In perspective

Want to start a fight? Ask a few photographers what effect the choice of lens has on perspective. Perhaps not a fight, but you will get a lot of hearsay rules and theories. But, as we know, a proper theory is one that can be falsified and makes testable predictions.

So a camera is basically a pinhole sitting at some distance from a sensor or film. The angle of view is set by the size of the sensor and how far away it is from the hole. A big sensor further away from the hole can have the same field of view as a smaller sensor closer to the hole.

Angle of view

Since the distance between sensor and hole is basically the focal length, this explains why different sizes of film or sensor need different focal length lenses to get the same angle of view. For example, a 50mm lens would be a telephoto (narrow angle of view) on an APS-C sensor, a normal lens on 35mm and a wide angle on medium format. Or, to put it the other way round, a standard lens on a small sensor would have a shorter focal length than one for a larger sensor – see A and B in the diagram above.

Let’s ignore the sensor size for now and just look at the angle of view of the lens.

Angle 1

The lens we have fitted has a wide enough angle of view to take in both the person in the foreground and the building in the background. If I stay in the same position and fit a lens with a narrower angle of view, it gets just the person’s face and a small section of the background.

Angle 2

What you will notice though, is that the relative sizes of the person and the building do not change, you just get a narrower slice of the wider version. You can test this by taking the same picture from the same position on both a wide and a narrow angle lens. Or use a zoom. Enlarge the wide-angle shot so that the central portion matches the narrow-angle picture and you will find that they match perfectly. This is the falsifiable test. This means that perspective, in the sense of the relative sizes of objects in the frame, does not change with your choice of lens if you stay in the same position. All that changes is how much stuff you get in the frame.

So what does a wide-angle lens change? If you get close to the subject, it changes the relative sizes of the nearby subject and the distant background.

Angle 3

In this diagram I shoot a head and shoulders with a narrow-angle lens (the dotted lines). It can see a narrow section of the background, so the background looks quite large in relation to the subject. If I get close to the subject with a wide-angle lens, so that I still get a head and shoulders (the solid lines in the diagram), the subject is the same size but I see more of the background and it looks smaller in relation to the subject. What changes is called the diminuition – the rate at which objects get smaller as they get further away.

This is why we usually avoid shooting portraits with wide-angle lenses. If we get close enough to fill the frame, the relative size of things near and further from the camera changes. These could be the nose or an arm or leg. But we do use wide angle lenses for landscapes, where we want to give prominence to a foreground object (like a Joe Cornish rock).

So there you have it – the angle of view of the lens only controls how much you can fit into the picture, providing you stay in the same place. You can use the angle of view of the lens to control how big the background is in relation to the subject, but only if you move nearer or closer to the subject.

What does this mean? That perspective is controlled by position, not the field of view of the lens.

Packing it all in

I’m away on my hollybobs. Special ones, too. But I might be taking more cameras than clothes. Let me explain.

I passed one of those milestone birthdays this year. The sort of birthday that your younger self couldn’t even imagine. I remember at school working out how old I would be in the year 2000, which seemed an impossible distance away. Anyway, to mark the event I’m doing something special – I am going diving in clear, warm water.

I have dived in clear water before, but never as an experienced diver. All my experience has been in British waters so I have never really seen what good visibility is like, or been able to dive without a duvet under my drysuit. But now I am off to parts abroad (after October, to be known as ‘parts foreign’). Clear water, warm, small or no tidal range, little or no currents. Filled with smiling fish and marvellous things. Huzzah! But what camera do I take?

I need to be able to switch between macro and normal, as I want to be able to show the environment as well as the residents. No-brainer then: take the digital plus housing. The camera itself is an old model of Canon. Perfectly adequate for the job but old enough that I got a second one off eBay for a fiver. That way, if I do get a flood, it’s a camera swap rather than a crisis. So that’s one housing in the main suitcase and a couple of small digital cameras in the carry-on. Plus their batteries, as airlines get nervous about Li-on cells where they can’t see them.

What about the Nikonos? If I take it, I will need to take the bracket and two flashguns. So that’s two suspicious-looking bits of electronics and a chunk of metal in the big bag and a heavy X-ray opaque camera and the flash batteries in the carry-on. Plus film.

What about shooting video? If I use the digital camera for that, I’ll need to take a video light. I have one and it can double-up with a grip as a dive torch. Sorted. Except that’s another battery for the carry-on.

Then, what do I use for my touristy shots on land? The spare Canon digital could do the job, plus the Nikonos is amphibious. Do I need anything else? But I would really like to take another ‘proper’ camera with settings so that I can do the arty-farty bit. But then I would need lenses. What about a point and shoot? My mobile phone has a very capable camera plus editing software, so I could just use that. What if I could find the 80mm lens for the Nikonos? No, that last one is daft. My sensible head tells me to use the spare Canon, as I am carrying it anyway.

So: Nikonos plus two flashes and bracket; housing plus two Canon digitals; video light. Rational choices, but the film freak in me still wants to take another film camera. And the Nikonos is heavy to carry around. So is it the tiny Olympus XA, accepting that it has the same 35mm lens as the Nikonos, or is it an old Pentax point and shoot that has a zoom lens but could die on me? But if it does die I just wind the film back and ditch the camera. And the built-in flash is far more capable than the one for the XA. OK, so add a Pentax to the pile, feeding from the same film stock as the Nikonos. And add a film retriever in case I do have to rewind a part-used film. That won’t look at all odd on the luggage x-ray. Not a bit.

Then add to the pile a bunch of rechargeable AA cells for the flashes. Plus chargers for them, the Canons and the video light. And for my phone. And some film – all in original boxes so the airport guards don’t get nervous. Sorted.

Unless I change my mind again.

Plus seven pairs of pants and tee shirts. I’ll let you know how I got on.

Too many socks?


And of course, I changed my mind again. The little demon of perversity sat on my shoulder during the drive to work and whispered in my ear. The Pentax point and shoot is as big as a housebrick, so why not take something smaller? The Balda folds up really small, and a couple of rolls of 120 film will take up no space at all. Plus it will fulfil my desire for something manual and awkward to fiddle with. And it delivers my real desire, which is to shoot black and white. So it’s Pentax out and Balda in.

Unless I change my mind again.


Guess what? I realised that the Nikonos was going to be hooked-up to its flashgun, and that I didn’t want to be undoing and re-doing the connection every day: too much risk of introducing a leak. Plus I weighed the bag and it was well under the limit. So I sneaked the Olympus XA in. So that’s one Nikon, two Canons, one Olympus and a Balda. Totally ridiculous, if it wasn’t for the need to take pictures underwater and on the surface, plus the desire to have enough resilience against breakage or problems.

Making a card rangefinder

I have referred to this a few times, with links out to pages on t’interweb where these things are spoken of. The drawback is that the web resources seem to use maths, when what we want is simplicity. So here’s my version.

What you need is a bit of card (I know, the title was a spoiler). Anything from credit card to an index card will do (ask your parents what a card index was). The main thing is that the card has one good right-angled corner. You also need a tape measure and a second scrap of card or paper.

Find a nice vertical line – a door frame or the edge of a wall. Measure a distance of say six feet from it and stand facing the target line with your toes at the distance mark. I say feet, but you might also measure the distance in meters. Use whatever units your camera lens is marked in.

Hold the card out in one hand at arm’s length. Choose the hand you will be using when you do this for real with a camera. If you are likely to be holding the camera in your right hand and using the rangefinder in your left, then hold it out in your left hand. Let’s assume you will be using your left hand. Close your left eye and line-up the edge of the card with the vertical target. Without moving the card, close your right eye and open the the left. Hopefully the vertical target will appear to move along the card, away from the edge that was originally lined-up. If it moves the wrong way, swap eyes.

That second scrap of paper is used to mark where the vertical edge appears to move to. Pinch it against the main rangefinder card and slide it sideways until your distant mark appears to consistently move to the same place. Keeping the rangefinder card and the scrap of paper pinched together, mark on the rangefinder card a line for that distance. In this example, six feet. Change the distance and repeat.

Card rangefinder
Left picture is what you see with your right eye open. Right picture is with left eye open – mark the measured distance where the yellow card joins the white one.

You can now throw away the scrap of paper and keep the rangefinder. You have built a rangefinder that works for you and your eyes and will measure close distances with enough accuracy to focus lenses using their marked distance scale.

Here’s one I made earlier. Marked in meters and made to be held in the right hand (which is why the distances come in from the left).

Go ahead and make copies of the card so that you can keep one with each camera. Laminate them. Print the scale on the back of your business cards. Get the lines tattooed on your finger or mark them with a pen before you go out.

The only time you will need to change the card is if the length of your arm changes, or the distance between your eyes. Or you decide to become a pirate.

Automatic for the people?

Imagine the shame – someone at the photo club noticed that my camera was set to Program mode. Even worse than being drummed out of the Brownies would be to be stripped of your spot-meter and have the covers torn off your copy of The Negative.

I know someone who has a very capable full-frame digital camera and always shoots in manual. Yes, I can see the point when the lighting is tricky or you are after a particular effect that would fool the meter (rather, the computer), but is there an acceptable level of assistance? Do real men twist their knobs?

What about aperture priority, where you take control of the depth of field but let the camera choose the shutter speed? Or shutter priority, where your choice of shutter speed is important? A lot of old manual cameras were probably used as virtual shutter priority: you would pick a shutter speed and leave it, as changing it meant taking the camera away from your eye and fiddling. So you would raise the camera, twist the aperture ring until the meter said go, and take the shot. That’s shutter priority using you as the actuator.

The reason that the camera-makers developed and sold automation was the delivery of the original Kodak promise: ‘you press the button, we do the rest’. Adding automation to a camera made it more likely that the results would be acceptable. And acceptable meant what what most people wanted – reasonably sharp and exposed. Most people wanted pictures, not cameras. Hence the rise of the point-and-shoot and the supremacy of the mobile phone.

So program mode was perfect for someone who wanted the potential for greater quality from a better camera without having to fiddle with the settings. Fiddling would mean less chance of getting an acceptable picture, negating the advantage of a better lens or bigger sensor. Automation also means speed and coping with changing conditions. I’ve been out in changeable weather with a manual camera, and it can be a pain to have to constantly check the light level. Really, this is what (many) digital cameras excel at: take a test shot, chimp it, apply a bit of exposure compensation if needed, then blaze away with a smile on your face and a song in your heart.

Prog mode
The work of the devil?

And then there is autofocus. We all use it, but pretend it’s not automation. Of course it replaces something that the whole of camera design was meant to make easy, but it’s just so durn useful. When you throw facial identification and follow-focus at sports or kids, it beats twisting your ring. And let’s be honest, if rapid manual focusing was so easy, the street-shooters wouldn’t all be using zone focusing.

What about image stabilisation? Yes, we know that Eisenstadt could hand-hold on the subway at 1/20th second. I’d love to see those contact sheets though – I don’t expect every frame was sharp. I LOVE having stabilisation on my digital camera, particularly as it works with any lens. I don’t even think of it as automation – it’s not replacing my finely-honed skills. Not really. Besides, nobody can see that I’m using it.

There is a more serious problem though, than the ridicule of my peers, and we have seen it already in artificial intelligence. Once an AI is trained and produces good results, we either forget or we don’t know how it works. And then it stops being accurate or it has an inbuilt bias, and we can’t tell or correct it: we just do what it says. The AI does magic and becomes a god, and we perform strange rituals to it (like peering at the back of the camera and chanting ‘ooh’). So perhaps there is some logic in knowing how to do it by hand? Even Lewis Dartnell’s book on rebooting civilisation from scratch had a section on recreating photography.

And anyway, what about light meters? Unless you guess the exposure, you are relying on at least some form of automation.

So where does this take us? There is no shame in automation. It is a tool that can increase your success rate. One should never be dependant on any particular tool existing, but there is no harm in using it well when it does exist. In a phrase used by an old friend “always use the most powerful tool for the job”. Automation can increase your options. But do learn how and why stuff works, it could save you from the cooking pot come the apocalypse.