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Monday, May 5, 2008

June 2008 HelpLine

Get The (Focal) Point?

This Article Features Photo Zoom




Photographing indoor performances can be tricky, but you can get good results if you use a fast lens and take a few practice shots to get your exposure settings right. When photographing comedian Louie Anderson, the hardest part was trying to keep the camera steady while laughing.


Capturing talent
Q) I want to start shooting photos of local bands and some other bigger acts that come through my area on a regular basis. I'm new to the D-SLR game and still learning all the things I can do with my camera. So I'm looking for some advice on what settings to use while in this type of situation. Of course, it's low-light and fast-moving action, along with light changing all the time. I'm in the market to buy a new lens specifically for this task, but would love to also use it in the field for the nature photography I'm starting to enjoy. I'll have access to the sides of the stage and the front of the stage on the calm side of the barrier, so I'd think that my shooting distances could range from about six to 25 feet.


Chet Coletto
Via the Internet

A) Your question is timely. I recently was assigned the task of photographing comedian Louie Anderson performing for a large audience in a large auditorium. I knew that the lighting would be challenging, so I brought my fastest lens with me, an ƒ/1.2. More than anything, I needed a lens that allowed me to capture the show with a shutter speed that minimized the performer's motion. Since I had access to get backstage and up close, I wasn't as concerned about focal lengths. Even so, I carried a second camera with a medium telephoto so I could capture different perspectives.

As far as settings, I usually switch between aperture and shutter priority. I typically shoot a couple of shots to see what kind of exposure I can use. If I'm really fighting the light level, I shoot aperture priority and leave it wide open, letting the shutter speed fall where it may. But if I have a little head room, I shift to shutter priority and shoot at 1⁄125 sec. so that I can let the aperture give me a little more depth of field. The problem with the fast lens is that the depth of field can be so narrow that the performers quickly move out of the focus range.


Q) Sharpening Your Understanding of Focus

I was reading an article about wide-angle photography that suggested I should use "hyperfocusing" to help ensure that the whole image was in focus. What is hyperfocusing, and how do I use it?

J. Lieske
Via the Internet

A)I think the article you read was referring to the use of hyperfocal distance when you focus your lens on a particular scene. (Either that, or maybe the author was concerned about focus and completely ignored any other aspect of photography!)

Normally when you set focus for a composition, you pick the most important subject and focus on that. You then hope that many other parts of the image are in focus, too. Hyperfocal distance relates to depth of field. Depth of field is the range before and after your focus point where objects appear acceptably sharp. I say "acceptably" because what's truly sharp is the focus point. For now, I'll call acceptably sharp "in focus."

Here's an example of depth of field (using round numbers that are easier to understand, rather than actual numbers based on a certain lens). If you focus on an object at 20 feet, depending on your lens and aperture, you might have a range that appears in focus from 15 to 30 feet. This is your depth of field. Depth of field is highly dependent on your aperture setting. When you increase the aperture of your lens, your depth of field narrows. It widens as you decrease your aperture. Going back to the example above, if you were to stop down the lens (make the aperture smaller), such as going from ƒ/8 to ƒ/16, your depth of field might increase to a range of 12 to 60 feet.

Hyperfocal distance is a specific focus point for a given focal length. It's the focus point that places the back range of the depth of field at infinity, maximizing the range that's in focus. This might be easier to understand with an example. Let's say you have a 24mm lens, and the hyperfocal distance is around 12 feet with an aperture of ƒ/8. The range from seven feet to infinity will be acceptably sharp. If you focus closer, the range might only be from six to 700 feet, and anything beyond 700 feet will be out of focus. If you focus farther away, on the other hand-say, at 15 feet-the range from 15 feet to infinity will be acceptably sharp, but you're throwing away that extra focusing range (from eight to 15 feet) that you could have had if you used the hyperfocal distance.

Hyperfocal distance isn't the same for all lenses, however. You can find online calculations for hyperfocal distances at www.dofmaster.com/dofjs.html. There are some "rules of thumb" out there that I find troublesome for estimating hyperfocal distance. Some say to focus "a third of the way in." In my experience, this has led to less than desirable results-often objects in the distance aren't sharp. I tend to err on the side of setting my focus point farther into the scene. It doesn't hurt to take several shots with slightly different focus settings. You can find a detailed tutorial on hyperfocal distance at www.cambridgeincolour.com/tutorials/hyperfocal-distance.htm.



Magnetic Personality
Q)
I have a few cameras, including a Polaroid i733 and a Kodak C643. I like to wear them on my jeans pockets. I couldn't find camera cases that hooked on my pockets or the sides of my purse (easy to grab), so I bought cell phone cases. They have magnetic closer tabs and magnetic fold-down sides. I was told that the magnetic field can affect my picture quality. Now I'm noticing it, and I need to know if this my imagination or not. I love to take pictures and work with them. I also love my camera cases. Please help me.


Judith Combs
Via the Internet

A)This question is similar to others I've received regarding airport security. With airport security, the concern is with the high-power X-ray machines-a thorn in the side of every film photographer. In your case, the concern is with the magnetic fields that surround the clasps found on the makeshift camera cases you use.

The memory cards in your camera aren't like floppy disks or other magnetic media. They don't store your image files based on storing a magnetic charge. So placing the cards next to a cell phone case with a magnet shouldn't have any effect on your image quality. (This goes for running your image cards through airport security, too.)

I'm a bit concerned that you notice a problem with your picture quality, however. Either you're imagining it or something else is going on. I'll leave it to you to determine what you're imagining,but I'd like to address some other possibilities.

While digital cameras are surprisingly durable devices,you should remember that they contain precisely aligned optical elements that are susceptible to damage or misalignment if they're exposed to abuse. Although there's a convenience factor in using the cell phone cases you've chosen, you should evaluate whether they give your cameras enough protection. Particularly since the cameras are worn on your jeans pockets, it's possible that unbeknownst to you, the camera is being knocked about. This could throw the optics out of alignment—which would lead to degraded picture quality.

Another detail to investigate is what the interior surface of the case is made of. Is it offering enough protection so that it doesn't scratch the LCD?

Lastly, how clean is the case? Dirt in the case can land on the body of your camera. Once on the body, it can move to the lens. Once on the lens, it can block light from hitting the photosites on your sensor or it can disturb the light enough to cause parts of the image to lose sharpness.

So keep your camera case clean and make sure it offers enough protection. There are many cases out there that offer good protection. I'm reminded of one manufacturer's representative (Kata), who routinely demonstrates how protective their cases are by throwing the case across the room. While I don't assume your camera has suffered from that kind of abuse, the small drops and bumps do add up. 

 


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