Tag Archives: Manual focus

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)

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 photographers.
See also: Editors ‘Bio’.
See also: Profile on Google+.

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Six things you must know for a night shoot

Night photography is fun. A little foreknowledge makes your night shoot easy

Night photography is fun. A little foreknowledge helps make it easy

Night shoots can yield great images with a little thought.

There are a few things that will help you get better results. Understand your equipment, ensure you have a steady base, work with your settings. After that it’s about your photographic skills.

1. Before your shoot

Plan ahead for your night shoot. A little thought about night composition is useful. Consider your safety too. In the dark it’s easy to injure yourself, break equipment and lose things. These two articles will help to prepare you:
Preparing for a Night Shoot
Out on a Night Shoot – Night Composition

2. Equipment

You will need to use longer exposures on a night shoot. This means that to get a sharp image you should use a tripod. Most night exposures in an urban environment are from about two seconds to about 30 seconds. Some could be much longer than that, especially if you are outside urban areas where there is little light pollution.

You cannot get a sharp image hand-holding your camera for extended exposure periods. Tripods provide a stable platform at at any time. At night they are essential. If you don’t have a tripod there are alternatives, although I have not found any as effective and flexible as a good tripod.

You can use any of your ordinary day equipment on a night shoot. Lenses, cameras and even flash can be used with no problem. However, you may need to use your equipment in very different ways to the daytime. Also, be prepared to get very different results. You will need to experiment to get familiar with your equipment in night conditions.

You can’t use a Flash-light (torch) when you are shooting, it will affect your local light conditions and the shots you take. Switching a torch on and off will also cause night blindness. You have wait while your eyes adjust to the change in light levels each time. You can get away with a red-light LED torch. I have one that I can wear on my head and it has a red and white light. Red lights don’t spoil your night vision so much. They do affect the shot. So don’t forget to turn them off when shooting.

It’s best to work with the ambient light if you can, especially in urban areas. Using your equipment at night requires that you have a finger touch familiarity. You will probably be surprised if you have been using your camera a lot. You may know many of the buttons by touch anyway. However, some buttons you may not know. Practice builds familiarity.

3. Anti-vibration compensation

One button you may not be familiar with is the one to turn on/off vibration compensation motors. These motors, usually in your lens, help stabilise your shots (Canon: Image Stabilisation; Nikon: Vibration Reduction). They help reduce movement from hand-shake. On a tripod the motor causes vibration which is amplified by the tripod – making the situation worse. This is not just a night shoot trick to reduce vibration, it should be used any time you are using a tripod. It helps your image to be sharper if you reduce anything that causes vibration or movement.

4. Auto-focus (AF) and Manual focus (MF)

At night it is quite likely AF will not work. It might appear to be ‘hunting’ for a focus but not find it. Don’t worry! If you focus on the margin between a light and dark spot it will work again. AF works by detecting contrasts. Anyway, it is better to turn off AF and use MF. Manual focus is much more precise at night. It also stops the lens from ‘hunting’ for a focus point.

5. Flash

Think about how you want to use your flash. If you are using auto-settings your flash may fire when you don’t want it to go off. Read your manual to find out how to turn it off. You will also find a way to change the light intensity of your flash. On-camera flash is a particularly poor tool at night and is very difficult to use to any effect at all. My advice is turn it off for your night shoot work. If you must use flash, consider off-camera flash. Now that IS fun!

In general, you don’t need flash on a night shoot for general shots. In an urban environment the lights are sufficient from the streets. However, the length of your exposure could be very long. You might usefully use off-camera flash to manually fire to illuminate something, a statue, a tree, a car… whatever. The pattern of flashes you fire will determine your local lighting. In the dark flash will only effectively light a small area around where it is fired. So, don’t expect it to light up your whole shot. There will be an article later on night-lighting shots.

6. Settings for a night shoot

If you are using auto-settings on a night shoot you will have problems. There may be a night-mode setting on your camera. Don’t expect to get great results with it. Best results come with manually setting the camera up yourself while doing a night shoot. You should consult your manual if you really want to use pre-programmed settings.

Learn how to use manual settings from the start. A night shoot is great fun. Getting the results you want makes it really worthwhile. Use ‘M’ – manual mode. This is the only certain way to get the results you want. Remember, the length of the exposure is the critical setting on a night shoot. You will be working with long exposures all the time. The shutter may be open between a tenth of a second through to, well, possibly hours. It’s more likely you will start with settings of around 1 to 30 seconds. After 30 seconds you will need to change to the ‘B’ or bulb mode setting on DSLRcameras.

Long exposures are like filling a bucket with water. Over time the bucket gradually fills up. Over a long exposure light fills the shot making it brighter and brighter. Even moderate local lights may overwhelm areas of your long exposure with brightness. However, without a longer exposure you will not get enough light for the darker areas of the scene. Here are some basic pointers.

  • A wide Aperture lets in more light (settings around f4 or less are wide open). You will have a lot of bokeh in the background with a wide aperture. To avoid that you will need a longer exposure (and a narrower aperture).
  • A high ISO will permit faster exposures. High ISO settings will create a lot of digital noise in the final image. To avoid that you should use low ISO and a longer exposure.
  • Longer exposures (shutter speed or time value) give you greater clarity and a wider depth of field in your shot. However, the camera will be much more vulnerable to vibration. (Tripod – remember?).

You will need to adjust your settings to create the correct exposure. If you have not used manual settings before you should consider this simple set up…
(Assumption: urban environment at night, some street lights and other lighting)
– Set ISO to 100 (Low ISO will give low noise – the best quality image).
– Set aperture to f8 for close focus. Landscapes/long focus, use f14.
– Set Time value (shutter speed) to about two seconds.
Now take a shot and check the screen to see what it is like (“Chimping”)
Black? Too dark? – OK, turn the shutter speed on one click and try again, and again, until your shot looks right.
In fact the internal light meter will show you when the exposure is correct. When you push the release button half way, the needle in the bottom of the viewfinder (DSLR) will be centred.

A little experimental work with longer or shorter shutter speeds will give you an opportunity to try out a few shots. Having a go is the best way to move forward with night shots. Everyone messes up quite a lot of shots to start with until you get the feel for the correct exposure. It’s really rewarding when it goes right! Have fun…

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 photographers.
See also: Editors ‘Bio’.
See also: Profile on Google+.

Get Started with Macro Photography

Looking through the front legs of a tarantula at its mandibles.

Looking through the front legs of a tarantula at its mandibles. Taken with a macro lens and additional extension tube. Effective focal length 125mm.

Getting started with macro is easy… here are some tips

The quickest way to try out macro is to buy yourself some “Macro Extension Tubes“. They are cheap, effective and very easy to use. The quality of the images are as good as your lenses and you can get started straight away.

So what are they? Extension tubes are simply a tube that fixes into your camera lens socket like your lens would. Then, into the outer end of the tube the lens is fitted into the tube. All extension tubes do is literally extend the focal length of your ordinary lens. As it does so it creates a magnification of the image that you would normally see.

You can buy extension tubes to fit to most cameras. The simple engineered tube types often have three different sized tubes to change the focal length. You can use one, two or all three of the tubes to extend your lens out from the camera. It depends on how much magnification you want to achieve. You can buy these for around £10 (approx $15). More after the jump.

Once you have purchased your tubes you can quickly mount one of your lenses to the camera. However, there are a couple of things to think off. If the lens you use is a short, wide angle lens it may cause your focus to be too close to the end of your lens. This stops you getting a focus. Normally any lens from about 60mm to about 200mm will do. Longer focal lengths give you more working distance in front of your lens. As you can fit tubes to almost any lens, you will need to practice with the lens you are using to adjust the working distance from the lens for the subject you have chosen.

Working with simple tubes means that the normal electronics in your lens do not work. This is because the tubes are a basic pipe. It does nothing except join the lens to the camera and lengthen the focal length. It does not carry the electronics that your lens normally uses. Actually this is a blessing in disguise. The focus on macro shots is absolutely critical. Often you only have about 2mm depth of field – tiny! So autofocus, although good, will often pick up things to focus on that are not what you want. Many experienced macro lens users turn off their autofocus anyway when using macro lenses. Then they can work with the more effective manual focus which is more precise at macro magnifications.

If you consider it worth the investment you can unbranded electronic focus rings. These do the same as the simple tubes. However, they can be five times the price or much higher for branded ones (Canon or Nikon are several hundred pounds to buy). I have used all three and find ordinary bare tubes to be the most versatile, light and easy to use.

When working at very small sizes it is often difficult to light subjects. So it is a great idea to use a tripod. Use this to get the shot lined up and focused. Then you can use a long exposure to make sure you are able to get a bright picture.

Tiny changes in focus means that the angle at which you take your shot is important. It is useful to try to get the face of your lens parallel with the part of your subject you want to capture. Otherwise the lens is only going to capture a thin sliver of your subject.

It is good to practice with a coin. Try to capture the whole coin surface in focus. Use a tripod to set up the lens so the coin-face and the face of the lens lie perfectly parallel. Then try the shot with the lens at a slight angle to the coin. You will see the focus is sharp where the axis of focus is clear on the coin. But the focus will soften as it falls away from the focus point.

Oat biscuit taken with a 100mm Canon Macro lens at 45 degrees. Approx. depth of field is 2mm.

Oat biscuit taken with a 100mm Canon Macro lens at 45 degrees. Approx. depth of field is 2mm. If you line up the face of the biscuit parallel with the face of the lens the whole surface would be in focus. Click to view large.

You will need to experiment with different lighting and length of exposure. But practice makes perfect and it is all about having fun. Enjoy!

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 photographers.
See also: Editors ‘Bio’.
See also: Profile on Google+.