Short Guide to Digital Photography

Although I am by no means an expert, I have been asked quite a bit about digital photography lately. Here's an article intended to be a quick reference for the people who asked me and for others who might stumble upon it. I will try to make it both short and comprehensive. All information in the article comes from my own experience and I'm sure there are better guides out there. I use a Canon 7D but the parameters of a photo are the same regardless of the instrument. And these parameters are:

How image noise looks like

Sensitivity (ISO) - on film, it refers to the density of thickness of the strip of film. In a digital medium, it is simply a measurement of the sensor's sensitivity to light. The higher the ISO, the bigger the sensitivity, so ISO will be increased when the amount of light is low. Increasing the ISO, however, results in image noise (granulation), so ideally you want to work with as low an ISO value as possible (ISO 100 is ideal, but not always possible, depending on lighting conditions). For Canon DSLR, it is recommended to use ISO values that are multiples of 160.

Also look up motion blur

Shutter speed (exposure time) - represents the length of time for which the shutter stays open, allowing the sensor to receive light. It is usually represented as fraction of a second. (1/10, 1/25, 0' 5" or 1/2). Obviously, the longer the time, the more light the sensor so for low light conditions you will want to use a longer exposure time. However, for long exposure times both the subject and the camera have to be still (ideally the camera would be on a tripod), otherwise you will get the ghost effect in the photo, or the full bright white areas. If the subject is moving fast, such as athletes at sporting events, then you will want the exposure time to be as short as possible while still getting enough light, so that the picture is crisp and there are no blurred parts. Normally you should keep the exposure time defaulted at 1/25 (which is close to the film camera speed of 24 frames per second - fps) and adjust according to the light conditions.

Depth of field illustrated

Depth of field (focus range) - The focus (not to be confused with focal distance) is defined as the distance from the lens at which a point object produces a point image. While precise focus is only possible at one distance, on each side of the focus plane there will be an area in which the subject will appear to be sharp and focused when viewed at a maximum image resolution. This area is called the depth of field. It varies according to the focal distance and the aperture.The bigger the focal distance, the further away the focus plane will be and the lower the aperture (the higher the f/ value), the bigger the depth of field. If you need a small depth of field (shallow focus), such as for a portrait, you will used a high aperture value (say f/2.8) and shoot from close by. If you need a big depth of field (deep focus), such as for a landscape, you will use a small aperture (f/16, f/22) and a focal length dictated by the distance to the closest object that needs to be in focus.

Aperture values represented

Aperture (focal ratio or t-stop) - it is represented by a number in a logarithmic series preceded by f/ (f/1.2, f/1.4, f/2, f/2.8, f/3.5 .. f/28) and it shows how big the hole through which light gets into the sensor will be. Aperture is probably the most counter-intuitive parameter of the camera and maybe the most important. The higher the f number, the smaller the aperture, so the less light will get into the sensor. This means f/1.2 is the biggest possible aperture, while f/22 means a very small aperture and should only be used in very bright sunny weather. While the crispiest images will be obtained with an aperture of 4-5.6, the value of the aperture used should be determined by the quantity of light available and by the depth of field required. For the aperture greatly influences the depth of field, them being in a reverse proportionality: the higher the aperture, the smaller the depth of field. f/1.2 will have the smallest depth of field, while f/22 will give you a huge depth of field. While I have used here the f/1.2 value, you will notice most prime lenses will have the biggest aperture set at f/2.8, while most zoom lenses have it at f/3.5. Meaning the aperture is a characteristics of the lens, not of the camera. But the point is: the more light, the smaller the aperture, the bigger the f/ value.

Focal length is given as a millimetre value

Focal length (zoom value) - is the distance between the image capturing medium (film or sensor) and the optical centre of the capturing lens. It is a characteristic of the lens, obviously, and on zoom lenses is indicated by its minimum and maximum values. The focal length dictates the field of view angle (the smaller the focal length, the bigger the fov angle) and the distance to the focus plane (the smaller the focal length, the smaller the distance to focus). The human eye has a focal length of about 35-40 mm, so this is the focal length to use if you want a 'realistic' field of view. A low focal length value will give you an optical aberration known as fish eye effect (bending of the edges of the image) which can be more or less obvious depending of the lens. Whenever possible, use prime lenses (an unique focal length) rather than zoom lenses (variable focal length), as they contain less glass and therefore give you more definition. Likewise, try and get closer to the subject rather than using the zoom, as using the lens at its smallest focal length position gives you the greatest control over the image.

The three colour palettes

White balance (K temperature) - is a parameter specific to digital imaging and it is defined as the temperature at which a black object should be heated to give the white colour on camera. This is dictated by your light source and it dictates the colour palette of your image. A low K temperature results in warm, yellow tones, for the naked eye while a high colour temperature results in cold, blue tones. While there are standard values for various light sources (3200K for tungsten lighting, 6400K for HMI lighting and standard outdoors), the white balance will be chosen according to the desired look of the final product. For a natural look you can either experiment with different values or use the AWB setting (auto white balance - this uses the camera specific algorithm to determine the k temperature). For a vivid colour palette (yellow tones), the white balance should be set to a higher value than the one of the light sources, while for a cold, blue, unnatural colour palette, the K temperature should be set to a lower value than the light sources.

These 6 are the most important features of the image, along with the image resolution (number of megapixels), which should always be set to the highest possible. There is a lot more to say about each of them and there are more parameters than this to a digital image. I have tried to cover the basics, although I have also provided links that go into more detail. It is my belief that understanding how these 6 concepts work and how they alter your image will be enough to put one on the path to become a professional photographer.

Not about Marius, nor Mules

S.J.A. Turney - Marius' Mules I (The Invasion of Gaul), CreateSpace, 2013

Nowadays, I hardly ever read fiction. And by no means would I have read Marius' Mules if it wasn't for an arbitrary series of circumstances: a Facebook advert was offering it for free and I wanted to learn how to use and to test how easy I find the iBooks application on my new iPhone.

Everything cliked and I started reading it. And in the course of doing so, I felt cheated a few times by this book: at first, I noticed it is the first one in a series, with a drug dealer type "first one free" technique. I feared I would get to the end only to be told that I need to buy the next book. Well, it's not like that. The Invasion of Gaul is a very round novel, with a classical beginning and end structure and a strictly chronological depiction of events. The ending is even built up, as the characters talk about it throughout. I am now however itching to read the next in the series, not because anything exciting is just about to happen to the heroes, but because I have come to know and like them and I have become too drawn into their lives not to follow them further. Besides, the price of the next books in the series is minuscule, and the author makes a point of it:

I do, however, have control over the price of the electronic editions, and I have deliberately set them as low as the publishing system will allow. The reason for this is that I am passionate about both reading and writing, and I believe that books are becoming too pricey. If things continue with the current trend, people will stop reading unless they're quite wealthy, and will rely on TV. I would rather lower the price and encourage people to read.

Next thing I came to notice is how close the action in the books follows Caesar's De Bello Gallico. A quick research and a note at the end of the book reveal the author's full disclosure though: his purpose was to fictionalize Caesar's dry historical account in order to make it readable for the contemporary world. I'm not sure how I feel about this: while I feel it is a laudable enterprise,  I think less of myself if I need fictionalization of the classics in order to access them. That's why I just started reading De Bello Gallico and will take up on Fronto's next adventures as soon as I finish it. So I'm guessing it's good then: a book that makes me read another book is always a good sign.

I do prefer fictionalizations in the style Charles Frazier writes, heavily documented and filling in with licences only when historical sources are mute. I did expect the main character, Fronto, to be drawn from some document or funerary stella and was a bit disappointed upon finding out it has not been the case. But Mr. Turney is excused considering this novel is spun solely out of passion for ancient Rome and he is not (or was not, at the time of writing) a professional writer.

That is not to say Marius' Mules is not heavily documented: on the contrary, the reader will be introduced to a lot of Roman terminology, way of thinking and military strategy. So much so that the book reminded me at times of Sun Tzu's Art of War. And I was always itching to play Rome: Total War and recreate Fronto's battles. It is just the characters that are plucked out of thin air, but they're all rounded out so well that it makes them all entirely credible.

An author's stated intention and a big plus of the book is to look at the men behind Caesar's successes and how they contributed to them. It is obvious that Julius Caesar could not have become the great commander he was without a number of supporters, but it is very easy to overlook the people whose name left no mark on the historical records.

A fault of the story is the chapter investigating the low morale of the army just before meeting the representatives of the Aedui tribes, and for now I cannot tell if the sub-plot is too thin because of the writing, because of the sources or due to a discrepancy between the Roman and the Western contemporary way of thinking. I did protest throughout about some lines that sound very British and very out of place when said by a Roman soldier, but I guess there's no getting around this: a Roman soldier would have an equivalent that would make little to no sense when translated literally from Latin. Another way around this would have been writing the whole damn book in Latin, but then we'd be talking about a completely different sort of an enterprise.

Just one last mention, and a very striking one at that: there is a very strong cinematographic feel to the book. Movements and costumes are described in so much detail that it would be a struggle not to view the action as a motion picture in the reader's mind. This book almost screams about being turned into a TV mini-series. I hope it will be, sooner rather than later and I would make an attempt at doing it myself, would it not be for the historical costumes and the huge number of extras involved, details that spell big budget production all along.

And that's pretty much it. I will probably have to say a lot more about not only Fronto, but also the likes of Aulus Crispus, Balbus or Ingenuus at the end of the seventh book. I am convinced that, would I have read this as a child, or even in my teen years, Fronto would have become one of my heroes, along with Winnetou the Apache, Tarzan of the Apes, D'Artagnan or Robin Hood. I can only hope that there is still a generation of kids out there who get their heroes from fictionalized history rather than Disney merchandise.

And I'm not sure if Marius' Mules reconverting me into reading fiction is a good thing or a bad thing.