Focusing quickly-help

[Jim Poor]

One time when manual focus might be useful is when there are a lot of things around the subject that could draw the focus. A bird in a tree, for example. Even then the MA setting is awesome on most of my Nikkor lenses.

[Chip]

For reactive shooting (sports, kids running around, etc.), there's no way I'm fast enough to focus manually. (I've tried with some of my old manual primes.) If I have some time to focus, then I'm fine using manual focus.

[kencaleno]

Originally Posted by pakyooh

Sorry to bump am old thread but I'm barely doing my homework after weeks of getting my dslr. I've completely gone manual all the way and focus is my main problem right now.

I've always wondered when is the best time to use auto and manual focus and I think I found the answer.

Here is the answer:

Focus

Is the measure of the degree of sharpness in our images.
All modern cameras have Auto-focusing, which works very well, but there are times when you need to focus manually. For auto-focus to work properly it requires a certain amount of contrast, if the contrast isn’t adequate you will need to focus manually.[ NOTE: In your camera’s viewfinder, depending on camera-flagship models generally have many focusing spots, and lesser, entry-level dslr’s will have around 5 focusing spots. With lens wide open, any of these spots can be used for selecting where to auto focus-But, depending on maximum aperture of lens in use, the ones you are able to use get fewer. Top-of-the-line cameras will only have the centre spot usable at F8,and entry level cameras at F5.6, and less than that, even these single spots aren’t reliable.]
Actually it is more beneficial to set auto focus by the centre spot, then re-compose, rather than use the peripheral spots-The reason being that only the centre spot has vertical and horizontal pixel rows. This means that if you use the peripheral spots (top and bottom spots have horizontal pixels only and right and left spots have vertical pixels only) To focus, you must have a part of the scene crossing a line of pixels at 90 degrees, and the centre spot gives you a more accurate reading ,having both vertical and horizontal pixels) It will pay you to manually focus most of the time, for full control of the situation. For instance, if an unnoticed reed encroaches into your image, when your are shooting a swan at the lake, for instance, your lens may auto-focus on that reed, rendering your actual subject out of focus.

Concerning Auto focus

There are times, you will find when auto focus will fail to respond favourably-although auto focus is able to lock on to any subject, there are certain conditions where it may not be possible ,even when the indicator lights are on, and the shutter releases.

Subjects with low contrast
Solution: Focus on something the same distance as the subject you want to make an image of, then aim at that subject
Subjects that do not contain vertical lines
Solution: Hold camera vertically, lock focus, then switch to horizontal
Subjects in excessively bright light
Solution: Focus on something the same distance as the subject you want to make an image of, then aim at that subject
Two subjects at differing distances
Solution: Focus on something the same distance as the subject you want to make an image of, then aim at that subject, and re-compose
Subjects with repetitive patterns
Solution: Focus on something the same distance as the subject you want to make an image of, then aim at that subject, and recompose
High speed subjects at close range
Solution: focus on another subject at the same distance-to-subject distance first, then re-compose your frame

To ensure you are in focus, there, in the viewfinder, is the electronic rangefinder icon, that comes on when you are in focus. NOTE: Each lens has its “sweet-spot”, that is when the aperture and zoom length combine to give optimum sharpness- 18-55 mm zooms usually have this “sweet-spot” at the 35mm distance setting and 2 stops back from wide open. On a 70-300mm zoom the “sweet-spot” would be around 185-200mm aperture 2 stops back from widest.
Auto focus is good for situations where you cannot focus fast enough, manually, such as sports and wildlife photography.
Depth of field appears to be the most confusing of focus elements. Depth of field is a range of acceptable sharpness in an image, from near to far. Three factors control Depth of field: Aperture: The wider the aperture, the shallower the depth of field. Focal length of lens, The longer the focal length of the lens, the shallower the depth of field will be. and Distance from subject, Landscape images have great depth of field, whereas Macro (extreme close-up) images have very shallow depth of field. Concerning depth of field, Hyperfocal distance seems to be even more confusing -Hyperfocal distance is a point of focus where at a certain aperture, Half the distance from that point to Infinity, (which starts at 30 feet, and extends to as far as you are able to see)) will be in acceptable focus, The best lenses for hyperfocal distance are 80mm or wider ; telephoto lenses, because of their relative short depth of field, are rarely used. (Prime lenses have a scale on them for this, zooms do not) Using a 18mm setting on your zoom lens at f16, Hyperfocal distance is somewhere around 5 ½ feet (1600mm), so depth of field at this aperture would be from 2 ¾ feet ( 800mm) to infinity, when focused at 5 1/ 2 feet. A good guideline for great depth of field for landscapes is to use the bottom focusing marker in your DSLR viewfinder, (either horizontal, or vertical) as this will focus 1/3 of the way into the distance, (It is on the lower third imaginary “Rule of Thirds” gridline!) ,as is usually recommended. [ NOTE: Unless your camera has depth of field preview, looking through the viewfinder all will not be in focus, because your lens, until you press the shutter button to make the shot, will be open at full aperture.]

To avoid camera-shake, always use a sturdy tripod. When using lenses equipped with VR/IS (vibration reduction-Nikon/Image stabilisation-Canon), on a tripod you will need to turn off the anti-shake, or lens will still try to counteract vibration that isn‘t there,, and cause unwanted shake. If, for some reason you cannot use a tripod, use your self as one-
Feet at “T-Stance”, left hand supporting camera, elbow against ribs
Camera pressed against nose and brow
Right hand also elbow against ribs, index finger on shutter button
Set shooting mode to continuous, and “Roll” index finger on shutter button - First couple of shots will probably be blurred, but somewhere between 3-4 and 5 you should have a shake-free shot of the scene. ( When using zoom lenses longer than 200mm-I usually set ISO to 400, when hand-holding)

An alternative way to turn yourself into a tripod/monopod, is to:

1. Extend your left arm out in front of you, palm down.

2. Bend forearm back, so fingers just touch right shoulder

3. Bring right hand and arm up inside that triangle, resting edge of right hand on crook of bent left arm-pull right arm back, so left hand grips right forearm.

4. That’s the grip, and with camera held by right hand, with lens resting in crook of left elbow, press camera against brow and nose for stability. ( I hope this is clear to understand)



“Trap” focusing:

This is a neat way to use auto focus especially for fast sports/wildlife action, I don’t know other maker’s settings but these are the settings for Nikon users:
Custom (pencil) menu:

Autofocus set to AF-S
AF area mode set to single
AE-L/AF-L set to AF ON

Compose your shot and set the focus by aiming the centre focus icon at a definite target at the precise distance you want, (Say a tree branch where a bird is about to land, or on second base where the baseball player's foot will land) and pressing the "AE-L/AF-L" button near the viewfinder. This will focus the lens, let go of AE-L/AF-L button. Turn away,
press and hold the shutter button all the way down. Point camera at pre-focused point when subject approaches, and your camera will take the shot
Much faster than Human reflexes.

Regards, Ken

[kencaleno]

Originally Posted by dcclark

I have never understood why anyone would feel compelled to focus manually when they don't have to! Most decent-quality lenses allow you to manually adjust the focus even when in autofocus mode -- let the camera do the hard work for you, and fine tune it if you really want to.

- For speed and accuracy. Ken

[autofocus]

On the top right side of the camera above the small LCD screen you will see 3 buttons. Press the one marked AF-WB, then turn the main dial to
A1 Servo, or A1 Focus. Either setting will help to maintain focus as your subject moves (and they all do!)

[dcclark]

Originally Posted by kencaleno

- For speed and accuracy. Ken

I would say that, in my personal experience, this is the reason to USE autofocus.

Of course, I usually select my own AF point or recompose, but that ability to tweak the automatic focus really negates the need for manual focus in all but the worst light.

[kencaleno]

Concerning Auto focus

There are times, you will find when auto focus will fail to respond favourably-although auto focus is able to lock on to any subject, there are certain conditions where it may not be possible,even when the indicator lights are on, and the shutter releases.

Subjects with low contrast
Subjects that do not contain vertical/horizontal(dependent on how camera is held) lines
Subjects in excessively bright light
Two subjects at differing distances
Subjects with repetitive patterns
High speed subjects at close range

Ken