Friday, September 3, 2010

Photography Case Study: “Fireside Chat”

After discussing a train wreck Tuesday, let’s have a look at a better result today. It is important to know your limitations going into a composition, and trying to work within those bounds. While this image only works up to about 9x12” – and then only with significant post processing I haven’t done for this presentation – I accepted that up front. I’m left with a usable image, albeit at a smaller size than I might care for, rather than a technically superior image (in terms of sharpness and noise reduction) that is garbage.

"Fireside Chat"

Image details.
Nikon D40, Nikkor 35mm f1.8 DX at ISO 400, f2.5, 1/60 sec. JPEG with automatic white balance set to Flash (I didn’t use flash but the lights in the image approximate the temperature of flash light), Neutral image setting. Aperture-priority exposure mode (A on most camera dials, Av on Canons) with Nikon’s 3D color matrix metering engaged. -2 1/3EV exposure compensation.

Environmental considerations.
The environmental considerations for this shot were different than those addressed last Friday. This is a photo of Wyoming Gov. Dave Freudenthal during a live television broadcast (on the right is Geoff O’Gara of Wyoming PBS).

As we’re live on television, no camera flash. Indeed, I took a flurry of photos both with and without flash before the broadcast began, see below.

The image is entitled “Fireside Chat” because the two men are sitting in front of a fireplace in the Governor’s Mansion, although the camerawoman in the foreground hides that fact. More reasoning at the end of the post, too.

The protrusions sticking out from her camera rig are not mics, but control the camera. Imagine the throttle and handlebars on a motorcycle and you get the idea: move the bars to aim, twist the handles for zoom and focus.

In a perfect world I would have moved the sofa in the right of the image, as well as the drink bottle. The camerawoman, a student at Central Wyoming College, very graciously agreed to work with me, although I’m not sure I was able to communicate exactly what I was up to because we had to be mouse-quiet. I didn’t have an opportunity to try the composition with only the camera, and not her, in it, but I doubt it would have worked as well. I was able to get this much across: please drop your hands to your sides and be still for a moment. I hope she didn’t also take from that, “…so I can get a photo of your butt.”

Figure 1.
This is an exercise in symmetry, which is why I really, really wish I could have moved that sofa. (Even if the noise weren’t a problem, there were two additional cameras on either side of the image, which you can’t see here. To illustrate, I’ve chopped the image in half down the vertical axis, flipped one half horizontally and then overlaid the two with the top set to 50% α (alpha, or transparency). The result is Figure 1.

It’s not perfect, but it’s damn close. Frankly, I’m surprised I got as close as this, and I’m surprised the PBS guys got as close as they did by eyeball. The light stands are nearly perfect, the chairs are nearly perfect, as you can tell by looking at the fireplace. Only some mild lens distortion creeps in: note how the wooden fireplace trim doesn’t quite stay straight. That it worked as well as it did makes me even more thankful to have gotten something useful, rather than asking too much from camera or conditions and blowing the whole works.

Lens characteristics.
I’ve covered most of this before. The D40 does not remove LCA, but at f2.5 that isn’t a problem, even staring at the corners blown up to 400%. I could have opened the lens all the way up to f1.8, but this $135 gem isn’t perfect: there may have been some blobbing (coma). I also needed some depth of field, as I explain below.

The focal point of this image also raises a challenge. The D40 has three autofocus sensors, at nine o’clock, center, and three o’clock. Shooting a vertical composition like this, there isn’t an autofocus sensor under what I was focusing on.

Three notes on shooting autofocus. Depending on your camera, not every autofocus “spot” can determine focus wide-open (smaller
f number) in low light. On the D40, only the center autofocus sensor can “see” at faster apertures than f5.6. Additionally, only the center autofocus sensor can determine both horizontal and vertical best-focus – this is what is meant by a “cross-hatched” sensor. The takeaway from these two nuggets of information is to always use the center autofocus sensor when shooting in low light or vertically. You will then need to recompose.

Now comes to my third note. At f1.8, depth of field is very shallow, even at 35mm. (The longer the lens, the shallower the depth of field at a given aperture.) Your autofocus system is taxed to its limit – and perhaps beyond – shooting in a low-light situation, and focus has to be dead on at f1.8. Knowing I would have to lock focus and recompose, I knew I couldn’t trust the autofocus.

Why is this? Because the plane of best focus is not a plane. It is a portion of a sphere. Confused? Hold a flat piece of paper in front of and parallel to you and imagine that is the focal plane at f1.8. (At f1.8, the focal plane is only about as thick as a sheet of paper.) This is not the focal plane. Using your two hands at nine and three o’clock, pinch the paper lightly and push both sides toward the middle, causing the paper to bulge a bit. This is a very rough representation of the real focal plane.

In theory, if nothing moves and if I turn the camera perfectly dead-still on the Y-axis, the spherical nature of the focal plane should keep my subject in focus. But without a precise rangefinder, how do I know that both the Governor and O’Gara are exactly the same distance from me? I needed a little breathing room in my depth of field. Let me boil all of the previous five or six paragraphs down to two general rules of thumb:

· When shooting vertically or in low light, only trust the center autofocus sensor unless you know the technical details of your camera and therefore which other sensors are capable of vertical and/or low-light use.

Figure 3. Perhaps I'll discuss this photo
someday. The lighting is thanks to
using two flashes.
· Try and leave yourself a margin of error in aperture so a tiny autofocus issue doesn’t leave you will blurry facial features (or whatever else you’re shooting).

Camera configuration.
As I’ve said, I knew this shot was going to be a compromise. Once I knew this, the camera settings configure themselves. (Well, I had to push the buttons and spin the dials, but there really wasn’t much decision making.)

I wish the D40 handled high-contrast low-light situations better, but it is what it is. (And this is picking nits. For $500 when new, the capabilities of the D40 are worth every penny.) Nevertheless, in this shot ISO 400 is pushing it. Let’s talk about noise reduction for a moment.

Figure 2.
Figure 2 is an actual pixel portion of the picture at 200%. It’s the back of the Governor and his chair. Figure 3 is a photo I took at a prom last year with the D90 at ISO 1600, or two stops higher ISO than the Governor’s photo.  Figure 4 is an actual pixel portion of that same photo at 200%, of the chin, neck and shoulder of the girl on the left.

The photos are similar in that both were taken at about the same aperture (f2.5 v. f2.2), similar shutter speeds (1/60 sec. v. 1/30 sec.) with similar lenses (35mm v. 50mm). Because the girls photo is taken on a 50mm, there is even less depth of field than the Governor’s photo. Have a look at Figures 2 and 4 and notice how edges remain edges with the D90, with less blocking.

Figure 4.
Why is that? Because, like most new cars’ traction and stability control, you really can’t turn off noise reduction in the D40. You can set it to “off” but the electronic nannies are always lurking in the background, ready to pounce and oversmear your images.

The reason the girl’s shoulder is roughly defined isn’t because of noise control – look at her chin – but because at f2.2 that’s how shallow the depth of field is.

So, ISO 400 was the highest I could go. In hindsight, I may even have tried to nail focus and gone with ISO 200, f1.8 and 1/40 sec. exposure, had I known noise reduction was going to get so out of hand.

As I mentioned, I set flash white balance because it matches the lighting PBS used – the big rectangles in the photo. I wanted the longest exposure possible while handholding to keep the aperture at a sane value, but I didn’t have much time so I left myself half a step margin of error.

Shot technique.
Communicate to the camerwoman my intentions, get in, exhale slowly, and shoot. I only had enough time to get two shots before she needed to adjust her own focus. I couldn’t use the D40’s continuous shooting mode (motor drive on film cameras) because I had to refocus and recompose for the second attempt.

Post processing.
There isn’t too much going on in post processing. I cropped and straightened the image, removing some dead space from the top. I couldn’t get any closer because it would have forced those handlebars into the Governor’s and O’Gara’s faces.

"Fireside Chat" at the moment of conception.
I cooled the white balance just a hair. Fortunately, the flash setting was pretty close to the warmth that my eyes saw in the room, and is helped by the fireplace.

Exposure is dialed down 1/5EV and there is a good deal of recovery dialed in. (With newer cameras, especially the Nikons with ADR, recovery isn’t as important.) I added 2 on the blacks slider, increased clarity as much as I dared and increased vibrance by about a third.

I applied a medium contrast curve and light sharpening.

That’s it.

Less artistic view of the interview.
Photography, whether film or digital, is a cross between engineering and painting. The technical pieces have to fit together but there has to be some vision behind the idea.

As in a previous composition, there are triangles here. One is positive and the other is negative. The positive triangle are the two men sitting, representing the corners of the base of the triangle, and the apex is at about the camerawoman’s neck, where the light tapers off into darkness. The negative triangle is almost exactly opposite: the two lights are the base corners and the camerawoman’s, er, butt, is the bottom of the triangle.

The predominant theme here, however, is the symmetry. The Y-axial symmetry and the balance between light and dark. Finally, there is the contemplative symmetry of what appears to be a very intimate experience – two men chatting in front of the fire – balanced against the intrusion of klieg lights and television cameras.

Image grade.
Original: A-
Post: D

I grade myself highly in the original attempt because I got the balance just about dead on and because I managed to capture an image with equipment not well-suited to the task. Thoughtful in-camera settings delivered the most I could hope for in the JPEG and left my post processing manageable.

A substantial investment in post processing, such as if I were to sell the image – would yield a higher grade. With tedious pixel-on-pixel tweaking, I could probably restore some texture where the NR routine has splotched over it.

I welcome and invite suggestions for this column and critiques of this composition. Please leave a comment on the blog or email me at I suggest you put “Photography Case Study – Fireside Chat” in the subject line so I find it if Google’s excellent SPAM filter eats it.

The title of this photo is a deliberate rip-off of FDR’s radio addresses, because I think it captures the final dichotomy I mentioned – intimacy and the illusion thereof – very well.

Next time…

"Who You Callin' Turkey?"
A discussion of knowing the rules, and when to break them. Specifically, this photo is lacking a bit of sharpness because I shot at too small an aperture, f16. But I had to.

Photos of the Day continue until I see you then!

(Technical / legal note: You may have noticed that the Governor photos are not ©'ed like most of the other stuff I have on here. That's because, as works commissioned by a government, they are public domain. "Figure 1" is ©'ed because it is an original work for this blog post, not the government. This means you could, if you cared to, print or otherwise present the photos without my — or anyone else's — permission. And if you did something to them that made them original, you probably could copyright them yourself. I'd consult a lawyer, first, of course.)

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