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02-01-2020, 06:21 PM   #1
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ISO questions

What does ISO stand for. Years ago I had understood it to be an acronym for International Standards Org. Also, is a particular ISO setting universal across manufacturers? That is, is ISO 1600 on a Pentax the same as 1600 ISO on a Cannon, Nikon etc. and especially on higher ISOs is the noise the same?

02-01-2020, 06:30 PM   #2
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Here some reading where it's been hashed out:
Why ISO?
02-01-2020, 06:31 PM   #3
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Hi Michael, hope this helps.

What Does ISO Stand For in Photography? ISO Settings Explained
02-01-2020, 06:40 PM   #4
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adding to the other explanations

there is an article for that [ and other terms ]
QuoteQuote:
Photography Terms Cheat Sheet
Widely used photography and camera terms
By Inexorable in Articles and Tips on Jun 30, 2014

. . .

ISO or Sensitivity
International Standards Organization. A measure of the sensitivity to light of the sensor or film. Higher the ISO, greater is the sensitivity. . . .


Read more at: Photography Terms Cheat Sheet - Articles and Tips | PentaxForums.com

02-01-2020, 07:02 PM   #5
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Very helpful. thanks
02-01-2020, 08:48 PM   #6
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QuoteOriginally posted by MichaelS Quote
Also, is a particular ISO setting universal across manufacturers? That is, is ISO 1600 on a Pentax the same as 1600 ISO on a Cannon, Nikon etc. and especially on higher ISOs is the noise the same?
The answer is NO. Strangely, ISO standards for digital cameras are tied to metering and while there are several options for ISO compliance, Japanese camera companies are required by CIPA to use one of the two below:
  • Recommended Exposure Index (REI): Whatever the camera manufacturer dictates for consistent JPEG output.
  • Standard Output Sensitivity (SOS): Referenced to an external gray-point standard (18% gray) determined from sRGB (TIFF) output.
The method used is recorded in the EXIF metadata. Pentax uses SOS and generally agrees closely with hand-held meters and traditional TTL metering on film cameras. Other brands may not agree as closely to the extent that cross-brand ISO equivalence is a frequent subject of heated online discussions with some brands being singled out for metered exposures suggesting two or more stops actual exposure than what would be indicated for a standardized light source.

https://en.wikipedia.org/wiki/Film_speed#Digital_camera_ISO_speed_and_exposure_index


Steve

Last edited by stevebrot; 02-01-2020 at 10:40 PM. Reason: Added link
02-02-2020, 08:02 AM   #7
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Thanks for this Steve. I was not aware of the differing standards.
02-02-2020, 08:11 AM   #8
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ASA vs. ISO

Both measures of sensitivity of camera sensors or film

QuoteQuote:
ISO and ASA

ISO and ASA are for our purposes the same, a measure of the sensitivity of camera sensors or film. Its use is in creating the ideal Exposure, the correct amount of light recorded to produce the ideal image.

The higher the number the more sensitive it is. The scale used is convenient for photography as a doubling or halving of the number represents one stop, as Shutter Speed also creates a one stop difference by halving or doubling a direct adjustment can be made. In this case the numbers go in the same direction, so if you had a camera set to ISO400 and had an exposure of 1/100 second, increasing the ISO by one stop to 800 would double the sensitivity and therefore you need only half the time for the exposure, and can therefore also double the shutter speed to 1/200.

ISO and ASA


Last edited by aslyfox; 02-02-2020 at 11:25 AM.
02-02-2020, 08:24 AM   #9
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QuoteQuote:
especially on higher ISOs is the noise the same?
This source also explains " noise " on digital cameras

ISO and Noise
QuoteQuote:
As sensitivity is increased on digital cameras beyond a point, noise also increases, later cameras having a higher point where this starts. Noise is random anomalies or odd bright pixels. Noise reduction software can reduce this but at the expense of sharpness. People with a film background accept more noise than those who have entered photography in the digital age, as film had grain that was often more destructive to the image than noise is. Noise is more noticeable on a computer monitor than when printed, as it often occurs in shadow areas. You need to experiment with your camera at different ISO values to see what level of noise you are happy with. If the choice is between some noise and blur from using two slow a Shutter speed, or the image being out of focus due to limits of Depth of Field (DOF), then you will find that the compromise with the noise present, is the best option. Noise can also be created in editing, especially pulling detail out of shadows.
ISO and ASA

Last edited by aslyfox; 02-02-2020 at 11:23 AM.
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