Wanted or not, the idea of a demonstration intrigued me, so I made one. Since most people don’t live in show homes, indoor shots of kids will usually have a cluttered background. This makes most shots of kids indoors look more like snapshots and less like portraits. The more you can blow the background out of focus, the more you can focus attention on the subject of your photo and the more portraity it will feel. Since I didn’t have a kid handy, I give you Portrait of a Bear with Bookshelf, in 4 parts. The scene is lit in typical indoor fashion with a couple compact flourescents and a smidge of natural light coming through a blind. A stuffed bear stands in for a portrait subject, and a bookshelf provides the cluttered background. To the right of the shot, it’s at about 1.5x subject distance from the camera, and at the top left it’s at about 3x subject distance.
The sample dSLR shot is a D40 with a 50mm f/1.4 lens. This gives you a 35mm equivalent fov of 75mm, just a hair short of the classic 85mm portrait lenses for film. Because f/1.4 is a bit expensive, I’ve stopped down to f/1.8 to demonstrate what you can get with a ~$100 lens, the old film kit 50mm f/1.8. By pushing ISO up to 800, I can get a 1/60s shutter speed using only available light, so no flash is required. 800 is pushing it just slightly on a D40, though you can’t tell with the downsized web resolution. A current body like the D3100 will give you this clean a look up through ISO3200, so you could get a little more shutter speed yet - to freeze a running kid you’d want 1/250 at least, and you could get there at f/1.8 and ISO3200 in this rather dim lighting. Do note that this picture gains a bit of apparent sharpness by being downsized significantly.
To simulate an HX1, we calculate what focal length we’d use for the same field of vision, and this works out to 13.5mm. Now I can do 13.5mm with my Sigma 10-20mm, but unfortunately at 13.5mm its max aperture is f/4.8. I’m not positive where the Sony will be at 13.5mm, but it’s an f2.8-5.2 lens, so I’d guess in the vicinity of f/3.2. So I won’t be able to get an exact match, but a bit of fiddling with a DOF calculator tells us that 13.5mm f/3.2 has got about the same DOF as 16mm f/5.3. That I can do. Because ISO 800 on a superzoom is going to be rubbish, I go to ISO200 and repeat my shot. Then I crop it to the same field of vision. Voila! Oops! Because of the lower ISO and narrower aperture, my shutter speed is up over a second. The background is blurry, but because of camera movement rather than DOF. To be fair, the Sony would be at f/3.2 rather than f/5.3, but that would still put shutter speed at a third of a second.
However, the Sony does have image stabilization. To simulate this (since I don’t have a stabilized lens at such a short focal length) I stick the camera onto a tripod without locking it down and shoot again. Not bad, but we still have a bit of camera motion apparent. And you would have at these shutter speeds, even with image stabilization. Not to mention the bear isn’t moving. If a child is motionless for a third of a second, she’s either asleep or physically restrained. But now we can see the difference in DOF quite clearly. Where with the dSLR shot the book titles were an illegible smudge on the near end of the bookshelf on the right, and the books themselves were indistinguishable at the far end over the bear’s head, now we can pretty much read the titles on the right and edges are still pretty distinct even at the furthest point of the bookshelf, which is about 3x subject distance from the camera.
Realistically, to shoot indoors with a compact we’re going to have to turn on the flash. Finally all motion blur is gone and we can see clearly that we can see everything clearly. And the white balance is showing white as white, rather than with the nice warm cast I get using AutoWB in compact fluorescent lighting. We could get the warm cast back if we wanted it, but we’re going to be stuck with the flat, extremely front-lit look of a flash shot.
Now, you can decrease the DOF on the HX1 by using longer focal lengths, but by the time you’re at the required focal lengths your house won’t be big enough for you to get far enough back. There are a couple other tricks - one is to manipulate the ratio of distances by moving the subject closer to the camera so that the background ends up a greater multiple of subject distance. However, this works against using a longer focal length given the finite size of rooms. I believe you can also simulate bokeh effects in Photoshop, though I don’t know how effective that is.
You’re going to have a hard time duplicating the depth of field in that shot (focal length 150mm, f/2.8, focal distance somewhere around 2’) with a superzoom.
