Tag Archives: focal length

the frame # 5 – different focal lengths & changing viewpoint

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.

the frame # 4 – different focal lengths

Shot during my walk in Glasgow necropolis 3 weeks ago and described in that post. To recap, I was using a Pentax Spotmatic F loaded with Fuji Superia 400 asa. The negatives were scanned at Snappy Snaps on Byres Road and aren’t that high resolution, but are adequate for on-screen use or making 6 x 4 prints. I have not spent too long trying to get the colour balance the same across all 6 prints, as this is not what the exercise was about (said he, by way of excuse).

Here are the pictures:

In all cases (apart from the last which was shot a couple of stops more open, to allow for the teleconverter) the pictures were all taken at f11 to keep everything in focus from the foreground to the far distance.

I don’t think I have ever actually done this  before (unless you count the first of the introductory exercises which involved a much smaller difference of focal length) and, although I knew in theory what would happen, it’s good to have that confirmed in practice. The things that leap out at me are both the way that detail in the background becomes ever clearer and the way the perspective flattens as the focal length gets longer. Also, the usefulness of carrying a tripod was hammered home here – it made both composition and eliminating camera shake with old heavy equipment much, much easier. And for the record, I think I like the 85mm shot best…

a couple of hours in the necropolis

looking east from the necropolis, glasgow

Pentax Spotmatic F. Jupiter 9 1:2/85 1/250th sec @ f11. Fuji Superia 400 asa

(Notes on my shoot for the fourth exercise in part 1 – using different focal length lenses from a fixed position)

This weekend I had a couple of totally free hours that I filled by going to the Necropolis for the first time in around 30 years. Back then it was all fairly dilapidated – I think you weren’t even meant to go in in case a vault collapsed under you – but now it’s been cleaned up, made sound and become part of the tourist experience.

As I spend a fair amount of time in Glasgow, I keep a Pentax Spotmatic-F and a set of lenses there to cut down on the amount of luggage I need to take with me when I travel up from London. Glasgow is also where I get film developed, at the Snappy Snaps on Byres Road, so if I finished the film I already had in the camera, there wouldn’t be a delay in viewing the results.

The Necroposlis sits on a steep hill separated from the cathedral by a steep valley and if you look back as you follow the twisty path up towards the monument to John Knox, there is a fine view west. I realised that this was probably as good a place as any to work through lenses with a variety of lenses:

  • Super-Takumar 1:3.5/28
  • Super-Multi-Coated Takumar 1:2/35
  • Super Takumar 1:1.4/50
  • Jupiter 9 1:2/85
  • Super Takumar 1:3.5/135 (2 shots, the second with a x2 teleconverter)

The camera was on a tripod, but some adjustment was made for composition as the frame tightened. All exposures, 1/250th second at f11. Film used 400 asa Fuji Superia.

The picture at the top of this post was taken later, on the other side of the hill looking east. It may form part of Assignment 1.

how normal is normal anyway, pythagoras?

One  footnote to the first of the introductory exercises is that I finally did the sums to work out the “normal” focal length for both a frame of 35mm film and for my smaller DSLR sensor and was slightly surprised to discover that:

DSLR: 23.7 squared + 15.6 squared = 805.05 or 28.4 squared: – ie the diagonal = 28.4mm

Film: 36 squared + 24 squared  = 1872 or 43 squared – ie the diagonal = 43mm

So, rather than being normal, a 50mm lens is ever so slightly telephoto and the nearest I can get to a normal angle of view with a prime lens on a film camera is my Olympus Trip 35 with its 40mm fixed lens. And on my DSLR I need a 28mm lens rather than the 35mm one I’ve blithely been using for ages now.

So there…


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

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:


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…