Tag Archives: angle of view

the frame # 5 – different focal lengths & changing viewpoint

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Taken on the way back to work after lunch one day, as I passed Oxford Circus tube and then walked up to the front of All Souls’ Church.

nikon d50; nikkor af-g 70-300mm len @ 70mm/105mm equiv; ISO 200; f8; 1/320th sec

nikon d50; nikkor af-g 70-300mm lens @ 70mm (105mm equiv); ISO 200; f8; 1/320th sec

nikon d50; kaleinar 16mm/24mm equiv lens; ISO 200; f8; 1/320th sec

nikon d50; kaleinar 16mm (24mm equiv) lens; ISO 200; f8; 1/320th sec

Again, while I knew what to expect, I hadn’t actually done this systematically before. And while some of the difference between the two pictures can be put down to the first being taken with the lens pointing fairly close to straight ahead, while the second was pointing seriously up (it would have been nice to have been able to float 20 feet or so up, but levitation wasn’t possible that day and I don’t know anyone who owns a tilt/shift lens) the difference in the sense of space is still quite remarkable! The openness of the second contrasts strongly with the flatness of the first; claustrophobia gives way to a sense of space dominated by the sky behind the church.

getting to know your camera # 1 – focal length and angle of view

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A straightforward exercise and something I’m surprised I’ve never actually done before. For it I used my Nikon D50 body, Nikkor AF-D 35-70mm f2.8 zoom at both ends of its range and a Zenitar 16mm f2.8 to give a final, wider version of the view. I was interested to see that – when looking through the viewfinder with the other eye open – sizes didn’t match at a focal length of 35mm (the normal/50mm equivalent for my camera’s sensor) but did when the lens was zoomed in to about 50mm. While the angle of view was correct for the 35/50 equivalency, optically the perceived size was correct only with a tighter focal length. Presumably this means that my “sensor size” (the retina of my eye) is closer to the frame size of 35mm film and while it is seeing a narrower angle through the viewfinder (approximating to a 75mm lens on a film camera) the visible size of the objects seen remains the same. Certainly, a couple of days later, trying a 50mm lens on a film SLR, it was still the 50mm lens that gave the same perceived size in both eyes. Now, it would be worth trying this with a medium format SLR and a 50mm lens, just to check whether a 50mm lens – acting as a wide-angle this time – would show objects the same size in the viewfinder as they appear through the other eye in reality.

Anyway, here is a composite of the three shots I took, with the tighter angled pictures scaled down to the equivalent size in the widest and then pasted over the original with the frame’s edges outlined:

Image

When I returned with 3 A4 printouts, I was just able to get my hands far enough away from my face for the 70mm picture to match the size of the original, the 35mm picture was ‘right’ with a slightly obtuse angling of my elbows and the 16mm picture would have needed to be too close to my face for me to focus.

Of course, I forgot to take a tape measure with me, but – back home with a ruler and relying on muscle memory, or whatever it’s called – I was able to estimate the distance at which the prints matched up in size to the view as being 70cm for the tightest and 35cm for the middle one. The widest was impossible to gauge, but it seemed to be almost right when the paper was around 10cm from my face; from the other two, it presumably would have been about 16cm given that (for an A4 print) focal length in mm equals arm’s length in cm…