Exposure Basics, lesson three?

Started Mar 18, 2013 | Discussions thread
Najinsky
Veteran MemberPosts: 4,598
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Re: Quick correction.
In reply to bobn2, Mar 21, 2013

bobn2 wrote:

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.

That was addressed earlier in the thread .

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.

It's neither. As already mentioned, repeatedly, the triangle is not an exposure guide or a definition, it is a visual list of the three settings that the camera chooses when shooting on auto and the three values we need to understand to take the camera off auto and take control. If you don't want to accept that as a role for the triangle, fine, I can live with that.

You can make as many assumptions as you like about how I could be using the triangles, so that you can then argue against using it in that way. You're a very imaginative fellow, I reckon you could play that game for months on end.

But when you've finished playing, it won't change the facts about how I did use them and that they served that purpose well. It happened, and you'll just need to get over it, or be satisfied with yourself living with your assumptions. It's your head you're screwing with.

And because your assumptions about how it's used are made up, the conclusion about high ISO leading to less noise is a conclusion based on that false assumption.

While the point about noise carries some technical interest, it is of little practical value in the introductory stages for our JPEG shooters, e.g., the class.

Increase the ISO in Av mode and the camera is going to increase the shutter speed to reduce exposure, leading to the extra noise seen when raising the ISO. Use EC to raise the exposure and you increase the risk of blown highlights that then can't be recovered in JPEG.

So there's really no practical way to use that information for JPEG shooters. Or to put it another way, the maximum exposure that a JPEG shooter desires, can only be achieved at base ISO. And as maximum exposure = minimum noise, we can rephrase again, as, minimum noise happens at base ISO. And as if by magic, the graphic appears correctly labled.

-Najinsky

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