Art of Photography

Rob Townsend


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Exercise – Focal lengths and different viewpoints

Brief:

Find a scene that has enough space in front of it to allow a choice of viewpoint, from near to far. Start with the longest telephoto lens and make a tightly framed composition. Then walk forwards in a straight line until you can fill the frame with the same subject at the widest angle setting, and take a second shot. Compare the two.

Equipment:

Canon EOS 650D with EF 18-200mm f/3.5 lens.

Method:

I chose the fountain in the grounds of Castle Howard and followed the straightforward instructions in the brief.

Results:

The first shot was at 200mm focal length, and it had the effect of dramatically compressing the distances between parts of the image; in reality the backdrop of the house itself was as far away from the fountain as I was on the other side, but in this image it appears to be immediately behind. Similarly, the water cherubs on each side look to be adjacent while in fact they were positioned one on each corner – so the true front-to-back distance was equivalent to the left-to-right distance you can see here.

200 mm

200mm

Filling the frame with the same subject with my lens at its widest focal length of 18mm gives a very different feel. The subject has gained more depth and more closely resembles its real-life dimensions. The cherubs are clearly spaced on each corner of the fountain base, and the house has receded into the distance, allowing a backdrop of sky. The relative position, size and distances in this image are much truer to life and therefore easier to assimilate.

18 mm

18mm

What I’ve learned:

Zooming in to a long focal length has a significant effect on the perceived depth in the image; it can produce a very flat image where the all parts of the image from foreground to background seem to be very close together. Wide-angle shots, on the other hand, more strongly convey a sense of depth. The resulting pictures from these two extremes are very different in feel and character. This is something I must start to take into account when deciding the focal length to use and the viewpoint from which I want to take a picture.

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Exercise – Focal lengths

Brief:

Choose a view that is open and at the same time has some details in the distance in the middle of the frame. Take a sequence of photographs from the same viewpoint at different focal lengths by zooming and/or changing lenses.

Equipment:

Canon EOS 650D with EF 24-105mm f/4.0 L IS USM lens, EF 80-200mm f/4.0 lens, tripod.

Method:

I chose the war memorial in Nice and set up my tripod on a plinth at the opposite side of the road to take in the entire monument in the wide angle shot. Then I proceeded to first zoom in and then change lens to follow the brief.

Results:

The first shot was at the widest my lens could go, namely 24mm (actually 24mm equivalent; as the camera body has a crop factor of 1.6x). Here you can see the entire monument in context, built into the rocky hillside.

24 mm

24mm

Zooming in to a focal length of 35mm, some of the distraction (e.g. the road) is removed to focus more of the monument itself.

35 mm

35mm

At 50 mm the framing starts to go slightly off as I’ve cut off the top and bottom of the monument.

50 mm

50mm

Zoomed to 70mm the balance is a little better, as I am clearly focusing on the central part of the monument and the framing looks more deliberate.

70 mm

70mm

At 105mm I hit the limits of my main lens. This is the first shot without the context of the rocks around the monument and so focuses on the monument in isolation, a subtle but significant framing difference.

105 mm

105mm

I switched to my longer telephoto lens at this point. At 135mm the wording at the top of the monument is becoming legible, yet the dome is still visible so you still get a good feel for the shape.

135 mm

135mm

The full extent of my zoom range. At 200mm the image focuses much more on the top segment of the monument and the place names inscribed. This gives a very different feel to the picture than the wide shots with the full monument in frame.

200 mm

200mm

As a comparison, and as suggested in the brief, I took a crop of the widest shot (24mm) in the centre of the frame to compare it to the longest focal length shot (200 mm). As expected, the content of the frames are the same – albeit the lighting and sharpness are different.

24 mm centre crop

24mm centre crop

What I’ve learned:

I’ve picked up two clear lessons from this exercise. Firstly, the obvious one that changing your focal length will narrow or widen the view that you can fit in the frame. Secondly, that choosing a focal length can also mean choosing what you include and exclude in the frame, which in turn can have an effect on the message you wish to get across, and the response you are aiming to elicit from the viewer.


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Exercise – Focal length and angle of view

Finally getting started with the actual coursework. The first exercise under ‘Getting to know your camera’ is about focal length and angle of view.

Brief:

Take three photographs, one at a focal length that gives a ‘standard’ (equivalent to human eye) view, one at a wide angle and one at a telephoto zoom length. Print each one at A4 size. Hold them up at eye level to measure the distance from eye to photo where the image is the same size as the actual subject. Observe the differences between the photos taken at the varying focal lengths.

Equipment:

Canon EOS 650D with EF 24-105mm f/4.0 L IS USM lens

Method:

I found this slightly confusing at first but worked it out after checking how other people had done it (and some had the same initial confusion as me, which made me feel better). I set up the camera on a tripod on a low wall in the garden and pointed the camera at a terracotta garden ornament, positioned at the foot of a tree with a few daffodils for background detail.

As instructed I worked out what 50mm equivalent would be on my Canon crop-sensor camera – a crop factor of 1.6x means that I should select 31.25mm (this was the part that had me briefly confused; makes sense now though). As it turned out, the EXIF data said I actually took the shot at 32mm, which is pretty close.

Then I took the wide angle shot at 24mm (widest I could go as this is the only zoom lens I own, for now anyway!) and the telephoto shot at 105mm. Printed them out on A4 as instructed and then did the measuring part. I needed help from my long-suffering assistant* (*wife) for the telephoto shot as my arms weren’t long enough. Then I did some mathematical checking against the theory and was reasonably pleased that it stacked up!

Results:

32mm

32mm

This was supposed to correspond to the ‘standard’ 50mm field of view which on my crop sensor should have been 31.25mm (close enough). this gave a corrected focal length of 51.2mm.

To see the image and the subject at the same size I had to have this 350mm away from my eyes.

24mm

24mm

This is the widest view, 24mm or 38.4mm equivalent when corrected for the crop factor. Not too different to the first one really. Wish I had kept my old Tamron 18-50mm…

To see the image and the subject at the same size I had to have this 290mm away from my eyes.

105mm

105mm

This is the furthest extremity of my zoom lens, 105mm. Or corrected for the crop factor, equivalent to 168mm.

To see the image and the subject at the same size I had to have this 1150mm away from my eyes.

Some maths:

I did some maths to check whether my findings were in line with focal length physics (with thanks to Martin Proctor, who inspired me to dig out the formula). Simply put, dividing the (corrected) focal length by 50 (as 50mm is closest to a 1:1 subject:image view) gives the magnification factor.

So: 24mm (corrected: 38.4mm) should give a magnification of 0.768x and an expected viewing distance of around 269mm compared to my 32mm (51.2mm) distance – I measured 290mm, so not far off.

Similarly, 105mm (corrected: 168mm) should give a magnification of 3.36x and an expected viewing distance of around 1176mm – I measured 1150mm, again pretty close. I’m putting any slight variances down to the gusty weather and me not wearing my glasses!

What I’ve learned:

After many years I think I’m finally getting my head how focal length affects an image. The concept of the ‘standard’ view makes a lot of sense now. I wish I’d had a wider lens range for this exercise but I think I’ve managed to demonstrate the principles enough for me to grasp the key points.

References:

Korpella, R. (2013) How to convert focal length to magnification [online]. eHow.com. Available from: http://www.ehow.com/how_6823034_convert-focal-length-magnification.html [Accessed 21 April 2013]