10 Jan 2010

Project: Focal lengths

When I first started photography I was stuck with a single focal length on my box brownie (quite wide angled as I recall).  My first SLR also only had one lens, a 50mm focal length, so I became adept at moving around to get the angle of view that I needed to frame my shots.  For the past 25 years I have had the joy of zoom lenses which have allowed me to become lazy.  I am well used to standing just about anywhere and crank my lens in or out to frame the subject, something I should probably try to avoid.  It is one thing to frame the shot well, perhaps excluding a scruffy object from the side of a nice landscape by tightening the shot slightly but completely another to accept the angle that your current view gives you as correct and use the lens to make up for moving your feet.  So a zoom lens has great advantages but can lead to bad habits.  It is also worth remembering that when your lens will only open up to f4.0 or in some cases as little f5.6 then it is hard to exercise really good depth of field control.  Not many of us can afford the really expensive professional zooms that can achieve f2.8 in a 70-200 zoom!

Exercise: Focal lengths

This exercise asks us to shoot a scene with a wide angle and then use a zoom lens to adjust the focal length to bring part of the shot into close-up.  

The view I chose was of over the city of Shanghai looking from the Pudong side of the Huangpu River towards the river itself.  This side of the city has many impressive buildings but at the time I chose many of them were in darkness leaving the streets and apartments to take centre stage.  I used a tripod and didn't move it from one shot to the next.  Of note, in the shots are the light trails left by the moving vehicles during the long 20 second exposure and the glow of the many orange sodium lights reflecting back from the cloud and pollution that lay over the city.

Shanghai city - 20sec, f8.0, ISO200, 17mm

Having shot my wide angle view, I switched to a 400mm zoom and concentrated on a couple of areas of the river side in the top left portion of the original scene.

River Police HQ - 20sec, f8.0, ISO200, 400mm

Dredger - 20sec, f8.0, ISO200, 400mm

The close up that can be achieved by zooming to 400mm is impressive but, as the text books suggest, the view is the same.  From the camera's point of view nothing has changed, just a narrowing of the size of the shot and a great deal of magnification.  Of note is that all shots needed the same time, f stop and ISO to achieved the same good exposure regardless of the amount of zoom used.  I also used the 'mirror up' technique on the long shots to reduce the amount of vibration on taking the photograph.

Exercise: Focal lengths and different viewpoints 

This exercise is similar to the previous one but rather than sitting at the same spot and using different lenses I am now shooting a subject with a long lens and then moving my position to bring it to the same relative size when using a short lens.  I have always been acutely aware of the startling difference that a wide angle lens can create when use close up to a subject when compared to shooting it from a distance with a long lens but now I can demonstrate the difference here.

With a long lens I first shot a couple of lion statues that guarded the entrance to a bank in Shanghai.

 1/640, f8.0, 
ISO200, 400mm

 1/800, f9.0, 
ISO200, 400mm

The composition is necessarily limited since from around 100 metres away there are very few options on how to photograph a statue.  The shot is very flat and the total area only covers the lion and a few stone blocks and part of the door or the single window behind. Of interest, the man walking in front of the right hand lion is a good 20 feet from the lion but the distance is foreshortened by the effect of the long lens.

In contrast the same subject shot at the same size in the view finder but with a wide angle lens shows a dramatically different view. 

1/320, f13.0, 
ISO200, f17

1/320, f13.0, 
ISO200, 17mm

The increased angle of view provided by a wide angle lens allows the inclusion of the entire sky scraper behind the lion with room to spare.  It has the effect of emphasising the closer parts ie the feet and claws to dramatic effect and giving an imperious tilt to the regal nose of the lion.  The whole effect is the opposite of the foreshortened long lens appearance as with the wide angle lens there is a great feeling of depth and soaring height.  It does, however, result in considerable distortion of the verticals causing much more convergence than is actually there.

These effects are also very apparent in the other example here.  The metal sculpture is called the 'Light of the Orient' and sits on a roundabout near the Innovation and Technology museum of Shanghai.

1/320, f13, ISO200, 150mm

1/320, f13.0, ISO200, 17mm

Although I only used 150mm to shoot the long lens version (there was too much in the way to retreat further) the effect is very similar to 300mm or more.  The sculpture is very flat and is surrounded by the lower part of the glass buildings behind.  The shot looks crowded and busy with traffic and light poles in front and a mass of structure behind.  It isn't an unpleasant shot as it puts the sculpture in the context of a busy city full of action and bustle.  On the other hand, the wide angle shot, which has the subject at a very similar size in the view finder has a completely different feel.  The sculpture looks long and dynamic as the shaft stretches up into the disc, pointing high into the sky.  The area around looks empty and quiet with the buildings set back and it gives the sculpture dominance over it's surrounds.  The feel of the shot is quite different with the sculpture being the whole purpose of the picture whereas the other view had the sculpture as part of it's surroundings.

No comments:

Post a Comment