How does ISO 12232 sensitivity compare to ASA/ISO ratings?
Asked 10/19/2018
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Camera sensitivity is often quoted as ASA or ISO, but some manufacturers cite ISO 12232 values such as Ssat instead. For example, Photron lists sensitivity using ISO 12232 saturation-based ratings, and I’m not sure how to compare that with the ISO/ASA figures used by other vendors. Is there a conversion table, or how should these ratings be interpreted when comparing cameras?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
7y ago
2 Answers
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There are five different methods for measuring ISO "speed" of a given image recording system. Photon is reporting the speed as determined from the saturation method.
Class Leading Light Sensitivity:
ISO 12232 Ssat
• ISO 40,000 monochrome
• ISO 16,000 color
According to the ISO standard, Ssat should be reported if noise-based measurements would lead to poorer exposure. In other words, the manufacturer is given its recommended ISO setting to put into an exposure meter in order to determine shutter speed (in this case probably determined by frame-rate) and f-stop settings to provide a proper exposure. There should be no need to "convert" this value to anything else (other than based on your own aesthetic choices); the "Ssat" is just indicating that this speed rating was determined using the saturation measurement and calculation method.
Originally by user26639. Source · Licensed CC BY-SA 4.0
user26639
7y ago
0
Generated from our catalog & community — verify before relying on it.
ISO/ASA sensitivity ratings are not always derived the same way. Under ISO 12232, there are multiple methods for determining a camera system’s speed, and one of them is Ssat (saturation-based speed). That’s what Photron is reporting.
Ssat is intended as a practical exposure rating: the ISO value you can put into an exposure meter to arrive at shutter speed and aperture settings that should produce a proper exposure. In other words, it is already an ISO speed rating, just measured by a specific method defined in the standard.
So there usually isn’t a simple universal conversion table from ISO 12232 Ssat to another maker’s quoted ISO number, because different manufacturers may use different ISO 12232 methods or reporting conventions. The numbers may not be directly comparable unless both were measured using the same method.
The key point: Ssat does not need conversion to ASA/ISO in the usual exposure-setting sense. It’s an ISO-based rating; the extra label just tells you how that rating was determined.
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