Sunday, August 22, 2010

Latitude and Grain

As well as the factors we have looked at, which are all indicated on the box the film comes in, there are other aspects of film you may want to consider.
Latitude.
Basically this is the amount by which you can over or under expose your film yet still get an acceptable result. Different types of film have differing degrees of latitude.
Standard colour negative film of 100/200 ASA , the stuff most people use, can yield a reasonable enprint (6x4) from a negative 1 stop under exposed to 3 stops over exposed.
Black and white negative film from 1 stop under to 2 stops over and transparency film from 1/2 stop under to 1/2 stop over.
At the extremes of film speed, very low or very high, latitude may be reduced.
As you can see colour negative film is very forgiving of exposure errors and will compensate for short comings in your exposure metering technique. On the other hand, if you would like to work with transparency material you must be able to expose accurately. Many people make the change from print film to transparency and are very disappointed with the results which are usually down to poor exposure technique which was not apparent using print film.
A films exposure latitude is not there to make up for your mistakes, although it helps, and you will always get the best results from accurate exposure.

Grain
Film consists of a layer or layers of emulsion containing light sensitive silver halide crystals coated onto a plastic base.

Coarse grain structure.
Coarse grain
After processing the image is made up of lots of clumps of silver from the developed crystals, dyes in the case of colour film, these are referred to as grain. A bit like a TV or monitor screen is made up of pixels so a photograph is made up of grain. Although, while your monitor may have thousands of pixels, even the lowest quality film will have millions of grains. For the photographer the issue is not so much the number of grains as the size. Grain size is directly related to film speed. Slow films have a finer grain structure than fast films. With a slow fine grained film the actual grain structure will not be visible in a print approx. 10x8 while with a fast film the grain may be clearly visible in a standard enprint.

Fine grain structure.
Fine grain
Finer grained slow films are able to resolve more detail than faster, coarse grained films. Grain in itself is not something to be feared. There will be times where you will have to use a fast film and accept the grain and there may other be times you will use grain for pictorial effect. Grain is simply a characteristic of film which you will have to take into account when choosing or using a film.

Over or Under Exposure.
This is just a quick look at the effect of under and over exposure on your photographs with different types of film. We are not talking about gross errors just what happens when you start to drift away from the correct exposure.

Black and White Negative.

  1. Over Exposure. Loss of highlight detail. Although the detail will be present in the negative special printing techniques will be required to render it correctly.
  2. Under Exposure. Loss of shadow detail. Unlike over exposure if their is insufficient exposure to record shadow detail nothing can be done to retrieve it.
Colour Negative.
  1. As above but with the added 'bonus' that under exposed shadows may have a colour cast.
With negative film you must avoid under exposure.

Transparency or Reversal Film
  1. Over Exposure. Loss of highlight detail. Bright areas will 'burn out' leaving just a clear section of film . When it's gone it's gone.
  2. Under Exposure. Shadows start to 'block up' and become solid black. Highlights and colours will become darker. Still viewable or printable using a bright light source.
With reversal/transparency film you must avoid over exposure.

How to choose the FILM??????

You won't get far without film but which one do you choose. Ask for a film in any photo shop and you will be faced with a choice from dozens of films from a load of different manufacturers. To help you make an educated choice we will look at some of the terms that may be helpful to understand and some of the factors you will have to consider when selecting a particular film for a particular purpose.

Film comes in a variety of shapes and sizes but for the purposes of these tutorials we will look at the most popular amateur formats of 35mm and APS although it is all the same stuff just cut up differently; apart from APS which is a little different and only comes in one size anyway.

  • 35 mm or APS. (Advanced Photo System)

    35 mm (135) film goes in 35 mm camera and APS film goes in an APS camera. Make sure you buy the right one. There are two main differences between 35 mm and APS:

    1 APS is slightly smaller than 35 mm.
    2 APS film has an extra layer which allows it to record information from the camera to be passed on to the processing equipment.

    The actual emulsion, the light sensitive coating that makes film work, is basically the same in both formats.

  • Negative or Positive. (Print or Slide.)

    Colour Negative.Negative. (Print)

    If your intention is to end up with a nice set of photographic prints then you want to use a negative film. Quite often says 'film for colour prints' on the box if you are using colour film. Your exposed film will have to be processed to create a 'negative' which has the tones , the light and dark bits, and colours reversed. The negative is then used to produce a print or 'positive'. This is done using an enlarger to project the negative image onto light sensitive printing paper. The paper is then processed to reveal the positive image.
    Black and White negative.
    Positive. (Slide/Reversal)

    Positive film, as you would expect, is the opposite of negative film. After processing the film you will have a set of positive images. You will usually get them returned to you in individual plastic frames as mounted slides. Many people call them 'slides' but they are more correctly referred to as 'transparencies'. To properly view slides or transparencies you should project them onto a white screen in a darkened room or use a purpose made slide viewer.

    Positive.

  • Colour or Black and White.

    This is down to personal choice. There are a huge variety of films available in colour negative, colour slide and black and white negative. If you would like to produce Black and White transparencies you are limited to a choice, at least currently, of Agfa Scala or processing negative film in a reversal process.

  • Film Speed. (more here.)

    The previous choices have been fairly straight forward but choice of film speed may require a little more thought. Slow films will have finer grain than fast film however slow films by their very nature may involve using shutter speeds which are to slow for the intended purpose. Faster films on the other hand may allow you to use fast enough shutter speeds to hand hold the camera or freeze fast movement. The downside of this apparent convenience is an increase in grain.
    General purpose films in the 100 ASA to 200 ASA range are relatively fine grained and sensitive enough to use under a wide variety of lighting conditions.
    If you feel you really need fine grain then you will have to accept the resulting slow shutter speeds and get yourself a decent tripod.
    If you really want those fast shutter speeds you will have to accept the increase in grain that comes with the extra speed.

In practice your choice of film speed will probably be governed by the amount of available light. The brighter it is the slower a film you will be able to use.

These are the steps you may take in choosing a film but there are a few more terms that you should may want to understand before using your film.

Conttrol your Exposure

We have taken a look at the creative or artistic bit of taking photographs, composition, if you read that bit, so now we will have a look at the science bit, exposure.
Unsurprisingly, exposure simply means allowing light to strike your film. The tricky part is knowing how much light you need and how to control the amount of light reaching the film. The former is taken care of by a light meter, usually built in to the camera, and the latter is achieved by means of the aperture and shutter controls on your camera.
You control the exposure by allowing light to pass through the aperture for a given amount of time. Right now we are going to have a look at the way apertures and shutters are used to control exposure but not the other important functions they perform.

Aperture and f-numbers.
The aperture is just a hole whose size can be varied to allow more or less light to pass through it. The size of apertures are expressed in f-numbers. You can calculate an f-number, if you are keen or don't have much of a life, by dividing the lens focal length by the diameter of the aperture. The range of f-numbers follows a standard sequence with each f-number being half as bright, passing half as much light, as the previous one. A typical aperture range may look like this:

f 1.4; f 2; f 2.8; f 4; f5.6; f 8; f 11; f 16; f 22; f 32

There are smaller and larger f-numbers but the actual numbers used are always the same and will maintain a constant value over different lens focal lengths. This just means that f-8, for instance , will always pass the same amount of light no matter what camera or lens you may be using. Similarly, f-16 will pass half as much light as f-11 and f-4 will pass twice as much as f-5.6. The difference in value between one full f-number and the next is known as a 'stop'. If you change aperture from f-8 to f-5.6 you will give your film one stop more exposure.
The smaller the f-number is then the larger the aperture is and the more light it will pass. The f-number is also used as a guide to the light gathering abilities of a lens. Lenses with large maximum apertures ( small f-number ) are described as being 'fast'.
Generally the aperture will always be held open at its maximum irrespective of whatever value you may have set it to and will not actually close down until the moment of exposure. The main reason for this is to produce the brightest image possible onto the focusing screen. To see the aperture in operation you will have to remove the lens, unless you have a preview control, and look through the lens while turning the aperture control ring.

Shutter and Shutter Speeds.
The shutter prevents light from reaching the film until the moment of exposure, when it opens for a predetermined time allowing light passing through the lens aperture to reach the film. Unlike the aperture, which is always in an open position the shutter is always closed. Like the aperture, shutter values or 'speeds' follow a standard sequence with each one being half that of the next, allowing half as much light to pass through. A typical shutter speed range may look like this;

1sec; 1/2sec; 1/4sec; 1/8th; 1/ 15th; 1/30th; 1/60th; 1/125th;
1/250th; 1/500th; 1/1000th; 1/2000th


Shutter speeds are expressed in seconds or fractions of a second. Slow shutter speeds run into seconds while fast shutter speeds will be shorter than 1/500th of a second. In normal photography shutter speeds will probably fall into the range 1/60th to 1/1000th of a second.
As you may have worked out, changing from one shutter speed to the next changes the exposure by one 'stop' in much the same way as changing the aperture.


This is boring !!
I know, and I am sorry but there is more. Now that you know what a 'stop' is you may realise that to change or control exposure you can alter either one and get the same effect. You may even have worked out that you can have loads of combinations of aperture and shutter speeds that will amount to the same exposure.
Here is a wee example:
Your light meter tells you to set your camera to f-8 at 1/125th of a second. You decide that you want to change it. You will find out why you might want to change it later.

You could reduce the aperture by one stop to f-11 (Stop down or close down). Now your film is receiving half as much light as it requires (underexposure). To compensate for this you select a slower shutter speed of 1/60th of a second so it now stays open twice as long as before and passes twice as much light as before.
Or.
You could increase the aperture by one stop to f-5.6 (Open up). Now your film is receiving twice as much light as it requires (overexposure ). To compensate for this you increase your shutter speed to 1/250th of a second so it now stays open for half as long as before and passes half as much light as before.

f-321/8th of a second
f-221/15th of a second
f-161/30th of a second
f-111/60th of a second
f-81/125th of a second
f-5.61/250th of a second
f-41/500th of a second
f-2.81/1000th of a second
f-21/2000th of a second
Alternatively, you could start by changing the shutter speed then altering the aperture to compensate. The important point is that you finish up getting the same exposure.
You could work your way through the whole range of aperture and shutter speeds as in the table on the right:
When you combine a shutter speed and an aperture you get an 'exposure value'. The table shows a range of shutter and aperture combinations which will all result in the same exposure value. If an aperture of f-8 at 1/125th of a second produces a perfectly exposed photograph then any of the other combinations will do the same.

Film speed
Here is something else just to confuse you.
In order for your lightmeter to come up with a suitable combination of aperture size and shutter speed it needs to know how sensitive to light a particular film is. A film's sensitivity is known as its ' speed' and is expressed as an ASA/ISO number. The higher the number the more sensitive it is and consequently the less light it needs to form an image. The lower the number the less sensitive it is and the more light it will require. Sensitive films are said to be 'fast' and will have a speed of 400 ASA/ISO or above. Films with low sensitivity are said to be 'slow' and will have a speed of less than 100 ASA/ISO. General purpose films suitable for everyday use fall into the 100-400 ASA/ISO range with 100-200 being the most popular.
Like shutter speeds and aperture sizes, film speeds follow a standard sequence.

25; 50; 100; 200; 400; 800; 1600; 3200

Wouldn't you know it ! Film speed goes up in steps just like shutters and apertures. Each one is twice as sensitive as the next. I know you have worked this out already but the difference between one film speed and the next is a 'stop'.
As far as exposure goes all you really need to know about film is its speed. It is very important that you set the correct film speed on your light meter before you start. Most modern cameras read the film speed from a magnetic strip on the film cassette and set the meter accordingly (DX coding). Otherwise you will have to set it yourself using whatever method your camera/meter is equipped with.

Over and Under Exposure. ( Briefly)
Giving your film more exposure than necessary will result in overexposure. Pictures will be pale or light with poor washed out colours.
Giving your film less exposure than necessary will result in under exposure. Pictures will be dark with poor detail in shadow and dark areas.

Almost done.
You will have realised by know that there are three factors involved in controlling exposure.

  • Film speed. Once set you do not alter on the same roll of film.
  • Aperture. Which you can increase or decrease.
  • Shutter speed. Which you can also increase or decrease.
    They in turn share another common factor, which crops up a lot in photography, the 'stop'. Changing either of them by one full setting will always half or double the exposure the film receives.
    Increasing one and decreasing the other by the same number of 'stops' gets you the same exposure.

    Putting it all together.
    Here is what will happen when you press the shutter release button:
    • The mirror will flip up out of the way.( SLR) That is the clunk you hear.
    • The aperture will 'stop down' to the selected value.
    • The shutter will open then close.
    • The mirror will come back down.
    • The film is wound on by one frame and the shutter is reset. Automatically if the camera has a winder or manually, by you, if it doesn't.
    But why ?
    You may be wondering why you can't just stick with one film speed, one aperture and just vary the shutter speed or one film speed, one shutter speed and vary the aperture. Well you can, in fact most cameras will allow you to do both of those things. What you need to know is how you do it and more importantly why you would want to do it.

    Coming up next.
    In the next couple of bits we will look at the unbelievably interesting use of shutter speeds and apertures. There will be a few pictures or illustrations so it should be a bit less of a drag than this bit was. Also, just to make sure you are paying attention I am going to set you a little test. Not too hard, just enough to make sure you know roughly what is going on with the stuff we have just done.


  • Metering of Camera

    We have mentioned shutters, apertures and 'modes' but we haven't looked at how we get the information needed on which to base our combination of aperture and shutter speed. Most, if not all, modern 35mm/APS SLR cameras come with some form of built in light metering system. The finer points of how specific lightmeters actually measure light may vary but the basic operation is the same for most built in systems. Once activated, usually by turning the camera on or by light pressure on the shutter release, the light meter measures the light reflected back through the camera lens from the scene in front of it. This type of lightmeter is known as a Reflected Light Through The Lens meter. Commonly referred to as a TTL meter.

    Using a TTL meter is a fairly straight forward operation. With the meter switched on simply compose your picture as normal and the meter will take a 'reading' from the scene. You will then be presented with information about the necessary aperture or shutter settings that may be required. These readings are based on the amount of light reflected back from the scene and on the sensitivity of the film you are using. You must inform the meter of the correct film speed either by setting it manually or using DX coded film( it has a bar code on it) if your camera supports this feature. Depending on the 'mode' you are operating your camera in you will be presented with some information about the shutter speed, aperture f-number or both.

    1. Manual Mode. What you see will vary according to the make and model of camera you are using but will probably be along the lines of the following.

      Plus/Minus meter.

      1. An illuminated plus sign (over exposure), minus sign (under exposure) or a zero (OK) symbol to the side of the focusing screen.(The bit where you look at your picture) in the viewfinder. You will not be able to tell how many stops over or under you are.
      2. An illuminated scale from plus to minus. Similar to the previous one.
      3. A range of shutter speeds with a symbol indicating the currently set shutter speed and a moving needle indicating the recommended shutter speed.
      4. As above but using LED's ( little red lights) instead of a needle. Steady LED for set speed and flashing LED for recommended speed.
      Match needle meter.

      Manual ScaleIn manual mode you have control of both shutter and aperture and can adjust either or both to reach the correct exposure. You are aiming to 'zero' on a plus minus system or match the two indicators on the other.(Match-needle system)

      Aperture Priority

    2. Aperture Priority. The meter will indicate its chosen shutter speed, based on the aperture you have set. This may be shown on a scale or simply as an illuminated number in the viewfinder. If you change the aperture the shutter speed will change to compensate. Try it to see it working.

      Shutter Priority

    3. Shutter Priority. The meter will indicate which f-number it will select, based on the shutter speed you have set. This will probably be shown as a number in the viewfinder. If you change the shutter speed the camera will change the aperture to compensate. Try it to see it working.

      Program Mode

    4. Program. The meter will indicate its choice of shutter speed and aperture. Or maybe it won't.

    The shutter speed and aperture are both represented by a number and to tell which one is which,and what they mean, we are going to have a look at each of them. There is no need to panic, there isn't any maths to speak of.

    Automation of Camera

    The degree of automation a camera offers you can vary from none at all, where you have to set all the controls manually, to fully automatic where the camera makes all the decisions and makes all the settings accordingly.
    First of all we will get focusing out of the way. With focusing you have two choices, autofocus (AF) or manual focus.There are different types of autofocus systems but basically you either have it turned on or you don't. Although autofocus is pretty standard on new 35mm/APS cameras these days not having this feature isn't really a drawback. AF can be quick, convenient and fairly reliable but is by no means essential.

    The area where you will find most automation is in the control of exposure. More specifically the control of the aperture and shutter. These different types of automation are usually referred to as 'modes'. Most modern cameras are 'multi mode'. Basically there are four modes you can work in.
    • Manual.(M) You set the aperture and shutter yourself.
    • Aperture Priority.(A) You set the aperture and the camera will automatically select the corresponding shutter speed.
    • Shutter Priority.(S) You set the shutter speed and the camera will automatically select the corresponding aperture.
    • Program.(P) You point the camera and it will select a suitable aperture and shutter combination.
    Within 'progam mode' you can have a another pile of 'modes' depending on what type of subject you are photographing. You could have;
    • Action mode.
    • Landscape mode.
    • Portrait mode.
    • Close-up mode.
    • Fill-in Flash mode.
    • Night mode.
    However, you will never find, on any camera, anywhere, no matter how much you spend and no matter how much the sales person tells you how invaluable a cameras multitude of 'modes' and 'features' are, you will not find a 'good picture mode' .
    An auto camera may simply select a shutter speed to match a pre-set aperture value or it may perform a complex decision making task involving information regarding the type of subject , lens attached and other data you may input. After all this calculation the camera will then adjust the shutter and aperture. And that,basically, is all they do.

    Your Camera

    Essentially a camera is just a light tight box with a small hole in it. In fact is relatively simple to build a camera using a cardboard box, some black tape and some tinfoil or a small piece of aluminiun from a drinks can. Unfortunately, pinhole cameras-that is what they are called- are not particularly sophisticated and your mates won't be to happy when you ask them to keep perfectly still for 20 minutes while you capture that party atmosphere with the box your shoes came in.

    The sort of camera we are going to look at is the more 'modern' 35mm SLR (Single lens reflex). By 'modern' anything built in the last twenty years will fit the bill, including APS which really is modern but isn't actually 35mm but the idea is the same.
    Click for a diagram.
    All modern SLRs share some basic features:
    • A body
    • A lens which is interchangeable. That means you can take it off and put on a different one.
    • An adjustable aperture which is inside the lens.
    • An adjustable shutter which is inside the body
    • A built in TTL lightmeter.(Probably !).Measures light coming Through The Lens
    They also share similar controls.
    • The aperture ring. This is a narrow rotating ring on the barrel of the lens. It is generally located close to the body of the camera.
    • The focusing ring. This will be a wider ring located near the front of the lens.
    • The shutter control. This is usually a small dial on the top of the camera next to the winder lever. If your camera is an electronic model with a load of 'modes' then the shutter may be altered by using a thumbwheel or presssing a button. Whichever it is the actual control will be located on the top right area of your camera.
    • The shutter release. Again this will be top right, either on the front of the top-plate or near the top on the front. Light pressure on the shutter release usually activates the built in TTL meter.
    • Film speed dial. On the top plate usually to the left. Newer electronic cameras set the film speed from the DX code on the film cassette itself. You may be allowed to over ride this or maybe you won't.
    These are the controls that you will have to get to grips with to get the most from your camera. Additionally there may be other knobs and buttons on your camera which could prove useful.
    • Depth of field preview control. Not very common but very useful. On the front near the lens.
    • Self timer. Has its uses.
    • Exposure lock . Has its uses as well.
    • Multiple exposure switch. Probably near the wind on lever, if you have one. Allows you to make multiple exposures on to one frame.
    • Exposure compensation dial. Allows you to over ride automatic exposure settings. Probably easier and quicker to switch to manual if you can.
    • Mirror lock up. You would be so lucky !
    • On/Off switch. Move to On to make your camera work . Move to Off to make it stop. Leave it on and you will have to buy a lot of batteries.

    Now that we have had a wee look at some of the controls we will go on to look at the different levels of automation that may be available to you. Your camera may sport a huge range of features but you will get by just aswell without most of them.

    Sunday, August 15, 2010

    The Last Goodnight ~ Pictures of you




    "Pictures Of You"

    This is the clock upon the wall
    This is the story of us all
    This is the first sound of a newborn child,
    Before he starts to crawl
    This is the war that's never won
    This is a soldier and his gun
    This is the mother waiting by the phone,
    Praying for her son

    [Chorus]
    Pictures of you, pictures of me
    Hung upon your wall for the world to see
    Pictures of you, pictures of me
    Remind us all of what we used to be

    There is a drug that cures it all
    Blocked by the governmental wall
    We are the scientists inside the lab,
    Just waiting for the call
    This earthquake weather has got me shaking inside
    I'm high up and dry

    [Chorus]

    Confess to me, every secret moment
    Every stolen promise you believed
    Confess to me, all that lies between us
    All that lies between you and me

    We are the boxers in the ring
    We are the bells that never sing
    There is a title we can't win no matter
    How hard we might swing

    [Chorus]

    [Chorus Repeat]