Medium grey and luminance level : experts and scientists help me!

superflash · Sep 28, 2017

Hello everyone.
Is there someone that know what is the ev value (or the luminance level) that correspond exactly to middle grey tone?
I know that it is variable, depends on iso (we can fix it to 100) and constant calibration (ex. 12,5 for rfelected light ).
But once I fix iso and constant calibration , whic value must assume EV to obtains a perfect middle grey pic?
Or in other words, once I point my spot meter to an homogeneous surface, what EV value I should have to consider the surface as middle grey?
Thank you to all those who will be able to help me.

markbarendt · Sep 28, 2017

superflash said:
Hello everyone.
Is there someone that know what is the ev value (or the luminance level) that correspond exactly to middle grey tone?
I know that it is variable, depends on iso (we can fix it to 100) and constant calibration (ex. 12,5 for rfelected light ).

There is no standard middle tone EV. None.

superflash said:
But once I fix iso and constant calibration , whic value must assume EV to obtains a perfect middle grey pic?
Or in other words, once I point my spot meter to an homogeneous surface, what EV value I should have to consider the surface as middle grey?
Thank you to all those who will be able to help me.

So when going direct to positive like with slides, polaroids, and digital; the reading a spotmeter provides will typically render the point you measured in the scene middle grey.

With negative film, where middle grey in the print falls is completely up to the person printing, there is no direct connection to what you may have measured in the scene.

superflash · Sep 28, 2017

markbarendt
Thank you very much. Your response is very useful.
I shoot only slide , no negative.
So also if I would to obtain a slide with a fixed reflectance (for ex 15%) , doens'n exist a method to know final reflectance on slide starting from a measured luminace value on the scene. Is this?
Thank again.

markbarendt · Sep 28, 2017

In a lab you may be able to nail an exact percentage, in a studio you might get very close, but in normal camera work you are chasing unicorns. With slide film nailing a perfect output for every subject means bracketing or scanning and adjusting the slide.

Sirius Glass · Sep 28, 2017

For get medium gray for slides. The exposure latitude is too narrow to mess around with EI and all the loony Zone System testing and "fun and games". Get the exposure correctly by not metering the sky only the subject.

markbarendt · Sep 28, 2017

Sirius is wise.

voceumana · Sep 28, 2017

Except at the extremes of brightness and dimness (?) the eye adjusts to see middle grey as middle gray (and white as white, black as black), so there is no EV that will give you middle grey under varying lighting conditions. An incident light meter is intended to expose the film to adjust for the lighting condition; a reflected light meter requires the human brain to interpret the values and adjust to achieve the required tones.

Bill Burk · Sep 28, 2017

What spotmeter do you have? Do you have an incident meter to compare it to?
For example if you had a Sekonic L758-DR the advice would be different than if you have a Minolta or Pentax spotmeter.

How accurate do you think your camera's shutter is?
For example, my vintage folding cameras have very slow high speeds (I cannot trust 1/250 of a second and think it might be as bad as 1/60), but I trust my 35mm OM-4 to be very accurate.

I do believe a gray card about 12.5% reflectance would be useful, but since most gray cards are 18%, you would be better off not fighting it.

Poisson Du Jour · Sep 29, 2017

I have never heard of an EV for a middle grey; is something else being referred to??

Sirius Glass said:
Get the exposure correctly by not metering the sky only the subject.

This is correct guidance.
Additionally, a mid-tone can be sought out within the scene if it is required, and serial readings of high and low values balanced around that. You can also use a grey card (spot meter from this and lock-in as a mid-tone)
Not all spot meters are calibrated to 18% grey. The Sekonic L758D for example has a baseline 12.6% incident and 16.2% reflected spot.

markbarendt said:
[...] With slide film nailing a perfect output for every subject means bracketing or scanning and adjusting the slide.

Bracketing slide film is more common in the smaller 35mm; it is less common larger formats. In professional experience, I never bracket RVP50 in MF because the methodology for metering and exposure has been worked out many years ago to give predictable, repeatable exposures under many different (and challenging) conditions, that do not require any adjustments in scanning or post. Perfect exposure, according to your needs and experience, is very much possible in-camera. As with everything, trial and error and experience determine how well the results come up.

markbarendt · Sep 29, 2017

Yes, I probably should have included highly experienced, professionally successful, large format work in my list of exceptions. Even there though, the one guy that I personally know that qualifies, always shoots two sheets so that the second can be developed differently if needed.

I do admire the precision you and he work with, y’all are part of a very exclusive and elite club.

darkroommike · Sep 29, 2017

For slide work I have always used a incident light meter and for important work I bracket that reading.

Confucius (famous 12th century photographer) said man with two light meters never knows what his EV is.

superflash · Sep 29, 2017

Here we are. Sorry for delay.
Thank you very much to all. I'm not an expert, so your advices are very helpful for improve my knowledge.
The article that I have read is this:
https://www.handprint.com/HP/WCL/color4.html (the first and central part)
Now I undersand that what I want to know is impossible ( is simpler win to lottery) because variables are too much.
I have a minolta spotmeter and gossen ultrapro with profi-spot but the concepts of "mid" and "grey" are complexes and subjective: we shold consider reflectancy, level of adaptation of human eye, light's cri, color spaces and so on.
So the best way is only experience (not science); if you have other advices to give me I appreciate them a lot.
Thank you again.

markbarendt · Sep 29, 2017

superflash, if you were to say, decide to take a trip to the Vatican, the destination is defined. Once that decision is made you figure out how to get from where you are to the Vatican, and when to do it, and...

Photography is similar. If know what you want as a final result, you can figure out how to get there.

The key there is that middle grey in the final result is reliable and consistent. Your spot meter will naturally try to place whatever you point it at as the middle tone on your slide.

If you point it at a bright white cloud, that cloud will be rendered middle tone. The slide will look dark and underexposed.

If you point your meter at the palm of your hand, and your hand is in the same light as the scene the palm of your hand will be middle tone. The slide will look very close to normal.

Your only real challenge here is picking the proper reference point. Some use their palm, some use gray cards, some use grass, some use their camera bag, it doesn't matter what it is as long as you know how it relates to your slide.

Sirius Glass · Sep 29, 2017

markbarendt said:
superflash, if you were to say, decide to take a trip to the Vatican, the destination is defined. Once that decision is made you figure out how to get from where you are to the Vatican, and when to do it, and...

Photography is similar. If know what you want as a final result, you can figure out how to get there.

The key there is that middle grey in the final result is reliable and consistent. Your spot meter will naturally try to place whatever you point it at as the middle tone on your slide.

If you point it at a bright white cloud, that cloud will be rendered middle tone. The slide will look dark and underexposed.

If you point your meter at the palm of your hand, and your hand is in the same light as the scene the palm of your hand will be middle tone. The slide will look very close to normal.

Your only real challenge here is picking the proper reference point. Some use their palm, some use gray cards, some use grass, some use their camera bag, it doesn't matter what it is as long as you know how it relates to your slide.

Good advice. I used the palm of my hand for decades when I was shooting slides and we know that slides have to be bang on the exposure or they are useless.

wiltw · Sep 29, 2017

markbarendt said:
If you point your meter at the palm of your hand, and your hand is in the same light as the scene the palm of your hand will be middle tone. The slide will look very close to normal.

Sirius Glass said:
Good advice. I used the palm of my hand for decades when I was shooting slides and we know that slides have to be bang on the exposure or they are useless.

To be precise, if you are Caucasian background, your palm will typically be about +1EV brighter than 'middle gray', so if you pointed your spotmeter at the palm of your hand, the shot would be UNDERexposed by -1EV (when compared to the exposure which accurately records the '18% (middle) gray' at the proper density.

nmp · Sep 29, 2017

superflash said:
Hello everyone.
Is there someone that know what is the ev value (or the luminance level) that correspond exactly to middle grey tone?
I know that it is variable, depends on iso (we can fix it to 100) and constant calibration (ex. 12,5 for rfelected light ).
But once I fix iso and constant calibration , whic value must assume EV to obtains a perfect middle grey pic?
Or in other words, once I point my spot meter to an homogeneous surface, what EV value I should have to consider the surface as middle grey?
Thank you to all those who will be able to help me.

superflash:

eV represents how dark or bright the subject is, not how it is going to come out in your photograph. Once you fix the ISO, any eV number will give you the "middle grey" with the correct combination of shutter speed and aperture. If you have an old fashioned spot meter, you can see that for yourself. Or on this chart on wiki:

https://en.wikipedia.org/wiki/Exposure_value#Table1

The relationship should work unless the camera has inaccuracies in the shutter speed or the aperture. You can check that by taking pictures of a grey card or a wall, taking a spot-meter reading and bracketing around the theoretical shutter speed/aperture combination. Examining your slides for the best "middle grey" as you define it will tell how much to overexpose or underexpose your shots.

:Niranjan.

Bill Burk · Sep 29, 2017

Ok good. You have an incident meter. Use the white dome on the Gossen and treat readings you take with that... as a benchmark.

That will give you the Correct exposure (greatly simplified but good to think of it that way).

Now switch to a spotmeter and experiment with different gray things. You will find that some things get close to the incident reading.

I'd say that's a good experiment for now. Just check things out and see how close you get to agreeing with the Gossen in incident mode. You can learn a lot that way.

Bill Burk · Sep 30, 2017

You don't have to try to get them to read the same. You should instead try to get consistent results and come up with an adjustment "factor" to adjust the reflected light reading for the gray that you metered. That way you can use white, black or any gray for a reference.... the Zone System teaches you to recognize and adjust exposure in reaction to different perceived gray values - so it can be a part of the experience if you are interested.

Sirius Glass · Sep 30, 2017

Sirius Glass said:
Good advice. I used the palm of my hand for decades when I was shooting slides and we know that slides have to be bang on the exposure or they are useless.

wiltw said:
To be precise, if you are Caucasian background, your palm will typically be about +1EV brighter than 'middle gray', so if you pointed your spotmeter at the palm of your hand, the shot would be UNDERexposed by -1EV (when compared to the exposure which accurately records the '18% (middle) gray' at the proper density.

I said that I used the palm of my hand for setting exposures. I never gave directions about how to I did it.

Bill Burk · Sep 30, 2017

Sirius Glass said:
I said that I used the palm of my hand for setting exposures. I never gave directions about how to I did it.

I assumed you always opened up one stop, right?

RalphLambrecht · Oct 1, 2017

superflash said:
Hello everyone.
Is there someone that know what is the ev value (or the luminance level) that correspond exactly to middle grey tone?
I know that it is variable, depends on iso (we can fix it to 100) and constant calibration (ex. 12,5 for rfelected light ).
But once I fix iso and constant calibration , whic value must assume EV to obtains a perfect middle grey pic?
Or in other words, once I point my spot meter to an homogeneous surface, what EV value I should have to consider the surface as middle grey?
Thank you to all those who will be able to help me.

my guess is EV15.

superflash · Oct 1, 2017

Mark Barendt:
thank you very much, yuo are given to me a perfect explanation of how to operate; So I don't need to evaluate neither the reflectancy of every object of the scene. However I prefer Oregon's Rocky mountains, paradise of landscapers, rather than go to Vatican.
Thank you again.

Sirius Glass and Wiltw:
also yours are a very good guidances; yesterday I have tried with my hand but there is a problem because my hand is like that of an albino and its colour temperature vary a lot from shadow to highlight : in this case I have to compensate colour temperature before or after the measurement?
Thank you very much to you.

nmp:
I know very well that table, I have printed it on paper more times. However thank you for the link. Now I still have a question: do exists a method to have on slide the same level of reflectancy yhat is on the scene? If i would obtain it , I should proceed for attempts?
Thank you again for your patience.

Bill Burk:
You made my day! Yes perhaps I have to revise "the negative" (I have it). That system is a goal for negatives but with slide is more difficult, slide don't admit mistakes. But with your advice I can increase my experience. I have 2 exposure meter because with the gossen I measure uniforms subjects with low contrast and thith the spot , it check the scenes with high contrast and details. Your advise is godd for all?
Thanks.

Ralph W. Lambrecht.
Good morning and thank you for your tip, I'll try it soon.

Have a nice sunday and see you soon.

wiltw · Oct 1, 2017

superflash said:
Sirius Glass and Wiltw:
also yours are a very good guidances; yesterday I have tried with my hand but there is a problem because my hand is like that of an albino and its colour temperature vary a lot from shadow to highlight : in this case I have to compensate colour temperature before or after the measurement?
Thank you very much to you..

No need to 'correct for' color tempterature! 'Calibrate' your palm against an 18% gray tonality surface, viewing the difference in reflected light meter reading with your palm vs. with the gray card, it will be about 1EV difference (my palm is +1.3EV different, as measured by spotmeter with 0.1EV increements)

Trask · Oct 1, 2017

When I use a spot meter, either on my M5 or Canon T90, or a handheld Pentax analog, I don't ask myself "what in the scene it Zone V" but instead "what do I want to make Zone V?" As I look at the scene, I look at the highlights and shadows and the main elements of the picture an dmeter a tone that strikes me as being between the darkest and lightest tones -- and, if I want to preserve highlights or get more shadow detail, I open or close appropriately. I could use a grey card as an absolute value when necessary, but in that case I'd use an incident meter (I like the Polaris).

Sirius Glass · Oct 2, 2017

Sirius Glass said:
I said that I used the palm of my hand for setting exposures. I never gave directions about how to I did it.

Bill Burk said:
I assumed you always opened up one stop, right?

Yep, it was especially useful when skiing since I did not have an incident meter then. A light meter would give an exposure that would show the moguls and the shape of the snow with everything else black.

Medium grey and luminance level : experts and scientists help me!

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