Darkroom & Film Processing Flashcards
Safe lights inside dark rooms need to be:
4 feet from work area
Proper bulb wattage
Covered by filter only allowing red end of spectrum
No film exposed more then 3 min
Safe light test?
incrementally exposing undeveloped film to dark room conditions in 30 second intervals for 3 min
what are the three Ts and what is it used for?
time, temperature, titration
used in processing
increasing these will cause film overdevelopment caused by processor induced fog forcing the development of unexposed SILVER HALIDE CRYSTALS film is darker
Manual processing
68 degrees, development for 5 min, fixer for 10min, wash 20min, dry 20-40min
image creation: Exposure
the film is exposed to light
99% of image created by light emanated by screen
1% of any visable image comes from direct exposure of a silver halide crystal by an x-ray photon
a small sensitivity crystal consisting of sulfur collects spare electrons formed by this process
in this state we cant see image on film LATENT IMAGE
Image creation: Development
developer donates electrons that creates elemental silver (black in color results in black and grey color on film
Image creation: Fixing
fixer removes all unexposed silver halidesstopping ant exposure afterwards
Image creation: washing
the final wash clears all chemicals on the film surface and in the emulsion
final wash prevents fixer chemicals from continuing to cause chemical changes
when washing is insufficient artifacts emerge over time
Developer pH is in what range?
10-11.5 strong base
Developer: activator
sodium carbonate- softens gelatonprotective cover on film preserves basic pH
Developmenter: Reducing agent
hydroquinone or phenidone reduces EXPOSED silver halide to black metallic silver
Developer: preservative
sodium sulfate
developer: restrainer
potassium bromide and acetic acid
Fixer: pH? and what is it called
acidic pH 4-4.5
known as a clearing agent
ammonium thiosulfate is the key ingredient dissolves silver halide
what is the tanning agent used?
potassium alum
Activator used is
acetic acid to neutralize the developer
What are the characteristics of an automatic developer system?
- Higher temp
- Stronger acid
- Constant agitation of chemicals
- Rapid through put of film
- Chemicals degrade more quickly at higher temp
- underreplenishment= grey appearing
- overdevelopment causes increase in fog and wastes chemicals
What are the causes of lowered contrast on a film caused by adverse conditions in the dark room
-safe light fog room temp chemical fog from too hot processor chemical fog from too concentrated chemicals film past experiation date
What needs to be done every 1-2 months
complete chemical chack and tank clean
check replenisher rates
check cycle time
Sensitometer is a machine that does what?
exposes the film to a step wedge of known densities
H&D curve is a graphic measure of what??
a graphic measure of how a film records density over a range
H&D curve graph
graph plots optical density vs log relative exposures
3 components: toe, body, shoulder
Toe of curve
starts above zero optical density even in the absense of any exposure as theres always a small amount of light absorbtion & “auto exposure”
Body of the curve
straight line component of the curve
short lattitude film has a high slope =high contrast smaller changes in grey density per unit exposure
long latitude film has lower slope and is a lower contrast film small change ingrey densty more shades of grey
shoulder of the curve
this represents maximal optimum density the fild will achieve no matter how much mAs or kVp you throw at it
if two H&D curves for two different types of film are plotted next to each other which one is faster?
the left one is faster
on the densimeter what is the scale? and what is the meaning of the maximum vs minimum value
0-4
0= zero absorbtion of light through the film or the film transmits 100% of inciedent light through the film
4= 100% absorbtion film is entirely black
What are the measurements we obtain to track performance of the processer over time?
speed index- finding step on sensitomeric step wedge strip
contrast index- difference in optical density
gross fog index- base plus fog
Gross Fog index
base plus fog
inherant optical density of a film when it has not been exposed at all and was just run through blank
the length of the toe of the H&D curve is related to the films sensitivity to fog
therefore, the longer the toe the less sentsitive to fog the film is
What are the fluctuations valus you should see for
speed index
contrast index
gross fog index
+/- -0.15 speed idex
+/- -0.15 contrast index
+/- -0.03 gros fog index
the spectral sensitivity of film is the bandwhidth of light that is most sensitive to during exposure
should match the spectral emission of the screens that it is paired with
speed vs detail film is a function of crystal size and looks like what?
slow speed with best detail: small crystals in thin layers
Medium speed with medium detail:
- medium sized crystals in a medium thick layer of the film
- large crystals in a thin layer
- small crystals in a thick layer
slow speed with best detail:
small crystals in thin layers
Medium speed with medium detail:
- medium sized crystals in a medium thick layer of the film
- large crystals in a thin layer
- small crystals in a thick layer
Fast speed with low detail:
large crystals in thick layers
