Exposure triangle explanation please.

Started Jul 9, 2013 | Questions thread
texinwien Veteran Member • Posts: 3,326
Re: could also be called auto ISO ...

Jeff wrote:

texinwien wrote:

Limburger wrote:

It's a matter of formulae and definitions. But photographically by whatever ISO will be replaced it will be in relation with shutterspeed and aperture just in the fashion it is now.

You need not know how the internal combustion engine works in order to drive a car.

It's already not necessary on some cameras. On my current camera, I almost always shoot at base ISO. I ignore the ISO completely.

I focus only on the aperture and shutter speed necessary to get the desired DOF and the desired freezing of subject movement, always trying to get as much light on my sensor as possible. In low-light situations, I just choose the aperture and shutter speed I need for artistic purposes, knowing that I'll end up with a noisier image.

Later, I apply the necessary gain to my photos to make them as bright as I want them.

You see, I'm able to forget about ISO, completely. I focus only on the 3 actual variables that are a part of the exposure equation - scene luminance, shutter speed and aperture. No need to confuse the issue with the ISO, since it's just applying gain. Why should I choose the gain applied before I take the photo? There's no good reason to if you're shooting RAW and applying the gain yourself later on.

Once this is possible in-camera for JPEG shooters, the concept of ISO is simply confusing baggage that can be jettisoned.

Furthermore, my camera, the OM-D E-M5 has a function that shows me, in the live few, which highlights I'm about to blow. This allows me to quickly adjust shutter speed and aperture to get the optimal exposure (most light possible without blowing important highlights - leads to the least visible noise in the resulting exposure) in situations where light is abundant.

Add this capability to the ability to quickly adjust an exposure's gain in-camera, and ISO is simply thing of the past. Good riddance

There's a lot that agree with in this post. What you're relying on, of course, is that your camera has enough dynamic range that you can postpone the determination of {gain|ISO|image brightness} until PP. With modern sensors in larger formats that can work as you've indicated within reason. Depending on tolerance for noise in your images, you'll have 4-5 stops of head room to work with. In effect, you're working in an auto-ISO mode where gain is determined at the end to produce the final image.

It's even better with my current camera, since my camera tells me which highlights will blow before I release the shutter. When light is abundant, this allows me to maximize the amount of light that hits the sensor without blowing important highlights, leading to the absolute best possible exposure (with the highest SNR possible) given the scene's luminance, plus the aperture and shutter speed dictated by my artistic goals.

I've been fooling around a lot lately with iPhone photography (don't judge, I enjoy the challenge and am having fun with it) where dynamic range is very limited. Shooting base ISO is basically forced because there is so little head room on the sensor. The f-stop is fixed, too, so effectively the only knob left to control image brightness is shutter speed. The point is that the small sensor format forces a different approach to exposure than the one you describe. At least for me, controlling {ISO|gain} at the time of exposure is still a very important aspect of creating the final image.

Why, though? How does it help to set the gain before you take the image, and to not be able to adjust that after the image is taken? Switch to your idea of auto ISO and an ISOless sensor, and let the user adjust the gain after the fact, if they want to. This is better than forcing the user to choose the gain before taking the photo, then not making it possible to change the gain after the photo has been taken.

In short, the gain is applied AFTER the exposure has been captured. Why force a user to make a permanent, unchangeable decision about gain before the exposure is captured, if the gain won't be applied until afterwards, anyway.

When the day comes that sensors -- both small and large -- have as much headroom as we encounter in typical photography situations, say 12-15 stops of headroom, then we can chuck {ISO|gain}. Until then, I'd rather hang onto the knob, or some proxy of it.

Again, if your camera shows you which highlights will blow given a scene's luminance and your shutter speed and aperture choices, you need much less headroom.

Even in cases where your camera doesn't do this, you only need to know the 'saturation ISO' of the sensor, if the sensor is ISOless. I know that the saturation ISO on my sensor is ISO 107, so I can calculate safe exposure values even if the function that warns me about highlights that are about to blow is turned off.

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You don't make a photograph just with a camera. You bring to the act of photography all the pictures you have seen, the books you have read, the music you have heard, the people you have loved.” -- Ansel Adams

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