Let’s do this thing!

Okay, I’m convinced. I’ll keep plugging away. 

I’ve decided to leave the rather limited sphere of small scale photography as just another part of this blog’s remit. This post will complete the short session on Depth of Field, started back on November 7, and then I’ll look at some of the other topics I jotted down. Right, into the fray…

These images were taken specifically to demonstrate why Depth of Field is important when photographing scale models. The set-up is simple: a length of track, a 4mm scale loco and seven wagons. Available light was from three standard five-foot fluorescent tubes, approximately a metre above and in front of the subject. The lens was a Sigma 10-20mm wide angle zoom (a tautology if ever there was one), set to a focal length of 16mm — which is almost the wide setting on most DSLR kit lenses. 

A series of shots were taken, stepping down from the widest aperture available with the lens at this focal length, ƒ/5.6. I used the “standard” ƒ-stop notches of 5.6, 8, 11, 16, 22, and 29. Almost every DSLR can give fractions between those settings, but I wanted to keep it simple. I let the camera work out the exposure required, after stepping down to the required aperture. I broke a cardinal rule by focusing at infinity, rather than the correct one-third distance along the subject. The upshot is you should be able to see the sharp area advancing from the end of the train towards the camera, but it means the final shot is not as sharp as it could be at the nearer end. For some reason, I set the ISO to 400. Normally, I'd work at 100 to avoid excessive digital noise. Finally, I did a spot of work in post processing, to brighten the images, sharpen them for viewing on screen, and cropping out extraneous image.

The shots are in order: ƒ/5.6, ƒ/8, ƒ/11, ƒ/16, ƒ/22, ƒ/29.

At the widest aperture, nothing of the subject is in focus. The far distance is there, but it’s not easy to see in this shot.

At ƒ/8, the brake van is beginning to get a little clearer, but little else is in focus.

Things are a little sharper at ƒ/11, but not great. As a side note, if I had focused at the correct point along the subject, more of the nearer part would be sharp now.

Interesting things begin to happen at f/16. While the wagon nearest the loco is still not sharp, much of the rest of the train is.

At ƒ/22, we hit pay dirt. The whole train is now sharp, and the cabside number is legible.

Finally, at ƒ/29, we get the best we can. The nearest part of the loco’s tender is not in focus, due to my not focusing at the correct distance to begin with. This also shows a pitfall of using an SLR — you simply cannot see whether the whole image is sharp using the viewfinder preview or the screen review after the shot is taken. A way to counter this problem might have been to favour the loco as my focal point, letting the brake van fade into slightly blurred obscurity — but then I’m trying to make a point with these images, not make a technically perfect portrait.

Did you notice how the exposure time got longer as the aperture got smaller? Did you think I was joking about having a lunch break while making an exposure at ƒ/22 in a dimly-lit exhibition hall? 

Okay, so we’ve seen how the sharpness of an image increases as the aperture gets smaller. I hope you could also see how the realism of the subject I chose improved as the depth of field got deeper. Not to blow my own trumpet, but the shots at ƒ/22 and ƒ/29 could be mistaken for the real thing. 

Finally, if the dratted image embedding lets me, I prepared a rather extreme pair of images to show DoF at work. This time I've focused at the golden point a third of the way along the subject, which is just at the front of the loco in this case. I’ve also stuck a lens close to the camera as a graphic DoF demonstration. The first shot is wide open at ƒ/5.6, the second is at ƒ/22.

(Third attempt at adding the images…)

I think that explains it quite well, don’t you?