grey 18%

[vetrofragile79]

Does anyone know the historical reason why the spot and semispot exposure meters were set to the 18% gray? And why today is 15% to 12.5%? It 's true that a landscape in a quiet sunny day with no clouds in our latitudes 18 reflects the incident light?

[Manfred M]

Short answer, your statement is not accurate.

Please read the following article: http://dpanswers.com/content/tech_kfactor.php

[vetrofragile79]

Short answer, your statement is not accurate.

Please read the following article: http://dpanswers.com/content/tech_kfactor.php

Thank u for the link, as I read the exposure currently do not require (or at most very little) adjustment. The reason for the choice of 18%, according this equation 214.64386 = 162/0.01 = (3200x100) / 12.5 = 25600. is the sunny 16 or 15 ev.
So Nikon, Canon and SEKONIC get 12.5 k to reach the ev 15 (or sunny 16)?

[William W]

. . . as I read the exposure currently do not require (or at most very little) adjustment. . .

I probably use Kodak, Photographic Grey Cards more often than most other photographers. I have a Sekonic Hand Held Light Meter; I also have a couple of Gossen Luna Six Light Meters which still work; I use Canon DSLR. I have adopted the habit of adjusting by ⅓Stop when using either Canon DSLR or Sekonic light meters. I do NOT think that adjustment is ‘necessary in the real world’, because the latitudes of the camera’s sensor could/should accommodate a ⅓Stop error, but it is an easy habit to employ and I just do it as a matter of course.

However, I think that it is important to note two points:
1. There are very few shots that I use a Grey Card.
2. For the shots where I would bring out the card to use – I would usually always tend shoot an exposure bracket of three, maybe five shots anyway.
Which kind of makes the initial adjustment by ⅓Stop, seem a silly practice, anyway.

My point being (and I do understand your question is about the history) but for practical shooting in the real world today, with digital cameras and TTL Meter with a Spot or Centre reading available – it is far more use for the Photographer to understand what in natural and manmade scenes that we encounter closely represents ‘Photographic Grey’ and how many stops to adjust for Subjects and Objects which to not represent ‘Photographic Grey’.
For example: knowing the adjustments for three skin tones (Caucasian; Asian; African) and knowing the relationship to ‘Photographic Grey’ of other elements such as: Building Concrete; Fire Truck Red; Common Asphalt; Lush Green Grass; Clear Blue Sky; typical Brown Tree Trunk . . . etc.

WW

Manfred - thanks for the article.

[Manfred M]

So far as I understand; 18% gray, or middle gray is the half-way point between black and white. It is Zone V in the zone system, as per Ansel Adams work. The actual difference between a 18% and a 12.5% gray is around 1/2 stop.

Frankly, I can't find any definitive answer (but lots of opinions) regarding 12% and 18%, and I am more concerned about getting a decent capture to work with.

Quoting some numbers, the Dutch photographer, Frank Doorhof has published:

0% = -4.5 stops (100% black)
1.1% = -4 stops
2.2% = -3 stops
4.5% = -2 stops
9% = -1 stop
18% = 0 stops (middle gray)
36% = +1 stop
72% = +2 stops
100% = 2.3 stops (100% white)

So we have a 6.8 stop difference between 100% black and 100% whilte, based on our meter readings.

[benm]

So we have a 6.8 stop difference between 100% black and 100% whilte, based on our meter readings.

Then what does it mean when a camera claims to have a 14 stop DR? You now have made me interested enough to go and research this.

[Manfred M]

Then what does it mean when a camera claims to have a 14 stop DR? You now have made me interested enough to go and research this.

I had the same thought and did a bit of hunting around and did not find anything satisfactory. Doorhof basis his work on the assumption that middle gray is 18% and does mention the 12% vs 18% "issue", but has no particular rationale for his choice (other than it seems to work).

If you do find something; please post it.

[William W]

Then what does it mean when a camera claims to have a 14 stop DR?

Not really related to Manfred's Chart.

The table which Manfred posted is an ADJUSTEMENT table of stops.

For example: if one were metering a 'black-black' Subject with the Light Meter (for example a Photographic Black Card as opposed to a Photographic Grey Card), one would have to stop down 4.5 stops for that Subject to appear the correct tone in the final image.

The Dynamic Range of a camera's sensor will allow the camera to capture a range of EV (Light Values / intensities of the illuminating light) in any scene - for example from shadows to highlights.

Does that make sense?

WW

[William W]

Expanding:

Let’s say we have a black-black dog and we are photographing him in direct front lit sun (EV15), when we point the Light Meter at him it will give an exposure setting of about:
F/3.3 @ 1/100s @ ISO100.

Now we know that MUST be wrong. The reason is the light meter is calibrated to read the black dog as a grey dog and therefore will give an exposure to render the dog as grey in the final image.

So that’s where Manfred’s Table comes into play – we must stop down about 4½ Stops (F/16 @ 1/100s @ ISO100) to ensure the correct exposure for the Black Dog.

BUT the SCENE where the dog is located might have darker, less lit areas under the trees in the middle-ground and those darkest shadow areas might be EV 6. So that is a DR in the scene of 9 Stops (i.e. 15-6), so we would think that a camera with a DR of 14 Stops would be able to record that scene OK.

*

However – if there is any ‘relationship’ between Manfred’s Chart for light meter reading corrections and the DR of the camera is –

Taking the above scene as the example again; when there is a white-white cat and also a black-black dog in the shadows of that scene and we still expose for the black dog IN THE SUNLIGHT – it will be easier to ‘see’ the detail of white cat in the shadows than to ‘see’ the details of the black dog in the shadows.

WW

[ajohnw]

Then what does it mean when a camera claims to have a 14 stop DR? You now have made me interested enough to go and research this.

When dynamic range is usually quoted it's often what the camera manages to put into a jpg. Some reviews also look at what can be obtained from raw.

14bit usually refers to the analogue to digital converter used to read the values from the sensor. From what i have seen it's doubtful if any camera really captures a fully usable 14 bits. I bit is related to 1 stop because bit counts double for each level of precision eg 0,1,2,4,8,16,32,64....................... would be said to be 7 stops - the argument is full of holes though as it doesn't relate to what we should see for each stop increase.

Johm
-

[Colin Southern]

Frankly, I'm not sure where Frank D is getting his data from, but I challenge anyone to find a real world black that's much more than 2 stops down from middle gray.

[loosecanon]

Measuring with a lightmeter is still a valid way when setting up to measure contrast and lighting ratios. In the studio it helps to set the camera on digital, expecially when using studio flash.
Not sure why with digital one would wish to reduce exposure by having a darker grey as a mid tone, after all the aim is to minimise noise which means expose to just avoid clipping highlights.
In the days of film one could of course develop monochrome so as to maximise the contrast without clipping highlights or blocking shadows - ah the joys of pan F and printing with a grade 1 paper.

Now the grey card or its equivalent is very useful to set white balance, and the tri targets are good when aiming to reproduce colours and tonal scale as accurately as possible.

[William W]

Frankly, I'm not sure where Frank D is getting his data from, but I challenge anyone to find a real world black that's much more than 2 stops down from middle gray.

I agree about the inaccuracy of the numbers.

I'd use about 3 Stops for 'Black-Black' - but I quickly add that there is not very much in the real world that is 'Black-Black': and as I already mentioned there is a latitude in the DSLR sensor anyway, for example I know that I can go ⅔Stop overexposed and still be safe 99% of the time - although going underexposed is not really a good idea at any time, usually.

***

I think that Frank (and I haven't researched the author 'Frank Doorhoff’) might be making the fatal flaw of trying to ‘fit in’ and ‘equate’ the Zone System (applicable to negative film) to the Digital Sensor.

***

Other numbers that I use for Canon EOS 5D Series DSLR TTL Light Meters:

Tanned Aussie beach goers’ Caucasian skin: Open ⅔Stop
Range of fair “peaches and cream” Caucasian skin: Open 1⅓~1⅔Stop
Light aboriginal/ native skin: 0 Stop
Rich aboriginal/native skin: Close 1 Stop
Deep-dark Aboriginal/native skin: Close 2 Stops
Rich Asian Skin: Close ⅔Stop
The palm of my own hand: Open 1 Stop

Lush Green Grass: 0 Stop
1970/1980 Architects’ hideous concrete buildings (not stained): 0 Stop
Fire truck red colour of my car duco: Close 1⅓ Stops

It is fairly easy to make your own list of common items that you have around your particular area or that are often included in your shots – notice that my list is biased to different skin types, because I photograph a lot of people - additionally there is often grass around where I shoot; I travel by my own car; and the is often one of the hideous concrete building around.

WW

[Colin Southern]

I agree about the inaccuracy of the numbers.

I'd use about 3 Stops for 'Black-Black' - but I quickly add that there is not very much in the real world that is 'Black-Black':

I agree - probably only something like black velvet.

although going underexposed is not really a good idea at any time, usually.

I'll often do it in the studio about 1/3 stop (foreground) when shooting a white background so that when I adjust things up again in post, it gives me a clean/solid white background. Having said that, there's not much difference doing it that way -v- over-exposing the background slightly. For black backgrounds I'll over-expose the foreground slightly so it helps clamp the background down when adjusted in PP. Generally in the studio I'll be shooting at ISO 100 with known good lighting, so I know I'll have many extra stops to dig into if I really need them for some reason.

[William W]

. . . yes, good points about the unders and overs in the studio.

Understood.

The studio is 'controlled'. A good driver knows just how far to push before the understeer or the brake fade begins.

Though film, in the studio, was much more forgiving!

Have a great evening.

[vetrofragile79]

If I shoot a picture in a black night as a reference spot a gray kodak 18% (+ or - 1/3 stop increments), the resulting pic will be much brighter than how my eyes have seen, this is because the exposure they say : this is the right time/aperture to have the famous 15 ev or 3200 or sunny 16

[William W]

If I shoot a picture in a black night as a reference spot a gray kodak 18% (+ or - 1/3 stop increments), the resulting pic will be much brighter than how my eyes have seen

Yes I think I understand what you are saying.

But the resultant pictures will not really appear brighter than what your ‘eyes have seen’ – but will appear different to how your brain interpreted the scene. When we look at a scene with our eyes – the eyes actually do very little work in so far as making the ‘picture’ for use – our eyes are not really like a camera at all. Our brain messes up all the information we get and makes the scene quite dissimilar to how a lens, camera and film/sensor would record the scene.

WW

[vetrofragile79]

I fully agree, the human visual system (eye / brain) is very different from the camera's sensor, i wrote the previous post to simplify the concept and keep the focus on the "main road". I was interested to know the reason why the exposure meters are set on 18% and the link seems to be clear: sunny 16 or 15 ev aka 3200 candles. So if the spot meter is pointed to surface reflects about 18% of the incident light will return a couple time/aperture that results like the pictures it was a day with lighting of 3200 candles.

[Manfred M]

If I shoot a picture in a black night as a reference spot a gray kodak 18% (+ or - 1/3 stop increments), the resulting pic will be much brighter than how my eyes have seen, this is because the exposure they say : this is the right time/aperture to have the famous 15 ev or 3200 or sunny 16

The sunny 16 rule (one I had never heard of before I joined CiC) applies only to 2 hours after sunrise and 2 hours before sunset at mid-latitudes (between the Tropic of Capricon and Tropic of Cancer?); so it doesn't work up in the Northern parts where a lot of photographers live.

The problme that you are seeing is that a camera's lightmeter is a reflective light meter and tries to make everything look middle gray. Take an image of a white object, gray object and black object, and with a reflective meter your camera will try to make them all look the same. If you used an incident light meter (i.e. measuring the light falling on these subjects), you will get these objects looking white, gray and black.

This is the reason that cameras have an exposure compensation control when one shoots in anything other than manual mode. Without compensation, night scenes tend to look brighter than when you shot them and light ones; snow scenes, for example, will look a lot more gray than they really are.

[vetrofragile79]

The answer is in the formula mentioned in the article that you've linked: to set the exposure on about 18% they put the value of 3,200 candles, which equal to 15 ev which is the sunny 16.

The spot meter or semispot when pointed at a surface 18% reflection it will always return a pair shutter speed / aperture required to give a 15 ev (circa) . Both night and day, both on snow in a cave .. always that value. is called "exposure technically correct" exposure compensation serves to bring exposure to your aesthetic taste and is usually called: creatively correct exposure. Each of us will compensate in a different way because we have different eye / brain and personal tastes.

I apologize for my English, I hope you understand.