Tag Archives: Autofocus hunting

Facts about focus… how much do you know?

Orb Out Of Focus

• Orb – Out Of Focus •

Focus is more complex than at first sight.

Focus, and the associated functions on a camera, take a little time to sort out in your mind. Here are some fundamentals and some obscure facts for you to think about.

Focus facts…
  1. When you point your camera at a single colour, blank space, solid blue sky or night sky the auto-focus will ‘hunt’ for some contrast. The lens will be unable to focus but keep trying. If it detects a difference of contrast in the frame it’ll be able to balance it out and use it to create a focus. If your lens is ‘hunting’, find something with a bit of colour or light contrast. Then it will stop hunting and focus. More…
  2. The light from your lens focuses on the “image plane”, the flat surface that is also the surface of the Digital Image Sensor. The circle of light it creates is bigger than the sensor. The light that falls outside the sensor area is normally inferior to the light which falls on the sensor surface. This is because the edges of the lens creates an inferior quality of light compared to the middle part of the lens. More…
  3. There is such a thing as a “fixed focus lenses”… they have no focus capability. They are put in the camera at time of manufacture and set to give a deep focus from a few meters through to infinity. Can you imagine why such a lens would be used in a camera? More…
  4. Bokeh appears in out-of-focus areas. Some people think that the prominent little circular highlights are the bokeh. This is incorrect. In fact bokeh is a statement relating to the quality of the out-of-focus blur. The blur itself is called… blur! More…
  5. Macro lenses are highly effective at focusing at short distances from the lens and to enlarging the image. Actually they will also focus at other distances too. Macro lenses produce a great portrait. More about macro lenses…
  6. When a lens lets light through the light follows something called the optical path. The focus is achieved on the optical path. However, in a DSLR when the mirror is down, the optical path ends up at the eye. The optical path is not the same all the time. More…
  7. Where you focus affects your exposure. Most people assume focus and exposure are two separate things. And, in fact, they are. But, your camera senses the light conditions where you are focusing and sets that focus at the same time as taking readings for the light meter. Change your point of focus and you may change the light reading. Even a tiny movement may change your exposure readings if your focus changes from a lighter to darker surface. Useful to know if you are in a darker environment with bright light sources around. Especially useful if you are trying to learn manual control.
  8. The ‘sensor plane’ is the surface on which the image is projected by the lens. It is the surface of the sensor itself. In former times it was the same surface that the film was laid upon. Any idea what other names might be applied to the same surface in a camera? More…
  9. Sometimes it is important to measure your focus distance precisely. For example if you want to repeat shots or vary the distance form camera to focus-point by a measured amount in a series of shots. Such measurements are often used in forensic photography, macro work and for working out scene sizes and distances. There is only one place where you can take a true measurement from on a DSLR. It is clearly marked. Know what it’s called and where it is? More…
  10. Consider turning off your auto-focus when using a tripod. The motor that works the auto-focus creates vibration that may affect your shot. It is less likely to have an effect on long exposures, but if you get into the habit of doing it you may help to sharpen your shots. Reducing any vibration is good when you are trying to sharpen your shots.
  11. The Plane of focus is a very important concept – it is about where you are focussing. It gives you an idea of what your focus is doing at any angle of the camera. You should really have a good idea about it if you want to make sure you are getting a proper focus on the subject of your shot. More…
Lots more to learn…

Focus is big subject and can become extremely technical. There is a lot more you can learn. These points are just some fun ideas to help you learn about different aspects of focus in general. If you have any comments, other ideas or want me to write about another aspect of focus – leave a comment at the bottom of the page.

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By Damon Guy (author and Photokonnexion editor)

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Damon Guy (Netkonnexion)

Damon is a writer-photog and editor of this site. He has run some major websites, a computing department and a digital image library. He started out as a trained teacher and now runs training for digital photogs.
See also: Editors ‘Bio’.
By Damon Guy see his profile on Google+.

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Ten simple ideas to improve your photography (and a fun quiz)

Ten Tips

Ten Tips and 12 fun quiz questions.

Simple things help you…

We should all take a step back and think about the basics sometimes. It helps us remember essential techniques and keeps us on our toes. Here are the basics with some fun quiz questions too.

The simplest techniques in photography are often the most important ones. In this post we make sure we don’t forget them…

10 essential things to know; 12 fun quiz questions
  1. Not knowing your camera: This is really bad news. If you are hoping to improve your photography make sure you learn what every lump, bump, dial, screen, lens and twiddly bit does. Read your manual regularly. Practice with each function until you have got it right. Then practice it in the dark so you can do a night shoot.
    Quiz Question 1: How many lenses are there on a camera? Answers at the end!
  2. Poor stance: Most people when starting photography don’t realise that the way they stand and hold the camera creates all sorts of problems and poor performance. If you are a keen photographer a good stance can contribute to improved sharpness (hand-held shots), better focus, more steady hand and better shot timing. Learn to stand properly right at the start and you will save yourself lots of re-training time later.
    Quiz Question 2: At what point in the breath cycle is it best to take your shot?
  3. Not using a tripod: classic mistake. Tripods save you lots of time and give you pin sharp photographs. They give you an opportunity to set your camera up properly and ensures that your are ready for your shot.
    Quiz Question 3: A monopod has one leg, a tripod has three legs. What is, and how might you use, a bipod?
  4. Not giving the camera time to focus: When you press the shutter button halfway down it causes the auto-focus to cut in which focuses the camera. But if you punch straight through that to the shot the focus has not had time to do the full focus. This normally happens on the first focus attempt when the focus is right off. After that the lens in nearly focused and will adjust more quickly. So don’t make your first focus attempt too close to the shot or it will be blurred.
    Quiz Question 4: Why do you have two rings on a modern auto-focus/zooming photographic lens? What do you call each of them?
  5. Taking pictures against a bright light? Cameras don’t like very bright lights. Especially if there are also very dark spots nearby. Shooting indoors while looking at a window out to a bright sky will cause a strong white spot. This is very distracting and draws the eye away from the subject. Not good. There are Light and Lighting resource pages on Photokonnexion for you to learn more.
    Quiz Question 5: How many stops of light can healthy human eyes see (20:20 vision)? How many can the camera (rough generalisation) cope with?
  6. Relying on flash (especially pop-up flash): Pop up light has a very small concentrated source. It discolours faces, washes out colours, creates harsh, sharp-lined shadows and is badly placed (too close to the optical axis) creating nasty highlights on faces. Try to use natural light more. It is much more forgiving and does not produce such harsh shadows most of the time.
    Quiz Question 6: What is often the result of using pop-up flash with respect to two parts of the face?
  7. Dead centre subject: If you put the subject of your picture in the centre it will usually be boring. If you off-set your subject the eye will be looking to see why the symmetry is broken. That keeps the eye hunting around the screen. Learn about the “Rule of thirds” and other Composition principles. That will help you make the shot more compelling to the eye.
    Quiz Question 7: What type of compositional perspective would you be working with if you want to promote a three dimensional feel to your picture composition?
  8. Horizon control: Make sure your horizon is level, especially if it is a seascape. If you leave it on an angle the picture will be ruined because it will look like the sea is sliding off the page! Horizons also induce mid-picture viewer-stupor. Make a decision. Either shoot for the sky in which case place the horizon in the bottom third of the picture. Or, shoot for the ground in which case the horizon goes in the top third of the picture. An off-set horizon is more dynamic and keeps the viewers eye moving.
    Quiz Question 8: If your main choice is to shoot for the sky, where would you take your exposure from? (Where would you point your viewfinder focus point?) a. The sky? b. The ground?
    Quiz Question 9: Describe autofocus hunting and why it happens?
  9. Simplify, simplify, simplify: The most effective way to show a subject to your viewer is to de-clutter the picture. Take out of your composition everything that is nothing to do with the subject. The more you make the viewers eye go to the subject the more effective your shot will be.
    Did I mention that you should simplify your shot?
    Quiz Question 10: What is it called when you paint out something from your picture in post processing to simplify a shot?
    By the way, did I mention that you should work really hard to simplify your shots?
  10. Go manual: Auto-modes on your camera are really best guesses about what the manufacturer thinks will be suitable for the average shots most snappers will take. Buy you are a keen photographer. To get the camera to do exactly what you want, and to make discerning choices about your images you should work on improving your manual control. Your understanding of photographic principles will improve, your skill at exposure will improve and you will find yourself making informed choices about how you want your picture to come out. You will turn from a snapper into a photographer.
    Quiz Question 11: What does the ISO control do? a. Adjust the sensitivity of the digital image sensor or b. Change the aperture size?
    Quiz Question 12: Does ‘shutter speed’ or ‘aperture’ control movement blur?
Answers to quiz questions
  • Quiz Question Answer 1: I am talking about any camera that has a lens, not just DSLRs. the number of lenses is a matter of variation. If you are discussing photographic lenses then only that one will count (but read on). Some people think of each glass element in the photographic lens as an independent lens. Technically that is not true. They are optical lenses or glass elements, not photographic lenses. However, if the photographic lens (and elements if you included those) were all you counted you would be wrong. Here is a short list of Possible lenses on a camera of any sort…

    There may be others.

  • Quiz Question Answer 2: You should take a shot at the full inhale point or full exhale point before inhaling or exhaling in the next part of the cycle. You can choose which is best for you. All you do is delay the next part of the cycle while you take a shot. This is the point in the breath cycle when there is least movement of the shoulders/chest. Read more about it in Simple tips for a good stance
  • Quiz Question Answer 3: A bipod is photographically uncommon. Understandably, it has two legs. Find out more here… Definition: Bipod
  • Quiz Question Answer 4: The two rings on an auto-focussing photographic lens allow one ring to focus the image – the focus ring. The other ring is for zooming the lens. The latter changes the focal length and is called the focal length ring.
  • Quiz Question Answer 5: Human eyes can see about 18 to 20 stops of light when healthy. However, by contrast the best commercially available cameras have to operate with a dynamic range of 8 to 12 stops of light. Research is pushing the boundaries but there is still a big gap to meet the dynamic range of the human eye (in 2013).
  • Quiz Question Answer 6: Pop-up flash is very likely to cause red-eye.
  • Quiz Question Answer 7: To make things look three dimensional in your image you should be working with three point perspective. Look for lines in your image that promote cube-like structures. For example buildings, walls and other objects with lines and shapes that have a solid feel in real life. This will trick the eye into believing that there is a solid object in the picture. Read: Simple ideas about perspective in photography and: Definition: Perspective
  • Quiz Question Answer 8: If you shoot for the sky you will need to be taking your exposure from the sky as that is the brightest point. This will leave the ground darker in your exposure than you would see it with your eye. You can use one of a number of techniques to correct that later.
  • Quiz Question 9: Auto-focus hunting is when the auto-focus in the lens cannot focus and will keep going up and down the focus range trying to get a focus. This is a common problem at night, in darker conditions, low contrast conditions and clear or totally grey skies. You can read more about it in: Auto-focus ‘Hunting’ Definition: Hunting, Auto-focus

  • Quiz Question 10: when you paint out something from your picture in post processing to simplify a shot? You normally use a cloning tool. You can find out more in: Definition: Cloning; To Clone; Cloned; Clone Tool.
  • Quiz Question 11: What does the ISO control do? It adjusts the sensitivity of the digital image sensor allowing you to work in bright light (low ISO setting) or low light (high ISO setting). There is an article on ISO here: ISO.

  • Quiz Question 12: Shutter speed controls movement blur. Aperture controls blur (bokeh) created by the loss of sharpness outside the zone of acceptable sharpness. This is traditionally known as the depth of field. More reading on: Definition: Exposure and related to aperture: Definition: f number.

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By Damon Guy (author and Photokonnexion editor)

Damon Guy - Netkonnexion

Damon Guy (Netkonnexion)

Damon is a writer-photog and editor of this site. He has run some major websites, a computing department and a digital image library. He started out as a trained teacher and now runs training for digital photogs.
See also: Editors ‘Bio’.
By Damon Guy see his profile on Google+.