OK. So here is what I do: I use the Canon Fv mode, set aperture to give the depth of field I want and what I consider an appropriate shutter speed, then ISO sets itself according to Canon's algorithm. Often I just set aperture and let Canon set ISO and shutter speed.
Is this not a good way to take photos, the raw files of which I then process in PhotoLab?
David
He's talking information theory, a la Claude Shannon. In that case, it's called a bit when the information is measured using base 2 logarithms.
LOL I spent most of my engineering career avoiding noise. But once I was asked to provide a noise source for a Synket synthesizer and used a zener diode like you. The composer complained that the noise was too white (only that was not how he described it), so I added a capacitor across it!
David
Using a minimum SS setting and exposure compensation to fine-tune the exposure (or) brightness when necessary, this is a perfectly valid way to shoot, and how I also shoot most of the time.
Then it seems we are talking at cross purposes: I am making an analogy with digital audio.
David
So you know more about shot noise than you thought.
And a bit is when it communicates one of two possible values. Noise doesn't count as a bit, because it doesn't communicate any information - you can't tell from its value what the original information was.
Same root. A bit of data carries one of two possible values. When it comes to information (which was the original sense) a bit is when it communicates one of two possible values. If you think about it, if a bit is consumed by noise it doesn't communicate any information, because its value doesn't tell you what the input information was. So typically as exposure goes down and the SNT reduces, the number of bits necessary to communicate the image reduces. If you look at the raw file for very high ISO settings the lower bits are all noise, and not contributing to the image.
There are many ways of making a photo lighter without touching the ISO dial. One of them is to add light ;) The "triangle" doesn't care about that.
Unfortunately, the exposure triangle has been used as a teaching tool to persuade many photographers that their cameras work in ways they actually don't. That has real world consequences.
It shifts attention away from f-stop and shutter speed as camera settings controlling important creative elements and exposure, to ISO as the primary source of noise in a photo. Photographers assume that using a low ISO automatically translates to a clean photo; one absent of noise. Then, they make photos using lower ISOs, see noise and immediately assume there's something wrong with the camera. In fact, the problem resides in the teaching tool used by so many to explain photography.
It also tends to block a photographer from taking advantage of options available to them when processing an image in a photo editing app. Suppose you're photographing a high dynamic range sunrise scene; one in which the brightest highlights and darkest shadows can't adequately be rendered in a single photo. Either the shadows are too dark when settings are used that prevent the highlights from being blown out or the highlights are blown out when settings are used that render the shadows light enough to show detail.
In the "exposure triangle" universe, the two outcomes would be described as overexposed (blown highlights) or underexposed (black shadows). In the real world, you can optimize exposure for the conditions. Start by selecting the widest lens aperture (smallest f-stop number) that will deliver an acceptable depth of field. Next, select the slowest shutter speed that will adequately render movement in the frame. You've ensured two important creative goals will be met and have optimized exposure in the process.
In this hypothetical, we can use ISO as an indicator of exposure. It's not directly affecting exposure but serves a purpose as the canary in the coal mine. The available light, f-stop and shutter speed determine exposure. The photo and histogram displayed on the rear LCD are indicators of our success at maximizing exposure without blowing out highlights. Without getting deep into the weeds, there are limitations and potentially real problems with relying on the in-camera JPEG and JPEG histogram as references. That acknowledged, they still can be useful tools.
The shadows in the resulting photo will look too dark and many photographers might feel they've compromised the image quality by underexposing the shadows. To the contrary, I'd suggest exposure has been optimized...at least, the exposure that can be captured in just one shutter actuation. The f-stop and shutter speed used meet the photographer's creative needs. They also maximize exposure within the constraints of the ambient scene lighting.
Putting any more light on the sensor would result in the highlights being blown and important details being lost. In digital photography, we have much less latitude to recover details in the highlights than we do in the shadows. Pushing exposure by more than 2/3 stop will put highlights at risk of being clipped. By contrast, shadows can pretty easily be lifted in post by a full stop and sometimes by multiple stops before image quality really starts to take a hit.
In this hypothetical, if the shadows can be lifted in post by a stop to make them more pleasing, the final version of the processed image looks better and is no worse from a raw image quality standpoint than if the same scene had been photographed using the same exposure settings (f-stop and shutter speed) but with a higher ISO. Exposure was optimized for the conditions and image lightness was fine-tuned in post.
Freeing ourselves from the mythical notion that ISO determines exposure and is the primary source of noise allows for this kind of thinking, image-making and workflow. It opens creative doors that would otherwise remain closed.
Or, as I see people say sometimes, that the'll get noise if you don't 'nail' exposure. Or, that you get noise if you 'push' exposure. Similar to David's discussion, if no-one told you where the noise comes from then you tend to make what seem to be reasonable assumptions.
Exposure - brightness - different things.
Exactly, and why I used two different words. Exposure compensation in Aperture Priority/Auto-ISO mode could be fine-tuning either.
My apologies. I've seen people use that x/y formulation when they were suggesting that they were synonyms.
Yeah, I see how it could’ve been read that way. I edited my previous response for clarity. Thanks.
noise is defined more openly as the meaning exposure, is it not ?
What the heck does that sentence mean?
Especially at the size of the image on the webpage. Sensors with large-scale correlated post-gain read noise blotches that are still visible after significant downsizing are mostly history these days. Intended display magnification can be a useful consideration when making read_noise/headroom compromises.
