Assignment, Week 2: Reducing shake
Theme: Urban Jungle
While we didn't have a chance to go through all of the photos from Week 1, one of the chief problems you may have encountered in low-light situations is image blur. Generally, blur is caused by inconsistency in where light falls onto the sensor - this might be caused by the sensor itself moving and changing its position in space, or by the subject itself moving, and thus changing where the light falls onto the sensor.
We'll focus on blur due to camera shake this week. If you're curious you can see a more rigorous derivation in the Week 2 presentation for the Advanced section, but in a nutshell the amount of blur from camera shake is determined by three factors:
As can be seen from this equation, the amount of blur you get (the unit for the above is image lengths, or blur as a % of the entire image) is a function of three things: average rotational speed (how fast you shake), exposure time (shutter speed), and angle of view (a function of focal length and the crop multiplier of your sensor). This jives with conventional logic - if we shake the camera faster, we get more blur. We tend to get more blur with longer shutter speeds. And if you use a larger angle of view (when you "zoom out"), you tend to have less blur. An important point to note is that each of these factors are multiplicative, rather than additive - zeroing one will zero the total amount of blur. So if you had a zero rotational speed, it doesn't matter how long your shutter speed is, or how narrow your angle is - the blur will be zero. Similarly, with an extremely fast shutter speed (say 1/10,000s - close enough to zero), we also zero the blur, no matter how fast we shake the camera.
There are several methods you can try out to reduce the amount of blur in your photos due to camera shake.
- Holding technique: With the advent of digital cameras with LCD screen previews, many photographers tend to shoot holding the camera with their arms outstretched. This is in fact one of the worst ways to hold the camera, because you tend to be a lot less steady with your arms outstretched. Instead, you should try pressing the camera up to your face, either using the little viewfinder if your camera has one, or just pretending that it's there. By pushing the camera up against your face, you have something to stabilize against, and your shots should be a lot steadier.
- Second shot: You might notice that whenever you fire a shot with your camera, pressing down on the shutter button exerts a force on the camera, which displaces its position a little bit, creating blur. By setting the camera into a "continuous shooting" or "burst" mode, you can take multiple shots at a time, and on average, shots after the 1st one will be significantly sharper because there isn't a deliberate shutter-press force exerted.
- Breathing method: When using firearms, there are a number of different breathing techniques in order to aim and fire the gun steadier, and these techniques readily apply to photography as well. One common tip is to fire while exhaling, as your body tends to be more still at this point.
- Multi shot: Like a lot of things in nature, the amount of blur you get in each shot isn't a constant amount, but will vary from shot to shot. While you might *average* a certain amount of blur, some shots will be blurrier than the average, and some will be sharper. Thus, you can use probability to your advantage - with a large enough sample size, you will eventually get *one* image that is acceptably sharp and blur-free, and that's all that matters, even if you're throwing away 99 other shots that are all blurry. This is useful technique that one couldn't really practice with film, but is now viable with digital since it costs nothing to record and discard an image.
- Angle of view: As shown by the formula above, the angle of view also determines the amount of blur. By using a wider angle, your image will get less blurry - instead of standing far back and shooting from a distance, zoom your lens to a wider angle and move closer to the subject.
- Improvised tripds: As some of you discovered in Week 1, a tripod doesn't always have to be a tripod - virtually any inanimate object will do in a pinch, so you can use any ledge or table or column as a stabilizing base for your camera. Another interesting do-it-yourself piece of gear is what's known as a "string tripod", which I could describe here in words but is perhaps better explained in this video:
If you want to try making one, all you need is a bolt, some string, and maybe a washer or something for you to step on. The size of the tripod mount is a 1/4", 20 thread size - just take your camera down to the hardware store to make sure you're getting the right size. I believe the ACE hardware store on University sells them for 19 cents or something.
For this week, the assignment will once again concern low-light photography. This time, go out to shoot extremely dark scenes that require long shutter speeds, and would normally give very blurry photos, but try to employ some of the techniques shown in class to see if you can get a sharp, usable photo out of the scene.
The "theme" for this week, which you can choose to follow or not, is "Urban Jungle". Upload photos to http://photodecal.org/gallery/main.php?g2_itemId=3027.
Assignment summary
- Shoot around in low-light situations, going for very dark situations and trying some of the blur reduction methods to see if you can get reasonably sharp photos.
- Theme for the week is "Urban Jungle"
- Upload photos here.
