EV (exposure value?)

Barney

Barney

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What is the point of this information and how could it help?
 
Exposure value combines the three major exposure settings into a single value to define the overall exposure of the scene. Because of the reciprocal nature of exposure time in stops, aperture in stops, and ISO in stops (which essentially assumes the recording media has no reciprocity failure), you can achieve the same exposure of a given scene with a single Exposure Value regardless of the aperture value, exposure time and ISO settings used within the limits of the camera/lens. In other words, you can meter a scene and achieve a given EV, then by adding 2 stop of exposure time, reduce the aperture size (increase f number) 1 stop and decrease the ISO by 1 stop, the overall exposure *should* be the same because the EV is unchanged. The concept is simplified if you assume a constant unchanging ISO (essentially the case with roll film formats).

Because of this relationship, you can start to assign EV numbers to certain reproducible conditions, and hence for some it makes setting roughly the correct exposure in a hurry a little easier.
 
Barney said:
how could it help?
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You could use it in various ways (and many photograpgers will be able to get away with not using it at all). I can only describe how I sometimes use EV.

It is useful to know the subject brightness range of a scene, so that you can determine whether your recording medium (eg film, paper, or sensor) will be able to record details in the darkest shadows that you want to have detail, whilst not burning out highlights. For black and white film, I would seek to keep the subject brightness range within 6 stops. If the range is greater than 6 stops, there are some processes that can help reduce that range /contrast, such as use of a compensating developer, reducing the development time, etc. If the subject brightness range is narrow, you might decide to take steps to increase the range / contrast, for example by increasing the development time. I know that you are familiar with these concepts, based on your previous postings.

You can work out the subject brightness range without using EVs. For example, if you meter the shadows where you want to have some detail and the meter suggests 1/15s at f/4, then measure the highlights at 1/15s at f/22, that gives a subject brightness range of 5 stops. (because f/4 -> f/5.6 -> f/8 -> f/11 -> f/16 -> f/22 = 5 stops)

You can think of an extra stop of exposure as being the same quantity of increase of light as one extra EV.

Not all exposure meters display EV numbers, but those that do make it just slightly simpler to calculate a subject brightness range because you just need to subtract the EV measured for the shadows from the EV measured.

In this context, the photographer is likely to want to use a spot meter to get those separate readings for shadows and highlights. Also, it's more practical to make use of this information to optimise the film developing regime, when sheet film is being used rather than roll film.

Some large format photographs will record the range of EV settings for each frame, together with the actual aperture and shutter settings used, together with their thoughts on required processing (N, N-1, N+1, etc), either in a notebook or an app. I strive to be that methodical but rarely achieve it (except perhaps in a studio setting) because I find it hard to juggle the camera, notebook or phone app, alongside change my spectacles between reading and distance, and watching out for an incoming wave or an over-enthusiastic dog.
 
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Thank you all for your time and trouble, I think I am starting to get a better understanding of the EV scale and I must say that the charts in Andrews link are a revelation, I think I now understand where the Sunny 16 rule was developed, but there is so much other stuff in there that I might print it off and stick it in my camera bag.
Kevin, thanks for illustrating how the EV differences in a scene can be tied into to my development regimen, as you say I am familiar with the concepts but using them to best advantage is another kettle of fish. On being methodical, I am an abject failure.
 
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Barney said:
What is the point of this information and how could it help?
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Some older cameras also come with adjustments for EV, including my Rolleicord Vb which has a scale of EV 4-18. Many handheld meters can measure in EVs and it's then really easy to juggle apertures with shutter speed for your preferred combination.
 
Peter B said:
Some older cameras also come with adjustments for EV, including my Rolleicord Vb which has a scale of EV 4-18. Many handheld meters can measure in EVs and it's then really easy to juggle apertures with shutter speed for your preferred combination.
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That's one of the situations where I noticed EV Peter on my Minolta V meter, I just happened to switch over a button which was labeled EV and was faced with a whole range of F stop and speed combinations, so much so that it gave me shutter speeds for F stops lower than 1 which I did not think was even possible !

I was also surprised that the light in my living room with a low watt bulb is only Ev 2.5
 
Barney said:
it gave me shutter speeds for F stops lower than 1 which I did not think was even possible !
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Rare, but not impossible. f/0.95 lenses are 'relatively' commonplace (as in you can buy one new right now) and Zeiss famously made a 50mm f/0.7 lens for NASA in the 1960s: Stanley Kubrick used three of them when he was filming Barry Lyndon to capture scenes that were lit only by candlelight.
 
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The theoretical maximum is f/0.5, which is easily proved and equally easily denied by those who confuse mirrors and lenses. I gave the proof once, and was shot down because a parabolic reflector does a better job... Since then, I've avoided giving the reasoning on things, and just made bare assertions.

I will make one caveat, in that one aberration if not corrected will allow greater light than the aperture should. Look it up if you want to know more - that way I avoid flak.
 
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You might find it interesting if you have a warped mind, to lookup aperture scales to see where the numbers came from. Or not, as the case may be.
 
StephenM said:
You might find it interesting if you have a warped mind, to lookup aperture scales to see where the numbers came from. Or not, as the case may be.
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My mind has been warped for a week now, suffering from covid/flu and can hardly think straight, no way I can focus on a book or look through a viewfinder!
 
Jammy Dodger said:
Hasselblad used EV on their lenses for the 500 series cameras.
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Using EV values with a manual light meter is really simple because you only have to deal with one number. If I dial in the EV on my Rolleicord I have all the possible shutter speeds and aperture values ‘locked in’ without having to change them independently. I wish all non-metered cameras had an EV option.

Having the EV option on my (gone but not forgotten) Hasselblad 500 was one of the big selling points after using them on my Rollei. Well…that and the stupid idea that carrying a Hasselblad would somehow make me a half decent photographer and much more attractive to women. Sadly, it seems Hasselblads only make you more attractive to other middle aged men with a passion for leaf shutters.
 
Musicman said:
Rare, but not impossible. f/0.95 lenses are 'relatively' commonplace (as in you can buy one new right now) and Zeiss famously made a 50mm f/0.7 lens for NASA in the 1960s: Stanley Kubrick used three of them when he was filming Barry Lyndon to capture scenes that were lit only by candlelight.
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I had a Voigtlander 25mm f0.95 for MFT. The widest I've had for FF is f1.1, if it was actually that. I have f1.2's that I believe. Sony claim that the widest aperture which can be used on their A7 series cameras is f0.63. I believe that 10 Zeiss 50mm f0.7's were made and as above Kubric bagged 3 for movie making.
 
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I found it very useful in calculating how off (in stops) my shutter speeds on are my LF shutter. With this information I can make adjustments to decide if I want to correct it
 
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