Blurry Backgrounds

Those blurred backgrounds we love? That’s why we have an SLR camera in the first place, right. A beginner’s note on this subject today.

As you know by now, a lower f-number (= a larger aperture) means a blurrier background. So a photo made at f/1.2, for instance, will have a blurrier background than one taken at f/32.

Photo made at f/1.2: blurry background.

Photo made at f/32: sharp background.

But the f-number is not the only thing that affects the depth of field (= how blurry the background is). The other two factors are:

  1. Proximity to subject. The closer you get to your sharp subject, the blurrier the background gets.
  2. Lens focal length. The longer the lens, the blurrier the background gets.

Take these two recent photos, both taken at f/5.6:

Photo taken at f/5.6: SHARP background

Photo taken at f/5.6: BLURRY background

Photo taken at f/5.6: BLURRY background

What is the difference?

The top picture was taken with a 16mm lens. The bottom pictures were taken with an 85mm lens. The 85mm lens is longer than the 16mm lens, so it gives us a narrower depth of field(= a blurrier background).

So you can only say: a lower f-number means a blurrier background, all other things remaining equal. In other words, you cannot necessarily say “f/4 will result in a blurry background”, or “f/16 will give you a sharp background”.

This is why using a prime lens is a good idea: you remove one variable, thus making it easier to get predictable results.

If this is not all clear to you, then do the following: with the camera in aperture mode or manual mode, go take pictures around the house, until you do get it. Try to alter only one variable at a time (i.e. do not alter zoom, distance and aperture all at the same time: you will have trouble seeing how it all works.

 

All the difference

Look at Mau the cat, who is pretending to not notice me:

I used my 85mm f/1.2 lens on the 1Dx body. The settings were 1/60 sec at f/2, 800 ISO.

Let’s think about that for a minute. 1/60 sec is about the slowest speed I can hand-hold: any slower and I would shake; and the cat would move visibly also. So that’s a given.

800 ISO is nice. Much more, and I start getting visible grain, certainly on cheaper cameras.

So unless I want to use a flash, f/2 in my kitchen is what I need.

Now… imagine I had a consumer lens,. like the 17-85 f/3.5–5.6. The latter designation means that when I zoom out I can get as low as f/3.5, but when I zoom in I cannot go any lower than f/5.6.

If I used this lens, I would have to go to a much higher ISO. To keep the same exposure, if I want to keep the same shutter speed, I would have to change ISO as follows:

  • At f/2 I need ISO800
  • At f/2.8 I needISO 1600
  • At f/4 I needISO 3200
  • At f/5.6 I needISO 6400

So with the cheaper “consumer” lens zoomed in, I need to go to 6400 ISO. Which would, especially on smaller cameras, give me a lot of grain; a bad quality picture, in other words.

So the more expensive, “faster”, lens gives me a huge benefit here. One not to be scoffed at, which is why we like prime lenses. Which are not all expensive: you can get a 50mm f/1.8 lens for just over $100.

Which I hope you have done!

 

Gelling!

In yesterday’s shoot with Vanessa Scott in Timmins, Ontario, I used gels to recreate the sunlight that was fast fading below the hills. All shot with Canon’s amazing 85mm f/1.2 len.

(1/200th, f/4, ISO100)

Vanessa looks like she is in that light, because I put a CTO (Colour Temperature Orange) gel by Honlphoto on the main flash, like so:

You will see also that I am using a second flash, fitted with a grid, for the hair light. Two flashes driven by Pocketwizards—that’s all.

One more from this amazingly versatile young woman:

1/60, f/5, ISO100 — I had to adjust for fading light


Again, the flash allows me to offset the subject against the background, which I keep dark. Without the flash, I would lose the nice colour and I would have to make everything, including that background, very bright.

And that’s how the cookie crumbles.

 

Today, a QUIZ!

Test your knowledge of the basics: a quiz for you today. Select the best answer. Tomorrow, the answers.

 

1. You are shooting a hockey game. Your autofocus should probably be:

❏  In AI Servo/AF-C focus mode

❏  On manual focus

❏  In One Shot/AF-S focus mode

❏  Out of focus

 

2. At f/5.6, your picture is too dark. You can try going to:

❏  f/8

❏  f/4

❏  f/11

❏  1/60 second

 

3. If I move a light three times farther away from the subject it is lighting up, the subject now gets:

❏  Twice as much light

❏  Half as much light

❏  One third as much light

❏  One ninth as much light

 

4. For a blurrier background, you can go to a lower f-number. You can also:

❏  Step closer to your foreground object

❏  Use a longer lens

❏  Zoom in on your foreground object

❏  All of the above

 

5. For a “panning” picture of, say, a bicycle, you could try the following as a starting shutter speed:

❏  1/100 sec

❏  1/1000 sec

❏  2 seconds

❏  1/15 sec

 

6. A 50mm lens is normally called a “standard” lens on a film camera. On a crop camera with a crop factor of 1.5 or 1.6 you could use this for the same effect:

❏  a 50mm lens

❏  a 135mm lens

❏  a zoom lens

❏  a 35mm lens

 

7. The “rule of thirds” says that an object would look good if it were:

❏  Exactly in the centre

❏  One third from the top or bottom, and one third from either side

❏  Anywhere

❏  The square root of 2 away from the centre

 

8. Going from f/2.8 to f/11 gives you:

❏  Three stops more light

❏  8.2 stops less light

❏  Four stops less light

❏  One stop more light

 

9. The larger the f-number, the…

❏  …larger the opening in the lens

❏  …sharper the picture

❏  …smaller the opening in the lens

❏  …more the colour goes toward red

 

10. In exposure terms, 1/500th second and f/4 is equivalent to 1/30th second and:

❏  f/1.2

❏  f/1.6

❏  f/4.85

❏  f/16

 

11. Going from f/2.8 to f/11 gives you:

❏  Three stops more light

❏  8.2 stops less light

❏  Four stops less light

❏  One stop more light

 

12. Going from 1/30 sec to 1/250 sec gives:

❏  Three stops more light

❏  Three stops less light

❏  Four stops less light

❏  220 times less light

 

13. For a high-key photo, I want my light meter to indicate:

❏  In the middle (“0”)

❏  On the minus (“–“) side

❏  On the plus (“+”) side

❏  Alternating between plus and minus

 

Autofocus point

An important point about autofocus (and forgive the pun).

You have a number of AF points. One in the middle, and then 2 more, or 8 more, or 40 more: whatever. Lots, on my 1Dx:

These “points” are sensors that look for focus by looking at lines and sharpening them. But did you know that some points are sensitive only to horizontal or vertical lines? That’s why, when you select one AF point, sometimes you cannot focus even though you are pointing the AF point at a nice lined surface.

The centre AF point is always sensitive to both horizontal and vertical lines. But many other AF points are sensitive to only horizontal, or only vertical lines.

What’s more, this even depends on:

  • The mode you are in
  • Auto or manual AF point selection
  • The minimum f-number of your lens. Some points are points (sensitive to both) when used with an f/2.8 lens,. but horizontal only, or vertical only, when used with an f/5.6 lens.

So, my strong advice: Read up on how your camera does it. And if in doubt, use the centre AF point, since it is likely more sensitive and a cross-type sensor.