A presentation to Aberdare Camera Club

Transcription

1 A presentation to Aberdare Camera Club

2 This presentation is divided into three parts: 1. Selecting a lens for particular genres of photography. 2. Matching camera and lens 3. Sorting the wheat from the chaff when buying lenses.

3 The right lens for the job You could easily think that 2 lenses, a short zoom and a long zoom is the ideal way to proceed as this covers all eventualities. To an extent this is true but it may well be too much of a compromise for certain types of photography.

4 Landscapes It is a common misconception that landscapes require wide angle lenses. It s true that most landscapes are shot on mm lenses (35mm/full frame) mm (APS-C) lenses, however longer or shorter focal lengths are used to provide special views. Before the advent of zoom lenses, landscape photographers commonly used 28 or 35 mm lenses and the standard lens which was 50 mm. (approximate APS-C equivalents 18 mm, 24 mm & 25 mm)

5 Landscapes Contd. Compression and Separation These effects will change the view significantly. At long focal lengths you get a compression of the view, in other words object appear closer together. The longer the focal length the greater the effect. At short focal lengths the opposite happens and you get separation, objects appear further apart. A focal length of approx 50 mm gives a neutral view.

6 Landscapes Contd. Understanding these effects can be a useful compositional tool as you give yourself the ability to either combine or isolate items within the image. It does, however, mean you will have to physically move in order to achieve the required composition and no merely zoom the lens. I was once told that the best zoom is your legs. From the point of view of composition this is true.

7 Landscapes Contd. Aperture is generally less critical unless you intend to operate in extreme lighting conditions as you are able to work using a tripod. Having said that if you are hill walking then a reasonably fast lens can be useful as can an image stabilizer as carrying a tripod is not so easy.

8 Action Shots/Sport For action shots the requirements are more complex. High shutter speeds are needed to freeze the action and if you are using longer focal lengths to overcome camera shake. Good image stabilizers (IS) are almost an essential as are fast lenses and ultra fast focus systems. Generally the standard arc drive focus motor of cheaper and older lenses will not be fast enough to keep up with the action. The USM, Silent wave, HSM and HSD motors are what is needed.

9 Action Shots/Sport Contd. The performance of your camera is an important factor for lens selection with this type of photography. If your camera has limited ISO capability you will definitely need IS and as fast a lens as you can afford as you do not have the headroom to push the ISO up. Remember if you are shooting at 200 mm you need a shutter speed of at least 1/200 th without IS and 1/50 th with IS. On a dull day in mid winter in the late afternoon at a rugby match this can be hard to achieve.

10 Nature Photography To a great extent nature photography has similar requirements to sports and action. Long focal lengths, wide apertures and image stabilizers are the order of the day. One additional requirement is that the lens needs to be capable of producing, sharp images with good contrast. Serious nature photographers will generally spend 2 to 3 times the value of their camera on a single lens That's not to say that you can t achieve great pictures with lesser lenses, but this will require a combination of good field craft, good photographic technique and a degree of luck.

11 Nature Photography continued If your kind of nature photography is botanical, then the lens choices will depend on the scale of the subject. Flowers, small plants, individual leaves may well require dedicated macro lenses to get the best results. Image stabilizers yet again can be useful as you will want to use smaller apertures in many cases as the depth of field will be very limited with the lens wide open.

12 Portrait, Fashion and Glamour Photography My favourite subjects. For best results I would go for prime lenses. 35mm, 50mm, and 85mm f1.8 or faster. However a zoom that covers these focal lengths is a good compromise, say 24 70mm and as fast as you can afford. The trouble is that this particular focal length range is quite difficult to produce so good lenses can be rather expensive.

13 Still Life, Tabletop and Macro I have lumped these together although they can be very different in requirements. Still life and table top photography generally use artificial light sources so lenses do not need to be super fast. You can usually use a tripod so image stabilizers are no important. Extremely good sharpness and contrast are essential as are good performance stopped down to f8 f11 as this may well be required in order to get sufficient depth of field.

14 Still Life, Tabletop and Macro continued Macro photography is quite specialized and does require macro lenses. Unfortunately manufacturers have a bad habit of labelling a lens Macro merely because it has a short minimum focus distance. True macro lenses are actually optimised to perform at their best over short distances. All the very best macro lenses are primes and have focal lengths between 50mm and 150mm. There are one or two zooms that give acceptable macro performance. Macro lenses need to be very sharp and have good contrast.

15 There is a popular misconception that it is not worth putting good lenses on cheaper cameras. WRONG, WRONG, WRONG. Most modern DSLR s are capable of producing high resolution pictures and will benefit from good glass. Further, whilst cameras are out of date after 2 3 years, good lenses commonly have a product life of 10+ years. For example: Canon list no less than 24 lenses that were first introduced before year 2000 and 5 that were introduced on or before Nikon have similar statistics. Investing in good glass is the best thing you can do.

16 Remember you can to some extent correct for limitations with the camera body by using a better lens. If you camera has poor ISO performance but is fine in every other respect, a fast image stabilized lens will help you to achieve better results in low light. Conversely if your camera has very good high ISO performance an image stabilizer is of less essential to you.

17 There are so many things to consider when buying lenses. Making a good choice will save money in the long term. Lenses have, as I previously said, a longer potential life than the camera body. You should always ensure that the lens is suitable for your requirements before checking on its performance. Reviews vary considerably and You need to look at several to form an opinion. If possible try the lens for yourself by perhaps hiring it.

18 There are so many it can be confusing but many have similar effects. Set out is a list of the ones that you will come across. 1. Aberration. Failing in the ability of a lens to produce a true image. There are many forms of aberration and the lens designer can often correct some only by allowing others to remain. Generally, the more expensive the lens, the less its aberrations (More attention to optical quality). While no single lens is called a 'perfect lens'. The "ideal" lens would reproduce a subject in a faithful, clearly defined image on film. Aberrations, which can be divided into six basic faults, affect the Ideal performance in an optical system.

19 a) Spherical aberration. Basically, a beam of light passing through a lens parallel to the optical axis converges to form 3 focused image on the film. Spherical aberration is the term for an optical fault caused by the spherical form of a lens that produces different focus points along the axis for central and marginal rays. b) Curvature of field. This optical defect causes points on an object plane perpendicular to the lens axis to focus on a curved surface rather than a plane. c) Astigmatism. Rays of light from a single point of an object which is not on the axis of a lens fail to meet in a single focus thus causing the image of a point to be drawn out into two sharp lines, one radial to the optical axis and another perpendicular to this line, in two different planes near the curvature of field.

20 d) Coma. This optical defect causes the image of an off-axis point of light to appear as a comet-shaped blur of light. Coma, as well as curvature of field and astigmatism, degenerate the image forming ability of the lens at the rims of the picture. e) Chromatic aberration. This aberration is caused by light rays of different wavelengths coming to focus at different distances from the lens. Blue will focus at the shortest distance and red at the greatest distance. Since the natural rays of light are a mixture of colours, each aberration will give a different value corresponding to each colour thus producing blurred images. All the above aberrations will tend to make images look soft, particularly toward the edges of the frame.

21 Other Faults a) Distortion. Even if these aberrations are totally eliminated, images could result that still have a distorted appearance. For an example, a rectangle may appear as a barrel or pin cushion-shaped object. b) Vignetting. Vignetting is where the corners of a photo are darker. On occasion vignetting is used by the photographer to draw attention to the centre of the photograph. Normally it is unwanted.

22 c) Lens diffraction. If you re using good technique and your images are still losing important detail, it may be due to lens diffraction. It s caused by using a very small aperture to gain a greater depth of field, and results is a slight softening of the image. This is caused by light rays being 'bent' (diffracted) as they pass through an aperture, the smaller the aperture the greater the diffraction. d) Lens flare. Lens flare can easily ruin or detract from a great picture. It occurs when a light source, usually the sun, reflects off elements within the lens. This is more likely to be a problem with cheaper zoom lenses. Prime lenses are least likely to exhibit the problem.

23 e) Bokeh. Bokeh occurs in areas of photographs that have been thrown out of focus. Bokeh appears as jagged looking circles. While all lenses produce Bokeh a good quality lens will produce it with a much softer and rounded look. This helps to make it blend into the background or even give it its own stylish look as part of a photograph. As a rough rule of thumb the more you pay for a lens the better your Bokeh is likely to look. Cheap lenses, including those that are sold as part of a Digital SLR kit can suffer a lot from bad Bokeh this due, in the main, to the design of the diaphragm.

24 Finally lets talk about Sharpness Sharpness is not one single thing but a combination of two factors: 1. The focusing ability of the lens 2. The contrast of the lens. A lens may focus sharply but if it produces poor contrast it will appear soft. You are, therefore, looking for a lens that performs well in both these areas. The standard way that these are measured is on an MTF (Modulation Transfer Function) chart. I won t attempt to explain the science behind these graphs but they are supposed to give an accurate measure of lens performance. Unfortunately this is not strictly true, although they can give an indication of performance.

25 Canon Lens Abbreviations and acronyms How Canon describe their EF and EF-s or L series lenses Canon produce an wide range of lenses for EOS cameras which married with Sigma, Tamron and Tokina gives Canon owners a collosal choice of Canon Fit SLR Lenses. The abbreviations used by Canon are as below. EF: Electronic Focus. Lens mount fitting the entire Canon DSLR system. EF-S : As above but only fitting on a Canon's APS-C sized digital SLRs such as the 60D, 7D and 500D, 550D, 600D & 650D. The S stands for "short back focus," meaning that the back of the lens is much closer to the CMOS (CCD) than with EF lenses. USM : USM is Ultrasonic autofocus. There are two types is USM. Micro- USM (a direct replacement for the systems on older FD motors) and a faster 'Ring USM' which includes manual override.

26 Canon Lens Abbreviations and acronyms Contd. DO: Diffractive optics. A technology which allows Canon to make lenses with long focal lengths without the normal increase in physical size. TS-E : Tilt-shift lens for architectural photography. altering the perspective of converging lines and depth of field. L Lenses : Canon's professional lenses. Refers to their optical quality not necessarily anything specifically functional. Usually white in colour. always having a red ring around the end. MP-E : Macro Photo Electronic are for macro work through the use of electronic aperture control. IS : Image Stabilisation.

27 Nikon Lens Abbreviations and acronyms AF DC_ Nikkor Lenses : Defocus-image Control that adjusts the spherical aberration and therefore the blur giving rounded defocussing effect often used in portraiture. CRC (Close-Range Correction) : Used in fisheye, wide-angle, Micro, and limited medium telephoto, offering high quality at closer focusing distances. DX Nikkor : As with Canon EF-S lenses, DX lenses are optimised for cameras with smaller sensors. They will fit on other cameras but this is not recommended. ED: Extra-low Dispersion glass. Gives superior sharpness and optimal colour by correcting the diferences between the angles that blue and red light travel in as they pass through the lens. IF : Internal Focusing. the focussing mechanisms are within the lens ensuring the lens remains the same size as focal length is changed.

28 Nikon Lens Abbreviations and acronyms Macro : Lens designed to capture subjects closer to the lens. G : No aperture ring. Aperture is adjusted electronically by the camera body. Nano Crystal Coat : non-reflective coating for clearer images with increased detail by reducing reflection from inside the lens. VR: Vibration Reduction : Nikon's version of Canons IS system, designed to cut down on the effects of hand shake. PC-E: Perspective Control similar to Canon's Tilt and Shift Lenses. RF: Rear Focusing. Uses the rear group of lens elements to focus giving faster and smoother AF. Silent Wave Motor : Silent Auto focussing (as Canons USM)

29 Sigma Lens Abbreviations and acronyms EX : Pro lenses offering highest optical quality. DG : Like EF lenses, DG lenses are designed to be used with both full frame and cropped frame sensor cameras. Sigma DG lenses also include additional coatings to reduce reflection. DC: Short for Digital Crop. They canonly be used on cropped frame cameras. they are also lighter and often less expensive. ASP: Aspherical lens. Smaller than normal lenses. APO: Apochromatic lenses with low dispersion glass to limit chromatic aberration.

30 Sigma Lens Abbreviations and acronyms OS: Optical Stabilisation. As Canon IS or Nikon VR. HSM: Hypersonic Motor. As Canon's USM system. RF: Rear focus. The rear elements are moved for quieter and faster focusing. IF: Inner focus lenses move the middle lens elements, ensuring the lens remains the same length throughout its focal range. This is useful on longer shots as it reduces hand shake. DF: Dual focus. Does not rotate while auto focusing.

31 Tamron Lens Abbreviations and acronyms ASL : Aspherical Glass. AD : Anomalous Dispersion. Reduces chromatic aberration.. Di : As Sigma DG lenses. Di II : For APS-C frame sized cameras (as Canons EF-S). IF : Internal focus. Lens stays the smae length reducing hand shake at longer telephoto lengths LD : Low Dispersion Glass to reduce chromatic abberation Macro : For focusing on nearer subjects SP : Super Performance. Tamron's best lens range. XR : Extra Refractive Glass for improved optical results. VC: Vibration Control as found on Canon's IS, Sigma's OS and Nikon's VR

32 Focal Length: 50mm (Single for prime lenses) Aperture: Aspherical: 24-70mm (min and max for zoom lenses) 1:2.8 (Maximum aperture constant for all focal lengths) 1: (Maximum aperture varies as lens is zoomed in) Aspherical elements in lenses are a way of reducing aberrations.

33 Elements & Groups: Elements refers to the number of individual lenses and groups to the number of composites (two or more lenses fixed together). The reason for this complexity it to correct aberration but this may cause other unwanted effects such as lens flare. This lens has 11 elements in nine groups.

34 APO (Apochromatic): Low Dispersion Glass: Corrected for both chromatic and spherical aberration. Glass that has a different refractive index. Used in a doublet with higher dispersion glass to produce a group that will reduce aberations.