Category Archives: Exposure

File Formats: RAW v JPEG

RAW & JPEG are two different types of electronic file

The principal differences between the two types are:

  • RAW files are literally the raw data as produced by the camera at the moment of pressing the shutter
  • They have no ‘built in’ file format
  • You are then free to adjust this data through Photoshop or a similar application on a computer
  • You can change; exposure, white balance, contrast, brightness, etc
  • You can return all settings to the start point and begin again
  • A RAW file is, in effect, a digital negative

 

  • JPEG’s are generated by the camera after exposure & are written onto the memory card
  • Preset data for exposure, white balance, etc will be embedded in the file & can never be removed
  • The parameters are decided by you in advance
  • Your latitude to change & make alterations afterwards are very limited
  • The file will be compressed & this is achieved by discarding information that can never be retrieved

 

If you are working digitally then having a camera that will allow you to shoot in RAW format as well as JPEG can be an advantage.
However a JPEG that is produced by the camera at the same time as a RAW is not as satisfactory as one that you generate yourself from the RAW file during post-production.
Many DSLR’s will do both RAW & JPEG at the same time but this will reduce storage capacity.

 

Why shoot RAW?

  • When creating digital prints of the highest exhibition quality & size
  • Shooting high ISO values in low light
  • When you want to make high quality monochrome conversions
  • Photographing a subject with a high dynamic range
  • When you are uncertain about the colour temperature of the subject

 

Why shoot JPEG?

  • When the end result is for small scale or low quality output
  • If you need fast workflow
  • When you need low res images for web or onscreen use
  • When you need to shoot quickly
  • When the end result requires minimal post-production
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Why QP Cards?

I started my photography career with analogue and the guys who I assisted and from whom I learnt; Gered Mankowitz, Dave Sherwin, Red Saunders, Gil Galvin and others, taught me the importance of accurately exposing film in camera.

Most images were being made on E6 stock; Kodak Ektachrome 64 and later Fuji 50D then Provia 100, the latitude for error was only about 2/3rd of a stop and over-exposure was not a possibility. Therefore it was fundamental to my practice to learn to correctly use the exposure meter, proof using Polaroid (later Fuji Instant) then relate that exposure to the film. It was common that films varied in colour caste and speed rating so each film batch would vary and needed to be compensated for in camera.

I still have a box of Polaroids in the attic of me posing in all sorts of sets and locations with the exposure and lighting diagram scribbled on the reverse.

When I switched to digital I began using QP Cards as a way of gauging and refining exposure. I felt the need to continue with a rigorous method of determining accurate exposure yet rather than examine Polaroids I now find myself judging the QP Card. I do this on the camera screen, in conjunction with the histogram and on a computer monitor when shooting tethered.

Screen Shot 2013-01-29 at 07.19.07

Shoot with test frame selected

With the eyedropper tool selected I neutralise White Balance by clicking on the grey square of the QP Cards.

Screen Shot 2013-01-29 at 07.31.50

Eye dropper tool selected

Then make any additional minor adjustments via the Tool Tabs for Exposure, Black & White conversion, etc.

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Tool Tabs bar for additional adjustments

Prior to copying the adjustments.

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Copy adjustments

Selecting all the relevant files & applying the saved adjustments to the entire batch.

Screen Shot 2013-01-29 at 07.51.15

Apply adjustments

The beauty of this is the way that it simplifies and speeds up my workflow.

I use Capture One Pro 7 for my image management but Adobe Lightroom is just as suitable.

Remember that QP Cards are not fool proof, nothing is, but then neither is a histogram, a flashmeter or even a Polaroid. You need to combine all of these elements together plus your own innate experience of your camera or film and different lighting situations.

PC_Shot01_0032

Entrance to disused Cruise Missile Bunker, East Anglia
© Julian Hawkins 2013

Details: Nikon D600, 17 – 35mm, ISO 200, 1/2sec , f10

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Photographic Exposure – a simple guide

This is a post intended for my BA students but others may find it useful too.

PHOTOGRAPHIC EXPOSURE

This is controlled by 3 different though inter-related methods:

1. ISO

2. Shutter speed

3. Aperture

Finger

ISO

This is the speed or sensitivity of the camera’s sensor & is selected by the photographer. Formally it was the sensitivity of the film that you chose to load into the camera.

At the time of writing (Sep 2012) most Nikon DSLR’s use 200 ISO as their base position whereas Canon’s begin at 100 ISO (though higher spec models have a greater range).

The lower the ISO value that is selected the less the sensitivity to light that the sensor will have and the less the electronic noise/interference that will result.

As a general rule you choose a low ISO when you have a lot of light to work with and you increase the ISO to higher values as lighting conditions become darker.

The progression of ISO values you can expect to find on a DSLR are:

100   200   400   800   1600   3200   6400 +

Each time the ISO value doubles or halves this is referred to as making an adjustment that is equivalent to 1 f-stop (more on this later).

On film the common ISO progressions are:

50   100   200   400   800   1600   3200   6400 +

Offerings at San Andrés

SHUTTER SPEED

This is the time for which the shutter is open and the sensor or  film is exposed to light.

Shutter speeds are referred to as being either slow (when the sutter is open for a longer time) and fast (when the shutter is open for a short time).

You select the speed to suit what you are wanting to achieve as well as for the conditions under which you are working.

As a general rule:

Slow speeds may result in camera shake so think about using a tripod.

Fast speeds for action photography where a clear, concise image is needed.

The progression is:

< 15sec  8 sec  4 sec  2 sec  1sec  1/2   1/4   1/8   1/15   1/30   1/60   1/125   1/250  1/500   1/1000   1/2000 >

There will also be a ‘B’ (bulb) setting. This allows you to open the shutter and it will remain open until you release it.

Some cameras &/or lenses have a ‘T’ (time) setting where you press once to open and again to close the shutter.

Both ‘B’ and ‘T’ as well as speeds slower than 1/8 sec should be used in conjunction with a cable release.

Jazz for Sax

APERTURE

This is the third (and sometimes most confusing) method for controlling exposure.

This refers to the diameter of the aperture formed by the iris diaphragm, which is a series mechanical blades built into the camera lens.

The diameter of this aperture is expressed as an f-number (f-no).

There is a set progression of f-no’s & each time you change this number you increase or decrease the amount of exposure by 1 f-stop. Thus the photographic convention of expressing exposure in f-stops. This is the inverse square law in action.

The size of the lens aperture influences both overall exposure AND the amount of subject that is in ‘acceptably’ sharp  focus – referred to as ‘Depth of Field’.

As photographers we need to consider how much depth of field we require in order to be able to achieve a given result. This in turn will influence the f-no we will want to select.

When the lens is fully open to it’s widest aperture there will be very little depth of field, when stopped down to a narrow (or small) aperture you will achieve greater depth of field.

Yet more confusion comes about because a wide aperture has a low numerical value (f1.4 or 2.8) whereas a small aperture has a high numeric value (f22).

Older, non auto-fucus lenses, will have their range of f-no’s inscribed on the barrel and sometimes also the intermediate positions which may be half of third f-stops. Thus you will hear people talk in terms of fractions of a stop when considering exposure.

The standard f-no progression is:

< f1.4   f2   f2.8   f4   f5.6   f8   f11   f16   f22   f32   f45   f64   f90   >

Beware though when using a DSLR. These cameras express the intervening fractional values as f-stops & this causes added confusion. On your cameras you will see f-no’s such as f9, f14, etc. But you will not see these marked on a lens barrel or a lightmeter.

In fact modern light/flahmeters will read a full f-stop followed by fractional units in tenths. So it just got more confusing!

An example of a lightmeter reading: 1/125 sec   f5.6 9

This translates as a shutter speed of 1/125th second with an aperture that is f5.6 & 9/10.

Your camera doesn’t work in tenths (yet!) so you have to be prepared to compromise & rounding up or down to the nearest full f-stop which, in this case, is f8 or the third of an f-stop interval if that is closest.

In actual fact a 1/10th of an f-stop is not going to make a huge difference to your exposure & if necessary can be adjusted in post.

Nighttime on the M11 motorway

Use these notes as a general guide, read around the subject for yourself & experiment so that this becomes familiar.

Further reading:

Diprose, G & Robbins, J (2012) Photography: The New Basics, Thames & Hudson

A first class read, thorough, easy to follow

Adams, A (1981) The Camera, New York Graphics Society

Old school and very technical, the best there is on the subject

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