Showing posts with label Aperture. Show all posts
Showing posts with label Aperture. Show all posts

Tuesday, 15 February 2011

Sigma 17-50mm f/2.8 EX DC OS HSM FLD Large Aperture Standard Zoom Lens for Canon Digital DSLR Camera

Buy Sigma 17-50mm f/2.8 EX DC OS HSM FLD Large Aperture Standard Zoom Lens for Canon Digital DSLR Camera Order Today!


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$669.00
Date Created :
Feb 15, 2011 08:17:05
Sigma's new 17-50mm F2.8 EX DC OS HSM large-aperture standard zoom lens covers a focal length from 17mm wide angle and offers a large aperture of F2.8 throughout the entire zoom range, making it ideal for many types of photography especially portraiture and landscapes. The OS, Sigma's anti shake feature offers the use of shutter speeds approximately 4 stops slower than would otherwise bepossible. The OS feature allows Sony and Pentax users the option of viewing a stabilized image in the viewfinder, a feature offered only by Sigma. HSM provides fast and quiet AF. Sigma's own FLD glass elements, which have performance equal to fluorite along with two glass mold and one hybrid aspherical lens, provide excellent correction for all types of aberrations. The Super Multi-Layer coating reduces flare and ghosting. This lens boasts superior peripheral brightness and provides sharp, high contrast images even atthe maximum apertures. With a minimum focusing distance of 11 inches throughout the entire zoom range and a magnification ratio of 1:5. When you need to stand ready for any photo opportunity you need a fast aperture so you can shoot in low existing light or at maximum range with a flash. This Sigma lens is perfect. With its compact size and light weight, it's a necessary addition to your camera bag Please Note Vignetting will occur if the lens is used with digital cameras with image sensors larger than APS-C size or 35mm SLR cameras.

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Sunday, 26 December 2010

How To Use Lens Aperture Correctly

camera lens


All camera lens apertures are controlled by a metal-bladed iris. The size of the iris can be set by the photographer using the standard aperture scale, which begins at 1, (the maximum aperture) and decreases on a logarithmic scale that is based on the square root of 2, which has the value 1.4142.

The trick really is to use an aperture with a shutter speed that gives the correct exposure. Fortunately, with today's digital cameras all you need to do is to select the appropriate aperture and the camera's electronics will select the correct shutter speed to give the right exposure.

This will always happen on a D-SLR that is set to Aperture Priority mode. If you want to get creative you can always put a D-SLR in Manual mode and independently set both the aperture and the shutter speed. Normally you choose the aperture first, and then set the shutter speed. If you do it in reverse it will not work.

You need to understand that when selecting large apertures you will always produce photos that have a shallow depth-of-field. This means that the background in particular and sometimes the foreground of a subject is out of focus. This result is ideal for portrait images, and when you do not want any distraction in a scene.

If you need much more of the image to be in focus you will need to select a smaller aperture. Unfortunately, a smaller aperture means that there will be less light entering the lens and therefore the shutter speed will be automatically reduced to maintain a good exposure.

A slower shutter speed means that there is more chance of experiencing camera shake, which inevitably leads to image blurring. It is a fine balancing act really. Either you lose depth-of-field to attain the right exposure, or you get blurring because there is not enough light.

However, there is a neat way around this problem. To reduce the risk of image blurring all you need to do is to set your camera on a bean bag or tripod, then use a remote release cable or the camera's timer, and away you go.

Lens aperture measurements are really fractions of the len's focal length and are expressed as f/numbers, like f/2.8, f/5.g, f/16, etc. These are also called f/stops, or just stops. The larger the f/number, the smaller is the aperture. So an aperture of f/22 is a lot smaller than one of f/6.3.

You can easily master lens aperture providing you follow the proven principles in this article. Mastering lens aperture is not difficult - it can be done. Use these strategies and very soon you could be the expert photographer you know you can be.

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