Intro to Digital Photography: Lenses Notes ===Slide 3 Lenses Are

Intro to Digital Photography: Lenses Notes

===== Slide 3 Lenses are classiﬁed by focal length or by use, such as tilt-shift lenses. When breaking lenses down by focal length, we can put them into three general categories:

Angle of View: Wide angle, Normal angle, Telephoto Prime lenses: ﬁxed focal lengths Zoom lenses: variable focal lengths

Point and shoot camera lenses have what is known as a 35mm equivalence. You might see this listed something like "28-56mm (14-105mm at 35mm)" -- this means that the lens on the point and shoot, if it were on a 35mm (or full frame digital SLR) camera, would give you the same photo as a 14-105mm zoom lens; 28mm on the point and shoot = 14mm on the digital SLR.

When taking photographs, it's all about the optics. I would rather have a superior lens on a mediocre camera body & sensor than a mediocre lens on a superior camera body & sensor. Superior optics will deliver a superior (i.e., optically sharp) image to the sensor. So, here is one of my personal rules about purchasing photographic gear:

Buy the best lens that you can afford at the time.

Another rule:

Buy factory refurbished whenever possible.

A general rule is that the more expensive the lens, the better optically it is. Many companies sell camera kits with inexpensive 18-55mm and 70-300mm (or something similar) lenses. There is a reason that they are called kit lenses: no one would buy them otherwise. Now, this being said, a kit lens is better than NO lens, and you can do a fair amount of things with kit lenses. However, you will eventually want to buy a better lens.

Another general rule is that prime (ﬁxed focus) lenses tend to be cheaper than zoom lenses. Prime lenses are relatively simple lenses while zoom lenses have variable focal lengths, which means that the optics are more complex, and this in turn equates to a higher cost. But the trade off is having one lens that, say, can go from 18-85mm focal lengths, or wide angle to normal angle of view as opposed to having multiple prime lenses such as one at 18mm, one at 35mm, one at 50mm, and one at 85mm. If you're walking around, one lens weighs less than four and you're not constantly changing lenses. If you're in a studio situation, prime lenses might be a better option; you can shoot a series of photos at one focal length, change out the lens, and you don't have to carry them. A third general rule about lenses is that the optics for them tend to be the sharpest from f8 to f11. This is the point of best sharpness versus depth of ﬁeld. Many photojournalists used the term "F8 and don't be late" and left their lenses set for f8.

===== Slide 4 Prime lenses can have a rather larger aperture than zoom lenses for the cost; these are known as fast lenses and are good for low light situations. Any lens with a maximum aperture of below f4 is considered to be a fast lens. On this image the lens is a fast lens with a maximum aperture of f1.4 and a minimum aperture of f16. In front of the front lens you can see some threads; this is where ﬁlters are screwed onto the lens. On this lens, below the focal length / maximum aperture numbers (50mm 1:1.4D) you can see an orange dot and a small piece of moveable plastic--this is the aperture lock, so you can lock your aperture down. This lens also has a manual aperture so you can physically set the aperture from f1.4 to f16.

This lens pictured is called by many the "nifty ﬁfty"--a fast prime lens that, as lenses go, is relatively cheap. Both Canon and Nikon make the nifty ﬁfty and the f1.8 version runs around $250 new.

There has been one argument brought forward about using lenses at their maximum aperture and sharpness. The argument goes that the maximum sharpness is not at the widest opening but one or two stops below; on the lens pictured here, that would mean that the widest you should open it is f2 or f2.8. I don't know if I buy into this argument, but I will agree that this lens, and others, would tend to have maximum sharpness between f8 - f11.

===== Slide 5 Zoom lenses have variable focal lengths, which makes the optics more complex and thus in general more expensive. Canon tends to put their aperture information on the front of the lens as seen here rather than on the barrel like Nikon. This lens has an effective aperture of 1:4-5.6; this means that when the lens is at the shortest focal length (17mm) then the maximum aperture is f4, and when the lens is at the longest focal length (85mm) then the maximum aperture is f5.6, a full stop less. On the front of the lens you can see the number 57mm: this is the diameter of ﬁlters that this lens takes. On the silver ring you can see a series of numbers: 17, 24, 35, 50, 70, 85: these are focal length points so that you know where the lens is. Just below the ring is "MACRO 0.35m/1.2ft"--this lens has limited macro photographic capability and can close focus of 0.35m or 1.2 ft (14.4").

===== Slide 6 This is another zoom lens, this time going from 24-70mm with a maximum aperture of f2.8 across the entire zoom range. This lens is around $2000, primarily based upon the maximum aperture across the zoom range--this is a moderately expensive lens based upon the superior optics. Prices of lenses can range up to the tens of thousands of dollars. ===== Slide 7 Tilt-shift lenses are specialty lenses. Their primary use is in architecture, though they do have a creative use. The goal of the tilt-shift lens is to alter how light hits the sensor, tilting it so that it doesn't hit the sensor straight on. If, for example, you try to take a photograph of a tall building while standing just in front of it, the top tends to pinch inwards even though you know that in reality the lines are parallel. This is due to the bottom of the building being closer to the sensor than the top and hitting the sensor more at a straight angle. The tilt-shift lens can correct for this distortion by shifting how light is traveling through the lens.

===== Slide 8 There are also creative lenses, such as the Lensbaby series. The Lensbaby is similar to the tilt- shift in that it can shift where light is hitting the sensor, which makes it a selective focus. Lensbaby lenses have drop in aperture rings with a ﬁxed aperture as well as interchangeable optics such as pinhole adapters. The Lensbaby lens claim to fame is a very soft focus that is excellent for portrait photography.

===== Slide 9 Angle of view is determined by horizontal, vertical, and diagonal degrees of view. The smaller the focal length of the lens the wider the angles of view it has. Wide angle lenses are divided into ultra-wide angle (below 24mm) and wide angle (24mm-35mm). Normal angle of view are those lenses that replicate the normal angle of view of the human eye--although area of focus of the human eye is actually a very small angle, around 3 degrees, more like the angle of view for a telephoto lens. Telephoto lenses range from 85mm through to 1200mm, and this range is divided into short telephoto (85mm-135mm), telephoto (135mm-300mm) and super- telephoto (300mm-1200mm). One major thing to know about telephoto lenses is that they tend to compress the image so that the background appears closer than it really is.

===== Slide 10 Short focal lengths and larger angle of view also mean a greater amount of distortion of the image, especially when there are objects close by. Wide angle have just the opposite effect of the telephoto lens, they make things appear further away than they really are. This is one reason why portrait photography is typically done with lenses of around 85mm to minimize this distortion which could have an adverse affect on the nose or ears, making them appear larger than they actually are.

This isn’t to say that you can’t take a portrait using a wide angle lens - you simply need to be aware of the distortion that can happen with it near the edges and frame your subject to minimize this distortion. I took a photographic class in Santa Fe where one of my fellow participants only had a wide angle lens on her mirrorless camera. The instructor was kind of dubious as to her taking portraits (which was what the class was all about), but everyone was really surprised as to the quality and little distortion she had in her portraits. Remember, the camera is simply a tool for you to make art.

===== Slide 11 Here is an example of maximum distortion that can happen with a very wide angle lens, in this case a 10.5 mm fish-eye lens. This photograph is taken from Edinburgh Castle looking over the “New Town” of Edinburgh. The camera was placed on the stone ledge for stabilization and then I took the photo. Notice that in the center of the image there is no distortion at all and the image is very sharp. On the edges, however, you get some maximum distortion and curvature - but even here the image is relatively sharp and not very blurry. This is the advantage that wide angle lenses provide - the ability to get close to your subject and still have a very sharp image. Companies have made wide angle lenses that have greater than a 180 degree field of view; if you use one of these lenses and if you’re not careful, you can photograph your feet in the image. These are specialty lenses that have a very unique niche. Other than taking the fish-eye lens to Scotland back in 2010, I haven’t used it since but I kept it just in case I want to play with it again. Great for making panoramas.