Part 2. Matrix metering, Expo-correction, Bracketing, Histogram - what that means and how it can help you
Matrix metering, Pattern Evaluative, E
It is also called multi zonal, multi segment, evaluative. In an auto mode the camera sets standard matrix metering exposition meter which is used more often than other. It is the most intellectual metering; the exposition is measured by the camera in several matrix zones. The zones - segments are distributed on the frame area for all cameras variously, and zones‚ priority is different too. The camera analyzes the data of each zone, luminance's ratio of separate zones, compares the information to the own database standard, of the most frequently repeating scenes. The matrix exposition meter is the most universal, however there are limitations for it, as illumination is not always identical and even on frame area, and the objects can be different. The matrix exposition meter is easy, when illuminating intensity of the scene area is approximately identical. But it is not always predictable, though in most cases you receive an exact exposition. It is recommended for beginners, who have not learned to use manual settings. Yet the matrix exposition meter will not manage in following cases:
In a mode of exposure priority or aperture (to expo correction will help to some extent),
Locking illumination, when a light source (sun, lamp, floodlight etc.) are arranged opposite of lens or sideways,
If it is necessary to make an accent on main, to set an object out of a background,
When you want to make a snapshot lighter or darker those, having changed a general snapshot tonality.
Art photography
The matrix exposition meter makes an exposition of all frames. The bright segments become overdone, and shaded become dark.
There is three-dimensional (3D) spatial segmental matrix exposition meter. In this variation of matrix meter the exposition is determined in different frame places separately from each other. Brightness, visibility and spacing interval up to different objects of the scene are taken into consideration. Three-dimensional exposition meter is applied basically in reflex cameras.
If there is a desire to learn to shoot not only in an auto mode "direct and click", having received traditional "photo on memory", and if you want to receive more expressive and interesting snapshots, it is meaningful to learn other ways of expometering.
Average metering, A
At this method the scene illuminating intensity averages on all frame area. All frame zones have identical priority. The integral metering aims at medium-gray tone predominance. The advantage of integral metering is that average value will be used without dependence from intensity of an indirect light. It is not for filming of the contrast scenes, and also black and white surfaces, clothes, animal, as a risk of an incorrect exposition occurs. Also it should not be used at poor illumination: the light objects will appear insufficiently light and dark will appear too dark. Shooting evening, you risk receiving a too light snapshot. The exposition in this case needs to be reduced on 1 or 2 stages. At filming white objects the back action a large exposition on 1 or 2 stages will help.
There is a spot and central - weighted expo metering. They will help you, when the light conditions will be unusual, when you will shoot the intricate plots, when you will plan to receive original outcome.
Spot metering, S
It is often called call as partial. This way of metering provides the most precise outcome, the exposition of an object becomes optimum. The spot metering is present at cameras with manual settings. The exposure meter of the camera in this case measures brightness on a small frame segment - usually 1-3 % of the area (or up to 9 %), depending on model of a photographic camera.
The measurement is carried out in a central point of frame. If the object of filming is not in the centre of frame, then, having directed a central spot on object and having half clicked the push button (not releasing it) or having disabled an exposition, you can recompose a frame. In more perfect cameras, for example professional reflex ones, the exposure meter spots are mated with points of the auto focusing and they can be displaced on the area of frame. They are mated with spots of an auto focusing. The number of such spots depends on concrete model of the camera; it may be 5 or more
At spot metering the background can be overexposed or underexposed, but the main object of filming, which you targeting, will be good, worked with maximum quantity of parts. The spot metering can be used at filming of contrast scenes, in locking light. That is when it is important to define an exposition for a plot frame part.
Centr-weighted metering, CW
It is called an average one. At this method the system estimates general scene brightness, but the main attention is given to a central part of frame, which covers approximately 9 percents or little bit more. This way of exposition metering is expedient for applying in following cases:
Portrait filming,
When the object takes a main part of a centr of a frame,
When the object is at a contrast background
Multi Spot metering, MS
The exposition is targeted on several spots of frame, and the camera averages the obtained values. Basically multi point exposition metering is applied in professional reflex cameras.
Expo-correction
The different surfaces reflect light obtained from the same source variously. That is for each subject the reflection is coefficient. A mean reflection coefficient is 18-20 %.
At filming of a medium-gray object the matrix metering will define an exposition - value of the aperture and exposure correctly. For object with echoing property of 20 percents the reflection coefficient will be 0, 2, for a black velvet tissue - 0, 02, and for snow - 0, 8. In order that these objects on a snapshot were not gray, it is necessary to make allowance in an exposition - that is to do an expo-correction. The summer landscape reflects on the average about 18 % of light, 8-10 % - if in frame verdure, leafage is present. If there is a sand, dry surface - 30-40 %. The skin of the person has large range of echoing property, the concrete factor depends on race and sunburn. For a light skin - 0,35, for very dark - 0,035-0,06.
In modern digital cameras there is a set of the subject programs, and frequently rich enough. So, for example, if you establish a mode "Snow "/ "beach", the camera will establish of set-up so that the snow will be similar, white on a snapshot. In this case expo-correction shouldn't be applied the push button " + /- " on a body of the camera controls expo-correction. Turning the disk of set-up or pressing the corresponding push buttons, it is possible to introduce the correction. Also for more simple models of cameras this function can be available through the menu.
Expo-correction is denoted by EV. EV (in abbreviated form from "exposure value". Value, value of an exposition.) is a conditional value including every possible combinations of exposure and aperture number, which provide identical expositions under invariable conditions of filming. The change of value EV per unit of (on one stage in any direction) corresponds the change of an exposition twice. If you enter +1 EV, the exposition will be increased twice. The step of expo-correction usually makes 1/3 stages EV. For example, to be saved from "gray color" in a bad weather, introduce the correction of an exposition on +1/3 or+2/3.
Bracketing
Bracketing is a series of frames, when in each frame the exposition parameters vary: the first frame is underexposing, the second one is exposed correctly, and third one is over exposed .In cameras there is a capability to set a step bracketing- difference of parameters of an exposition from the norm. Bracketing is applied in a case, when the illuminating intensity in frame is difficult for defining and it is required to make "a test".
Histogram
If the histogram is biased to the left, it means, the picture is with predominance of dark tones, if to the right - with predominance of light tones. It is desirable, that the histogram was not "lacerated", that is had no sharp differences, "splashes".
In a number of digital cameras the histogram enters in a structure of the service information recorded together with a snapshot. It allows at possible repeated filming of frame to improve its balance or helps to select a method of a light-tonal correction of the picture at editing it on the computer. In more perfect photographic cameras the histogram is superimposed atop of the picture of selected frame on the display. It allows previously to evaluate quality of the future snapshot and at once to change light conditions or composition, or to enter exposition meter correction.
Noise of digital cameras is a very actual problem today. How do the different cameras behave at increase of photo sensibility and what to orient at selection of cameras on?
The matrix of a modern photographic camera is a digital clone of a film. The small microcircuit of the rectangular form on which the picture is projected through a lens. Sensing elements - pixels, the converters of light in an electrical signal, play key role here. The more physical size of a pixel, the more area of absorptive light and the lower a noise level on a snapshot. Furthermore it is necessary to take into consideration, that in a work-time the sensors are heated, that also causes a noise. That's why the noise appears show at filming long exposure. The noise appears on a snapshot as chaotically distributed color spots. Noise in shades is specially seen. Also noise can be seen as grain, on a highly sensitive film - such distorting do not influence chromaticism and contrast of a photo and do not irritate (if, certainly, this grain is not characteristic of all snapshots).
By camera choice the number of mega pixels often becomes a convincing argument for the benefit of definite model. However it is not necessary to run behind mega pixels, as the sizes of pixels and sensors are much more important accordingly. You see the more pixels are located on a matrix, the less their size is and the more tightly they are arranged. Densely "packaged" sensors are fast heated, and noise can appear at a minimal sensitivity and at a short exposition. Therefore try to select a photographic camera, which has more matrix area - actual sensitivity will be higher.
Most low level of noise for full-frame format reflex cameras with the size of the sensor 36 24 mm. It is such cameras as Canon EOS Mark II 1Ds, Canon EOS 5D. They manage with ISO 800, and even at sensitivity ISO 1600 the snapshots, made by them, look not bad.
The matrix of reflex cameras such, as, for example, Canon EOS 20D is less than a film frame, it is 22,5 15 mm, that also allows to shoot on enough high sensitivity. This format of the sensor has received a title APS-C. Certainly, although they are inferior to full-frame format reflex cameras with full-frame format matrix, but comparatively with any compact cameras the outcome will be much better.
For today the only camera with a fixed lens, which has a large matrix of the format APS-C is Sony R1 Its noise level at high photo sensibility is comparable with a level of reflex cameras.
For majority of compact cameras the noise appears at sensitivity from 200 units ISO already and above. So that, despite of a capability to establish ISO 800, 1600 or even 3200, forget about these values, as the picture most likely will be simply unsuitable for usage. The noise, even at short exposure, becomes so strong, that it is possible to forget about detailing and valid color transfer. The sharp sensitivity, stated by the producers, in practice appears simply non-working. Do not trust to what that is written, trust your eyes! See raw test full-scale snapshots made in different light conditions and on different sensitivity.
However not all compact sets are "friends" with a high sensitivity. For cameras Fuji film sensors are made of own unique technology. Due to matrix design features , the noise level really notably is reduced as contrasted to by remaining types of sensors at the same physical sizes. What is it explained by?
The conventional film contains chips of argentumhalogenid of the different forms - from highly sensitive grains with large area of surface, sensitive to a poor light, up to low-sensitive grains with small area of surface reacting on a glare.
And the off-the-shelf camera FinePix S6500fd allows changing sensitivity from ISO 100 up to ISO 3200. Certainly, so high sensitivity as 3200 hardly will ensure you a reasonable picture. But there is no doubt that the camera will work fine on ISO 400,
But this works for cameras Fuji only! For the other compact sets high photo sensibility is very weak place. For example, for the popular ultra zoom Sony H5. the maximum sensitivity is ISO 1000 But the camera starts having a noise already at ISO 400 practically, and at higher values the snapshot precisely will lose all attractiveness. There is noise at the installation ISO 400 for Canon PowerShot S2 IS In many cases the flash helps to solve this problem.
The ultra compact sets have the worst characteristics in the amateur class. At first, their matrix has the smallest sizes. The tiny sensor has a noticeable noise, of course Secondly, optics is also extra small, and that does not promote image quality too. Though, optics does not influence the noise, the sensor is responsible for it only.
Some advantages have the cameras with optical stabilization. If there is an optical stabilization in the camera it allows to increase exposure and to not increase value ISO at a lack of illumination. But the optical stabilization helps only on two, maximum three stages. And if the camera has the small sensor, even the stabilization will not help here. A vivid example - super popular series of cameras Panasonic Lumix FZ. Available for many photo amateurs FZ30 today. As a whole it is a very good camera, having a lot of advantages: excellent design, ergonomics, functionality, high detailing, color transfer etc. But the main minus of this fine stylish camera is its noise. It is very visible on the picture even at low sensitivity, not speaking already about ISO 400, when the noise makes the picture impossible for usage simply.
The every possible system of noise blanking built-in in a photographic camera does not save from noise. They smooth grain effect, of course, but after that the detailing is degraded, and the color transfer is distorted. The picture looks unnatural, "tinted". You will not receive the real qualitative picture at such a high sensitivity at such approach. It is better to underexpose frame on 1-1,5 stages and then to "prolate" it at the graphic editor processing, than to receive noisy and useless picture at the end.
There are certain advantages at the filming in the RAW format, as this format contains more information. The snapshot does not pass processing inside the camera; therefore this format is called "raw". It is much easier to "prolate" snapshots which were written to RAW, in the special converter.
The JPG format supposes a lossy compression and introduces a distortion to the picture. Thus the part of details is lost. At preservation in the best quality the distortion is not visible to an eye, but at further editing and saving the file it is compressed, the data are lost again. If you are going to process the JPG-file (for example, it is necessary to reduce a noise), you should reconvert the file JPG to the graphic format which is not introducing distortions to an initial picture, for example TIFF.
At filming at long exposure there is an effect of so-called "hot pixels". This is because of the technological causes. The matrix for different copies of the same model can differ by their availability in different segments of different sensitivity that becomes noticeable at a long exposure. It is well visible at increase of a picture. The cause may be the tiny motes, which accumulate on a matrix. If you raise matrix sensitivity, "the hot pixels" rush in an eye even more. It is possible to clean them by image processing on the computer also. The function Pixel Mapping is built - in some cameras: the camera makes a snapshot, not opening the gate, the obtained picture is analyzed by the processor on presence of light points, and then the camera corrects them by built-in software. Hereinafter light segments do not show any more.
As a whole conclusion is unfavorable, though it is predictable good activity on high photo sensibility for compact sets and ultra compact sets is rather an exception, than the rule. To avoid noise appearance on snapshots, set minimum sensitivity ISO value which ensures reasonable result.














