Sigma 100-300 mm

The Sigma 100-300 has been in the market for a long time, and they were updated in 2005. The lens comes with a constant f/4 aperture and it was designed to fit the full frame DSLR sensors. The lens comes in a variety of body mounts and has a lens hood and a tripod mount.
The lens also comes with a new multilayer coating that offers a great color performance and at the same time reduces ghosting or flare created by reflections. By design, the Sigma 100-300 will also maintain a minimal light fall-off and ensure that the peripheral brightness is of superior quality. You should expect high optical performance, which is displayed all through the zoon range.
With the Sigma 100-300, you will not worry about aberrations because the two SLD glass elements in the front and rear of the lens enable optical corrections to offer superior quality all through the zoom range. The lens is also available with an inner focusing system, which is responsible for eliminating the rotation of the front element of the lens.
Users of the Sigma 100-300 will benefit from the smooth movement of the zoom and focus rings because they come with the right resistance levels. The rings are made of rubber and this makes it better to handle and easy to turn. The focusing ring will end in soft stops on the different spectrum of focus. Sigma 100-300 also comes with 150 degrees of turning fidelity, making it easier for the users to focus the lens manually. The filters attached to it will not rotate as the lens focuses. 

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Sigma 70-200mm

The Sigma 70-200 is a popular choice for many serious photographers because of the various features it comes with.  It comes with a constant aperture that will make it easier for people to capture photos in different situations. It is also good for taking pictures in lower ISO. This will come handy for shooting in and low light situation. This lens is great for action photography as well.
When it comes to color and contrast, the Sigma 70-200 is excellent. The creamy background blur is facilitated by the presence of the 9-blade apertures. The chromatic aberration is well controlled, but the flare is not so, especially in higher focal ranges. At the 200mm mark, you need to have the sun and other sources of bright light far out of their pictures so that they do not end up with flare that robs the photo of its contrast.
You will not have to worry about distortion when using the Sigma 70-200. The lens shows a little barrel distortion on wide end and pincushion distortion at 100mm, which increases as it reaches the 200mm focal length. When it comes to vignetting, there will be little shading from 135mm to 200mm when the lens is at f/2.8. This phenomenon is especially visible if you use it with full frame cameras.
In order to avoid such problems, it is important that you stop the Sigma 70-200 lens down one or two stops from the maximum aperture. The users will also benefit from the fast and silent autofocus thanks to the Hyper Sonic Motor (HSM). The HSM is not only crucial for internal focusing but also helps in internal zooming. The front element of the lens will not rotate, making it possible to use it with the petal shaped hood.

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Sigma 50-150mm

The Sigma 50-150 combines the focal length range, size and weight as well as the wide aperture from the more professional telephoto lens. It comes with a flat plane of sharp focus but with a slight curve or distortion at the wide end. It comes with the latest optical technology and offers the users a good correction for ghosting, flare and aberration thus assuring them of high quality images all through the zoom range.
While the flare is well controlled at the 50mm mark, it is at its best at the 150mm. For the focal length, the transition is linear. Users will start noticing a mild barrel distortion in the center of the frame when the Sigma 50-150 lens is at 50mm and pincushion distortion at 80mm and 150mm. It can be quite strong on those two focal lengths.
When it comes to chromatic aberration, it is noticeable at 100mm at the corners, although it is not present at 50mm and 70mm. It becomes even stronger at the 150mm mark. With the Sigma 50-150, users will also experience vignetting at the corners at 150mm. Fortunately, they can clear up all the shaded region by f/4 and f/5.6 for corners that are evenly lit.
The Sigma 50-150 also comes with nice physical features. It has the HSM mechanism that is suitable for internal and rear focusing mechanism. The AF is not only moderately fast but also quiet. Manual focusing will produce some squeaking noise, but it is not loud or significant at all.

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Sigma 18-200mm OS

The Sigma 18-200 OS comes with a 11x zoom range and an image stabilization feature that makes it a versatile tool, especially for those who want a travel lens. With this product, the users will be able to capture different focal lengths ranging from telephoto to wide angle.
It comes with two SLD glass elements and two hybrid aspherical lenses that will correct the different types of aberrations. The housing of the Sigma 18-200 OS is not only compact but also light in weight. It weighs 14.3 ounces and measures 70mm in diameter and 78.1mm in length. It also comes with a new lens coating that will not only reduce both flare and ghosting but also b ring about an optimum balance in color.
What makes the Sigma 18-200 OS different from its predecessor is the Optical Stabilizer function - a unique technology from Sigma. This system applies tow sensors that will detect the vertical and horizontal movement of the camera so that it compensates the camera shake. This makes it a great choice for those people looking to take great handheld shots. The users will be able to capture photos in low light conditions without using a tripod.
The optical performance of the Sigma 18-200 OS is facilitated by a special low dispersion (SLD) lens and 3 aspherical glass elements. They will correct the aberrations and offer high quality images across the zoom range.

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