The variable aperture - the iris. A new definition for 'Diaphragm Iris' is in the photography glossary. Click to visit the definition.
The light coming into your camera is controlled by the iris
The aperture size regulates the amount of light that you allow into your camera while taking a picture. However, it is the ‘Iris Diaphragm’ mechanism that controls the aperture size. It is a sophisticated mechanism in today’s cameras. In former times the diaphragm was a component of the lens in its own right. Today the iris and the diaphragm are one mechanism which together control aperture size .
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’.
Tin Mine. In very bright conditions the ND Filter helps control exposure.
Top: Unable to wait for better light the shot was washed out and too bright.
Bottom: Seconds later, an ND filter restors the colour, pulling back details.
No serious landscaper would be without their set of NDs and ND grads (neutral density and graduated neutral density filters). Sometimes you just cannot do an adequate job without them. After seeing this video I feel better about buying the right tool for the job.
Neutral Density Filters
A Neutral Density Filter (shortened to ND filter) reduces the light intensity without affecting the colour or hue of the light that passes through it. The filter affects all wavelengths of light equally so there is no colour cast or odd light variations.
An ND filter is used in a number of ways. The reduction in the intensity of incoming light allows you to open the aperture wider or to keep the shutter open longer, or a combination of both. As you can see from the photograph above an ND filter can simply help cope better with very bright conditions. If you use an ND filter can keep your shutter open much longer. This allows you to add creativity into your shots. Here is a list of uses for ND’s…
Blurring the motion of water (e.g. waterfalls and rapids).
Shallow Depth of Field in bright light (wide aperture would normally over-expose).
Make fast moving objects invisible.
Add motion blur to moving things in your shot.
Extend your exposures to capture more detail.
Increasing contrast/lowering brightness – great for moon shots
With a long shutter opening you can create wonderfully milky shots of moving water. This Google page shows a gallery of shots using ND filters. Although it takes a little practice, here is how you do it. Instead of reducing the aperture to lower the light in your camera use an ND filter. This allows you to set the shutter speed appropriately for the motion blur. Of course you will have to do this in manual. Also, you will have to try out a few shots to get the shutter timing right. The camera light meter will be miss-leading behind the filter and because the light conditions will be variable. After a little practice you will find it is easy.
You will notice that the ND picture above looks rich and well exposed despite the bright sunlight. Tripod mounted shots of flowers in bright sunlight are easy because you can prevent the colours washing out and have a wide open aperture. This allows you to have a shallow depth of field so the flower is thrown into sharp focus and the background is out of focus.
Slow moving things can be blurred by using an ND filter. Just take a shot using the ND filter and the slow moving object will develop motion blur. You can do this in low light with the hands on a clock.
Fast moving objects tend to disappear in long exposures. Take a picture of a building from across the road and passing cars will normally ruin your shot. If you use an ND filter and set up a very long shutter opening one or two cars the cars will not bother you or ruin your shot. If you are doing a 30 second exposure two cars, total 0.5sec in front of the camera will not be there long enough to show up.
If you set your aperture to a really high f-number, say f22, and take a landscape shot with an ND filter, you will be able to control the light and at the same time the sharpness. the long exposure will ensure that you can put your ISO on a low setting and get a high quality result. Taking a shot this way will allow you to get detail in your shot right through to infinity.
Finally, if you use an ND filter to take a shot of the moon you can do around a 15 to 20 second exposure without the moonlight blowing out the picture and just appearing as a round bright disc. The ND filter cuts down the light and helps the detail to come out.
ND filters also come in two sorts – full filter and graduated. So far I have mostly talked of the full filter. The filtration is applied uniformly across the filter. However with a graduated ND filter (or ND Grad.) the filtration is taken only half way across. This can then be applied to the sky above the horizon to bring down the brightness of the sky. At the same time the un-filtered half allows all the light through so the land beneath the sky remains un-dimmed. This helps create an even balance of light across the shot. ND grads are used a lot by landscape photographers who would rather get the shot right in camera than spend hours in photoshop.
ND filters come in a variety of strengths. The ND2 halves the light allowed through. The ND4 lets only 25% of the light through. An ND8 allows only 12.5% of the light through. In fact every succeeding strength halves the light of the proceeding strength. You can buy ND filters that let in less than 100th of the light through. In most cases amateur photographers find an ND8 is the strongest they will need for most ordinary purposes. Again, a little practice is required to see which strength is most useful for different light levels and shots. The best way to learn to use the ND filter is to get out there and try one.
There are a big range of types of filters. If you want to know more about filters in general I will be doing some more articles on this subject in the future. It is definitely worth trying them out. I use different filters for different purposes. However, it is worth buying a starter kit. Here are some suggestions…
Please remember that filters do a lot of different jobs. It is worth finding out about them before you buy. Here are some starter points. There are two types:
Slide-in filters go into a front mounting frame on the end of your lens. A fitting kit with adapters allows you to fit the kit to a range of different sized lenses. Make sure you buy the right one fitting kit for your camera.
The other type of filter are dedicated round ones that screw into the thread on the front of your lens. You can buy adapter rings for these too. In general people buy the one for their lens and only use it on that lens. Screw on ones have limited use compared to the box loaded ones. Since they fit only one lens size they tend to be restricted to one lens unless all your lenses are one fitting size.
If you would like to find out more about filters here are some great books on the subject…
By Damon Guy (author and Photokonnexion editor)
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’.
Posted onMay 7, 2012byDamon (Editor)|Comments Off on How Does the Lens Create an Image on the Sensor?
What is projected onto the sensor from the lens? How focussed is the image?
Sharp or Unsharp depends on tiny circles
Each tiny point of light that reflects off our subject is projected onto the sensor. How it comes out in the final image, sharp, or ‘unsharp’ depends on something called the ‘Circle of Confusion’.
The new term is fully explained in the the new entry to our Glossary of Photographic Terms. Now you can find out all about the ‘Circle of Confusion‘.
Contribute A Definition?
Send us a definition for our list of photographic words and phrases. Simply write a clear definition and send it in. Include an original picture if you wish. Give us your name and a link to your website and we will credit your work.
The aperture is one of the key control mechanisms in the exposure process. We use the aperture every time that we take a photograph. Understanding this essential attribute of a camera is one of the keys to understanding exposure. You can get a better grasp of your camera by reading our new entry in our photographic glossary on the… Aperture
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. 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!
Related Books:
If you like the ‘Dummies’ books, there is one on macro photography which provides a very good round-up of getting started in Macro.
If you like to work with explanations and practical examples this book provides an excellent introduction to Macro Photography with lots of useful advice and clear projects for you to work with. I really liked this book.
By Damon Guy (author and Photokonnexion editor)
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’.
Understand your sensor – hidden insights into your shots
It sounds technical, but the size of the image sensor in your camera can effect your shot. If you are thinking of buying lenses or a new DSLR you should know what you are buying. The sensor size in a digital camera can affect how you frame a picture, its relative size compared to other cameras, its noise levels and the depth of field capabilities.
Lenses are usually measured in terms of focal length. Actually, a 50mm focal length lens on one camera may not be able to take the same picture on another camera. The focal lengths of lenses are measured against a standard 35mm sensor – that is a legacy from the days of 35mm film. Today, different companies have various technologies and have created varying sizes of sensors. The impact of this is that your sensor may not see the same as a camera with a different sensor – even though the same lens is used.
Below is a video that explains in simple terms all about sensor sizes. It also looks at other ways the shot is affected by sensor size. The video is 7.5 minutes and aimed at non-technical photographers.
I have inserted a chart overlay below of the various sensor sizes. You can check the sensor size of your camera in the technical specification of your camera manual.
Diagram showing the comparitive sensor sizes of various cameras. (Source: Wikipedia)
Posted onApril 7, 2012byInCamera|Comments Off on Ruin Your Shot Using Optical Stabilisation
As bizarre as it sounds, using image stabilisation (IS) or optical stabilisation can actually ruin your shot! Manufacturers are always claiming that it improves your shots. Well, not always. Sometimes the cause of movement in your camera is the technology itself.
Hand-held shots are definitely improved by the use of IS. It stabilises the shot and helps to iron out any shake created by the hand-hold.
When it comes to using a tripod things are different. The action of the stabilising motor in the lens has an impact. Any photograph taken with IS turned on will cause the motor in the lens to try and smooth out any movement. The same applies to the action of the autofocus… it hunts for a focus using mechanical changes which causes movement. The two play off each other. What actually happens is that both the auto-focus and the IS system create their own movement. This is translated into vibration in the tripod. The IS system then trys to iron out the movement in the tripod – which makes things worse!
The result is that the auto-focus and the IS create movement, not prevent it when on a stiff mount like a tripod. This leads to a deterioration in your picture quality. You may find that the shots you get with these turned on are quite ‘reasonable’. However, I would rather see excellent, not reasonable shots. Sharpness in your photography is a quality goal that needs to be pursued at all costs. As you get better you want more sharpness.
The simple answer is to turn off auto-focus and your IS system when using the tripod. The IS is not needed anyway because the lens should be steady on the tripod; the auto-focus is not ‘hunting’ for the sharpness. This leaves you in control and doing your own manual focus.
It is a small improvement we are looking for when turning off the auto-functions. Yet, if you add this to the other techniques you use to get sharper shots you begin to see vast improvements in the outcome of your pictures. It all adds up in the end!
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’.
Privacy & Cookies: This site uses cookies. By continuing to use this website, you agree to their use.
To find out more, including how to control cookies, see here:
Cookie Policy
