dee
Well-known
Errrrr how does the old ASA ref. Compare to ISO , especially as it,s all electronic these days .
dee
dee
Silly Question ASA / ISO .
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dee
Well-known
Answered my own question equal !
sevo
Fokutorendaburando
For what definition of OLD? There was one major and one minor change to the definition in the late fifties and early sixties, together they had black and white negative photographic films shift up by 2/3 to one stop (i.e. from ASA200 to ASA400 or sometimes 320).
After since that, only test procedures have been changed (to harmonise ASA and DIN testing to the point where they could be merged into ISO), with no effect on published ratings for photographic film. The ISO definition merely combined the ASA and DIN numbering - what previously was ASA400/27DIN now is ISO 400/27 (and since its introduction it has become common to omit the ex-DIN part).
After since that, only test procedures have been changed (to harmonise ASA and DIN testing to the point where they could be merged into ISO), with no effect on published ratings for photographic film. The ISO definition merely combined the ASA and DIN numbering - what previously was ASA400/27DIN now is ISO 400/27 (and since its introduction it has become common to omit the ex-DIN part).
Freakscene
Obscure member
And the digital ISO speed definition is completely different from the film one.
Marty
Marty
kiemchacsu
Well-known
How come?
I still use my meter Minolta for both digital and film and both work totally fine and consistent.
Am I missing something?
I still use my meter Minolta for both digital and film and both work totally fine and consistent.
Am I missing something?
sevo
Fokutorendaburando
The definition of film speed is built around densitometry - you can't put a densitometer to a sensor, so they need a entirely different definition.
marcr1230
Well-known
ISO is "International Standards Organization"
ASA is "American Standards Association"
DIN is "Deutsches Institut für Normung"
ISO and ASA are equivalent/equal
DIN used a logarithmic (base 10) scale
on older cameras and light meters, you sometimes see DIN/ASA markings
ASA is "American Standards Association"
DIN is "Deutsches Institut für Normung"
ISO and ASA are equivalent/equal
DIN used a logarithmic (base 10) scale
on older cameras and light meters, you sometimes see DIN/ASA markings
jsrockit
Moderator
But you can use a digital camera as a meter for a film camera and at the same ISO / ASA, you have the same exposure.
css9450
Veteran
willie_901
Veteran
The role of ISO/ASA/DIN is to inform/calibrate the light meter. By the way, the 'light meter' can be a person with significant experience at setting exposure parameters.. The goal is to make life easier for photographers who switch between film emulsions or digital camera bodies. And the five or so different ISO standards for digital sensors used around the world attempt to make exposure for film and digital media similar.
For film the meter has to know how much light is appropriate for a film formulation when the shutter is open. A secondary consideration involves the development process. While a film formulation's sensitivity to light can not be increased, development techniques can accommodate some degree of under or over exposure. The meter calibration also informs us how to modify the development method. When we write ISO 800 on a role of Tri-X we know the meter calibration (ISO setting) requires a modified development process.
For digital the meter has similar roles.
The first is to avoid overexposure of the sensor (a.k.a exceeding the sensor sites' full-well capacity) when the shutter is open. This level is fixed and can not be changed. This sensitivity is the base ISO.
If the appropriate shutter time and, or aperture require the sensor to be under exposed, the meter will advise the photographer to manually increase ISO or provide data to the camera's automation algorithms to increase ISO. In both cases the higher ISO parameter increases the global brightness in-camera after the shutter closes. In other words, the sensor's sensitivity to light never changes [1].
In some designs the IQ does not suffer by increasing the brightness of raw file rendering in post production[2]. These designs are called ISO invariant. So the camera can be left at base ISO and the photographer only has to be concerned with over exposing important highlight regions.
[1] Recently dual-gain sensors have appeared where the sensor sites' full-well capacity actually increases at higher ISOs. The FWC increases because the sensor electronics uses switches between two difference capacitors. The sensitivity (quantum efficiency) does not increase but the ability to store more signal (information) does increase.
[2] Older designs use different signal amplification electronic to increase the signal levels after the shutter closes. Raw data from these designs benefits from an increase in ISO because the camera electronic noise is minimized. The signal levels (exposure) are increased by ISO amplification but their information content is not.
For film the meter has to know how much light is appropriate for a film formulation when the shutter is open. A secondary consideration involves the development process. While a film formulation's sensitivity to light can not be increased, development techniques can accommodate some degree of under or over exposure. The meter calibration also informs us how to modify the development method. When we write ISO 800 on a role of Tri-X we know the meter calibration (ISO setting) requires a modified development process.
For digital the meter has similar roles.
The first is to avoid overexposure of the sensor (a.k.a exceeding the sensor sites' full-well capacity) when the shutter is open. This level is fixed and can not be changed. This sensitivity is the base ISO.
If the appropriate shutter time and, or aperture require the sensor to be under exposed, the meter will advise the photographer to manually increase ISO or provide data to the camera's automation algorithms to increase ISO. In both cases the higher ISO parameter increases the global brightness in-camera after the shutter closes. In other words, the sensor's sensitivity to light never changes [1].
In some designs the IQ does not suffer by increasing the brightness of raw file rendering in post production[2]. These designs are called ISO invariant. So the camera can be left at base ISO and the photographer only has to be concerned with over exposing important highlight regions.
[1] Recently dual-gain sensors have appeared where the sensor sites' full-well capacity actually increases at higher ISOs. The FWC increases because the sensor electronics uses switches between two difference capacitors. The sensitivity (quantum efficiency) does not increase but the ability to store more signal (information) does increase.
[2] Older designs use different signal amplification electronic to increase the signal levels after the shutter closes. Raw data from these designs benefits from an increase in ISO because the camera electronic noise is minimized. The signal levels (exposure) are increased by ISO amplification but their information content is not.
kshapero
South Florida Man
All I know is that due to age I keep saying ASA in conversation and the younger folk keep saying, "Huh?"
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With LOL and OMG speak one would thing The youngins could pick up ASA quickly.....
B2 (;->
B2 (;->
Roger Hicks
Veteran
Not exactly. ASA was based on Kodak research and used a fractional gradient criterion. DIN, on the other hand, was based initially on development for maximum contrast and a minimum density. There's more about how they were reconciled in http://www.rogerandfrances.com/subscription/ps expo neg.html and http://www.rogerandfrances.com/subscription/ps iso speeds.html and quite a lot more in our book Perfect Exposure, http://www.rogerandfrances.com/photography/exposure.html
Cheers,
R.
Dwig
Well-known
Actually, to be perfectly correct it should be "from A.S.A. 200 to ASA 400 ...". As part of this change, they changed from using periods to omitting them. The lack of periods was meant to indicate that the rating used the new standards.
Many meters never used the periods, but if you dig out ancient early 50s or 40s Kodak spec sheets or technical publications you'll see the periods used.
