The histogram is oddly enough overlooked, not paid attention to or misunderstood, but if used right extremely helpful. I consider it one of the most powerful tool in my camera. It displays the luminance distribution that shows how many pixels of a particular brightness exist in the picture, in other words a graph of the tonal distribution.
Some people will tell you “every good photograph must have a nice even histogram”; I say find someone else to pay attention to, such advice makes no sense. As my Photo Hero Ken Rockwell says, “The best way to evaluate exposure is to look at the picture, not a histogram”. Remember that histograms is not representative of the final image on DSLR’s, but merely an impression of the image monitored on the screen. The reason behind this is that the histogram will differ from the result, based on aperture setting, etc. Most times is the histogram just the perfect measuring tool, but not in all situations. Flash photography or in cases of low intensity, such as night sceneries, are they mostly worthless.
Word of warning
Sony Alpha A99V has two sets of histograms. One the monochrome, which display prior to recording and the RGB displayed on playback. Use the single monochrome as a guide; do not make them rule you, as they ARE often misleading! Monochrome histograms can indicate correct exposure while coloured areas can be overexposed. If you want an expanded explanation then read Ken’s elaborate arguments. Should you want to look into RGB histograms, Ken has a written a wonderful guide here as well.
How the Monochrome Histogram Works
The way that the histogram works is that is breaks up the pictures in pixels, forget about colours, it is all about tonality. All the black pixels is then organized and stacked to the left, all the white pixels stacked to the right and all the pixels on equal tonality in the middle, showing you a quick graph. The camera is measuring this in 256 levels.
What you see is a histogram as a graph of how intense the tonal value is, seen over the grey palette. The histogram spans from Jet-black on the left to White on the right.
What we generally is after is many pixels in the midtones and shadows and avoid having pixels of black and white. The histogram will give you a quick judge if this is too bright or too dark. If you over expose your photo then all the curves will be at the right side of the histogram. If you underexpose it will be on the left side of the diagram.
Backlit
If you are shooting with backlit, is your histogram readings likely will indicate that you are going to blow out your image. This is obviously not an indicator of you having to reshoot the photo with entirely different settings. However, it is helpful, while we are searching to find the fine balance between the foreground and background.
Teach yourself to interpret the signatures of the Histogram
Even after having bashed the histograms under Word of warning, I still use the monochrome histogram as a guide, obviously not following these to the letter, but still letting their pattern lead me into towards a certain behaviour.
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Blownout. |
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In this photo Both highlight and shadows are clipped. This happens when the scenes tonal range is greater than what your camera can handle. Apply a Natural Density filter or shoot with a different time, may help reducing the contrast. Alternatively, compose your images in such a way that highlights is not clipped. |
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Low Contrast |
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Contains no highlights or shadows. Exposing to the right is the solution to look for her here. By increasing, the exposure of an image allows for the maximum amount of light and optimum performance of the digital image sensor. |
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High Contrast |
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Smile and be happy J |
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Studio White Background |
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When shooting studio, with white background will you not see any shadows, and you will see high indication to the right, indicating a burned out scenario. This is perfectly desirable in this situation. |
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Studio Black Background |
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When shooting studio, with black background it is perfectly normal to see a peak on the left. |
How to find the Histogram on the Sony Alpha A99
The Golden Hour 
reply from ..Ross Hamamura
Jørgen Guldmann “for me” the larger DR of Sony Senors, Live Veiw, and “Zebra” make Histograms obsolete. On a RAW in general I am pushing to the Right at least 1/3 stop. (ETTR only slightly , and within the #Sony Sensors ability to recover) … Then, I use the ZEBRA to determine “Where” the blow outs are, and if they are important to me. The location of the blow outs is more important vs IF . Because I try to blow out some most of the time. because that alone will give me more information on the shadow end (left) … Then, I do a simple and “automatic” thing on a Import Pre-Set into Lightroom , I Pull Back the Highlights (1/3 stop). Now I have more information to work with on the RAW , and the skin tones are easier to deal with. from LL ” Because CCD and CMOS chips are linear devices. And, of course, each F/Stop records half of the light of the previous one, and therefore half the remaining data space available. This little table tells the tale.
Within the first F/Stop, which contains the Brightest Tones
2048 levels available
Within the second F/Stop, which contains Bright Tones
1024 levels available
Within the third F/Stop, which contains the Mid-Tones
512 levels available
Within the fourth F/Stop, which contains Dark Tones
256 levels available
Within the fifth F/Stop, which contains the Darkest Tones
128 levels available
This realization carries with it a number of important lessons, the most important of them being that if you do not use the right-hand fifth of the histogram for recording some of your image you are in fact wasting fully half of the available encoding levels of your camera.” https://luminous-landscape.com/expose-right/
Ross Hamamura
A very simple test can prove it to yourself on a RAW. Shoot a face. Under Expose a LOT (one stop of two might do it) . take another shot of the Face Over Expose 1 stop. … now , in the RAW file try to get that Skin tone looking beautiful. … I can tell you , the more you underexpose the harder it gets. … On the Over Expose you will realize there is a point of overexposure where adjusting for skin tones is easy on the pull back. and you learn how far you can go. … in time on the ZEBRA you will know at what point that is. … just my experiance.
Ross Hamamura
On RAW on skin tones the old school way was to watch the RED histogram for blow outs. … as DR keeps increasing , and with ZEBRA , that is Dead. No Zebra on the Face , ETTR one stop for increase data bits = NO Problem. … But, the KEY is DR. Dynamic Range , this is why it is soooo important to RAW shooters.
Its worth mentioning that the Sony Alpha A99V do not feature the ZEBRA functionality. This is new to the A7R.