Chapter 3- Focusing fundamentals,shutter types and aperture

Question 1

Focusing Fundamentals: What is occurring in reference to the lens and the film or sensor when you are focusing your camera?

Answer 1

Change the position of the plane of sharp focus. This involves the lens moving away from the film/sensor for close up images and towards it for landscape views. This separation is mathematically related to the distance between the lens and the subject

Question 2

Focusing Fundamentals: Understanding the relationship between subject and camera means the lens can be moved in or out with what?

Answer 2

A threaded barrel - this allows for precision of distance between sensor/film and lens

Question 3

Focusing Fundamentals: What is the range that the focusing scale goes from and up to?

Answer 3

1-2 meters to infinity from the camera

This is not good for close ups so most cameras have a built in focusing aid

Question 4

Focusing Fundamentals: 35 mm film format SLR cameras has a viewing screen that have focusing incorporated into them. The most common screen incorporates which three elements?

Answer 4

Split prism finder (shows displacement of an out-of-focus subject)
Plain screen (for more detailed focusing)
Microprism grid (scrambles unfocused image)

Question 5

Focusing Fundamentals: Most cameras have auto focussing. How do these work?

Answer 5

Use one or more array sensors. The number, position and type of autofocus points contribute to the robustness and flexibility of the system.

Question 6

Focusing Fundamentals: Describe what the Passive autofocus system is

Answer 6

When the autofocus sensors are positioned in various arrays across the images field view and each sensor then measures relative focus by assessing changes in contrast at its respective point in the image. Maximum contrast is then assumed to correspond with maximum sharpness

Question 7

Focusing Fundamentals: What are the two types of autofocus sensors called?

Answer 7

Cross type sensor- two dimensional contrast detection= high accuracy
Vertical line sesnor- one dimensional contrast detection= lower accuracy

Question 8

Focusing Fundamentals: What other equipment do cameras have to assist in autofocus?

Answer 8

Assist beam- method of active autofocus that uses visible or infrared beam to help autofocus sensors to detect subjects- good for limited light areasor when the image is of low contrast
Compact cameras have built in infrared light source for assist
DSLR have built in or external flashes

Question 9

Shutter Principles: Why is the lens cap called that?

Answer 9

In olden times, a cap was used to put over the hole when film had been placed in

Question 10

Shutter Principles: Why has a shutter mechanism been invented when there was no need for it at the start?

Answer 10

Due to exposure times becoming quicker and quicker (from hours to fractions of seconds)- the role of it is to protect the film or sensor from the light until it needs to be exposed

Question 11

Shutter Principles: Almost all shutters have a range of speeds it can operate at. What is the pattern in the speed settings? Why is this important?

Answer 11

Can double from 8 seconds down to 1/4000th of a second
With high end DSLR’s 30 seconds to 1/102,400th

Doubling sequence coincides with the doubling and halving sequence of lens apertures which enables the simplification of exposure calculations- e.g adjusting from one speed to the next faster speed cuts the level of light down by exactly one half

Question 12

Shutter Principles: Control of the shutter speed can be mechanical or electro-mechanical as in all present day DSLR cameras. What is exposure duration precisely timed by?

Answer 12

A quartz clock mechanism

Question 13

Shutter Principles: What is the pattern between aperture setting, relative light and shutter speed?

Answer 13

As the aperture increases (so the f number decreases, remember, the smaller the f number, the larger the aperture!), the shutter speed becomes quicker and relative light increases.
E.g- f22, relative light= 1x and shutter speed= 16 secs
f1.4, 256x and shutter speed 1/15 secs

Question 14

Shutter Principles: What sort of situation would you use a shutter speed of 1-30 seconds?
What about 1/2 to 1/30th of a second?
How about 1/250 to 1/5000?

Answer 14

1-30= night photography, low light, fireworks etc
1/2 - 1/30th= add motion blur to background
1/250th - 1/500th= to freeze everyday sports/action subject movement

Question 15

Shutter Types: Focal-Plane shutters

Where are they located?
What do they look like/made out of?
How does it operate?

Answer 15

In the body of the camera/ separate from lens
Resemble roller blinds, sometimes made out of fabric but mostly metal plates or aluminium foil
Two roller blinds, one at top and one at bottom- The lower blind starts fully over the window (unrolled) and the top one is full rolled. On exposure, the bottom one rolls up, the ‘window’ is left exposed for a specific time and the top one then unrolls covering it. This then resets after
The faster the shutter time, the smaller the slit between the blinds but the time it takes to go from top to bottom is the same

Question 16

Shutter Types: Do all cameras have mechanical shutters?

Answer 16

All DSLRs do. Most compact cameras only have electronic ones that simply turn on/off the light-reading capability of the camera sensor when required

Question 17

Shutter Types: Leaf Shutter

Where are they located?
What is it made of?
How does it operate?

Answer 17

In lens
Thin metal plates that overlap one another when the shutter is closed, thereby preventing light to pass through
When the shutter release button is pressed, the leaves spring apart, allowing light to pass through

Question 18

Shutter Types: What are the limitations of the leaf shutter?

Answer 18

Mass of the blades which are incapable of accelerating or resting at an instant- max. speed = 1/500th of a second

Question 19

Shutter Types: What format cameras are leaf shutters associated with?

Answer 19

Medium and large format cameras and 35 mm compact cameras and other small format cameras such as 110 instamatics

Question 20

Lens Aperture: What is the control of aperture determined by?

Answer 20

The Iris Diaghragm, which is a series of crescent shaped blades that make a circular opening at the centre of the lens

Question 21

Lens Aperture: Small apertures such as f22 let low amounts of light through. Large apertures such as f12.8 let high levels of light through. How does this affect the depth of field in the image produced?

Answer 21

low apertures (f22)= good depth of field
high apertures (f12.8)= poor depth of field

Question 22

Lens Aperture: The aperture ring is calibrated with a series of numbers called f-stops which are a measure of size of aperture. What aperture is said to be f1.2, f1.4, f1.8 and f2?

Answer 22

These are said to be fully open aperture

Higher ones such as f22 are very little aperture, letting very little light through

Question 23

Lens Aperture: As mentioned before, to get the same exposure mode, shutter and aperture controls just half or double. Try work out which combination would give the same as:

Light meter indicates that correct exposure will be a combo of 1/60th of a second shutter speed at an aperture of f5.6. What is an equivalent of this?

Answer 23

1/125th of a second and an aperture setting of f4 (can look at figure 7 in booklet)

Question 24

Typical available camera exposure modes are:

Auto
Program (P)
Aperture Priority
Shutter Priority
Manual
Bulb B

What do each allow you to control?

Answer 24

Auto: camera automatically selects all exposure settings
Program (P): camera selects aperture and shutter speed but you choose ISO (Image sensor or film)
Aperture Priority: You select aperture and ISO speed and the camera determines shutter speeds
Shutter Priority: You specify shutter speed and ISO and your camera does aperture
Manual: You select everything
Bulb B: Useful for long exposure- you specify aperture and ISO speed, shutter speed determined by remote release cable (operated by you)