Exposure Basics, lesson three?

Started Mar 18, 2013 | Discussions thread
bobn2 Forum Pro • Posts: 50,987
Re: Quick correction.

Najinsky wrote:

bobn2 wrote:

The essence of why it's not a good communication aid is here:

bobn2 wrote:

Najinsky wrote:

But later in the course when the different values have become much more familiar, it evolves into something much closer to this as, a recap aid:

from www.wired.com

You've labelled the "ISO' side back to front.

Now, I see you chose to completely ignore that, and instead embark on some rather irrelevant rhetoric. But you they have labelled the 'ISO' side back to front. So, here is a conundrum, a 'communication aid' but one that is communicating the reverse of what actually happens. So, why is that?

The rhetoric . <snipped loads and loads more rhetoric, avoiding the issue>.. hopefully without the 'so why is that?' games.

And we come back to it. In the diagram above, the ISO scale is labelled the wrong way round. There are two ways of looking at it, either one ends up with it being the wrong way round. Either:

i) If you are intending that the other two sides of the triangle be adjusted as the ISO is adjusted. In that case, as you move towards low ISO, the f-number will decrease, so one of the ISO and f-number is the wrong way round, or as you go towards hight ISO the shutter speed will increase, so one of the shutter and ISO is the wrong way round. Taking the majority view, it is the ISO that is the wrong way round.

ii) If you are intending that the three sides are independent, then we leave the shutter and f-number the same, and adjust the ISO. In that case on the vast majority of cameras the noise will decrease as the ISO is increased.

Either way, the ISO is the wrong way round, yet this diagram is supposed to aid understanding? At best it is useless, at worst harmful. It's rooted in a misapprehension that raising ISO of itself increases noise, which is a nonsense. What increases noise is reducing exposure.

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