Had a few requests for this after the last guide so here goes. I'm just covering the basics for people new to DSLRs, if you're spending a grand on a fast telephoto hopefully you know what you're doing anyway! I'm ignoring crop factors as this is pretty redundant info, and I've only covered Canon and Nikon fit lens as this should cover 95% of people. Very hard to not make this all sound a bit complicated, but it's pretty straightforward once you get the hang of it...
Focal Length
The first thing is to forget "12x Optical Zoom" or anything along those lines, it means nothing when you get to the world of DSLRs and interchangeable lens, you're now dealing with millimetres.
When people refer to telephoto or wide angle etc, this is approximately what they mean in millimetres:
10-15mm: Ultra Wide Angle
18-25mm: Wide Angle
30mm: Standard (This is pretty much what you see with your eyes)
70-300mm: Telephoto
300mm-600mm: Super Telephoto
The kit lens bundled with many DSLRs generally covers the range of 18-55mm, so this covers wide angle, a standard view and a very short telephoto focal length.
Focal Length Examples
10mm (Sigma 10-20mm f4-5.6)
20mm (Sigma 10-20mm f4-5.6)
50mm (Nikon 50mm f1.8)
80mm (Sigma 70-300mm f4-5.6)
300mm (Sigma 70-300mm f4-5.6)
420mm (Nikon 300mm f4 with 1.4x Teleconverter)
Speed (Aperture)
This may not seem important initially, but the numbers here can make the difference between a £100 lens and a £1000 lens. Essentially, the lower the number after the "f", the better the lens light gathering abilities are, and in broad terms, the better the lens full stop. Where two numbers are quoted it means that the maximum aperture decreases as you zoom in, so for a 70-300mm f4-5.6, the maximum aperture at 70mm is f4, and this gradually increases up to 300mm where the maximum aperture is f5.6. Where just the one f number is quoted, it means that the lens has a constant maximum aperture, and this doesn't change no matter which point of the zoom you are at.
f1.4 - f4: (Fast) Lens with maximum apertures in this area can gather lots of light, they are known as fast lens.
f4.5 - f6.3: (Slow) Anything with a maximum aperture in this area is known as a slow lens, it will not let in as much light as a fast aperture lens.
Benefits of fast lens
A Sigma 70-300mm f4-5.6 costs £90, a Sigma 120-300mm f2.8 costs £1900. This should give you an idea of how big the difference between those f numbers really is. But why the difference, and what benefit is a fast lens to me?
Low Light Shooting - Because fast lens can gather more light, you can continue using fast shutter speeds into darker conditions. This allows you to shoot handheld with less risk of blurry photographs.
Autofocus - The camera always autofocuses at the lens maximum aperture, the more light it can gather, the quicker it can autofocus. Therefore fast lens can often focus much quicker.
Blurred Backgrounds - Using wide apertures such as f2.8 can create out of focus backgrounds if required. This is good for isolating backgrounds and gives photographs a more professional feel - particularly portraits. See the "Crash Course" guide stickied here for more information on how you can creatively use apertures.
300mm @ f4 - note the blurred background which is isolating the main subject
As always there are downsides, apart from the cost, fast maximum apertures require more glass, this becomes very apparent with zoom lens. A Sigma 70-300mm f4-5.6 is 12cm long and weighs 0.5kg, a Sigma 120-300mm f2.8 is 27cm long and weighs 2.6kg, not to mention that it's also twice as wide.
Prime Vs. Zoom
Prime (Fixed) Lens: This is a lens with no zoom capability, what you see is what you get. At first glance this may not seem like a good idea, but they are easier to construct and therefore can be made faster without excessive cost. The most common example is the 50mm 1.8, whilst the focal length is fixed to 50mm, it does make the lens very compact and very very fast.
Nikon 50mm f1.8
Zoom Lens: Exactly what it says on the tin, these lens can zoom between two focal lengths and everything in between, versatile but more complex to construct, fast zoom lens get very expensive very quickly.
Sigma 120-300mm f2.8
Third Party Lens
The manufacturer of your camera will have a wide range of lens available, but there are also a number of third party manufacturers. The main ones are Sigma, Tamron and Tokina. Almost all the lens they make are available for Canon and Nikon cameras, but they also offer their most popular lens for other cameras such as Olympus and Sony.
Designations
You could fill a book with the various designations listed after lens, here are some of the most common:
Image Stabilization - Combats the effect of camera shake, in theory helping you to get sharper photos, even in darker conditions where you might normally start struggling.
Canon = IS
Nikon = VR
Sigma = OS
Tamron = VC
Autofocus Motor - Improves the autofocus speed, also extremely important for entry level Nikon users (D40, D60) as the actual camera has no motor built in, therefore you will need an AF-S or HSM lens for it to autofocus.
Canon = USM
Nikon = AF-S
Sigma = HSM
Premium Lens
Canon = L
Sigma = EX
Tamron = SP
(Nikon do not have a specific 'premium' branding)
Accessories
Filters
Filters would need a whole other guide, but the first thing you need to know when selecting a filter is to check what size you need, this can usually be found on the lens, or on the back of the lens cap...
67mm filter required:
52mm filter required:
There are many filters available, but you will probably want to start with one that protects your lens. UV, Haze or Skylight filters all pretty much do the same thing - nothing - but have the benefit of covering your expensive lens with something relatively cheap with virtually no loss in image quality.
Close Up Filters
Close up filters can turn a normal lens into a macro lens by allowing closer focusing distances. They comes in several strengths such as +1, +2, +4 etc, and can be stacked for even greater effect. Whilst the quality isn't as good as a dedicated macro lens, it's a cheap way of trying it out and with high quality lens such as the 50mm f1.8 offers excellent results.
Teleconverters
Teleconverters sit between the camera body and lens and essentially act as a magnifying glass - increasing the focal length of the lens. These come in 3 sizes, 1.4x, 1.7x and 2.0x although 1.7x is fairly uncommon. There is a downside though, they also reduce the amount of light coming into the camera, a 1.4x generally loses 1 full stop , a 1.7x loses 1.5 stops, and a 2.0x loses 2 full stops.
1.4x
f2.8 becomes f4
f4 becomes f5.6
2.0x
f2.8 becomes f5.6
Common examples:
- An 80-200 f2.8 becomes a 120-280 f4 with a 1.4x, and a 160-400 f5.6 with a 2.0x
- A 300mm f4 becomes a 420mm f5.6 with a 1.4x
This is important to know, because most cameras will not autofocus if the maximum aperture is more than f5.6. So adding a 2.0x to a lens with a maximum aperture of f4 will create a lens with a maximum aperture of f8, this doesn't allow enough light in for the autofocus to function correctly. Therefore, teleconverters should only be used with fast lens.
Nikon 1.4x Teleconverter
Specialist Lens
As well as the standard range of lens that cover various focal lengths, there are also many lens designed for specific uses:
Macro
A true macro lens is one which has a 1:1 reproduction ratio, which is to say the subject is the same size projected on the sensor as it is in real life. Unfortunately it has become a marketing term in recent years, and anything from 1:4 and better is often described as a macro lens (a 1:4 reproduction ratio means that the subject is only life size when developed on a 6x4 print)
If you want a true macro lens it's best to do some research first, true macro lens are often prime (fixed) and generally fall somewhere between 50 and 150mm.
Fisheye
Fisheye lens have the ability to capture an extremely wide angle, well beyond anything your eyes could see without looking around. There are two types and it's important to know which one you actually want:
Circular: Circular Fisheye lens capture a circular image in the centre of the frame with black borders, very few are available for digital cameras as these are generally designed for full frame cameras. The Sigma 4.5mm f2.8 is one of the only examples available and captures a full 180 degree image.
Diagonal: Diagonal Fisheye lens fill the entire frame with an image.
Focal Length
The first thing is to forget "12x Optical Zoom" or anything along those lines, it means nothing when you get to the world of DSLRs and interchangeable lens, you're now dealing with millimetres.
When people refer to telephoto or wide angle etc, this is approximately what they mean in millimetres:
10-15mm: Ultra Wide Angle
18-25mm: Wide Angle
30mm: Standard (This is pretty much what you see with your eyes)
70-300mm: Telephoto
300mm-600mm: Super Telephoto
The kit lens bundled with many DSLRs generally covers the range of 18-55mm, so this covers wide angle, a standard view and a very short telephoto focal length.
Focal Length Examples
10mm (Sigma 10-20mm f4-5.6)
20mm (Sigma 10-20mm f4-5.6)
50mm (Nikon 50mm f1.8)
80mm (Sigma 70-300mm f4-5.6)
300mm (Sigma 70-300mm f4-5.6)
420mm (Nikon 300mm f4 with 1.4x Teleconverter)
Speed (Aperture)
This may not seem important initially, but the numbers here can make the difference between a £100 lens and a £1000 lens. Essentially, the lower the number after the "f", the better the lens light gathering abilities are, and in broad terms, the better the lens full stop. Where two numbers are quoted it means that the maximum aperture decreases as you zoom in, so for a 70-300mm f4-5.6, the maximum aperture at 70mm is f4, and this gradually increases up to 300mm where the maximum aperture is f5.6. Where just the one f number is quoted, it means that the lens has a constant maximum aperture, and this doesn't change no matter which point of the zoom you are at.
f1.4 - f4: (Fast) Lens with maximum apertures in this area can gather lots of light, they are known as fast lens.
f4.5 - f6.3: (Slow) Anything with a maximum aperture in this area is known as a slow lens, it will not let in as much light as a fast aperture lens.
Benefits of fast lens
A Sigma 70-300mm f4-5.6 costs £90, a Sigma 120-300mm f2.8 costs £1900. This should give you an idea of how big the difference between those f numbers really is. But why the difference, and what benefit is a fast lens to me?
Low Light Shooting - Because fast lens can gather more light, you can continue using fast shutter speeds into darker conditions. This allows you to shoot handheld with less risk of blurry photographs.
Autofocus - The camera always autofocuses at the lens maximum aperture, the more light it can gather, the quicker it can autofocus. Therefore fast lens can often focus much quicker.
Blurred Backgrounds - Using wide apertures such as f2.8 can create out of focus backgrounds if required. This is good for isolating backgrounds and gives photographs a more professional feel - particularly portraits. See the "Crash Course" guide stickied here for more information on how you can creatively use apertures.
300mm @ f4 - note the blurred background which is isolating the main subject
As always there are downsides, apart from the cost, fast maximum apertures require more glass, this becomes very apparent with zoom lens. A Sigma 70-300mm f4-5.6 is 12cm long and weighs 0.5kg, a Sigma 120-300mm f2.8 is 27cm long and weighs 2.6kg, not to mention that it's also twice as wide.
Prime Vs. Zoom
Prime (Fixed) Lens: This is a lens with no zoom capability, what you see is what you get. At first glance this may not seem like a good idea, but they are easier to construct and therefore can be made faster without excessive cost. The most common example is the 50mm 1.8, whilst the focal length is fixed to 50mm, it does make the lens very compact and very very fast.
Nikon 50mm f1.8
Zoom Lens: Exactly what it says on the tin, these lens can zoom between two focal lengths and everything in between, versatile but more complex to construct, fast zoom lens get very expensive very quickly.
Sigma 120-300mm f2.8
Third Party Lens
The manufacturer of your camera will have a wide range of lens available, but there are also a number of third party manufacturers. The main ones are Sigma, Tamron and Tokina. Almost all the lens they make are available for Canon and Nikon cameras, but they also offer their most popular lens for other cameras such as Olympus and Sony.
Designations
You could fill a book with the various designations listed after lens, here are some of the most common:
Image Stabilization - Combats the effect of camera shake, in theory helping you to get sharper photos, even in darker conditions where you might normally start struggling.
Canon = IS
Nikon = VR
Sigma = OS
Tamron = VC
Autofocus Motor - Improves the autofocus speed, also extremely important for entry level Nikon users (D40, D60) as the actual camera has no motor built in, therefore you will need an AF-S or HSM lens for it to autofocus.
Canon = USM
Nikon = AF-S
Sigma = HSM
Premium Lens
Canon = L
Sigma = EX
Tamron = SP
(Nikon do not have a specific 'premium' branding)
Accessories
Filters
Filters would need a whole other guide, but the first thing you need to know when selecting a filter is to check what size you need, this can usually be found on the lens, or on the back of the lens cap...
67mm filter required:
52mm filter required:
There are many filters available, but you will probably want to start with one that protects your lens. UV, Haze or Skylight filters all pretty much do the same thing - nothing - but have the benefit of covering your expensive lens with something relatively cheap with virtually no loss in image quality.
Close Up Filters
Close up filters can turn a normal lens into a macro lens by allowing closer focusing distances. They comes in several strengths such as +1, +2, +4 etc, and can be stacked for even greater effect. Whilst the quality isn't as good as a dedicated macro lens, it's a cheap way of trying it out and with high quality lens such as the 50mm f1.8 offers excellent results.
Teleconverters
Teleconverters sit between the camera body and lens and essentially act as a magnifying glass - increasing the focal length of the lens. These come in 3 sizes, 1.4x, 1.7x and 2.0x although 1.7x is fairly uncommon. There is a downside though, they also reduce the amount of light coming into the camera, a 1.4x generally loses 1 full stop , a 1.7x loses 1.5 stops, and a 2.0x loses 2 full stops.
1.4x
f2.8 becomes f4
f4 becomes f5.6
2.0x
f2.8 becomes f5.6
Common examples:
- An 80-200 f2.8 becomes a 120-280 f4 with a 1.4x, and a 160-400 f5.6 with a 2.0x
- A 300mm f4 becomes a 420mm f5.6 with a 1.4x
This is important to know, because most cameras will not autofocus if the maximum aperture is more than f5.6. So adding a 2.0x to a lens with a maximum aperture of f4 will create a lens with a maximum aperture of f8, this doesn't allow enough light in for the autofocus to function correctly. Therefore, teleconverters should only be used with fast lens.
Nikon 1.4x Teleconverter
Specialist Lens
As well as the standard range of lens that cover various focal lengths, there are also many lens designed for specific uses:
Macro
A true macro lens is one which has a 1:1 reproduction ratio, which is to say the subject is the same size projected on the sensor as it is in real life. Unfortunately it has become a marketing term in recent years, and anything from 1:4 and better is often described as a macro lens (a 1:4 reproduction ratio means that the subject is only life size when developed on a 6x4 print)
If you want a true macro lens it's best to do some research first, true macro lens are often prime (fixed) and generally fall somewhere between 50 and 150mm.
Fisheye
Fisheye lens have the ability to capture an extremely wide angle, well beyond anything your eyes could see without looking around. There are two types and it's important to know which one you actually want:
Circular: Circular Fisheye lens capture a circular image in the centre of the frame with black borders, very few are available for digital cameras as these are generally designed for full frame cameras. The Sigma 4.5mm f2.8 is one of the only examples available and captures a full 180 degree image.
Diagonal: Diagonal Fisheye lens fill the entire frame with an image.
