Andy C Knight: I'm having difficulty understanding this line...
"There are three factors that affect how much light is available for your sensor to capture: your shutter speed, the size of your aperture (not f-number) and the size of your sensor."
I keep thinking... Shutter, F number & sensor size or...Shutter, physical aperture size & focal length.
Can someone explain where I am going wrong?
Andy C Knight, you're absolutely right. I've corrected my mistake.
Mikity: Good article. I think the changing exposure/changing ISO section is needlessly convoluted though - and it's not obvious you can hover over the images!
I take your point, I'm just not sure what I can do to make the 'buttons' more obvious, without breaking our style sheet.
Anastasiadis Lazaros Thessaloniki Wedding: I read the article and I personally don't agree with a lot of things. Raindrops inside tubes don't behave like light in photos, sensor size does not matter the technology and quality of the sensor does not have to do with its size. This article tries too hard to impress the amateur photographer with magic tricks but actually it does not offer anything new except maybe some confusion about how you should take photos without much noise.
The technology and quality of the sensor certainly have a role to play, but that's what part 2 of the article will be about.
However, with the exception of some quite specific examples, the dominant source of noise in most tones in most photos comes from shot noise: not the camera. And the sensor size *generally* plays more of a role than the specifics of its technology.
falconeyes: Interesting and important article.
However, it should have used fewer words. The article makes a simple matter look more complicated than it really is. And may discourage some to read it.
Everybody thinking that noise is (mostly) a camera artefact should read the article tough.
It's something I've been thinking about recently (and whether we should expect this from a camera company or from independent developers). The Auto ETTR stuff that Magic Lantern are doing support my theory it'll probably be the latter.
As soon as you start thinking through the implications of a true ISO-less camera, you realise how much of conventional camera design you would probably end up throwing away (which I think makes it more likely that these changes would come from outside the industry).
tlinn: Great article, Richard. A couple questions:
1) Does shot noise present as primarily luminance noise or color noise too?
2) Am I correct to infer that part 2 of this series will answer the question of whether or not it is beneficial to ETTR at ISOs other than the base ISO?
1) My understanding is that it appears as both chroma and luminance noise, but there may well be people able to give a more precise answer than this.
2) Part 2 will address why the best approach varies between cameras and will clarify the sections of our reviews that look at this.
Thank you. And I must admit it's ended up longer than I planned.
Rex1227: Does that mean the a shot at a specific ISO cannot get any cleaner up to a point since the amount of photon noise cannot be reduced?
For each sensor size, f-number and shutter speed, there will be a certain amount of shot noise associated with each tone in the image. That will act as a hard limit on how good a particular ISO setting can get.
jon404: ***** Five-Star Article!Thanks, Richard. Your writing is so clear and informative... VERY much appreciated.
Credit should also go to Rishi. This article stems from many, many discussions about noise, sensors, the ISO standard and how people use cameras. It wouldn't be the same article without his input.
RichRMA: "Output size" I thought was determined by pixel count?
"In turn, this is why we talk about different sensor sizes representing an image quality/size/price balance: because, so long as the sensor's electronic performance is similar, the effect of shot noise means that sensor size is the major determinant of image quality. Yes, pixel count can make some difference, but shot noise tends to play a much bigger role, if you compare images at the same output size."
If you cut a FF sensor in 4 parts, essentially making it a 4/3rds size sensor, the individual pixels will still render the same noise as when it was a full-frame sensor. Overall light collection does not effect the response since the pixel size does not change and therefore the noise will not change. You could do an experiment by inserting a physical cropping mechanism in front of the FF sensor and see this is the case. All that will happen is the angle of view of the scene will be cut in half, which has no impact on noise.
Output size is entirely up to you. View images on your monitor or print them out and you've probably rescaled. It's certainly unlikely that you'd choose the size based on the captured image's native dimensions.
Take a 1/4 crop from a full frame image and yes, the pixel-level noise will be identical to any other part of the full image (and to a 4/3rds size sensor). However, scale (up or down) the image to the same viewing size as the whole sensor image and the noise will be more apparent.
Photato: About Sensor Size.Strictly speaking Sensor Size should not be a factor in Noise, because lenses can concentrate the same light (photons) in a large or small area.So much so that you can start a fire concentrating Photons with a magnifying glass in a small area.
What happens is that normally smaller sensors have a higher Density of pixels making it less efficient in photon collection.
For instance. A Small Sensor filled with 8 Micron Pixels should be able to collect the same amount of Photons than a Bigger Sensor filled with 8 Micron pixels. The difference is that the Bigger Sensor would have higher resolution.
Photato: there are always complicating factors (for instance a pixel that captures too much light means you can run out of bit-depth to fully encode everything it's capturing in the shadows), but *broadly speaking*, shot noise plays a larger role in most situations.
Part 2 will talk more about the role of electronic noise (though it'll need a much more length piece or, perhaps, a book to detail every possible source of noise covering every possible case).
mpgxsvcd: he was suggesting 'condensing' the light that would usually cover a large sensor down onto a smaller size.
Which, as you say, changes the net focal length and hence the f number.
Eg: 35mm F1.8 on FF vs the same lens with a 0.66 condensing lens behind it. The net focal length of the 35mm lens and condenser would be 23mm. On this shorter focal length, the (unchanged) aperture would now give an f-number of f/1.2.
Consequently, a 1.5x APS-C sensor would see the same field-of-view as the full frame sensor, but it would experience greater light per-unit-area if the lens was left wide-open. So you'd get the same field of view and the same depth-of-field but, since you're essentially now using a 23mm f/1.2, you'd be more prone to over-exposure if you kept the same shutter speed.
If you could make small pixels with the same full-well capacity, then yes, you could use something like a SpeedBooster to condense the light down onto a small sensor, and hence get the same light capture and the same noise performance.
Without this, if you have the same pixel *size*, then the pixels on the smaller sensor over-expose faster (because you've condensed the light into a smaller area, so each pixel on the smaller sensor now receives more light). You then have to reduce exposure to protect the highlights and you end up back at the same point: with the smaller sensor getting less total light and showing its shot noise more readily.
mpgxsvcd: I agree with everything you said for short exposure photography but what about long exposure photography like astrophotography(Several minutes or more)? There longer exposures increases the electrical read noise and decreases the shot noise because the signal is more consistent over the longer period of time.
It would be interesting to find the shutter duration at which shot noise is surpassed by electrical read noise in particular cameras.
In addition stacking light exposures along with dark frames can reduce the shot and read noise by using some form of averaging with multiple frames. Since the noise is random the difference between each frame is the “unwanted signal”.
Heat and the effects of image stacking are two good points. I'll see if they can be incorporated into part 2.
sina_hml: I know it's an old article but i hope someone can explain some of my questions.Here is how i understand it:I have a 5d and a 450d and a 50mm 1.8. Both cameras have identical flange distance, so the lens is producing the exact same image at the sensor plane.450d captures a smaller part of this image. I think everyone agree with me so far.The part i don't understand is why do some insist that the picture that 450d sees is darker than what 5d sees? it is a smaller amount of the total light that is entering the lens but it is also used to illuminate a smaller area. I assume that the amount of light that each pixel (photo cell etc.) receives is the same between the cameras.
You're right: the two cameras will receive the same amount of light on every square mm of their sensors.
However, the larger sensor has more square mm capturing that same brightness, so captures more light in total. And, as [this article tries to explain](http://bit.ly/shotnoise), the more light you can capture, the less noisy your images will appear.
Iliah Borg: > your camera's exposure meter and exposure guides are all based around correctly exposing the midtones of JPEGs
I would use "correct placement on the brightness scale" maybe instead of "exposing". Technically, the current fashion for tone reproduction is like this: start the shoulder at L*≈70, but place the skin tone (L*≈65) where it belongs - that is, the accurate reproduction starts at skin tone, which is higher than midtone.
Does this work better, do you think:
'The other downside is that, because your camera's exposure meter and exposure guides are all based around putting scene midtones at the correct JPEG brightness level, they're not as helpful as they could be for assessing when you your Raw file has been correctly exposed to the right.'
Dennis: Richard, great article. If you find time, at some point, to elaborate on a couple points, the illustration showing the test tubes makes it clear that SNR increases with exposure time, but doesn't address the confusion some people have with photosite size; if you have a 16MP and 24MP sensor, both are the same size, but each photosite on the 24MP sensor sees fewer photons and should therefore have more visible noise. There's no explanation of the difference between the 100% view and the downsampled or printed view. Therefore, when you say:
> And, since we've established that capturing more light improves your signal-to-noise ratio
I'm not sure you got there; you've explained how an increase in exposure increases the SNR, but without talking about averaging, you could argue that 36million (FF) photosites versus 16million (APS-C) should have the same noise (same test tube size, after all).
J A C S is right that I was trying to keep the article accessible, but I'll see if I can find a way to clarify these issues.
Wouldn't that be more of a decision about the shape of the tone-curve? My understanding was that the ISO standard is (rather loosely) based on representation of mid-tones.
JEROME NOLAS: Can you explain in two sentences, it's too long... :)
The main source of noise comes from the light you capture: not your camera. The more light you can capture, the less you'll notice the noise.
p1726: Is this really a hands-on?
I see your point: we haven't included any images of the camera in our hands. All the images you see are shot by us, in our studio (we have had our hands on it).
audiobomber: Hopefully the K-3 II review will be written by Dan Bracaglia and Rishi Sanyal. They did a great job on the A77 II review, especially the focus testing. The K-3 was sabotaged by all the wrong settings for the AF-C test.
You're absolutely right, I'm not a regular user of Pentax (or any brand), so there's always the possibility of us not discovering the optimal settings.
However, I have reviewed several Pentax camera (which involves using them for extended periods), we did experiment with settings (there are AF Hold on and off examples included in the review, for instance), and discuss with Ricoh to ensure we didn't get it *totally* wrong.
That's never going to be a substitute for the >year of experience that you've now built up, but we put in a lot of work to try to get the best out of the system and I'm confident that we got it broadly right.
One of the problems with AF testing is that you can't model all possible shooting situations (BIF for instance), but I can assure you that we didn't just run outside, take a couple of pictures of a cyclist and then draw our conclusions from that.
With the work Rishi's doing, we should be able to be more certain in our findings, this time round.