Sigma 18-250/3.5-6.3 DC Macro OS HSM
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By revolutionizing the optical and structural design of the Sigma 18-250mm F3.5-6.3 DC OS HSM, this new lens achieves a compact size and a minimum focusing distance of 13.8". New material, Thermally Stable Composite (TSC) maintains its structure and has little contractility especially in varying temperatures, is incorporated into the lens barrel. It is convenient when you wish to keep your equipment to a minimum and yet still be prepared for all opportunities and situations, such as travels.
A wide range of photography is possible in one lens
Covering wide angle 18mm to telephoto 250mm, this versatile lens designed exclusively for digital SLR cameras, is suitable for all-purpose photography including landscape, sport, and macro photography. It is convenient when you wish to keep your equipment to a minimum and yet still be prepared for all opportunities and situations, such as travels.
Excellent for macro photography
Close-up capability is improved with the minimum focusing distance of 13.8" throughout the entire zoom range, and maximum magnification ratio of 1:2.9. In APS-C size equivalent, macro photography with approximately 1:2 magnification ratio is possible. In addition, with this lens, the size and flaming of subjects can be adjusted by rotating a zoom ring, making macro photography easier than using fixed focal macro lens. For further convenience, the maximum magnification ratio at each focusing distance appears on the side of the lens barrel.
Revolutionizing the design foundation results in compact size
Optimization of the power arrangement by such things as incorporating double-sided aspherical lenses, and reexamination of design, the filter diameter size is reduced. This compact size lens has the approximately 13x high zoom ratio with the filter size of diameter 62mm, and dimensions of diameter 2.9" x Length 3.5". It ensures portability and overall ease of use, making it perfect for travel and leisure photography.
New material TSC (Thermally Stable Composite)
The new material "TSC (Thermally Stable Composite)", which has little contractility especially in temperature changes, as well as maintaining firmness, is incorporated into the lens barrel. Compared to Polycarbonate which is generally used, TSC has higher elasticity by approximately 25%. Since thermal shrinkage is low, it has high affinity to metal parts which contributes to high quality product manufacturing. It also contributes to the parts such as the zoom ring and scaling to be slimmer
In a conventional lens, focusing requires an extension of the entire lens or the front lens group. However, to better accommodate autofocusing mechanisms and closeup photography, a need has arisen for lenses that do not change their length during focusing or suffer from focus-dependent variation in aberration. Therefore, Sigma has developed focusing systems that only move elements within the lens barrel. These incorporate smaller and lighter moving lens elements which help improve auto-focus speed. With their unchanging barrel length and small variation in the center of gravity, these lenses also enhance balance and stability for the photographer. Furthermore, since the front of the lens does not rotate, polarizing filters can be used with extra convenience.
MTF (Modular Transfer Function) is one of the measurements that evaluates a lens' performance, and it contrasts sensitivity at different spacial frequencies. The horizontal axis is in millimeters and shows the distance from the center of the image toward the edges, and contrast value (highest value is 1) is shown in the vertical axis.
The readings at 10 lines per millimeter measure the lens' contrast ability (red lines), repeating fine parallel lines spaced at 30 lines per millimeter measure the lens' sharpness ability (green lines), when the aperture is wide open. Fine repeating line sets are created parallel to a diagonal line running from corner to corner of the frame, are called Sagittal lines (S) and sets of repeating lines vertical to these lines are drawn, called Meridional (M) line sets.
effective distortion: When you take a picture of a lattice pattern, it will appear as the blue dotted line shows. the red line illustrates how the lattice pattern will appear in the actual picture when any lens distortion is taken into account.
relative distortion: In this chart, the horizontal axis shows the ideal image height (the distance from the center to the edge of the image [mm]). The vertical axis shows the extent of distortion. The extent of the distortion is represented by how much Y, which is the actual image height, grows (or shrinks) against Y0 which is the ideal image height.
Extent of distortion: D[%]=(Y-Y0/Y0)x100
When you take the picture of a square object, if the distortion amount show a minus value, the image will be seen as expanded (Barrel distortion). If the distortion amount is a plus value, it will be seen as a recessed (pincushi on distortion). When the distortion value is close to 0, the appearance of distortion is very minimal.