DSLR Buying Guide - Choosing
DSLR sensors come in different sizes. These are described by the FLM which indicates the proportion of the sensor in relation to 35mm film. A camera with a sensor the same size as 35mm film is called a Full-Frame camera and therefore has a FLM of 1. Smaller sensors are called Cropped-Sensors. Most common factors using in DSLRs and Mirrorless cameras: 1.5Nikon, Pentax, Sony, some Sigma, Konica-Minolta and Fuji., 1.6Canon only. and 2Olympus and Panasonic..
The top 5 consequences of sensor-size are:
- Larger sensors gather more light during a given exposure. Physics says that more light gathered equates to less noise and greater dynamic-range. Technology innovations make sensors perform better but a larger sensor will always be superior to a smaller one based on the same technology.
- Larger sensors require larger lenses for more light to reach the sensor. This makes cameras with smaller FLMs more vulnerable to lens defects near the outer edge of a lens. Digital cameras with a larger FLM use the best part of a lens but may stress more its ability to resolve tiny details.
- Larger sensors show less depth of fieldBetter for portraits, worse for landscapes and architecture at a fixed aperture. This increases their ability to isolate a subject from its background, particularly at close focus distances. Conversely, the lens on a camera with a larger sensor has to be stopped down more to get the same depth-of-field. Full-frame DSLRs usually have larger pixels, so they can be stopped down more before hitting their diffraction limit.
- The angle-of-view of a lens is proportional to the sensor size. The effective focal-length of a lens is equal to the actual focal length multiplied by the FLM. On a full-frame DSLR, a lens for a film SLR has the same angle-of-view. On a camera with a 1.5X for example, the angle of view of a 50mm lens is the same as a 75mm lens on the full-frame since 50mm x 1.5 = 75mm.
- Lenses are designed for a minimum FLM. So, a full-frame lens is designed for a FLM of 1 and can be used on smaller sensors too, like those with a FLM of 1.5. The converse is not true. Some full-frame cameras allow the use of lenses for cropped-sensors by automatically cropping the image.
The FLM, also called Crop-Factor as mentioned in the previous page of this DSLR Buying Guide, is sometimes given names instead of numbers. A crop-factor of 2X is called Four-Thirds based on the name of the standard which introduced DSLRs with a 2X FLM and aspect ratio of 4:3. A crop-factor of 1.5X is called APS-C which is a historical name for film with that size. APS-C is also used to describe a crop-factor of 1.6X when talking about Canon DSLRs. APS-H is the name for a FLM of 1.3X and Full-Frame is the name for a FLM of 1.
Anti-Shake and Stabilization
Two approaches exist for reducing the effects of camera shake by involuntary movements of the photographer. One way is to incorporate stabilization into the camera body. This way was pioneered by Konica-Minolta and works by moving the sensor to compensate for camera movements. It was originally called Anti-Shake. Sony, who purchased the technology, calls it Super-Steady-Shot. Pentax developed similar technology which it calls Shake-Reduction. Olympus takes the same approach and simply calls it Image Stabilization.
The second approach that all other manufacturers take is to embed stabilization in select lensesMostly in lenses with a long focal-length. by moving an internal lens element. Each manufacturer has a name for it:
- Canon - IS
- Nikon - VR
- Panasonic - Mega OIS
- Sigma - Optical Stabilization
- Sony - OSS
Both sensor-shift and optical stabilization appear to be equally effective, allowing at least 2 to 3 extra stops of hand-holding ability, although manufacturers claim up to 5 now! In other words, shutter-speeds can be 4 to 8 times slower than without stabilization. The difference between these two mechanisms is:
- Body-based stabilization applies to all lenses and its cost is incurred once per camera. This is excellent for legacy lenses and for those without stabilized counter-parts such as bright prime lenses and fisheye ones.
- Optical stabilization is only available on selected lenses and its cost is incurred once for each such lens.
- The effect of optical stabilization can be seen through the viewfinder. This possibly makes it easier to frame hand-held with very long telephoto lenses.
A lens mount is the physical connection between a DSLR and lenses. The specific mount used by a DSLR is decided by the brand of camera. Choosing a particular camera brand gives access to the lens line-up of that manufacturer and is in fact one of the most important considerations when buying a DSLR. This is detailed in Choosing a DSLR brand which is the next page of this guide.
A lens mount has 2 purposes. It connects and enables communication between a camera body and its lens. Since physical connections have seldom changed, most lenses can be physically connected to a body with the right type of mountEach manufacturer has its lens mount, except for Fuji DSLR which uses a Nikon lens mount.. As lenses were modernized, new features were added to newer lenses and mounts. The consequence of this is that most older lenses can mount on cameras from their manufacturer but not all such lenses fully function on DSLR cameras.
Certain third-parties make lenses for multiple mounts which generally differ specificationwise and qualitywise from camera manufacturers' line-ups. When purchasing a third-party lens, it is critical to choose the one with the correct mount depending on your camera.
There are two major types of lenses: zoom and prime. A zoom lens is one which can change its focal-length, causing it to vary the angle-of-view it covers. A prime lens has a single focal-length and does not zoom. It approximatelyThere is often a small variation as the lens focuses. shows a fixed angle-of-view on a given camera at all times.
Zoom lenses are very versatile and perfectly precise when it comes to framing. For this reason, they are the most commonly sold and uses lenses.
Prime lenses are generally advantageous in terms of weight and size. Their simpler design, compared to zoom lenses, lets them have a wider maximum aperture which lets more light inThis is mostly important for low-light and indoor shots and produces images withmore shallow depth-of-field. They have a reputation for higher image quality which is being disputed.
When a zoom lens is labeled with two maximum apertures, one is the maximum aperture at the shortest focal length and the other is the maximum aperture at the longest focal length. When a lens is labeled with one maximum aperture value, the maximum aperture is the same across all focal lengths. Almost all modern lenses are auto-focus lensesThey can also be focused manually., as opposed to manual-focus ones that must be focused manually. A lens which can focus closer than a typical one is labeled as a macro-lens.
Like cameras, lenses come in different qualities that cannot be guesse from specifications alone. Also, each manufacturer has designations for lenses of various qualities. Lens quality determines its potential sharpness, resolution, contrast and aberrations. Lens quality strongly influences autofocus-speed when it includes a focus-motor. Canon lenses with a quick and quiet focusing system are labeled USM, Pentax labels those SDM, Nikon calls those as AF-S and Sony calls them SSM.
TIP Read the Lens Buying Guide for more information about understanding and choosing lenses.
Lenses must be primarily chosen by their angle-of-view on a particular DSLR. Commonly, the 35mm equivalent focal-length is used instead. In 35mm terms:
- A 50mm lens is considered normal because its shows perspective similar to the perception of a single human eye.
- 35 to 70mm lenses are considered standard. They are used for general purpose photography and snapshots.
- Lenses longer than 70mm are considered telephotoTypical for close-ups.
- Lenses longer than 250mm are considered ultra-telephotoTypical for wildlife.
- Lenses shorter than 35mm are considered wide-angleTypical for indoor shots and architecture.
- Lenses shorter than 24mm are considered ultra-wide angle and show pronounced perspective distortion. Much shorter lenses are mostly fisheye lensesLenses which do not preserve straight lines unless they pass through the center of the frame..
- Portraits are often taken around 105mm, since it produces a pleasing perspective.
To get started on which lenses are needed:
- Select a range of useful focal-lengths and divide by the camera's focal-length-multiplierFor example, the 35mm equivalent 36-120mm range on a camera with a FLM of 1.5 is 24-80mm.
- Divide the maximum by the minimum focal-length to determine the optical zoomIf the range is 35-105mm, then the optical zoom is 105 / 35 = 3X.
- If the optical zoom is higher than 15X, then more than one lens will be required.
- If the optical zoom is higher than 6X, it may be possible to get a single lens but such a lens typically compromises on image quality.
- A single zoom or several prime lens can be chosen when a short range is required.
- Select one or more lenses to closely match the desired range. Additional requirements such as maximum aperture and minimum focus distance can be considered here to make a final decision.
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