Here you have it. You hold the Nikon D5100 in your hands, a great camera incredible for its price. You can take great still pictures and record HD video in 1920 by 1080 pixels at 30 frames per second! Just fantastic!
So you skim through about eight pages of the 300 page manual, mount on your lens, fumble with it and by 11:00 at night, you finally figure out how to shoot video. You start recording thinking about how incredible this cute video of your cat running around the house is going to look on YouTube.
You get it on your computer and you notice some problems right away. The video looks really noisy. It goes dark and then brightens up like that video you’ve recorded on your old cellphone. It’s out of focus, in focus and back out of focus again.
Crap. Video on this camera sucks.
You couldn’t be further from the truth.
Like most tech gadgets today, there’s a bit of a learning curve to getting good video out of the D5100. You need to set up the camera so you can control it, throttle back the willy-nilly and plan your shots a bit so you can take that video quality up a notch or two.
Over the next few posts I’m going to explain the problem and give you a few solutions that have worked for me. In this article, I’m going to explain what’s happening to cause these problems and the next two will be divided into configurations to set up and then what to do for when you want to shoot the video.
Sorry, I can’t help you with your choice of content. That might be better left for a psychologist to work out your cat obsession.
So What’s Happening?
Basically, these problems are happening because Nikon is trying to save you from yourself. To make video, there are some standards that have to be adhered to and demand for more automated features has limited choices even more. On top of that, there are physical limitations in making video and Nikon had to make the hard call so you can just set the mode and start recording.
So what are these issues and why do they happen?
The Grainy Video Problem
Shutter speed, ISO and aperture are the three corners of what’s called the “Exposure Triangle”. To get the right amount of light in your images, you have to get the balance of all three correct. If exposure drops due to an increase of the shutter speed, you have to increase the ISO or open the aperture (or a combination of both) to bring it back to proper exposure.
Frame rate is effectively a minimum shutter speed. You can’t record 24 frames in a second if each image takes 1/10th of a second to expose. To emulate a filmic look, shutter speed should ideally be double the frame rate that matches what film cameras typically record and matches what we’re used to seeing for the motion blur in each frame. So for 30 fps, you’re shutter speed would be 1/60th of a second and for 24 fps, 1/48th (or the closest equivalent, 1/50th) would be used.
Because of the physical limitation of framerate and shutter speed in recording video, the camera can only control ISO and aperture to get the right exposure. And due to a limitation in how LiveView works or by you’re choices for recording, aperture is usually removed from the equation as well. This is why a video in lower light situations get so noisy.
How do you control it then?
You have to get your exposure into a sweet spot where you have the optimal shutter speed, ISO and aperture. To do that, you have to alter the lighting to accommodate this range. Either you get some light on your subject or open up your aperture (lower f-stop number) if it’s too dark and if it’s too light you need an ND filter or to close down your aperture (higher f-stop number).
There is one more option.
If you can adjust your aperture and balance your shutter speed and ISO, you can find that sweet spot yourself. I’ll explain aperture control and getting more realistic ISO settings for the D5100 in the third part to this series.
The Changing Brightness Problem
When the video switches brightness around while filming, it’s due to the exposure adjusting as the lighting conditions change. Your camera is trying to keep your exposure in the ideal exposure settings by adjusting the ISO and shutter speed in the manner I’ve explained in the last segment. That doesn’t lend well to capturing quality video and is something you can’t easily correct in post (trust me on this).
The best method of preventing automatic exposure adjustments from happening mid-shot is to use a full manual mode (setting the ISO, shutter speed and aperture explicitly). Unfortunately, the D5100 doesn’t use your settings for shutter speed or ISO at all while recording video, so you have to do the next best thing. You lock the exposure.
I’ll describe some settings to help with locking the exposure and make it a bit more predictable in the next few posts.
The Hunting Focus Problem
One of the most frustrating problems with filming video on a DSLR is the horrible hunting of focus, where it focuses in and out and back again. By the time it’s done, you’ve burned about three seconds of video having nothing but blurriness. What’s going on?
First some basic information on how digital cameras focus. There are two main focusing techniques used by cameras, one is called “phase detection” and the other is called “contrast measurement”.
What is Phase Detection?
Phase Detection uses some deflectors in the viewfinder mirror to redirect some light coming in from the lens down to sensors in the bottom of the camera. Those are those dots you see when looking through the viewfinder. The sensors can not only figure out the image is out of focus, but how far out of focus the lens is and which way it’s out of focus. Because of this, the camera knows almost immediately which way and how far to adjust the focus to get a tack sharp image.
Phase detection does have its faults, but it’s fast and efficient. One of the down-sides of phase detection is it requires the mirror to be down to work in the D5100. LiveView requires the mirror up for the sensor to show you what the lens sees full-time so that excludes using phase detection for video recording.
What is Contrast Measurement?
The other option, Contrast Measurement, is used by LiveView and works a bit differently. The camera’s computer examines the area of focus for contrasting lines, seeing how sharp of a contrast between two shades in the area are. If it can’t find a sharp area, it has to adjust the focus and remeasure to see if the contrast worsened or improved. Then it knows a bit better which way to go, either more in the direction it’s going or reverse direction and go past where it was originally. This leads to the lens focusing out and back until it sorts out where ideal focus is.
One issue that can occur with contrast method is if the area of focus is on a blank wall or the ice on an ice rink (between the painted lines), it won’t ever find focus because there is nothing to compare for contrast sharpness. Sometimes the camera will try to improve its luck by increasing the contrast in LiveView so it has more information to work with, but it affects what’s being recorded as well. This will only happen if you partially depress the shutter release button to force a refocus.
There are more advanced contrast measurement methods, but sadly the D5100 doesn’t use them.
How Do I Make Focusing Work?
This is where you have to work with manual focus or a method I’ll describe that lets you set your focus and then start recording without it hunting. But we’ll save it for the following articles.
Problems Described, Now What?
Hopefully I’ve described the issues at hand enough for you. The next article will help with some settings on the D5100 in preparation for filming and the last of this series will go into the procedure to go through when you want to record video in the best quality this camera can produce.
Now this isn’t covering all the potential problems with shooting on a DSLR but is intended to cover the problems that are easier to handle directly in-camera, no extra equipment or investment. Some problems like moire, shutter roll and shaky cam I might cover later but this article is primarily in getting closer to par with the nay-sayers who say “it can’t be done on the D5100″. It can be done, it’s just a bit harder to do so.
Note that you don’t have to go through all the actions to record video whenever you want. They’re tips for you to take into account to be able to produce better quality video with the intent of editing together and making a more professional final product. You might want to run with auto-focus and auto-exposure enabled and unlocked so you can capture some great moments of your son’s hockey game, but if the auto-focus isn’t doing it, now you know why.