Lots of references to the exposure triangle (ISO/Shutter Speed/Aperture). Now, I am comfortable with the relationship between the 3 elements, but has anybody got a good explanation of how to use the triangle to define the relationship and how to use the triangle?
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Exposure triangle explanation please.
- Thread starter AnthonyL
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If only that were actually true.
With today's sensors, {gain|ISO} does have an effect on the final image which is the introduction of noise. If I expose an image such that very high gain is required in PP, then that may not be a good result. I may prefer to accept creative constraints on aperture and shutter in order to keep noise under control.
As you've noted, highlighting in live view allows you to avoid blowing highlights. So that's a situation where you accept creative constraints on aperture and shutter to avoid problems in the final image. The other problem is losing shadow detail or noise due to underexposure. For that I accept a cap on ISO, and therefore need to manage ISO at time of exposure.
Perhaps I'm more cautious about this because I've been trying to work with iPhones for the last few months where both extremes are present in almost every scene.
Here's a shot from two nights ago -- Believe me, with small sensors we are definitely not in anISOless world!
But I want to, because I want at least some control *at the time of exposure* over noise and shadow detail in the final image.
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texinwien
Senior Member
Think about how you'd operate if you only had a single ISO. If everything but base was created via digital amplification.TTMartin wrote:
So analog gain of the sensor changes the sensors ISO, but, digital manipulation of the image of the image after capture doesn't?texinwien wrote:
As I posted elsewhere, my camera is ISOless above ISO 800. It has ISO settings up to 25,600, but since it's ISOless above 800, I ignore the higher settings.JTC111 wrote:
Two questions:texinwien wrote:
It's already not necessary on some cameras. On my current camera, I almost always shoot at base ISO. I ignore the ISO completely.
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
If you " almost always shoot at base ISO," as you've stated in at least two different posts, then you occasionally do adjust your ISO setting, right?
I can agree with that.
As a RAW shooter, I also only use ISOs that are created by analog amplification of the sensor. I have partial ISO steps disabled in my camera, and do not enable the expanded high ISO.
They need to know the saturation sensitivity. DXOMark calls this the 'saturation ISO', I believe. They express it in ISO terms, currently.
Digital gain available - in the future, I don't see a reason to cap the digital gain that's available. You'll just need to know that if you apply 10EV of digital gain you're likely to have a resulting image that consists mostly of a combination of white pixels and noise, but why artificially cap the gain?
Actually, as I've stated elsewhere, my camera warns me when I'm about to overload its sensitivity. It does that in realtime, allowing me to adjust shutter speed and aperture down until I've reached an exposure that won't overload its sensitivity. I think this is the direction things will continue to move in.
No, why?
I'd like to see manufacturers communicating the saturation sensitivity of their sensors, as DXOMark does, currently. Olympus labels the base ISO on my E-M5 as ISO 200, but the actual saturation sensitivity, according to DXOMark and expressed in ISO terms is 107.
Even if my camera didn't show me the highlights I was about to blow, I could use this saturation sensitivity to calculate optimum exposure values. That's all you need, especially if your sensor is ISOless, and you only have a single saturation sensitivity to keep in mind.
texinwien
Senior Member
I said it's useless assuming you have an ISOless sensor. I've said elsewhere that the sensor on my camera is ISOful up to 800.
Are you being obtuse?
Tan68
Veteran Member
Well, I was confused as well. You previously stated you operated with ISO-less concept. Based on this, I also presumed (inferred is the better word) you shot at base ISO.
The last several posts you have varied between barely ISOful and mostly ISOless. You might have to be a little forgiving of confusion.
I think JTC111's question is not a bad one. It sounds like many cameras are still barely ISO-ful. A lot of the argument here relies on JTC111 having an ISO-less camera. I have an only partially ISO-less camera. This is a thing yet to come.
Let's think about this a bit. This is what you do when you're about to overload its sensitivity.
What do you do when you are about to undershoot sensitivity? Undershooting sensitivity has consequences, too, including noise and loss of shadow detail.
--
Jeff
http://www.flickr.com/photos/jck_photos/sets/
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JTC111
Leading Member
You say its useless but you use it. And you refuse to explain why you use this useless tool.
One of us is certainly being obtuse ...and it ain't me.
bobn2
Forum Pro
Two errors here. One is that ISO is not gain. ISO is simply the relationship between exposure and tonality in the final image (for digital defined as a number in a sRGB file). It's a mapping between two dissimilar quantities, exposure in lux seconds and 'lightness' as a position of a defined scale of 'lightness'. The ISO standards say nothing about how that mapping is achieved, analog gain may be a part of it, or it may not.
Secondly, increasing the ISO does not either in theory or in practice introduce noise. There is a popular opinion that 'ISO noise' is casued by 'amplifier noise' but this simply isn't true. For the most part, ISO noise is simply photon shot noise made visible, because low exposure regions of the image are being mapped to more prominent levels of brightness.
In fact, what you are coming close to is the ISOless way of seeing things. Since the major determinant of noise is exposure (more exposure, less noise) then the aim of exposure management is to maximise exposure in order to minimise noise, rather than to achieve 'correct' exposure for some predecided ISO setting.
--
Bob
bobn2
Forum Pro
What would you mean by 'undershoot it's sensitivity'? The aim of exposure management to minimise noise is to maximise exposure, but that has to be subject to your pictorial constraints, DOF, motion blur and how much light you have available. Whether or not the outcome of that maximised exposure is acceptable depends in part on the distance between the brightest parts of the image and the noise floor (known as the dynamic range).
Even if a company introduced a 23EV sensor tomorrow, which would create what you are calling an ISOless sensor.
Until all output media matches the 23EV of the sensor, where the midpoint of the exposure in terms of the output media will need to be set.
So if I am shooting a JPG photo I might want the bottom 8EV of that 23EV sensor represented by the 8 bits of my JPG file. I need to be able to tell the camera to do that.
ISO settings are the most familiar tool available to photographers to choose that point.
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texinwien
Senior Member
I'm not so sure about that. In practically every discussion of ISO that I see, a number of people who are obviously confused about ISO generally pop in and make their confusion well-known.
Excellent - I'm glad you found my explanations enlightening.
Only if you're shooting RAW.
I'm not saying you should be kept from setting a target gain up front, but you shouldn't be forced to do so, it should be possible to change that target gain after the fact, and novices shouldn't be required to factor it into their thinking when preparing to capture an exposure.
Give them two variables to think about (shutter speed and aperture) rather than forcing the third one on them, as well.
What's right with it, especially if it causes so much confusion?
I'm sorry, what? How would the changes I describe be to the benefit of smaller, more noisy sensors? Please explain
This is theoretically and practically incorrect, and shows that you haven't yet understood today's lesson about ISO, unfortunately.
Well, you're wrong on this front. I know several full-frame camera shooters who have the same complaints about ISO that I have.
Again, please be specific about how such a change would benefit crop-sensor cameras more than it would benefit full frame (or medium format or any other format) cameras.
I'll save you some time and tell you it won't, in any way. Feel free to make your case if you continue to disagree.
Again, what recognizable benefits would the owner of a crop sensor camera get that the owner of a D3S wouldn't? The answer is still 'none'. Feel free to offer concrete examples if you disagree.
I know another D3S user whose knowledge of the physics behind photography far outstrips mind, and he makes the same case against ISO that I do. The ISO model offers no benefits to full frame shooters that it doesn't offer to crop sensor shooters. Switching to something more logical would offer no benefits to crop sensor shooters that it wouldn't offer to full frame shooters, either.As a user of mostly three full fame cameras, including a Nikon D3S, I see no issue with the current method of describing gain.
You're just wrong on that count.
You're an excellent example for why ISO should be done away with and replaced with something more intuitive. It's quite obvious that you have a very tentative understanding of ISO. It's obviously a confusing topic to you, based on your words in this post. If the topic is confusing to someone like you, who obviously has a lot of experience with photography, well, I can't think of a better proof that we need to replace it with something more intuitive.So, for most people, I don't see any reason to change how we describe an effect which looks and acts the same for both sides.
Guidenet
Forum Pro
Hey Bob. I'm not sure you can go on much of the old film texts. Many of my old texts taught only aperture and shutter duration were the only two things which contributed to exposure, but a lot of that was changed by Fred Archer and Ansel Adams when they codified The Zone System in 1938, making the calculation of exposure much more accurate. We now considered scene subject luminosity in the same stops we used for the other two. We had to properly interrelate this in our exposure calculations and we did much better for it.Bobn2 wrote:
No, it's correct. The definition now used concurs with all the classic sensitometry texts, including my old Focal (Ilford) Manual of Photography, which I had before the Web existed. the present definition is definitely not something thought up by Wikipedia, it is the correct and science based definition of exposure.TTMartin wrote:
Interesting how that Wiki article has been manipulated through the years, to imply that photographic exposure has nothing to do with the photographic medium. It has been changed from a definition of photographic exposure. To simply one of light exposure, which is incorrect.texinwien wrote:
That's the wrong formula. It's an artificial formula built specifically to tell the photographer how to adjust the exposure values (aperture, shutter speed, scene luminance) to match the ASA / ISO.clack wrote:
APEX camera exposure equation:
A: relative aperture (f-number)
T: shutter speed in seconds
B: average scene luminance ("brightness")
Sx: ASA arithmetic film speed (ISO goes here)
K: light meter calibration constant
K is a constant, B is not part of the camera settings.
This leaves the camera operator - or, camera control chip - with A, T and Sx.
Voila, the exposure triangle is part of 'the' exposure equation...
Exposure (photography)
In photography, exposure is the amount of light allowed to fall on each area unit of a photographic medium (photographic film or image sensor) during the process of taking a photograph.
Note: Nothing about ASA or ISO above, and neither ASA nor ISO have any effect on the amount of light allowed to fall on each area unit of a photographic medium.
Exposure is measured in lux seconds, and can be computed from exposure value (EV) and scene luminance in a specified region.
What's EV, and how do we calculate it? Let's see:
Exposure Value
EV corresponds simply to a combination of a shutter speed and an aperture setting, independent of any ISO setting—independent even of whether there is film in the camera or any light available.
...
So, Exposure can be computed from scene luminance and EV (which, in turn is computed from the shutter speed and aperture setting). This leads us back to my previous post - the only 3 variables involved in the equation used to determine photometric exposure are scene luminance, shutter speed and aperture setting (or t-stop to be extra technical).
From the Exposure article linked above, this is the equation (photometric / luminous exposure) you need:
Hv is the exposure, Ev is the image plane illuminance (determined by the scene luminance and aperture setting) and t is time (aka the shutter speed).
et voila, APEX isn't the equation used to determine photometric exposure. It's simply a formula that photographers can use to adjust the three variables that make up the photometric exposure equation - shutter speed, aperture and scene luminance (where possible) - based on a given ASA or ISO.
--
Bob
Also, the Zone System taught us the importance of processing and how we treat the sensitivity of both film and paper is also a consideration of the whole exposure process. We learned about temperature and timing and how they also contributed. We learned that even the level of contrast in our paper made differences we never expected prior to that.
So, I understand what you're saying and it makes sense from your view, but I think the entire concept of exposure is much less simplistic in real world conditions and there's still a place for those who wish to meter and place items on their zones. There's also a place for considering processing functions as part and parcel of their exposure procedures whether in my wet darkroom or digital darkroom.
Take care and have a great afternoon.
--
Cheers, Craig
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I reserve the right to make mistakes in reasoning and logic as well as to change my mind anytime I wish. I also ask forbearance with respect to my typos. Please take a look at my gallery here at DPR.
texinwien
Senior Member
I said it is useless on an ISOless sensor. I said my sensor is not completely ISOless, but many new ones are, and, I think most will be at some point in the near future.
Not sure what's so hard for you to understand about that. It's completely clear and logical.
Until all output media matches that of your theoretical ISOless sensor, where the midpoint of the exposure in terms of the output media will need to be set.texinwien wrote:
Think about how you'd operate if you only had a single ISO. If everything but base was created via digital amplification.TTMartin wrote:
So analog gain of the sensor changes the sensors ISO, but, digital manipulation of the image of the image after capture doesn't?texinwien wrote:
As I posted elsewhere, my camera is ISOless above ISO 800. It has ISO settings up to 25,600, but since it's ISOless above 800, I ignore the higher settings.JTC111 wrote:
Two questions:texinwien wrote:
It's already not necessary on some cameras. On my current camera, I almost always shoot at base ISO. I ignore the ISO completely.
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
If you " almost always shoot at base ISO," as you've stated in at least two different posts, then you occasionally do adjust your ISO setting, right?
I can agree with that.
As a RAW shooter, I also only use ISOs that are created by analog amplification of the sensor. I have partial ISO steps disabled in my camera, and do not enable the expanded high ISO.
So if I am shooting a JPG photo I might want the bottom 8EV of your theoretical ISOless sensor, represented by the 8 bits of my JPG file. I need to be able to tell the camera to do that.
ISO settings are the most familiar tool available to photographers to choose that point.
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The biggest reason I can think of is because I don't want to apply the gain later on. I want the pictures to be completed in camera so that when I get home, all I have to do is download them to a sub-directory on my hard drive and enjoy a slide show on my monitor.
Possibly, though I doubt that I'm the only JPEG shooter who wants to avoid rather than embrace later manipulation of the images.
texinwien
Senior Member
Which style would that be? I'll tell you - it's the style that, based on the laws of physics, results in the best image quality possible.
Neither do I - where did that come from?
Increasing ISO doesn't increase noise. This is yet another part of the ISO story that confuses so many people, and it's another reason I think ISO should be replaced with a more intuitive concept.
Again, I'm talking about constraining the ISOless sensor to its one and only MOST efficient, native sensitivity. No other constraints are needed. At this sensitivity, you are guaranteed to have the most DR and least noise possible, all other things remaining equal.
I think you're right on the cusp of figuring this out.
It won't be. Abundant dynamic range is not necessary for an ISOless world to make sense.
Clearly you haven't thoroughly thought this out, and at this point are just making wild, nonsensical statements.
I'm done.
Limburger
Veteran Member
With a small sensor you hit the wall quicker and would reveal the benefit what you try to point out quicker.texinwien wrote:
I'm not so sure about that. In practically every discussion of ISO that I see, a number of people who are obviously confused about ISO generally pop in and make their confusion well-known.
Excellent - I'm glad you found my explanations enlightening.
Only if you're shooting RAW.
I'm not saying you should be kept from setting a target gain up front, but you shouldn't be forced to do so, it should be possible to change that target gain after the fact, and novices shouldn't be required to factor it into their thinking when preparing to capture an exposure.
Give them two variables to think about (shutter speed and aperture) rather than forcing the third one on them, as well.
What's right with it, especially if it causes so much confusion?
I'm sorry, what? How would the changes I describe be to the benefit of smaller, more noisy sensors? Please explain
This is theoretically and practically incorrect, and shows that you haven't yet understood today's lesson about ISO, unfortunately.
Well, you're wrong on this front. I know several full-frame camera shooters who have the same complaints about ISO that I have.
Again, please be specific about how such a change would benefit crop-sensor cameras more than it would benefit full frame (or medium format or any other format) cameras.
And going to your final image, on screen or print would anybody notice?I'll save you some time and tell you it won't, in any way. Feel free to make your case if you continue to disagree.
Again, what recognizable benefits would the owner of a crop sensor camera get that the owner of a D3S wouldn't? The answer is still 'none'. Feel free to offer concrete examples if you disagree.
I know another D3S user whose knowledge of the physics behind photography far outstrips mind, and he makes the same case against ISO that I do. The ISO model offers no benefits to full frame shooters that it doesn't offer to crop sensor shooters. Switching to something more logical would offer no benefits to crop sensor shooters that it wouldn't offer to full frame shooters, either.As a user of mostly three full fame cameras, including a Nikon D3S, I see no issue with the current method of describing gain.
You're just wrong on that count.
You're an excellent example for why ISO should be done away with and replaced with something more intuitive. It's quite obvious that you have a very tentative understanding of ISO. It's obviously a confusing topic to you, based on your words in this post. If the topic is confusing to someone like you, who obviously has a lot of experience with photography, well, I can't think of a better proof that we need to replace it with something more intuitive.So, for most people, I don't see any reason to change how we describe an effect which looks and acts the same for both sides.
The final medium I think should be thrown in as well.
JTC111
Leading Member
But it doesn't answer my "why" question. So let's try this another way. You say you vary your ISO settings from 100-800. Why not just leave your camera set permanently at 800 since that would effectively give you the ISO-less camera you very much desire?
texinwien
Senior Member
No, my argument is pure physics. Whether I state it clearly enough or not, it is correct. The physics are on my side. Whether you understand it or not, it is correct, and will always be so, because it is based purely on physics, like it or not.
With this in mind, I suggest that you try to understand why it is correct, rather than fight against it. Your call. I'm trying to be helpful.
Adjusting ISO has nothing to do with whether a camera is ISOless or not. Now I understand your confusion. I suggest that you read up on the topic of ISOless cameras. It's a real thing, not something I made up, and it has nothing at all to do with whether a camera has an ISO setting that's adjustable.
No, that is not correct. Again, please do some research on the topic of ISOless sensors. Your knowledge of the subject is too basic to step into this conversation at this level. Your lack of knowledge is making it impossible for you to make any progress here.
On an ISOless camera, adjusting the ISO will not help you at all. This is not being clever, it is telling you the truth. You may have an ISOless camera with ISO settings from 200-25,600. If the camera is truly ISOless, you nothing by using any ISO other than the base.
Honestly, this is the truth. It's not me being clever. Your failure to understand is yet more proof that the concept of ISO is confusing and not well understood by far too many photographers.
And I'm not saying that to be mean - I used to be in the same camp.
Tan68
Veteran Member
From some of the previous posts, I gathered ISO was being used synonymously with gain. Regardless of technical distinctions. Either twiddle 'ISO' in camera which doesn't exist on a mostly ISO-less camera or twiddle one in PP.
This could be part of the schism here. I believe we have people supporting a school of thought designed to maximize captured light and trying to teach this new school of thought to people that already maximize light captured consistent within constraints of the scene at hand and then fiddled with ISO or whatever it should be called.
ISO-less or partially ISO-ful, we all capture the same light.
From the comments most of us are making, I don't think this group is the type to say 'better set ISO 800 for this job because it is after 8pm' regardless of the conditions at hand. I doubt I will see this group taking pictures of a pot of flowers at 1/1500. Well, this pot of flowers is at rest and hasn't been hurled at someone.
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