A look at cheap lenses vs pro lenses, offering practical examples of the differences in terms of function, aperture and image quality.

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Hi. This is Tom Greenwood from sydneyportraits.com.au and greenwoodmedia.com.au.

Lenses come in all shapes and sizes.. and yes, prices.

It can be a little confusing when comparing different lenses that cover a similar focal range, for example a general purpose zoom that goes from reasonably wide-angle to long. They do roughly the same thing – but have vastly different price tags.

In this clip we are going to look at two lenses – one cheap and one not so cheap – and ask: what’s the difference in functionality – in other words what can the pro-level lens do that the cheap one can’t – and what’s the difference in image quality.

I’ll be comparing Canon lenses simply because I use Canon equipment. This is not intended as a lens review – we’ll be looking at general guides that should apply equally to cheap and pro lenses from Nikon or any other brand.

Also, I’m not saying there is anything wrong with using cheap lenses. We’d all love to have the best equipment, but, that said, some of my favourite shots were taken with a cheap zoom lens. Remember – it’s not what you’ve got, it’s how you use it.

So here are the lenses:

First, the Canon 35 – 80mm f4-5.6. This is what’s known as a ‘kit lens’ – a lens that is usually sold as a package with a camera body. This lens is no longer on the market and I believe newer kit lenses are better quality. I bought this lens second hand as a package with this old film camera – total cost: $50.

The other lens is the Canon 24 – 70mm f2.8. It’s part of Canon’s L range, which essentially means it’s a ‘pro’ lens. I bought it second hand but in ‘as-new’ condition for $1,300.

Put the lenses together and we see some obvious differences. First, the L lens is huge in comparison. It also weighs roughly 5 times as much as the 35 – 80mm.

Not surprisingly, the lens barrel for the cheap lens is made mainly of plastic, whereas the L lens is metal. The L lens is therefore much sturdier. It’s also weather sealed to protect the internals from moisture.

Let’s look at the mount-end of the lenses. This gives us a clue as to an important difference in functionality. The glass element for the cheap lens is much smaller than for the L. This indicates the aperture of the lens – and relates to those mysterious numbers: f2.8 for the L lens and f4 – 5.6 for the cheap lens.

To understand what this means, let’s take a practical example:

We’re shooting with the cheap lens at 35mm – so this is as wide-angle as the lens will go. The first shot is at f8. OK, let’s try and blur that background a little more with f5.6 (changing the ISO to keep the same exposure). Let’s blur the background further to f4. Remember that number.

Now let’s change the focal length to 85mm – as long as the lens will go. Here’s f8 (notice the fact that we’re using a longer focal length makes the background naturally blurrier), and now f5.6. But when we try and get to f4, we discover we can’t. This is because the lens has an aperture of f4 – that’s at its widest angle – but only f5.6 at its longest focal length.

So now with the L lens. We’re at 50mm. So here’s f5.6, f4 and beyond to f2.8. Notice the level of blur we get in the background. This lens is f2.8 across its focal range. So here it is at f2.8 at 24mm – its widest angle – and 70mm – its longest.

Having a wide aperture isn’t just useful for background blur. It also gives us much more leeway for shooting in low light.

Here we’re shooting in pretty gloomy conditions. We’re on a veranda sheltering from the rain.

We’re using the cheap lens at 80mm. In terms of aperture, we can only go as open as f5.6. With a sensible shutter speed of 1/100 that means we have to set ISO at 1600. This results in quite a ‘noisy’ image.

Let’s try wide-angle at 35mm. This allows us an aperture of f4, but that still means ISO 800 – still quite noisy.

With the L lens we can shoot as wide as f2.8 – actually we’re shooting just short of that at f3.2, which allows us ISO 500. That’s less noisy.

Now we’ve looked at the functional differences between the lenses, let’s try comparing image quality. This is not a scientific comparison – rather my impressions on looking at the images side by side. All the images used in this video were shot on my trusty Canon 5DIII. They are also unprocessed – so straight out of the camera – unless otherwise stated.

The first thing to notice is a haziness to the cheap lens. The colours are not as vivid and the nice contrast of the L lens is lacking. The highlights – the bright areas — are similar but the shadows are distinctly washed out.

Let’s also take a look at the corner of the image. You’ll notice that, using the cheap lens, the image is a bit soft. That’s not uncommon in lenses of this quality.

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