A proper exposure

[ir0nma1den]

This is embarassing, but what dictates a perfect exposure?

What I mean is when I shoot, I tend to eyeball the exposure until I don't have any overblow highlights. This is not a technical method, and I'm starting to believe that it is not optimal for retouching.

Say that I have a beauty dish as a high key and I want to get a perfect exposure, so I meter for the highlights, correct? When I meter the highlights, what value am I looking for in order to get a "correct" exposure?

[Tony W]

I feel that the answer to what dictates a perfect exposure is simply the one that produces the final luminosity value that you want to see in your print or on screen for the object you are photographing. This may be quite a departure from the reality of the scene and will depend on how you visualise the final result.

Checking the histogram in camera (I assume you are talking digital here!) and making sure that you are not clipping any RGB values can be very useful. Although you need to be aware that what you are seeing with most (if not all) cameras is a histogram based on a jpeg preview - the cameras RAW file may have a little more headroom relating to clipping.

As far as metering for the highlights remember that all meters either in camera or hand held are dumb instruments they just do not know what the object is - it may be a black cat in a coal cellar or snow covered mountain!. The meter will generally give you an exposure value that will produce a mid grey.

So unless your subject just happens to be this mid grey, or you want to record it as such you will need to adjust the camera exposure to compensate. In the case of a highlight where you want to retain detail you may find it beneficial to open from the meters suggested setting by 2 f/stops to record the value correctly e.g. meter suggest f/11 open up to f/5.6.

While some corrections can be made in PS it is always better to get it correct in camera

[ir0nma1den]

Originally Posted by Tony W

So unless your subject just happens to be this mid grey, or you want to record it as such you will need to adjust the camera exposure to compensate. In the case of a highlight where you want to retain detail you may find it beneficial to open from the meters suggested setting by 2 f/stops to record the value correctly e.g. meter suggest f/11 open up to f/5.6.

Wouldn't opening up two stops produce overblown results? In digital, aren't slightly underexposed shots preferred?

[andrewrodney]

Before we can discuss proper exposure, the question has to be, are you capturing raw or JPEG? The two are not the same. A properly exposed JEPG is an under exposed raw due the vast differences in the data. See:

http://www.digitalphotopro.com/techn...g-for-raw.html

As you’ll see, the exposure information from the camera is based on the JPEG not the raw data.

[Tony W]

Originally Posted by ir0nma1den

Wouldn't opening up two stops produce overblown results? In digital, aren't slightly underexposed shots preferred?

If you meter an important highlight area where you want to retain detail/texture and use the meters suggested setting you will record that value as a mid tone i.e. you will have underexposed in the case of a very light or white object. Or in the case of a very dark subject you will have overexposed. Meters tend to average the brightness of the reflected light they see to give an exposure that will print as a mid grey (around 12% approx. i.e. 1/2 stop less than a 18% Kodak grey card)

While you can recover underexposed shots in post you run the potential risk of a. losing shadow detail and b. increasing noise in lower density areas - which may or may not be important depending on your subject matter.

By opening up the f/stop or decreasing shutter speed you are attempting to 'place' an object value where it should be (or where you want it to be in the histogram) to record at the lightness value you desire in your print.

You can easily check out how your meter interprets light by shooting three frames. Set your camera to one of its automatic modes and:
1st frame fill the viewfinder with an evenly lit very light surface and fire off a shot
2nd frame same but fill frame with a middle grey surface
3rd frame same settings but fill frame wih a very dark surface

When you examine these you will see that they are all very close in value and only the 2nd frame will actually be close to the actual object.

Read the article in Andrews link for a more thorough explanation

[ir0nma1den]

Originally Posted by andrewrodney

Before we can discuss proper exposure, the question has to be, are you capturing raw or JPEG? The two are not the same. A properly exposed JEPG is an under exposed raw due the vast differences in the data. See:

http://www.digitalphotopro.com/techn...g-for-raw.html

As you’ll see, the exposure information from the camera is based on the JPEG not the raw data.

I always shoot in RAW, either in a studio setting or an onlocation shoot with strobes.

[ir0nma1den]

Originally Posted by Tony W

If you meter an important highlight area where you want to retain detail/texture and use the meters suggested setting you will record that value as a mid tone i.e. you will have underexposed in the case of a very light or white object. Or in the case of a very dark subject you will have overexposed. Meters tend to average the brightness of the reflected light they see to give an exposure that will print as a mid grey (around 12% approx. i.e. 1/2 stop less than a 18% Kodak grey card)

While you can recover underexposed shots in post you run the potential risk of a. losing shadow detail and b. increasing noise in lower density areas - which may or may not be important depending on your subject matter.

By opening up the f/stop or decreasing shutter speed you are attempting to 'place' an object value where it should be (or where you want it to be in the histogram) to record at the lightness value you desire in your print.

You can easily check out how your meter interprets light by shooting three frames. Set your camera to one of its automatic modes and:
1st frame fill the viewfinder with an evenly lit very light surface and fire off a shot
2nd frame same but fill frame with a middle grey surface
3rd frame same settings but fill frame wih a very dark surface

When you examine these you will see that they are all very close in value and only the 2nd frame will actually be close to the actual object.

Read the article in Andrews link for a more thorough explanation

I understand now, thank you. This is really eye-opening, I did not know that the meter exposes for midtone values.

So lets say I am shooting a model with a beauty dish and I want to retain the detail in highlights on her forehead without underexposing the image. I use spot meter on the forehead and then find the suggested exposure, increasing that exposure by 1-2 stops, correct?

[Tony W]

From your first post I made some assumptions that you were using a reflectance type meter, either metering in camera or a seperate hand held meter to measure the light reflected off your subject.

As you are now aware these meters generally give a reading that is close to a midtone regardless of the actual luminosity value of the object you are pointing the meter at, therefore you will need to apply a correction to the given reading to compensate and place the object value where you want it - so in the case of an important highlight where you want to retain texture and detail opening up between 1-2 stops should place the area read by the meter more accurately to the right of the histogram. You will still need to keep an eye on clipping other areas and as pointed out in Andrews article this is difficult to do just relying on the camera lcd as the histogram info. is based on a jpeg preview. So a little experimentation and interpretation will be required if you are relying on the camera lcd.

Your last post mentioned a beauty dish and spot metering therefore I assume the beauty dish is a continuous light source not flash lighting and you are using your spot meter to measure the reflected light of the area of interest in this case the forehead? If this is the case then the above suggestion should be helpful in getting the 'correct' exposure. On the other hand if you are actually using flash as your light source many photographers prefer to use a flash meter in incident mode where you actually measure the light falling on the subject and in most cases the exposure shown by the meter will be correct for the subject matter.

[andrewrodney]

Reflective meters are kind of dumb in that they look at a black cat on coal and see a gray cat. Or a white dog on snow and see a gray dog. The same issue applies to skin! If you understand that, then your suggestion to open up two stops works fine. In fact you can turn your hand into an incident meter this way. That said, an incident meter is ‘smarter’ in that it measures the light falling on the subject. After all that is said and done, both kinds of meters are built for film, not linear capture of raw data. That’s why if you use either, you’ll get a fine JPEG exposure which is under for raw.

[kav]

Originally Posted by ir0nma1den

I understand now, thank you. This is really eye-opening, I did not know that the meter exposes for midtone values.

So lets say I am shooting a model with a beauty dish and I want to retain the detail in highlights on her forehead without underexposing the image. I use spot meter on the forehead and then find the suggested exposure, increasing that exposure by 1-2 stops, correct?

You're shooting with strobes. You can get a meter that also takes incidental readings rather than relying solely on the one in camera (ugh). They still vary, but that is why you just test it against your camera. Make sure it's appropriate for flash too as opposed to something like a cine meter, and make sure it can fire off pocket wizard controlled strobes without an additional connection. This stuff just takes a little testing.

[Tony W]

Sorry but I missed the point in post #6 where you said you shoot with strobes in the studio or on location

You suggested that you used a spot meter 'I use spot meter on the forehead and then find the suggested exposure', could you go into a little more detail e.g. make and model of spotmeter and how you actually use it to measure exposure?

[ir0nma1den]

Originally Posted by Tony W

Sorry but I missed the point in post #6 where you said you shoot with strobes in the studio or on location

You suggested that you used a spot meter 'I use spot meter on the forehead and then find the suggested exposure', could you go into a little more detail e.g. make and model of spotmeter and how you actually use it to measure exposure?

In my beauty dish scenario, I am using strobes (elinchrom) and reading the metering that my in camera meter (Nikon D300) is giving. When I say spot meter, I mean using the spot meter function, taking a reading from the meter, and adjusting my aperture and shutter speed to expose 1-2 stops above the suggested reading.

[ir0nma1den]

Originally Posted by kav

You're shooting with strobes. You can get a meter that also takes incidental readings rather than relying solely on the one in camera (ugh). They still vary, but that is why you just test it against your camera. Make sure it's appropriate for flash too as opposed to something like a cine meter, and make sure it can fire off pocket wizard controlled strobes without an additional connection. This stuff just takes a little testing.

What do I do if all I have is the internal camera meter?

[ir0nma1den]

I think I'm beginning to understand the internal camera meter. Since it is a reflective meter, some of the light directed towards the model is being absorbed, while the larger portion is being reflected back towards the camera. Since we are only measuring the reflected light, we are essentially "losing" light, which is why we increase our exposure.

It's either that, or since the camera attempts to meter for neutral gray, it treats any tone as gray and gives a proper exposure for neutral gray regardless of the actual tone. So if we are metering for highlights we want to increase exposure, and if we are metering for shadows (blacks) we decrease exposure.


While we are on this topic, another question came to me. I also shoot video with a hacked GH2 on the highest settings (1080p @24fps). I know this isn't technically RAW data, but would the same exposure trick work here too?

[kav]

Originally Posted by ir0nma1den

I think I'm beginning to understand the internal camera meter. Since it is a reflective meter, some of the light directed towards the model is being absorbed, while the larger portion is being reflected back towards the camera. Since we are only measuring the reflected light, we are essentially "losing" light, which is why we increase our exposure.

Stop right there. You are describing the reflective behavior of skin. It's not so much absorbed anyway. The issue is more one of subcutaneous reflection and sometimes mild translucence with thin areas like the ears (note how they tend to glow with heavy backlighting. The problem described is that skintones vary in reflectivity and density as influenced by porous texture, oil on the surface, melanin, and a few other things. You should be balancing to the light falling on skin rather than try to guess its properties. Otherwise you're just trying to make everyone the same color or compensating by guessing. You're using a beauty dish so you should be balancing a primary point of focus then adjusting lighting to get the correct falloff without creating shadows so deep that they start to go noisy with the rest being pushed to post after that point. If you start making up fake physics and bad napkin math, you're just going to make the problem worse.

Originally Posted by ir0nma1den

What do I do if all I have is the internal camera meter?

You end up testing and guessing. This means that you test different skintones for how many stops you should compensate above or below for a good exposure. If you're using strobes on someone with reflective skin, you should probably be careful what part you use for metering. Big shiny skin reflections are going to influence it. It is important that you stop making up bad math though.