Photography

Question 1

Why is photography useful for engineering

Answer 1

As a recording method for engineering inspections, it has proved to be very useful:
 An objective recording method.
 Permanent record.
 Photographs are typically high quality.  The minimum is six mega-pixels subsea.
 Optics of the camera can magnify the subject.
 Modern systems are relatively inexpensive.

Question 2

Why are digital cameras used

Answer 2

 Vast array of photo equipment available for
underwater use - great degree of adaptability.
 Digital photos do not require development –
the image is immediately available & reviewed
prior to leaving the site.
 Processing available using computer software.

Question 3

What are some disadvantages of using digital

Answer 3

Digital photography does have some disadvantages:
 It is a fallacy to believe that good photographs are
simply a case of pointing the camera in the right
direction & pressing the trigger.
Not true.
 The photographer must have an understanding of
the techniques used to frame & focus the image &
– most importantly – control the lighting.

Question 4

Explain digital cameras

Answer 4

Digital Cameras.
 React to light electronically - the image is recorded immediately the exposure is taken.
 The image will be good or bad, depending on how the shutter speed & aperture are selected by the circuitry.
 A digital camera is the same as a film
camera, the quantity & quality of light falling onto the recording medium must be correctlycontrolled.
 In other words the exposure must be correct.

Question 5

Explain film speed

Answer 5

Film Speed:
 Was the basis for monitoring & controlling the amount of light entering the traditional camera.
 The film manufacturers, grading the Silver Halide crystals used on the film stock, determined this.
 The larger the grains - the faster the film.
 Film manufacturers marked the film speed by evolving a numbering system that indicated this by increasing numbers.

Question 6

Explain ISO

Answer 6

 ASA system (American Standards Association).
 DIN system (Deutsches Institut fŭr Normung).
 International Organisation for Standardisation (ISO) combined these into one International Standard.

Taking 100 ASA as an example:
 This will react twice as quickly to a given quantity of light than 50 ASA but only half as quick as 200 ASA.
 This relationship is known as being a one stop difference.
 It is worth noting that the ISO setting can be altered frame by frame with most digital cameras.

Question 7

What is a camera in its simplest form

Answer 7

The camera, in its simplest form, is just a lightproof box with a hole in it.
Modern cameras have evolved &, as the film stock became standardised, so cameras developed standard controls to meter the amount of light entering.
Digital cameras only differ from conventional cameras in the recording medium.
A Charged Couple Device (CCD) is used as an image sensor instead of film.
They have comparable controls.

 All cameras have a lens system containing three elements.
 The most fundamental; a diaphragm - called the aperture - that has a certain diameter, which can be adjusted by the aperture control.
 The aperture control is calibrated to integrate with the ISO numbering system although the units are different.
 Aperture controls are calibrated with f-numbers & the size of the aperture is called the f-stop.

Question 8

Explain the aperture control

Answer 8

Altering the aperture control by one stop, will either double or halve the amount of light entering the camera.

The aperture control steps are called stops because each step down, stops a metered amount of light from entering the camera.

Question 9

Explain the shutter

Answer 9

The Shutter
 Can be thought of as a kind of curtain between the recording medium (CCD) & the light.
 If the speed of opening is either halved or doubled, so the light entering the camera will also be halved
or doubled.

Changing the lens settings by one stop will either halve or double the quantity of light entering the camera

Question 10

Camera general

Answer 10

 Camera Manufacturers.
 Understand it may be necessary to alter the light sensitivity for different circumstances.
 They provide an option to change the equivalent ISO number of the pixels.
 This may be either an option on the camera’s computer menu or a physical control.
 Either way, how quickly it reacts - is adjusted electronically.
 ISO number system is kept because it is so universally understood.

Question 11

Explain bracketing

Answer 11

Bracketing
 Mostly, digital cameras will automatically select a correct exposure value.
 Occasionally, a difficult lighting situation may occur & the camera selection does not give an acceptable result.
 The camera can be made to bracket the exposure.

That means adjusting the controls one stop above and one stop below the original picture in order to obtain the right exposure.

Question 12

How is focusing achieved in the water

Answer 12

Focusing is automatic in digital cameras, with a manual override.
 Underwater, it may be difficult to see if the focus is correct.
 Setting the focus to a pre-determined distance, & using a measured prod to gauge the standoff can solve this

Never take photos at a standoff greater than 1/3rd visibility

Question 13

What other factors affect photography in the water

Answer 13

Other factors to consider when focusing the camera:
 The focal length of the lens.
 The depth of field.
 Framing the subject in the centre of the shot.
 If measuring the physical distance using a prod, allowance must be made for refraction.
 All these factors can affect the quality of the final image.

Question 14

Explain focal length

Answer 14

Focal Length The distance between the optical centre of the lens when set to infinity (∞) & the image sensor.

Question 15

Explain Depth of Field

Answer 15

Depth of Field

Distance in front of (foreground) & behind (background) the point of focus (the subject), which appears in focus.

Question 16

Using the camera

Answer 16

Using the camera
 May seem to be the easiest part - having set all the controls, just point in the right direction and shoot.
 This is not the case.
 Unless, extreme close-up photography is considered, where special close-up lenses are used with specially designed close-up frames.
 It is the photographers own responsibility to ensure that the subject is in the centre of the frame.

Question 17

How to frame the picture

Answer 17

With digital cameras
 The subject is framed in the mini-screen built into the camera, so there is no problem with framing.
 Underwater, the mini-screen may be difficult to see because of the effects of refraction, reflection & parallax.

Question 18

Refraction & Reflection

Answer 18

Refraction & Reflection
 Image on the mini-screen is inside a housing in air.
 Image path from the air-filled housing to the outside water is both refracted & reflected.
 Light path must then go through another water to air interface to get to a diver’s eyes.

The preferred orientation is at as large- an-angle to the centreline of the camera lens as possible

Question 19

What is the most common lighting equipment

Answer 19

Most common form of lighting is electronic strobe lights; LED’s are now very common.
Electronic Strobe Lighting.
This uses an electronic capacitor discharge device to produce intense, short duration, white light.
Recycles quickly & has a very long life, capable of tens of thousands of exposures.

Question 20

Mosaic photography

Answer 20

Mosaic Photography.
Divers may be required to take close-up photos to record the results of CVI or MPI
The following should be noted:
 Subject area is small so framing is critical.
 Depth of field is minimal so focus is critical.
 Lens determines the camera standoff.
 A scale is required in each frame.
 Ensure a minimum of 40% - 50% overlap.

 The subject should be in the middle-third of the frame.
 The tape must be visible, & any markings relevant to the inspection.
 The joint-angle should be bisected.

Question 21

Recording

Answer 21

 Each photograph recording inspections must include:
 A Scale.
 The subject in frame centre.
 Identification of the component.
 In addition:
 Ensure no items hanging in the frame.
 Make sure no exhaust bubbles in shot.
 Avoid camera shake; be comfortable before shooting.
 Position lighting to avoid backscatter.  Be prepared to bracket the exposure.

Question 22

Care of Equipment

Answer 22

Before use:
 Charge batteries & fill out any charging log sheets.
 Pre-set camera as required (f stop, shutter speed).
 Ensure a photo log sheet is ready for use.
 Choose suitable lens for task.
 Set up data chamber (day, date etc).
 Inspect, lubricate & secure all seals.
 Take test shots of ID board with colour reference &
log them.

Question 23

After use

Answer 23

After Use:
 Wash in fresh water.
 Dry thoroughly.
 Download images to computer, Back-up on a CD.
 Check for damage.
 Recharge batteries, complete charging logs.