Tuesday, August 24, 2010

Lesson 03 - Depth Of Focus (DOF)

I haven't had much chance to get out and about photographing 'stuff', so I thought it was about time to post another official 'lesson'.  Today, I'm going to talk about something you'll often see referred to as DOF.  DOF stands for Depth Of Focus (it also stands for Depth Of Field - there is a technical difference that I won't bore you with, but they mean the same thing as far as your pictures are concerned...)  DOF is about how much of your picture is in focus - from the closest things to the furthest things.  Let me show you an example...

In this picture I took while wandering around Hyde Park, it's obvious what the picture is of... isn't it?

Of course it is - Poppies!  Lots of them... all different colours, close-up, middle distance, far away... Poppies, Poppies, Poppies!

In fact, there are probably a few too many Poppies.  When you first look at the picture, your eye may be drawn to the white one in the middle, or the orange one at the bottom, but then what..?  Your eye wanders around trying to find other things to focus on and look at...  hmm - that's an awful lot of Poppies - just excuse me for a few minutes while I check out each one...

This is where we can use the concept of DOF to help.  Roll down to the next picture of the same scene.

Now, see the difference?

Immediately, the eye is drawn to the cluster of Poppies at the bottom of the picture (ok - this is purely for demonstration purposes - don't start flaming me for the really lousy composition). Your eye may then briefly check out the rest of the image - discover there is nothing much to report, and return to the real subject and check it out in more detail.

So used in this way, DOF is being used to isolate a particular part of the image by keeping it IN focus, and making as much as possible of the rest OUT of focus.

DOF to isolate a subject like this works best with something close, and a reasonably distant background, such as the scene you see here, or portait close-ups for example.  The closer you can get to the thing you want in focus, the 'shallower' your depth of focus will be - check out a few macro shots of bugs, that are taken from just a few inches away - even in the width or length of the bug, you'll see how one part is in focus, and the rest (just a fraction of an inch away) is out of focus. 

So what did I do differently in the two pictures?  Change the aperture - that's all (ok, you got me - when I changed the aperture, the camera changed the shutter speed accordingly, to keep the same amount of light coming in to the sensor).  The first shot was taken with a very small aperture of f/32 (remember - big number means small hole).  This renders a lot of the picture in front of and behind your subject, in focus.  The second shot was taken with a wide aperture of f/5.6 - this reduces the front and back focus spread considerably.

Having mentioned macro photography, this introduces the other side of the DOF coin.  In this case, you want to increase the DOF as far as you can to get more of that bug into focus.  How?  Well, the easy part obviously, is to use a very small aperture - as small as you can get.  However, since the idea of macro work is to get really close, the other option of distance is out of the question - it's no good having your bug 6 feet away to ensure the whole thing is in focus...  Working with a small aperture will mean longer exposure times, and this may lead to needing extra lighting, in the form of flash, studio lights, or a light box/tent, or perhaps a ring flash for macro work (just be careful not to cook your bug) - however, before I get too carried away, lets stop there, and accept that (assuming you have enough light) you can increase your DOF by using a small aperture.

So, in summary...
  • DOF (Depth of Focus or Depth of Field) is an indication of how much in front and behind your subject is in focus. 
  • Use a wide aperture to get a 'shallow' DOF, and isolate your subject against a blurry backdrop. 
  • The closer you can get to the subject, the greater the isolating effect of DOF is.
  • Use small aperture (and possibly more light) to get a deeper DOF, and have more of the foreground/background in focus.
Until next time
happy snapping.

Tuesday, August 17, 2010

Right Place, Right Time...

I took my camera into work yesterday - it was a lovely sunny day, and I planned to go out for a photowalk at lunchtime... which I did... and I got some photos - but I'm saving them for another day.  Half way through the afternoon, there was a load roaring rumbling vibration outside my 23rd floor office window, and just outside was an Army Black Hawk helicopter, buzzing around and between the high rise offices - I grabbed my camera, and started snapping away - but after the excitement of getting the first few shots, I started to think a little more about what I was actually doing.

The camera was set on ISO 400 and P mode (which on my camera seems to give a wide open aperture, and adjusts the speed accordingly as its starting point) - so with ISO 400 and f/5.6, I was getting shutter speeds of 1/800 and 1/1000 second - which was freezing the rotor movement (but giving me crystal sharp pictures).

I wanted a bit of blur on the rotors, so I adjusted the balance towards a much smaller aperture of f/20 - but I think that was too far, as it gave me shutter speeds of around 1/80 second - which combined with a 200mm lens - even with Vibration Reduction - is a bit too slow.  So the next few shots gave me the motion blur on the rotors, but at the expense of blur everywhere else too :(

I decided that sharp pictures were the better option, so I opened up the aperture again, but did reduce the ISO to 200, as the 400 setting was going to give me some grainy noise - especially if I had to crop into the detail too much.  Luckily, the sun was bright, and I was still able to get pretty quick shutter speeds.

The helicopter was doing some manouvres from down low (way down below me), and swooping up towards me, then banking off behind the building opposite, before popping up over the top - right at my level.  In the first picture (uncropped), you can see how hard it is to see the helicopter at all - but the next two are crops into the detail of that same photo, and a second pass a few minutes later.  I call these my Quentin Tarantino shots.
I think the second pass shot was more successful, due to the lighter background of buildings, and also the angle of the helicopter.

Then it popped up from behind the other building - it was like an action movie.  I quite expected a force of elite paratroops to drop down ropes onto the roof and invade the building... Now that WOULD have made a good shot - and it would have been sold to the Sydney Morning Herald by now!!!

As it finally departed for goodness knows where, I caught this last shot as it left its shadow on another neighbouring building.

In all, I had 9 minutes of shooting time of this spectacular close-range display of flying.  Boy, was I glad I chose to take the camera to work!!

Until next time - keep snapping.

Friday, August 6, 2010

Man on a mission

In an effort to drag myself out of a period devoid of photographic excitement (I hadn’t taken a single photo in over three weeks), today I set out on a mission to put things straight – and check my camera still works!
The current assignment on the Digital Photography School forums seemed like a good starting point – “Motion Blur:People or Animals”.  I figured that a photowalk in the city should offer me plenty of opportunity, so I went out during my lunchbreak.

Now, obviously to catch motion as a blur, requires a longer than normal exposure, so I tried a couple of approaches… the first was to use the camera in Aperture Priority mode, and set the aperture as small as I possibly could (remember – a small aperture has a BIG number).  This would ensure that the camera would use the longest exposure I could possibly get for the light conditions.

I hopped on a train to Central and tried a few locations on the platforms - my first real experience of 'street' photography. I got a few odd looks from people, but nobody actually assualted me either verbally or physically - which was encouraging. So I tried getting people getting on and off trains, but...

...problem – NO TRIPOD!  Using this method, I was sometimes getting exposures of around a second.  Not ideal for handheld pictures – even bracing the camera on the back of a bench was still giving me blur where blur ought not to be...

I switched to Shutter Priority, and adjusted the length of the exposures myself (between 1/20th and 1/4 of a second), to take more control over the amount of blur.  I quite liked this one of a girl standing perfectly still checking her phone, with all the movement going on around her.  I chose this one as my entry for the assignment.

Finally, I walked back to my office, and decided to have a final play at this busy crossing.  I was quite pleased with it, but I think the exposures were a bit on the long side, as there is too much 'blur' and not enough 'people in motion'.  I think the one above has just the right amount of blur, but this one too much.

So - I got out for a walk for a change, broke out of my photographic doldrums, and got the grey matter working to think about my motion blur exposures.  But what did I learn?
1 - don't attempt long exposures without a tripod... Well, I knew that, but had to do the best I could with what I had to hand...
2 - motion blur isn't JUST about a long exposure time - you have to ask yourself "just how long does long have to be".  What kind of motion are you trying to catch - leave it too long, and it becomes somewhat less obvious where it is motion, and where it is just a ghost...

Until the next time...
Happy Snapping.