Camera Lenses

Digital Camera Lenses

Lens makes the image of the object on the image sensor. The photographer’s skill goes through the lens. Lens manufacturers work very hard to release new lens models with lower geometric distortions, better image clarity at continuously decreasing price. Its importance is obvious. This article highlights some basic aspects of camera lenses for better use of any lens and recommends you the best lenses for major subject categories.

 

Crop factor is the number showing the ratio between the diagonal of 35mm film format and the diagonal of a particular image sensor. Full-frame image sensor collects the entire image of the lens designed for 35mm film camera; therefore the sensor gets the entire light collected by the lens, as you see in Cropped Images schematic. With a full frame camera, you expect the best outcome in angle of view and also in picture details. For full-frame sensor, camera sensitivity is limited only by the image sensor’s technology for a given lens. We recommend the best wide angle lenses for digital SLR:


APS-C sensor has 25.1×16.7mm with aspect ratio 3:2 and crop factor 1.6. It is encountered in Canon EOS Rebel T3i,18MP, CMOS APS-C Sensor, DIGIC 4 Image Processor and also in other very successful digital SLR cameras. With its 18MP pixel count at relatively small size, the sensor renders very well fine details of the image, as you can see in the sample image below.

 


The link between the lens for digital SLR and the image sensor is obvious. Lenses for digital SLR must fit the entire line of cameras, from the lowest cost up to high-end units of the same manufacturer. Major differences between different camera grades come from the combination image sensor and digital image controller. Smaller-size image sensor at lower cost crops from lens image the central part with inherent loss in sensitivity or in ISO_number. Full-frame image sensor has the same angle of view like 35mm film camera captures the entire image from the lens. APS-H is an older version of image sensor with crop factor 1.3. It is encountered in products such as Canon EOS 1D Mark IV, 16.1MP CMOS Digital SLR Camera. However, you should keep in mind that the image sensor might see less from the image than you see through the viewfinder. Lower the crop factor, less image area covers the image sensor. The picture always shows what the image sensor has on its surface. We recommend the best lenses for APS-C sensors:




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Focal Length defines the size of the viewing angle of the lens. Smaller focal length lenses have larger viewing angle and gets less details of the scene. Longer focal length lenses have smaller viewing angle, but you get more details from the scene. The schematic Focal Length Comparison above give you an idea about the pictures of the same subject shot with two lenses with very large difference between their viewing angle. The available focal length of today’s lenses cover a broad range, from 10mm to 800mm. Lenses can have either fixed focal length or can have variable focal length or “zoom” within a certain range to expand part of the scene. Generally, fixed focal length lenses give pictures with more details and less distortions than the zoom lenses. With a zoom lens, you can select quickly just part of the scene without changing the lens or the the distance from camera and the scene. With a zoom lens, you just increase the focal length of the lens until you reach the desired detail, of course limited by maximum focal length. This can be very useful in many situations. Sometimes, you cannot go close to the scene as you wish. However, the “default” lens of the camera is subject to the operator’s choice.

 


Aperture marked on the lens as f/# selects the depth of field and also controls the light flux through the lens. Smaller f/# gives a clear image within a small depth of field, providing better image resolution or sharpness within the depth of field. Larger f/# gives larger depth of field, but with some loss in details. Diffraction is the physics behind this.


 


Exposure and Image Focusing jobs are preferable to be transferred to digital cameras. The digital SLR cameras have very sophisticated methods to measure the light. The diagram Light Metering Zones shows the light metering zones used by major digital SLR camera manufacturers such as Nikon and Canon. For most cases, auto focus does a better job than any operator unless special effects are targeted through manual settings.

Image sharpness as explained above assumes neither camera shake, nor subject shake when shooting, picture size selection on camera as medium or large, and no zooming when viewing the picture on 1920x1000pixels LCD monitor. Briefly, blur in digital images comes either from shooting conditions, or from electronic conditions such as storing and viewing. Some comments on image blur from shooting conditions can be helpful.

 


In the schematic Blurred Image Cases, the top row shows on the left hand side an image improperly focused on far field, behind the subject, sitting in the front. The correct picture is beside it. The middle row shows on the left hand side the situation when the camera moves during shooting: everything is blurred. Beside it is the correct picture. In the picture on the bottom row, left hand side, the subject is moving during shooting: it appears blurred, compared with the clear surrounding. In the picture beside it, the subject does not move during shooting and the picture appears clear everywhere.

Hint: Improve your photographic skills by analyzing your bad pictures. The examples above refers only to blurred pictures, but can be other situations such as improper lighting, exposure, framing, to name just a few, which will be discussed later.

 


Image Stabilization is a very interesting lens feature, almost standard encountered at digital camcorders. Image stabilization provides sharp image when the camera shakes for different reasons. Read more about image stabilization in Advanced Lenses article.

We recommend several Image Stabilization lenses from Canon. For more lenses with Image Stabilization feature, follow the link.



Below we show sample images shot with recommended Canon Image Stabilization lenses.


 

We recommend several Vibration Reduction lenses from Nikon. For more lenses with Vibration Reduction feature, follow the link.



Below we show sample images shot with recommended Nikon Vibration Reduction lenses.



 

Camera lenses is a very competitive market. Certainly, lens price is strongly linked to its features.

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