DPR chickens out (part 2)

Started Apr 20, 2013 | Discussions thread
boggis the cat Veteran Member • Posts: 6,324
Utility is the crux

Jack Hogan wrote:

boggis the cat wrote:

Jack Hogan wrote:

ISO is a subjective, qualitative, sensing medium dependent indication by manufacturers to help you/your camera choose the Exposure that will generate an adequate output level to produce a good picture, whatever that is.  It depends on the physical characteristics of the sensing medium and a multitude of subjective, qualitative factors.

A light meter will be calibrated to give recommended exposure based on the ISO setting.

Hi Boggis.  Indeed, the meter needs to know the 'Sensitivity' of the sensing medium in order to suggest values for Exposure.  But whoever said anything about being in Auto Metering mode?  That's a different topic and thread.  We could still determine Exposure that generates output levels that result in a good picturewithout a meter (even without knowing the sensitivity of the sensing medium) - that's how photography worked in its first 100 years or so. ¬†Exposure still worked then

Of course that is true.  You are talking about an era when very long exposure times were required, of course, so it was easier to get an acceptable exposure.

The variability in what is considered a 'correct' exposure is a (slightly) confounding issue, but you still need to consider ISO (whether sensitivity of film or the signal amplification from a sensor used to emulate a given film sensitivity) when considering photography.  It is a factor as important as aperture and shutter speed.

Due to this, I consider ISO to be 'part of exposure' even if it can be argued that it isn't.  After all, if I set the ISO sensitivity too low, then my photograph will be under exposed.

The sentence above is incorrect both in form and substance.  But it is useful because it brings us to the crux of the matter, which has nothing to do with substance and all to do with form:

Q: If Sensitivity ('ISO') is not part of Exposure, then why do I find the Triangle - which includes ISO - so useful when changing Exposure in the field?

A: Because the misnamed Triangle helps to quickly estimate output level relative to a given starting situation when changing Exposure and Sensitivity parameters in the field.

Key word here is output level, as controlled by Exposure and Sensitivity.  So ISO changes (is related to) output level, not Exposure: the two are independent parameters physically and in-camera, unless you ask your camera to take over and make the decisions for you in various types of automatic configurations.  For example in your example above, if you set ISO too low you may end up with a lower output level (a proxy for brightness?) OOC, while possibly still maintaining the same perfectly good Exposure for your artistic intent, and possibly also resulting on better overall IQ - depending on the characteristics of your camera.

Perhaps the best way of explaining the 'triangle' is that the exposure parameters are fixed, while 'ISO / sensitivity' can be altered after the fact.

Once you take a photograph at f/x over time y s then your choice of x and y have been permanently set (ignoring some digital techniques to simulate e.g. focal zone changes etc.) -- but you can always review the photograph afterwards and dial in more or less 'exposure' by means of effectively shifting the apparent ISO.

I think it is a mistake to imply that 'ISO' is somehow no longer an important factor.  The argument for 'ISO-less' cameras would seem to negate this, when such cameras are available and deliver true 'ISO-less' operation.  But even then, there will always be a noise floor and saturation level for a given sensor.  So you then run into what 'ISO range' you can use for the dynamic range of the sensor (or you require some similar concept -- so similar that I see no advantage in not continuing to use ISO).

Abandoning ISO / sensitivity as a useful concept doesn't seem like a good idea.

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