Viewing Films(8)

Question 1

Film viewing condition variables:

Answer 1

• viewing equipment
• location
• lighting conditions
• film density
• visual acuity
• image quality
• film condition
• volume of film to be viewed

Question 2

Film viewing equipment must:

Answer 2

• be capable of providing enough light

- have a means of controlling light levels

Question 3

The average individual can detect a ___% change in density under proper illumination conditions.

Answer 3

2%

Question 4

Light reaching the eye should be provided from a ____ source. under _____ lighting conditions

Answer 4

single source. under subdued lighting conditions.

Question 5

Why are opaque materials or masks used when viewing films?

Answer 5

To remove excessive light, a result from drastic film density change, edges of film or reflections and glare from external sources

Question 6

What purpose does the dimmer switch provide?

Answer 6

reduces eye fatigue and prevent need for adjustment every time a new film is to be viewed.

Question 7

The amount of ambient light from the viewer environment should be limited to:

Answer 7

20lux or 2ft candles

eyes are most sensitive to light at this level.

Question 8

How long should dark adaption time be when coming from a full sunlight environment?

Answer 8

5 minutes

Question 9

How long should dark adaption time be when coming from a regularly lit environment?

Answer 9

3 minutes

Question 10

How long should dark adaption time be when using a full brightness viewer and switching radiographs?

Answer 10

30 seconds

Question 11

Film viewers should be capable of emitting how much light through what density of film?

Answer 11

20lux / 2ft candles evenly distributed throughout films with densities of 3.0 - 4.0.

densities of 4.5 are possible

Question 12

Humans ability to detect changes are dependant on:

Answer 12

• degree of contrast
• distance and angle from eye to film surface
• transmitted brightness

Question 13

What is point size?

Answer 13

a fixed size unit equal to 1/72 of an inch.

Question 14

Visual size of an object perceived by the eye is ____ than the actual size.

Answer 14

different

Question 15

What is visual size?

Answer 15

the perceived size of a point size letter at a certain distance.

Question 16

Doubling viewing distance will do what to the perceived visual size?

Answer 16

reduce it by 1/2

Question 17

Optimal viewing placement is:

Answer 17

perpendicular (90°) at 25cm (10-24in) away.

Question 18

What is Signal to Noise ratio?

Answer 18

the relationship between two density variations.

describe the number of photons that reach and interact with the film for a given exposure.

Question 19

Define “noise”

Answer 19

differences in photon interactions or photon spatial distribution across two separate areas of film of similar size.

• interferes with the complete visibility of fine detail

Question 20

What factors affect the signal to noise ration?

Answer 20

• amount of exposure or exposure time
• relative film speed
• contrast
• energy level
• specimen geometry

Question 21

How can the condition of film can affect viewing?

Answer 21

• artifacts can cover details
• artifacts can mistaken for discontinuities
• density variations from poor processing can:
• film discolouration from contaminated chemistry
• blurred (improper fixing/residual thiosulfate)
• streaks, stains, discolouration from dirty washing
• fogged from partial exposure of unexposed film, high temp, high humidity.

Question 22

Measurement of incident light formula:

Answer 22

D = log (Io/It)

D - film density

Io - original light intensity

It = light intensity transmitted through film