Lenses

Lenses truly aren’t that difficult to understand once you wrangle a little basic camera-speak.

Most of the time you will be able to discern exactly what type of lens you are looking at within a matter of seconds just from its markings.

Here are the common terms that will help you navigate the world of lensery.

• Focal length: How big is it?

• Aperture: The physical opening in the lens which controls the amount of light entering the lens. This opening is controlled by a number of aperture blades which open and close.

• Coma: The bending of small points of light such as stars. These dysmorphic bendings distort the circular shapes of light due to the shape of the glass elements within the lens. Not really a problem with modern lens.

• Chromatic Aberration: This is a colour halo effect generally observed when using wide apertures. Most often seen as green or purple fringing around contrasted objects within the frame. Again, not something we worry about and easily fixed in post processing.

• Barrel Distortion: This is an optical phenomena that cause the edges of an image to bend. The image will appear as if it is bulging. Usually, this is common when using wide angle lenses. Modern cameras tune the lenses and adjust in camera … or sort it in post.

• Bokeh: Say it with me ... “bow-kay” is a Japanese term for the varying aesthetic quality of the blurred background within a photograph.

What is an F Number:

This is classed as the speed of the lens. It is determined by the hole (aperture) that the light comes through. If your 50mm lens has a hole in it that is 50mm it is classed as an f1.1 lens, (though most people do not use the first figure, so that would be a f1 lens) It is determined by (loosely) following the powers of the square root of two. So we start at F1 then F1.4, f2, f2.8, f4, f5.6, f8, f11, f16, f22, f32, f45, f64, etc. etc.

Each of these numbers represent half of previous numbers ability to transmit light. So an f2 lens will allow twice the amount of light as a f2.8 but only half as much light as a f1.4. These are only the whole numbers, you might have f1.8 or f3.5. these are defined as click stops, usually plus a third or two thirds of the previous setting.

What is focal length?

The focal length of a lens is literally the distance between its optical centre and the camera sensor. You can usually find this written on the lens. If it is a prime (fixed focal length) lens, this will be a single number, such as 24mm or 135mm. If it is a zoom (variable focal length) lens, it will be a range, such as 15-35mm or 70-210mm.

The focal length of a lens also determines its field of view

Remember back in school you used to use a protractor, that half circle thingy that let you measure angles? Now imagine holding that at eye level and you have your horizontal view.

All these are for a full frame sensor.

(For APSC multiply focal length by 1.5 & use the nearest (ie: 50 x 1.5 = 75) 75 approx 30°)

(For Medium Format, multiply the length by 0.62 (ie: 55 x 0.62 = 34.1) 35 approx 63°)

Beware, most manufacturers measure their angle of view from corner to corner, not much bleeding use holding the camera at 45° to get the max number of degrees they claim, but their numbers look good on paper!

So listed here are the actual horizontal degrees for common lens sizes.

Lens Focal Length ... Horizontal Field of View

8 ... 180°

15 ... 115°

17 ... 102°

20 ... 94°

24 ... 84°

28 ... 75°

35 ... 63°

45 ... 49°

50 ... 46°

55 ... 42°

85 ... 28°

100 ... 24°

135 ... 18°

200 ... 12°

300 ... 9°

400 ... 6°

500 ... 5°

600 ... 4°

800 ... 3°

1200 ... 2°

and lenses can be divided into a few categories.

A FISH EYE LENS. This is a lens that has a field of view of 180° (Nikon did a 6mm lens that is much sought after, with a field of view of 220° it can literally see behind itself!) Great for taking whole sky shots or getting your feet in every shot! I have a 8-15mm fisheye (it was cheap!) that produces a circular image on a full frame camera @ 8mm and can zoom out to a 180° corner to corner @ 15mm. Its fun but limited!

An ULTRA WIDE ANGLE lens falls between 11 & 18mm. Though they can be pricey, they offer around peripheral vision, making the view as close to human eyesight as a camera can get.

Don’t be confused, peripheral vision isn’t normal vision, this is the side to side view you are aware of, but until something moves in these side areas, you tend to ignore it.

Your ‘normal’ vision … try closing one eye … is around 45°, like that of a 50mm lens

These Ultra Wides will give an approximate field of view 113º horizontal @ 11mm closing down to 90º @ 18mm

Ultra-wide angle lenses are great for capturing vast landscapes, night sky and giving viewers the feeling of being immersed in a scene.

Standard WIDE ANGLE lenses generally lie between 18 & 40mm. They’re not quite as glamorous as their ultra-wide counterparts, but they are perfectly capable of capturing expansive landscapes and environmental portraits.

Viewing angle of about 90º @ 18mm down to 48º at 40mm

They are a great choice for beginners as they are relatively lightweight and surprisingly durable. My fav go-to lens is a 17-40mm zoom.

MID RANGE lenses (between 28 & 85mm) are sought after primarily for their versatility.

Although they do not serve as a strong wide angle or a strong zoom, they’re often capable of attaining low apertures and offer something outside of the scope of the standard kit lens. Great for street photography, portraits & landscapes.

Around 75º @ 28mm closing in to 28º @ 85mm.

A lens that falls between the range of 70 to 300 mm is known as a MEDIUM TELEPHOTO. They are an excellent choice for shooting small subjects like flowers & wildlife. Although not a great choice for landscape photographers, they are good for picking out detail. They’re also incredibly helpful when photographing subjects in the distance that might be overlooked by a wider lens.

Field of view from 30º @ 70mm down to 7º @ the 300mm end

Any lens that exceeds 400mm is a SUPER TELEPHOTO lens. Incredibly large, heavy and can be fragile, these giants comprise the most expensive lenses available and are not recommended for beginners. They’re often restrictive when capturing close subjects. However, they’re excellent for wildlife and sports photographers that require close up shots from a far off vantage point.

5º @ 400mm/500mm. 3º for 600/800mm & 2º for 1200mm.

Macro Lens - lets you see the world in close up, classed as anything up to life size. The bigger the lens, ie: 105mm, the farther away from your subject you can be.

Pair with an extension tube to go bigger than life size on the sensor.

Tilt Shift - as the name suggests, the front element can be moved. Remember seeing pictures of those old big format cameras with the huge bellows on the front … the photographer would set his lens so that the buildings appear vertical. This is what a tilt shift lens will emulate.

Look at the early Fred Spalding shots of Chelmsford High Street, then try to replicate with our modern marvels …

Mirror Lens - you don’t see so many of these, nowadays. What they do is copy a telescope design, they have mirrors within the lens that reflect the light back and forth which increases the light path. For instance, a 500mm lens, by folding the light can have its physical length reduced by two thirds. They are typically a fixed f stop too.

Which is best … ZOOMS or PRIMES?

Ok, let’s start with a few pros & cons from both camps

ZOOMS

Pros - Can cover many primes, a 28-70 takes in a 28, 35, 50 & 70 plus any number in between. You don’t have to change lenses on the beach or in dusty conditions. Smaller kit bag. Zooming means you don’t have to move closer or step back to fill the frame.

A triplet of a 18-35 a 24-105 & a 70-210 will cover most situations,

and replace 20, 24, 28, 35, 50, 85, 100, 135, 150, 180, & 200mm primes

Cons - less light getting through typically ƒ4. Heavier, Costly when you get to faster optics. A 28 - 70 ƒ2 Canon is lots of pennies, for the same dosh, you can buy a faster 28, 35, 50 & 85 and still have change. Zooms can make you lazy. You tend to fill the frame with the zoom feature, missing out on the possibility of a better shot if you move!

Phone Zooms - don’t get me wrong, having a camera with you at all times is a nice bonus, but if you intend to go out and take photos, take something else.

For instance, if I zoom in with my DSLR, the lens does all the work. Yeah, it’ll have idiosyncrasies but the zoomed image is what makes it to the sensor.

When I zoom in with my iPhone (I know … it’s an old one) the program interpolation just cuts out part of the image. So, if I zoom in 4X, the camera’s 10meg sensor now becomes a 1.25meg sensor. The clever programming will fill in the gaps with some great software, but you’ve lost that detail.

PRIMES

Pros - Image Quality: Prime lenses are often known for their superior image quality when compared to zoom lenses.

They have fewer moving parts, which can lead to sharper images as the light travels through less glass.

Low Light Performance: Primes usually have wider maximum apertures (lower f-numbers), which let in more light.

This can be a major advantage in low-light situations, and it also allows for more control over depth of field, facilitating beautiful bokeh and background blur.

Weight and Size: Prime lenses are often smaller and lighter than their zoom counterparts.

This can be a significant advantage for photographers who need to carry their gear for long periods, assuming you are only going out with a couple of lenses.

Price: Although there are some very expensive prime lenses, many are surprisingly affordable.

Focus on Composition: Since you cannot adjust the focal length, prime lenses encourage photographers to move around and experiment with composition, which can lead to more creative photos.

Cons of Prime Lenses

Lack of Flexibility: The most significant disadvantage of prime lenses is that they have a fixed focal length, meaning you can’t zoom in or out to adjust your composition.

This lack of flexibility can be problematic in certain situations, such as standing on a cliff or shooting wildlife, sports, aeroplanes, or other types of photography where you can’t always control your distance from the subject.

Need for Multiple Lenses: If you need to shoot at a variety of focal lengths, you’ll need to carry multiple prime lenses.

This can add bulk to your bag. Even though individual primes are generally lighter than zooms, they still take up room.

Changing Lenses: If you’re using primes and need to go wider, you’ll have to change the lens. This can be time-consuming and may expose your camera sensor to airborne particulates, sand and or dust.

Don’t forget to turn off your camera before exposing the sensor. The electrostatic nature of the sensor will suck that shit in!

Cost: While individual prime lenses can be more affordable than zoom lenses, the cost can add up if you need to buy all the primes to cover the same focal length range as a single zoom. Take o look at my 18-135, I’m gonna need a 20, a 24, 28, 35, 50, 85, 100, and a 135.

Sweet Spot A lens isn’t much use to a photographer if it doesn’t produce sharp images.

But what a lot of people don’t realise is that lenses are not uniformly sharp at every aperture or every focusing distance.

In addition, if you’ve got a zoom lens, they’re also not equal across the zoom range.

There is a sweet spot (ƒ stop) at which your lens will give you maximum sharpness.

You can perform a simple sweet spot test to ascertain for yourself each lens’ sharpest aperture

Sharpness vs. Depth Of Field

But, before you do, it helps to better understand sharpness vs depth-of-field. It’s easy to confuse sharpness with depth of field.

When you stop down to smaller apertures, increasing your depth of field, you bring more of the image into greater overall focus. Not necessarily sharp but acceptably sharp. This is great for huge vistas

So images shot at ƒ16 or ƒ22, for example, appear to have more in focus than images taken at a wider aperture such as ƒ2 or ƒ2.8.

However if you’re shooting a portrait, you don’t want the eyes ‘acceptably sharp’ … you need your lens to be able to resolve the finer details.

How to Determine the Sweet Spot of your lens.

The easiest way to do this is to switch your camera to Aperture Priority mode, you want to control the aperture but let your camera sort out the shutter speed and ISO.

It’s also best to put your camera on a tripod, so each shot is consistent.

Focus on a subject and take around seven or eight shots through the lens’ aperture range (from say ƒ1.4 to ƒ11 for example), making sure to concentrate on the apertures you think are most likely to be the sweet spot, but also making sure you take some at the smallest and largest apertures.

For zoom lenses, repeat at widest, half way and full zoom.

A little tip here – try including some writing/text in the image, as this makes it easy to ascertain sharpness.

Now upload these images to your computer and zoom in to 100%.

You should quickly be able to see which aperture gives you the sharpest overall image.

So now, armed with this knowledge, try to get as close to the sweet spot as the conditions will allow.

But …

don’t let it be the be-all & end-all of your shooting, I’ve got loads of ‘less than perfect’ photos in my library, but if you have the time …