How to compare camera film ISO number to quantum efficiency?

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Discussion Overview

The discussion centers around comparing the ISO rating of digital cameras to the quantum efficiency (QE) of scientific cameras. Participants explore the implications of these measurements in terms of sensitivity, noise, and practical applications in photography and astrophotography.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants note that the ISO rating for digital cameras does not directly correlate with quantum efficiency, as ISO relates to the electrical signal after photon conversion, while QE refers to the physical conversion itself.
  • There is a suggestion that increasing ISO through ADC gain does not improve signal-to-noise ratio (SNR), leading to concerns about the practical meaning of high ISO numbers.
  • One participant mentions that while higher ISO settings allow for shorter exposure times, they also introduce more noise due to amplification of both signal and noise.
  • Another participant highlights that the ISO rating is a processing technique that simplifies image adjustments for users, contrasting it with the manual processing required in astrophotography.
  • Some participants express skepticism about the meaningfulness of digital ISO ratings, suggesting they may serve more as marketing terms rather than reflecting true sensitivity.
  • There is a discussion about how different sensors and their associated electronics handle high ISO settings, with some sensors performing better in low-light conditions than others.
  • One participant points out that the base ISO for a sensor is influenced by its quantum efficiency, photosite size, and noise characteristics, but this base ISO is often not what is advertised.

Areas of Agreement / Disagreement

Participants generally agree that there is no clear way to equate ISO and quantum efficiency, and multiple competing views remain regarding the significance and implications of ISO ratings in digital photography.

Contextual Notes

Limitations include the dependence on specific sensor characteristics, variations in processing methods, and the lack of a standardized definition for ISO in the digital context.

  • #31
how Iso connect to potential barier??
 
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  • #32
Andy Resnick said:
Interesting... I never thought of that. I figured it was field-of-view related, like the bright sky tended to get included in the metering if I used my wide angle...
Most cameras provide Spot Metering so that you can avoid that problem but it is hard to use it any better than just using the auto setting and compensating later. It's something else to learn about and can be avoided if you are prepared to use bracketing shots. Also, if you shoot with Raw, you have a fair amount more tolerance than when using JPEG files. (But I now see I have made a similar point before on this rather elderly thread)
 
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  • #33
parinaz said:
how ISO connect to potential barrier??

that was a bit difficult to understand what you are referring to ?? I will assume you are referring to the individual pixels on the sensor

The ISO setting doesn't affect that. All the ISO setting is, is an amplifier that takes the signal from the sensor and increases/decreases the signal level by changing the gain setting electronically.
Increasing the ISO = increasing the gain ... it amplifies signal + noise. This is why, particularly on lower end cameras, greatly increasing the ISO is pointless as the noise level becomes unacceptable even at moderate ISO settings 800 - 1600. High end DSLR cameras, like
the Canon 5D Mk3, 6D, Nikon D810 and the like have much higher quality sensors and amplifier electronics to reduce the noise level so that the ISO (gain) can be increased higher before noise become so much of a problem.Dave
 

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