Again, why "fast" lenses?

A tip for newcomers to SLR photography.

I often hear: “Why do I need so-called “fast” lenses – like the 50mm f/1.8 lens Michael keeps talking about? Surely my 18-55 lens also covers 50mm?”

Well yes it does. But:

  1. Less sharply. A “prime” (i.e. non-zoom) lens is sharper.
  2. A prime lens is also smaller and lighter.
  3. And especially: the prime lens has a lower minimum “F-number” – i.e. a larger aperture. The lower the “F”-number, the better. Your kit lens is f/3.5-5.6 (meaning zoomed out it can go as low as 3.5; zoomed in it can go only as low as 5.6. The 50mm f/1.8 can go as low as 1.8).

Why is this important?

So in today’s class I took two shots of a student in available room light. One at f/5.6, and that is what you would get with your standard “kit”-lens. It looks like this:

Two things happen:

  1. Because of the small aperture (high “F-number”), the camera has to keep the lens open for a long time. This means that unless I use a tripod and tell the subject not to move, in indoors light I will get camera shake (the shot needed 1/10th of a second). And sure , do.
  2. The lower the “F” number, the shallower the depth of field, i.e. the blurrier the background. The higher the F-number, the sharper the background.F/5.6 gives a background that is somewhat blury.

Now look what happens when I use an aperture of f/1.8 (for which you need a lens that can do that, like the 50mm f/1.8 lens):

Much better – a pretty dramatic difference on both counts!

So the best way to immediately get great portrait shots is to:

  1. Get yourself a 50mm lens. On most cameras this is simple; do note that on a Nikon D40/D60/D3000/D5000 you need to manually focus this lens (that is why I recommend Canon cameras at the entry level).
  2. Learn Aperture Priority mode (A/Av) and use a low “F-number”.
  3. Turn the camera sideways and get close!

Have fun.

(Wow, three numbered lists in one blog post!)


Photography is about composition/subject + moment + light. I reckon I got several of these right here:

From earlier this year. Using a 35mm lens on a 1.3 crop camera (meaning it’s 50mm), set to f/2.8 at 1/160th second.

Moral of the story: a “standard” lens is great. This is equivalent to a 50mm lens. Do take lots of pictures and do not forget the “moment” aspect.

That dreamy look

If you want portraits to have that dreamy look, use a lens with a wide aperture (a small F-number, like 2.8).

I took this picture yesterday, using a prime 35mm lens (the Canon 35mm f/1.4L) on a Canon 7D, at an aperture of f/2.5 and a shutter speed of 1/50th second.

That 35mm on a 1.6 crop factor camera is like 50mm on a traditional full frame camera. So it’s a “Nifty Fifty”.

A that focal length, I was able to go quite close to Mr Pumpkin without much distortion, as you can see.


That gives you a very nice look. The close proximity combined with the f/2.5 aperture gives me nice soft bokeh (the creamy quality of the background blur). Even the back of the head is soft.

Beautiful: reason for a smile.

"What lens should I get?"

“What lens should I get?”

I hear that question a lot from students, and I am always delighted to help answer it.

Of course “help” is all I can do. And I will, over time, in this blog. I can explain the difference between:

  • Zoom and prime.
  • EF and EF-S (or non-DX and DX).
  • Wide and telephoto.
  • Normal and specialised, like Macro and Tilt-Shift.

And I can explain what to use them for (long for sports and safaris, short for environmental, parties, and photojournalism).

And with that knowledge, you can, for instance, buy the lenses I use – or at least understand why I bought them:


So this is a typical photojournalist collection, consisting of fast (f/2.8 or better) lenses:

  • Zooms: 24-70 2.8L, 70-200 2.8L and 16-35 2.8L
  • 100mm macro
  • Fast primes, 35 mm f/1.4L and 50mm f/1.4

But “fast” does not have to mean “expensive”. The first lens you should buy is the lens I shot my lenses with – the cheapest Canon lens (and Nikon has one too): the 50mm f/1.8. The “nifty fifty”. And while the lenses above range from $500 (50mm) to $1,000-$2,000 (all the rest), the 50mm f/1.8 is just over $100. And boy, is it fast and sharp. Zoom in to see!

And that nifty fifty on a crop camera turns into an 80mm portrait lens.

One thing to feel good about: when buying a lens, you are investing. Unlike a camera, which loses value as quickly as a PC, a lens keeps its value for many years.

Do I need a fast lens?

When students ask me “should I really buy a fast lens?” (For beginners, that’s a lens with a low “F-number”, like f/2.8), my answer is “it depends.”

What are you shooting? Landscapes (no need for a fast lens, since you will shoot at f/16 or above) or nightclubs (which need a fast lens for low-light abilities), portraits (which need a fast lens for blurry backgrounds) or sports (which need a fast lens for fast exposures)?

And if you like blurry backgrounds, does it make sense to get a pro lens like an f/2.8, or is my kit f/5.6 lens enough? That’s an easy one to answer. It depends. On whether you like this, taken yesterday during a course at f/5.6:


..or whether you prefer the same shot at f/2.8:


You decide. View them full size to really see the difference.

Know that every stop faster (from 5.6 to 4, or from 4 to 2.8) doubles the lens price. But if you like the blur (“Bokeh”) in the bottom shot, there’s no substitute for fast.

And I did not say expensive – at least not necessarily so: while some lenses like my f/1.4 35mm cost $2,000, an excellent 50mm fixed (“prime”) f/1.8 lens (a “nifty fifty”, which on a crop camera is  great portrait lens) can be had for as little as $150 or less.

So yes, low f-numbers make a difference and that’s why photographers are willing to pay lots of money for them. But don’t worry: good lenses keep their value.