camera lenses
choosing a lens
a lens as an investment - reliability and redundancy
many photographers will tell you that money spent on a good lens will be a better investment than money spent on the camera
this is historically generally true
money spent on “kit” zoom lenses is generally not a good investment as these lenses generally have average build quality, average optics and poor apertures which severely limits their utility in low light and for creating blurred backgrounds
users are generally advised to buy a wider aperture lens of better optical quality
digital cameras in particular now are almost “disposable” with even the high end expensive cameras having a real life of perhaps only 5-7 years, and will depreciate rapidly in value as they will be surpassed by cameras with more features, better sensors and better AF, IS, HD video and connectivity technologies
high quality, mechanical, manual focus lenses will generally last for decades if they are not dropped, scratched or allowed to develop fungus on the optics
modern AF lenses will fail over time as they have rapidly moving parts and electronic components - both have failure rates and when used frequently are likely to fail over their 1st 10 years
additionally the lens features may make it redundant over time - particularly as an investment:
the AF motors in the lenses are continually improved, particularly for the new contrast detect AF cameras which rely on newer technology AF motors
the
image stabiliser technology continues to improve making older lenses less effective
optics tend to be developed over time to provide improved sharpness to better match the higher pixel density in modern sensors - old lenses often do not allow these sensors to shine
those purchasing a system may well consider the benefits of buying a system where the image stabiliser is built into the camera such as Sony NEX E-mount camera system or Micro Four Thirds system, as this not only means EVERY lens gains IS capability without requiring optical IS and its increased failure and redundancy rates, and you potentially gain the benefit of improved IS every time you upgrade the camera to a newer camera which you will have to do anyway with any system.
those who cannot tolerate extended outages from delays in repair, need to consider access to service and turnaround times - this is a major reason why many pros stick with Canon or Nikon as they are more accessible worldwide
finally, demand for particular lenses changes over time
what focal length?
this is not an easy question to answer as it entirely depends upon YOU like to photograph
the following are focal lengths in terms of a 35mm full frame camera system
most will be able to photograph most subjects they need with just 3 lenses:
compact, light 3x zoom lens covering 24-70mm region
compact wide aperture 35-40mm prime lens
wide aperture short telephoto lens
other lenses as per their individual needs
use
Lens-GAS free software to rapidly chart the focal lengths of the photos in a folder to see which ones are most commonly used
the compact travel zoom lens
this is the lens you take when you have plenty of light (eg. outdoors, daytime), and you really have no idea what you might suddenly want to photograph, so a range of focal lengths becomes very handy
you will have to decide upon the compromises of zoom range, aperture, image quality, cost, weight and size
for many, a small, light 3x zoom lens covering 24mm-70mm or 28-85mm will fit the bill
some who are prepared to carry a heavier, longer lens, may opt for a 10x zoom covering 28-280mm
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compact, low light party/candid/street lens
wide aperture short telephoto lens for portraits, blurred backgrounds or indoor sports
the classical portrait lens has a focal length in the range 85-120mm and has a wide aperture to give a shallow
depth of field (DOF) and allow the subject to stand out from the blurred background
such a lens will be far more useful for most enthusiasts than a slow 3-4x 80-300mm kit lens with widest apertures around f/5.6, lower optical quality, slower AF and poorer bokeh.
it should have:
a nice quality to the background blurring (
bokeh)
sharpness across the frame at widest aperture - mostly we do not want our subjects in the centre of the image
relatively compact so it is not intrusive upon the subject
relatively compact and light so we will bring it with us
fast AF, preferably with precise AF selectable on one or other eye of the subject (this is generally a camera functionality - such as Olympus
Micro Four Thirds system)
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full frame users often use 85mm f/1.4 lenses, or 70-200mm f/2.8 zoom lenses although these zooms are big, heavy, expensive, intrusive and prone to failure
Canon pro users sometimes use the 85mm f/1.2 lens but this has slow AF and is not an easy lens to use well
Canon and Nikon cropped sensor dSLR users often resort to a relatively cheap 50mm f/1.8 lens
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night urban street walking wide angle lens
macrophotography lens
what makes a good lens?
other lens design factors
diaphragm blades
this is only important if not shooting wide open
curved or rounded blades allow nicer out of focus blurs without the sharp straight edges of non-rounded blades when the aperture is stopped down
odd number of blades allows for better looking “sunstars”
clickless aperture is better for video work
weathersealing
closest focus and magnification
focus range limiters
optical image stabilisation
autofocus motor system
most dSLR lenses uses the older USM AF motors designed to work only with PDAF technology
lenses optimised for mirrorless cameras have linear stepping motors which may oscillate at 240Hz to optimize both PDAF and CDAF technologies
how silent is it?
how accurate is it?
how much “hunting” does it do
does the front filter rotate on focusing?
does the lens length change on changing focus distance?
most internal focusing lenses have a constant lens length during focus
some lenses extend on focusing and / or on zooming which can make them more intimidating and distracting as well as at risk of dust and water