Stretching my exposure triangle

Not the same as stretching Benner’s Box, but my boundaries are now wider. I just bought a more capable camera. And by capable I mean it has a bigger exposure triangle.

What I’m used to is what I grew up with: the common range of shutter speeds, apertures and ISO. Looking at even the best of my kit the shutter speeds might run from 8s to 1/2000 and the apertures from f1.4 to (usually) f22. My ISO options run from say 6 for a very slow film to 3200 for my fastest film or sensor. So let’s say the sides of my available exposure triangle are 13 stops on shutter speed, 11 for sensitivity and 9 stops for aperture.

Then along came digital. So now, with a modern camera, I have more to play with. My shutter speeds now span 19 stops and my sensitivity 14 stops. The aperture range is the same, as the limit at the large number/ small hole end of the scale is the diffraction of light. Perhaps we could stretch to a range of 10 stops if I bought some of these new lenses coming in at f1. Even so, I have a lot more capability to use with this new camera. And even better, it’s in the places I need it. My film cameras get their 11 stops of sensitivity at the low end: they can shoot 6 or 3 ISO film. The digital camera gets its range at the top end with an ISO that goes up to 819,200. That’s far more useful, especially as the shutter will go up to 1/8000 so I can still shoot wide open in bright light, even if the ISO doesn’t go lower than 100.

Of course, being of an inquisitive nature, I had to work out what my old and new exposure triangles looked like. So the older cameras could range within a triangular volume with sides of 13, 11 and 9. The new one has sides of 19, 14 and 9. Similar to a colour space: it’s volume of the shape that gives you the space you can explore. So, using Heron’s formula and a bit of Pythagoras I make the old camera’s volume 644 and the new one’s 1197; nearly double. So we should actually talk about the exposure prism rather than triangle <\pedant>. But here’s a fun game for the family on a rainy day – plot the exposure space of your cameras. The practical side of this is that a film camera only gets a horizontal slice of the prism in use, as you set the ISO by the choice of film and there is not much opportunity to change the ISO on the fly. Sorry – geek diversion ends here – back to the plot.

The three axes at the origin should be at right angles. I bent them to fit better on the paper.

The shake reduction that comes with digital also gives me nearly seven stops of extra exposure space at the slow shutter speed end. No more than that because the world is a rotating sphere, but we knew that.

Why do I need this cleverness? Because I find myself pushing the limits of what my current kit will do. For example, a local band was playing in a pub garden during the early evening. The best camera I have for higher ISO work can do 800 and be pushed to 1600, but the quality suffers.  I was using a convenient post to steady the shot and still getting only 1/30 on shutter speed.

Yes, there is a story behind the band’s name…

I had a go at star photography with my ‘best’ camera and the results were awful. Not that I regularly do the lit-up tent and Milky Way thing, but it would be good if it did work when I was out in the hills and darkness.

Looks like Kendal is on fire

There is also the crop factor. My old camera has an APS-C sensor, so it effectively multiplies the focal length of my old 35mm lenses by 1.5. Very useful for sports and action, less so for wide angle. The old camera also has pretty poor noise at higher ISO, so things used to get a bit tight in dimmer light, with a long lens and a moving subject. The new camera is full frame, or the same size as an old 35mm film frame. So now all my wider lenses will work as they were meant to. The camera also has an option of using just the central part of the sensor to act as though it was APS-C, so I get the equivalent of a 1.5x teleconverter without losing one stop in exposure. (Or I could just crop the picture). What it does mean though is that I can still use my APS-C lenses. I do like a bit of backwards compatibility (and this is not a euphemism). And on that subject, I was delighted to find my 15 year old dedicated flash also works on the new camera.

So, having justified this extravagant purchase to myself, what am I going to use all this expensive cleverness for? After all, I could have bought a Famous Rangefinder for the same money.  Extending my options is the plan. My tilt and shift lenses go back to being mildly wide angle rather than telephoto. My wide angles do what their name suggests. I can start scanning all my medium format negatives (since my flatbed scanner died) at a reasonable level of quality. And I’m off to shoot more pictures of things that go fast in fading light.

Author: fupduckphoto

Still wishing I knew what was going on.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Create your website with
Get started
%d bloggers like this: