Chapter 21 Film Sensitometry Objectives Objectives Sensitometry

Chapter 21 Film Sensitometry Objectives Objectives Sensitometry www.phwiki.com

Chapter 21 Film Sensitometry Objectives Objectives Sensitometry

Watters, Judy, Host has reference to this Academic Journal, PHwiki organized this Journal Chapter 21 Film Sensitometry Objectives Calculate speed points, speed exposure points in addition to relative speeds from D log E curves Calculate gamma, gradient point, average gradient in addition to latitude from D log E curves Objectives Analyze D log E curves to determine speed, contrast in addition to latitude relationships Discuss the relationships between speed, contrast in addition to latitude

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Sensitometry Measures the response of film to exposure in addition to processing Sensitometric Equipment Penetrometer or sensitometer Used to create a uni as long as m set of densities on a film Densitometer Provides measurement of light transmitted through film Measures optical density Penetrometer Stepwedge Used to monitor x-ray equipment Also used to monitor film/screen combinations Not recommended as long as processor monitoring

Sensitometer Uses a controlled light source Produces same amount of light each time it is triggered Sensitometer Available in 11- or 21- step versions 21 step version increases density by a factor of the square root of 2 (1.41) as long as each step Densitometer Uni as long as m light source in addition to an optical sensor Calibration control allows as long as easy calibration

Optical Density Numbers Formula: OD=log10 Io/It If 100% of the light is transmitted through the film, it has an OD of 0 If none of the light transmits through film the OD is 4 Opacity Ability of a film to stop light transmission Formula: Io/It The D Log E Curve Describes relationship between density in addition to exposure This is done through sensitometry

The D Log E Curve AKA Sensitometric curve Characteristic curve Hurter in addition to Driffield (H & D) curve Sensitometry’s roots lie in analysis of photographic film The Sensitometric Curve Plots OD vs. LRE Log relative exposure Allows large range of exposure displayed in a few numbers The Sensitometric Curve Log relative exposure Log102 represents doubling exposure Log102 = 0.3

Densitometer Reads on a scale of 0-4 0 meaning that all light is transmitted 4 meaning that no light transmits through the film Typical diagnostic densities range between 0.25 to 2.5 Parts of the Curve Base + fog Toe-Dmin Where the density becomes light Straight line portion Used to demonstrate the relationship to the film’s exposure vs. the density transmitted Parts of the Curve Shoulder-Dmax Where the density becomes dark

Film Properties Base density Inherent in a piece of film due to dyes etc. Value is usually 0.1 OD Fog Density Inadvertent exposure during storage h in addition to ling etc. Fog density should not exceed 0.2 OD Base + Fog Cannot separate base in addition to fog density measurements Typical range of OD as long as Base + fog 0.18 to 0.23 Should not exceed 0.25 Toe Dmin Controlled by phenidone Fast acting reducing agent in developer Produces gray tones on film

Straight Line Portion Area of curve between toe in addition to shoulder Contains range of useful densities Typically 0.25 – 2.5 or 3.0 Shoulder Dmax Controlled by hydroquinone Slow acting reducing agent in developer Produces blacks in image Reversal or Solarization Once a film has been exposed to Dmax, it will begin to lose density after further exposure Duplication film has been solarized

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Film Characteristics Resolution Speed Contrast Latitude Resolution Ability to accurately image an object AKA Detail Sharpness Definition Resolving power Resolution Inversely related to size of silver halide crystals

Speed Ability of an IR to respond to low exposure measures its sensitivity or speed Speed index Specified by 1.0 + base + fog Speed Faster film will have a curve closer to y-axis of graph Speed Film sensitivity is affected by: Size of silver halide crystals Number of sensitivity specks Thickness of the emulsion All of the above are directly related to film speed

Average Gradient Slope of line that is drawn between And 2.0 above base in addition to fog density Higher the average gradient, the higher the contrast Latitude The lower the slope (the more horizontal the line) the wider the latitude Latitude Low scale of contrast in film More latitude Margin of error higher

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