Telephoto lens

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About telephoto lens

telephoto lens is one constructed so that the length of the lens is shorter than the focal length, but in the vernacular, it has come to mean "any lens with a focal length longer than a 'normal' lens." For 35mm photography, it is usually applied to lenses 135mm and longer, although lens in the range from 75mm to 135mm lenses are sometimes refered to as "short telephoto" lenses.

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Zoom Lenses
Some lenses have a fixed focal length, some can vary over a range of focal lengths. They are commonly called "zoom" lenses and are usually designated by the range of focal lengths they provide 28-72, 80-200, etc. Technically, many of these lenses are not true zoom lenses, but vari-focal lenses. With a true zoom lens, if the subject is in focus, then it will remain in focus when the focal length of the lens is changed. With vari-focal lenses, after zooming, the subject has to be refocused.

More about telephoto lens

A telephoto lens is technically defined as a lens longer than the standard focal length of 50mm. As such, lenses with focal length of 85mm and above can be classified as telephoto lenses. Compared to wide-angle lenses, it is much simpler to use a telephoto lens as issues such as distortions and vignetting do not appear as much in telephoto lens. However, telephoto lenses presents its own unique set of handling techniques which I will explain in this article.

this lens can be an indispensable imaging tool used when it is physically impossible to approach the subject, either because of the danger involved for an instance, a rocket launching sequence, hazardous wildlife etc. or because there is something in the way as obstacles between photographer and subject of interest. The 1,200mm has a very restrictive angle of view of merely 2° and its depth of field is limited almost to the plane of focus unless the aperture is stopped down to f/22 or f/32. The distinctive compression of perspective makes subjects appear to be stacking right behind one and another. One major problem is its ability on magnification of camera vibration or movement caused by photographer

As most of you know by now, the longer the focal length of the lens, the more difficult it is to keep it steady. A longer focal length magnifies the size of the subject in the image, so any camera shake will be magnified proportionately. A 200mm lens will magnify a subject more than a 50mm lens, so any image shake is more evident in the final image. This is compounded by the fact that longer lenses are usually more heavy than wider lenses. Proper holding techniques are the prerequisites to taking great telephoto pictures!

How do you hand hold a telephoto lens? Your left hand should hold the lens firmly (but not too tightly), while your right hand operates the controls on the camera. The weight of the camera and lens should be mostly (but not totally) on the left hand, leaving the right hand free to operate the camera and direct the direction of the camera.

Each lens has a position known as the center of gravity - a point where the lens is balanced best. You can find out for yourself where this point is by holding the lens with the camera, and holding it at various positions. The point where the entire feels most balanced in your left hand is the center of gravity. Why is it important to hold the lens at this position? Because it is most balanced at this point and you do not need to focus on fighting against unecessary upwards and downwards motion. Always try to hold the setup at the centre of gravity at the moment of shooting, so you spend less effort balancing the setup and more focus goes into the picture-taking process.

Telephoto and other long-focal-length lenses are best known for making distant objects appear magnified. This effect is similar to moving closer to the object, but is not the same, since perspective is a function solely of viewing location. Two images taken from the same location, one with a wide angle lens and the other with a telephoto lens, will show identical perspective, in that near and far objects appear the same relative size to each other. Comparing magnification by using a long lens to magnification by moving closer, however, the telephoto shot appears to compress the distance between objects due to the perspective from the more distant location. Long lenses thus give a photographer an alternative to the type of perspective distortion exhibited by shorter focal length lenses where (when the photographer stands closer to the given subject) different portions of a subject in a photograph can appear out of proportion to each other

Tuck your elbows into your body to create a triangular formation, which will allow you to steady the lens better. This position allows your upper arm to rest against your chest, lessening the burden of the lens on your biceps. Of course, this means that the lens will move with every movement of your chest, so proper breathing technique is in order. Before you shoot, take a half-breath by filling your lungs partially with air, hold it for a few seconds and then fire off by pressing the shutter release button fully and not releasing it abruptly. The rationale behind the technique is simple. When you fill your lungs with air completely or when the lungs are totally empty of air, you feel uncomfortable and you're thus unable to focus on the shooting. The few seconds afforded by the partial fill of air gives you enough time to fire off your shot. Do not squeeze the shutter button abruptly as this may lead to camera shake, but gently depress and hold it for a couple of seconds after the shutter has fired. Push the camera against your face (don't overdo it though) for greater stability

Telephoto lens, a lens in which the focal length is greater than the dimensions of the lens itself. This is achieved by designing the lens to have a negative rear element, which increases the focal length by moving the rear nodal plane (from which the focal length is measured) forward to a position in front of the lens itself. The earliest telephoto lenses were simple small Galilean telescopes with the eyepiece racked out far enough to produce a real image. The first fully designed telephoto lens was produced by Zeiss in 1898. It had a variable power of ×2-×3, and was thus an early example of a varifocal lens.

The photographer often moves to keep the same image size on the film for a particular object. Observe in the comparison images below that although the foreground object remains the same size, the background changes size; thus, perspective is dependent on the distance between the photographer and the subject. The longer focus lenses compress the perception of depth, and the shorter focus exaggerate it. The perspective of the so-called normal lens, 50mm focal length for 35 mm film format, is conventionally regarded as a "correct" perspective, though a longer lens is usually preferred for a more correct perspective for portraits

Always use a tripod for optimum sharpness if you can, but if you are unable to use a tripod, there are various holding techniques to assist you in getting better stability while shooting. If there are walls, benches, trees or lamp posts to lean on, they can provide a very stable support for you.

Alternatively, if you have a bag or a jacket, you may also use it as a soft support to prop your lens against. Some photographers use a soft bag filled with beans or sand to support their long lens, while being able to shift the lens in a flexible manner due to the non-rigidity of the bag support.

selective focus

The longer the focal length, the less depth of field the lens has. Telephoto lenses have very narrow depth of field, which makes accurate focusing much critical than when shooting with wide-angle lenses. This can also be used to good effect, when you want to use selective focus to draw attention to a certain aspect of the image. Many portrait photographers prefer to use longer telephoto lenses (such as 135mm or 200mm) for the narrow depth of field, so that only the subject is in focus and the background is blurred to focus the attention only on the subject. In such cases of selective focus, make sure that at least the eyes of the subject are in focus.

 In the image of the autumn maple leaves on the right, I photographed them with a 180mm lens shot wide-open at f/2.8 to throw the background out-of-focus. Not only does it focus the attention on the leaves, it also makes the subject looks more crisp and sharp because the eye is forced to focus on the areas that are sharp.

 Compression effect

The optical nature of the telephoto lens creates the illusion of bringing the foreground and the background closer together, creating a compression effect. The image of the left illustrates how the background seems so compressed with the foreground, making it seem so much closer than in reality. This optical quality of telephoto lens is used by some photographers to make repeating patterns more obvious. 

Isolation technique

Because of the longer focal length of telephoto lenses, you can use the telephoto lens to pick out certain elements of the scene you find more interesting. For example, rather than taking the picture of the entire building, you may find certain aspects of the architecture more intriguing than the rest. The use of a telephoto lens can help you isolate the individual elements and present a more selective and personal view of the scene

However, stacking teleconverter lenses does have some drawbacks.

  1. Since the use of a converter lens reduces the image quality of the resulting image, the lenses to be stacked must be of very good quality. Stacking two average lenses will get you poor to very poor results. The reason is very simple. The converter mounted on the camera lens magnifies all sorts of defects coming from the front converter, and delivers a not-so-good image, coupled with its own defects of course, to the camera lens. Consequently, the defects of the first and second teleconverter lenses will be magnified twice and once, respectively. In this way, how could we expect an image of good quality?
  2. Not every two randomly selected teleconverter lenses can be stacked. Let us don't get into too much technical details. The first converter projects an image to the second converter; the second converter takes this image and magnifies and projects the result to the camera lens; and the camera lens takes this image and projects it onto the sensor. If the projected image from the second converter is not large enough to cover the angle of view of the camera lens, vignetting occurs. The same applies to the image projected to the second converter by the first one. Therefore, making sure that the second converter can see completely the image projected by the first converter and the camera lens can see a complete image projected by the second converter is the key of avoiding vignetting. Unfortunately, no lens maker publishes technical data telling us the entrance and exit pupils that are important for us to avoid vignetting. As a result, we can only do experiments. In general, mount the converter lens with a higher power on the camera lens and stack the less powerful lens on the higher power converter. In this way, we are sure the second higher power converter will see through the image projected by the first lower power converter properly. However, the camera may have to be zoomed all the way in to see the final image.
  3. But, the key question is whether two converter lenses can be stacked together. Certainly, one of them must have a front thread. If the higher power one has a front thread, we are lucky. If only the lower power one has a front thread, we may see some vignetting, although we must test to determine if vignetting is really a problem. Most people can live with some vignetting and crop the image. But, no one would like to see a significant vignetting that only shows an image circle!
  4. All front mounting teleconverter lenses will increase the minimum focusing distance. As a result, stacking teleconverter lenses will usually increase the minimum focusing distance drastically. It may be worthwhile if you wish to shoot distant subjects. On the other hand, if the subjects are close to the shooting position, the use of the camera lens or only one teleconverter lens may be more promising. 
  5. Good teleconverter lenses are usually heavy, and stacking two together would be even heavier. Furthermore, the image stabilization feature may not function well because the combined focal length could be too long for the OIS system to work properly. A tripod is definitely required. However, the FZ-10 has a tripod hole not on the line of view and mounting heavy converter lenses on a camera may tilt the camera downward and may also damage the lens barrel and tripod hole. As a result, a lens support may be needed

We all know that magnification increases if we stack two or more close-up lenses together. The same holds true if we stack two teleconverter lenses. In general, if one converter has power A and the other has power B, stacking them together would yield a teleconverter of power A×B. For example, the Sony VCL HGD1758 and Olympus TCON-14B have powers 1.7X and 1.45X, respectively. If we can find some way to stack them together, the resulting lens will have a power of 2.465X = 1.7×1.45.

But, what is "stacking lenses" anyway. Actually, it is very simple. We just connect a number of teleconverters together. Because the combo has a higher power, it extends the focal length of the camera lens. The following shows an extreme example: a Sonly VCL HGD1758, an Olympus TCON-14B and a Nikon TC-E15ED 1.5X teleconverters are connected together, forming a "new" teleconverter with a power of about 3.7X = 1.7×1.45×1.5. This combo is mounted on a Nikon Coolpix 5700, and extends the longest focal length of the 5700 from 280mm to 1035mm