Depth of field is the amount of distance between the nearest and farthest objects that appear in acceptably sharp focus in a photograph. A preferred selection Depth of field ("DOF") in a focused subject in an image can be quite subjective. Remember this, adequate selection of DOF for one situation, application may be unacceptable for another photographer. It is all a matter of personal preference when trying to determine the appropriate use of DOF to enhance an effect in a photograph.
A typical example of a photo with shallow depth of field control. (only the main suject of interest is enhanced by throwing other elements out of focus.
A typical example of a photo with extended depth of field control (From near to far in sharp focus)
You have to recognize the eventual effect of depth of field control that can bring to your photo but HOW TO ?? Simple, read on and digest.
In simpler term, we define depth of field as the zone of sharpest focus in front of, behind, and around the subject on which, when lens is focused on a specific subject; with TTL (through the lens) SLR camera, DOF can be previewed in the viewfinder of a camera - the preview is very handy for critical type of work. For an example, when taking a product shot, when you require absolute certain if DOF is adequate to cover the object you intend to photograph Generally, the closer the subject to the camera, the more evenly with the distribution of depth of field in front and behind the subject. As distance of focus extends, DOF usually will be more behind than in front of the focused area.
A few factors may have a direct relationship with depth of field, they are: 1) the diaphragm opening of the lens (the Aperture), 2) the focal length of the lens in use, and 3) image size (it has a direct relation to distance).
T h e R e l a t i o n s h i p : The general rule of thumb for selecting the right aperture for a desired depth of field is: give the same object distance and the image size, the bigger lens opening (aperture) used (like f/2.8, f/2, f/1.4 etc.) will have a narrower band of depth of field - meaning critical focusing will be required in this kind of situation because when you use a large aperture (in particularly when focuses at a near to the subject), the zone of sharpness (DOF) can be very limiting; while on the other hand, if extended depth of field is required, you can just choose a smaller lens opening like f/8, f/11, f/16, f/22 to make the plane of sharpness is extended, so everything will be in sharper focus.
Depth of field increases with distance. The farther you place the camera from your subject, the more depth of field you can obtain. Landscapes have great depth of field, while macro photographs tend to have very little depth of field because the subject is so close to the lens.
<<<--A wide angle lens combined with a smaller aperture should be good enough for great depth of field to register a crystal clear details from near to far. Copyright ©-Free image collection 2000. leofoo ® Malaysian Internet Resources
The "amount" of light allows to strike the film plus the duration (time) for the light to strike the film forms an exposure. The camera has two mechanisms to control exposure, the lens diaphragm (lens section - aperture) and the timing of the OPEN/CLOSE of the shutter curtain (camera section - shutter speed). If this confuses you, the lens diaphragm (inside a typical SLR camera lens) consists of multiple blades which can be open and closed to certain size openings, the variations in the lens opening is called aperture. The size of the aperture determines the amount of light which will fall on the film. Various sizes of the lens opening are indicated by a set /series of numbers called f/stops or f/numbers. Each f/stop represents a specific quantity of light that pass through the lens. The smaller numbers are called large f/stops while the larger numbers are called small f/stops. This is because the larger numbers represent smaller apertures and allow less light to pass through the picture taking lens. Each time you move from one f/stop to the next smaller f/stop (larger number the amount of light allowed through is exactly halved. In effect, the amount of exposure itself is also halved. Using f/2 as an example, the amount of light reaching the film will change according to f/stop as indicated below:
* Half f/stops.
The larger number such as 11, 16, 22, 32 marked on the lens is called the lens minimum aperture. The smaller f/number indicated on the lens (such as 1.4, 2, 2.8 etc) is called the lens maximum aperture. The maximum and minimum apertures differ according to the lens-types. The maximum lens aperture is important because it indicates the largest amount of light that the lens will transmit through it to strike the film "hiding" behind the camera shutter.
NOTE:- Certain camera/lens manufacturers have their lenses with the maximum aperture providing half-f/stop reading rather than a full f/stop as printed on the aperture scale. Now supposing you have the camera set for a certain exposure value ("EV"), say the exposure you get with f/4 at 1/60 sec. You can recalculate other combinations (aperture and shutter speed) which will effectively give you the same exposure as that above. As we use the above data as reference, some of these combinations in the above example includes f/5.6 at 1/30 sec. and f/2.8 at 1/125 sec. You simply move up and down the f/number and shutter speed scales as well as adjust the speed via camera settings to achieve that.
Quick Reference Guide: Depth of field is governed by three factors: aperture, lens focal length and shooting distance. Remember the following relationships:
- The smaller the aperture, the deeper the depth of field (the other two factors remaining the same). For example, if the lens focal length and the shooting distance stay the same, the depth of field is much deeper at f/16 than at f/1.4.
- The shorter the lens focal length, the deeper the depth of field (the other two factors remaining the same). For example, comparing a 28mm lens with a 50mm lens at the same aperture and shooting distance, depth of field is deeper with the 28mm lens..
- The greater the shooting distance, the deeper the depth of field. i.e. other two factors remaining the same). For example, if the subject is photographed from three and then from seven meters away, the zone of sharpness in the foreground and background is greater at seven meters.
Another characteristic of depth of field is that it is generally deeper in the background than in the foreground.
Depth of field decreases with increasing focal length (given equal subject distance) In other words, if subject distance stays the same, a long lens gives less depth than a short. (A new theory emerges lately, indicating contradictory report that focal length is depth of field independent, I have to find out this in real life application).
One of the most used application is using Depth of Field control for portraiture photography. A clever photographer would use Depth of Field intelligently to emphasize a specific effect of the main suject of interest (in this case, the model) by limiting DOF away from confusing background via use of a larger aperture and/or using a smaller aperture to enhance the visual with pin sharp details from near to far (such as scenic, travel , landscape etc.). Below are more examples. The photo at the left hand side is achieved with the intended result via combination of a long telephoto (300mm) lens + a larger aperture (f/2.8).
<<<-- Oh.. Morris.(35k JPEG) leofoo ® Malaysian Internet Resources Copyright ©-Free image collection 2000.
Another example of a shallow depth of field effect for close up as the distracting background is "thrown" out of focus to draw the viewer's attention to the main subject. Next, remember we discussed earlier:- the nearer of the subject in focus to your camera, depth of field will be more "shallow".
This is the OPPOSITE. Maximum depth of field is required to show the details of the scene that attracted my interest and so, if I want to show the entire scope of the scene from NEAR to FAR in sharp focus. A smaller aperture is used along with a 28mm wideangle lens to achieve the objective.
It works on other usage such as dealing with scenic, candid, portraiture or even street photography.
Here is another example of smaller aperture is used on the lens section for MAXIMUM depth of field to ensure all the elements are in focus.
There are times when you need to affect the amount of depth of field for a particular scene. In a scenario like low light where you need to to shot wide open and wish to have extended depth of field or cases where you are force to live with a fixed-aperture mirror lens, if you suspect that the aperture is too wide to deliver adequate depth of field, simply move back. The depth of field surrounding your subject will expand.
Please note it may has some compromises when you decide to do this:
First, the apparent perspective is different from your original when you move backward to gain the extended depth. It affects the both your original composition and the relative image size in the frame. I put up a simple trick that may help to resolve your problem, that is by mean of cropping. You may be able to achieve the desired extended depth of field with no compromise on your original composition and image size except slight trade off with sharpness and decrease in resolution. In fact, with today's modern film & emulsion technologies, slight cropping of 5 to 7% won't see the differences with the original. If you don't agree, let me ask you this, except some top of the line pro 35mm cameras, virtually all 35mm cameras can only show you 92-95% of the actual image in the viewfinder and yet no one is complaining. In short, provided you are not cropping from a tiny segment from a picture frame, the increased grain and the slight decreased resolution will not be even notice at all.
Generally, most photographers hate cropping with their original - what I trying to suggest is a way where situation you may need to do a trade off or the slight extra in depth is of priority to you.
When combining the relative characteristic of short focal length lenses with depth of field, it can help you to be more reactive in responses. Note: Most manual lenses have hyper focal distance indicated on the lens barrel (the modern autofocus lenses have less definition) but more useful can be the depth-of-field scale indicated usually by correspondent colored line left and right from the focusing index.
This is especially handy when you are using a wide-angle lens. Longer focal length lenses is more difficult to determine using the scale (It is recommended to use Depth of field Preview lever or button for longer focal length optic).
Older manual focus zoom lenses generally have excellent and considerate continuous colored depth of field scale for you to refer - a feature heavily missed in today's autofocus lenses.
Note: Some of the newer SLR now only require you to 'lock' the lens at minimum aperture setting or in a "A' setting. The aperture value is input through a input dial to set the aperture on the camera instead of the aperture ring on the lens.
The pity fact is, some lens manufacturers are omitting this useful features with their lenses which generally regarded as a cost saving measure as the colored coded indicators were generally painted by hand. Virtually all autofocus lenses are not color coded anymore and has bare minimum aperture scales painted for such easy reference. I used this feature very often on some of my early "Cari Makan" (MAKING MONEY) days of photography. Given a 28mm wide angle lens set at at a distance of 8 feet at an aperture of f8, the effective depth of field is started from around 6-7 feet to beyond 18 feet! Which mean to say, you can practically use a tape to lock your lens and move yourself around determine the the rough image size, just snap without even have to worry about focusing! Anyway, I learnt this a trick from a news photographer during that time. This technique is more effective when combine with shorter focal length lenses like 28mm & 24mm where the depth of field is more generous and "fail-safe".
There are recent studies on depth of field indicating a soft focus lens can also increase the depth of field other than the general factors mentioned above. I never own a soft focus lens before and I have never tried that. If any one of you have this type of lens, try and give me some illustration to prove this new theory and I will published here for you, home work ? No. Just let us share your finding.
Relative: Aperture Value | Shutter Speed = Exposure
OTHER SIMPLE, YET EFFECTIVE TECHNIQUE
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