Film and Sensor Speed or Sensitivity

Originally posted 2013-04-12 19:32:08.

Four key factors in photography are linked: aperture, shutter speed, film or sensor sensitivity and subject brightness. These are linked in such a way that if any one is changed, then one or more of the others must also be changed to compensate. The first two, aperture and shutter speed, are easily controlled on camera, and now we will look at the third factor, which is also under the photographer’s control: film or sensor sensitivity.

In pre-digital days this was always referred to as ‘film speed’ and this is convenient; we continue to use it to describe digital sensor sensitivity — sensor speed. A number of indices or scales were established to measure film speed, but the one that became the most widely used was the American Standards Association, or ASA, scale, which was eventually adopted by the International Standards Organisation or ISO. This is an arithmetical scale, so that a doubling of the ISO value indicates a doubling of sensitivity or speed, and a halving the opposite. (This is as opposed to the more complex DIN scale which was logarithmic.) Because the ISO values are arranged in this way, they conform exactly to the conventions we have already met for aperture and shutter speeds, where each stop or step is a doubling or halving of the one before. So it is easy to apply the same logic to film/sensor speed.


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Photo Technique 3: Shutter Speed and Movement

Originally posted 2013-04-12 19:30:34.

shutter speed motion flash rod fleming
Freezing the action, here using flash. Pic: Rod Fleming

Shutter speed is one of four interdependent parameters that are central to photography. These are : Aperture, Shutter Speed, subject brightness, and film or sensor sensitivity. IF any ONE of these is changed then AT LEAST one other must also change to maintain the same exposure. The most common example of this is that if aperture is altered, then shutter speed must also be altered, reciprocally. So if aperture admits less light, then shutter speed must admit more.

We have already discussed aperture, and seen how the f-stops marked on the aperture ring are calculated and what they are. To recap, the focal length divided by the aperture gives the f-stop, so a 50mm lens with a 25mm aperture is f2, and the they progress f2, f2.8, f4, f5.6, f8 and so on. Each of these allows half as much light to pass as the f-stop before, counting from low to high.


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Stopping down, Depth of Field and Bokeh

Originally posted 2013-04-12 19:28:25.

rod fleming depth of field
Limited depth of field, as seen here, can separate the subject from the background and strengthen the image. Pic: Rod Fleming

In the last article we looked at the optical principles that govern focus and depth of field. Now let’s explore how these are applied practically in the camera. For the moment we will assume that we are using a single-lens-reflex (slr) or rangefinder type camera, either digital or film.

If you look at the lens barrel you will probably see a ring which controls the aperture diaphragm. This will be numbered in f-stops, which on modern cameras will run f1.4,2, 2.8, 4, 5.6, 8, 11, 16, 22, (32, 45, 64). I put the last three in brackets because you’re pretty unlikely to have them but you might see them on view cameras. Note that the numbers double on every second step—2,4,8 etc and 2.8, 5.6, 11 etc. The f-stops are determined by dividing the effective aperture into the focal length, so a 50mm lens with an aperture of 25mm is f2, and with 12.5mm is f4. Each f-stop, going from low number to high, admits half as much light as the one before, so f2.8 is half of f2 etc. It’s easy to work out why if you’re mathematically inclined, but if not, just remember it.


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The Naked Truth

Originally posted 2013-11-03 23:31:55.

I grew up in a world where photography, especially monochrome photography, was synonymous with ‘truth’. That was never strictly accurate, of course, and as a photographer I knew the extent to which the truth can be manipulated. Nevertheless, as evidenced by the incredible work we saw every day in the newspapers of the 60s, which I consumed with passion while still at school, a photograph was regarded as an equivalent to reality; it was not just a representation of truth, but an affirmation of it.

“Look,’ it said, ‘This is a true thing; I stand witness to that.’ Even today, when PhotoShop has put tricks of the trade that I spent years learning at the click of an amateur’s mouse, photographs brook no argument. The leaves really were that green, the sunset that orange, the woman so perfect. Yet perfect beauty was never in the sorcery of the darkroom or the airbrush artist’s hand, nor is it in the magic of digital manipulation; real beauty is actually real. It needs no PhotoShopping or dastardly manipulation, only to be seen and known, and recorded.

The other part of my life, however, is very different from the ascetic artist whose delight is in the expression of pure form or idea. As a musician, I am by definition an entertainer. And my professional photographic career has been mainly in Photojournalism. Indeed, long before I immersed myself in Weston and Brandt I was mainlining Cartier-Bresson and Don McCullin. Continue reading “The Naked Truth”

Focus and Depth of Field

Originally posted 2013-04-12 19:23:44.

Focus and depth of field are related, and the advancing photographer should understand the relationship between them.

If you are used to using a digital compact, then focus may be something you take for granted. Things just are in focus. But if you are thinking of buying a DSLR or a film camera, then focus becomes much more important. In fact it is one of the primary creative tools the photographer has.

 

About Lenses

Lenses resolve the light emitted from objects in the world into an image that we can use. Sometimes, as in a telescope, this is for direct observation, and the focus is inside the eye; in photography, resolution is always on a plane behind the lens.


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Arbroath January 1972

Originally posted 2016-08-16 17:43:12.

Arbroath January 1972 . I was living in the house at 9 East Grimsby. My Dad had died the previous year and I was still struggling with it.  But I had a few things going for me: music, a camera and my books. It wasn’t a lot but it helped.

Russ Black, the art teacher at school encouraged me to use its darkroom. I had lost my own a couple of years before when we moved house. This is one of the earliest rolls I still have from then.

The camera was a Leica Model III fitted with a Ross Xtralux 50mm f2, an excellent lens. I used the name ‘Xtralux’ for a band some years later, in Exeter. Film was Ilford FP3.

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Strömholm’s Beautiful Transsexuals

Originally posted 2016-08-14 10:15:42.

Strömholm ‘s Transsexuals: Les Amies de Place Blanche

Christer Strömholm (1918-2002) was ‘the father of Swedish photography’. A talented and influential photojournalist, he favoured direct contact with his subjects. He never ‘stole’ candid pictures and instead always had a relationship of some kind with the person or people he was photographing.

Christer Stromholm

For over a decade, beginning in 1958, Strömholm documented the lives of a group of transsexual women (male-to-female) living in an area of Paris called the Place Blanche. His body of work is remarkable. In 2011 Aman Iman Publishing in Paris republished it as Les Amies de Place Blanche. The price is a very reasonable 45 Euros.

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Reflex-Reflection: Photography’s Genius

Originally posted 2016-07-19 19:21:49.

The unique mechanism by which photography distinguishes itself from every other visual art is something I call reflex-reflection.

Photography, although shunned by the establishment in its infancy, became the quintessential, defining art of the twentieth century.

This was not simply because photography’s roots were in the five decades immediately preceding the year 1900, nor that it blossomed, came to maturity and ultimately transformed with the ageing of the century itself.

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