and therefore puts more image information onto the the SD-card with the same – or even lower – bitrate. This codec causes far less visible compression artifacts than in video compressed with h.264.  The typical compression artifact is shown as pixels or chunks in parts of the image. The h.264 drawbacks are visible in most types of sceneries, but especially in complex motives with a lot of movement. Like moving aerial images, for instance. A look at the video clip above shows how the Panasonic camcorder easily beats the Canon in regards of detail – and this motive isn’t even moving. Also, with the AVCHD codec, there’s much more information left for post processing.

Stabilization

The modern consumer and semi professional camcorder usually has built in image stabilization. The stabilization system is designed to increase shakyness caused by hand held camera operation – and it usually does it very well. When filming from a small helicopter, good image stabilization is crucial for  usable raw material.
The Canon cameras don’t have any built in stabilization. There are lenses – usually telephoto ones and zooms – that are equipped with such. But they are made for taking sharp still images of lions at 200 meters distance  – not to produce smooth looking video. And, unfortunately, they’re very heavy. In addition, for aerial images you usually want to use a bright/fast wide angle lens, and they don’t come with stabilization.

Frame rate and resolution

The canon DSLR shoots progressive video, and so does the Panasonic SD-800. But in full HD (1080 lines vertical), the Canon is limited to a frame rate of 25 fps (30 fps is possible but then it has to be down converted to fit the European standard). The SD-800 shoots in 1080 as well, but in 50 fps. And moving scenery is greatly favored by a higher frame rate. If shot in 25 fps progressive, a moving scenery tends to look blurry. Pans will also cause very strange looking artifacts, like lines cutting across the image.

If the Canon is set to film with the smaller HD resolution of 720 lines vertical, 50 fps recording is possible. But since we quite likely will need to stabilize our aerial material in post production, the higher origin resolution we have, the better the end result will look. So the SD-800 wins this match as well.

Dynamic range

A large sensor has a greater dynamic range than a smaller one – that’s something we can’t contradict. Poor dynamic range is best visible in images with both dark parts (shadows) and brighter parts (highlights).  With poor dynamic range, the shadows will go 100% black and the highlights 100% white, burning out the gradients in these parts of the image. With a better/higher dynamic range, small differences in luminance in the dark and the bright part of the image still will be visible. And yes, the Canon 550D has a little better dynamic range than the Panasonic. We solve this by underexposing the Panasonic one stop, and by recording in a low contrast mode. This gives a softer contrast that can be adjusted later in the post production process, but decreases the risk of, for example, burning out a bright sky completely.

Weight

Finally, an advantage of the SD-800 that is strictly connected to the flying part. Yes, we can fly your DSLR. But it will be around 1 kg heavier than the Panasonic. And a heavier camera means a heavier helicopter, which means slower and more careful flying.  With greater weight, flying time is also decreased. Our long range camera flying (550 meters so far) have been made possible thanks to the low weight of the Panasonic.