Weekly Challenge – Converging Lines

Railway Bridge 1


The dPS challenge for this week is Converging Lines.  According to the Oxford Dictionary, “converge” originated in the late 17th century from a Latin word convergere, which is a combination of con “together” and vergere “incline”.

I use these challenges to learn more about the gadgets and gizmos on my digital camera.  But it’s been hit and miss, with learning only occurring when I stumble and need to work out why.  It’s time to stretch myself a little more.  This week, I selected at random a page from the camera’s manual to incorporate into the challenge.

Page 61 Selecting The AF Point.

That’s the auto focus point, for other beginners. And as a beginner, my camera only has nine focus points.  By deploying them all, the reliability of the auto focus is maximised.  By selecting one, the camera now works with a specific component of the image.

The next decision is “where to focus?”, and this is where depth of field comes into play.  I’ve recently read about the “circle of confusion”, a phrase used to capture the idea that there is no critical point of transition between sharply focussed and not sharply focussed.  The transition is gradual but only appears as such if something solid is occupying that space.  I’m not sure why it’s a circle.  I still think in terms of planes.

The guiding question for this week

Will it be possible to capture the idea of incling together, converging, while specifying a focus point and limiting depth of field?

I can think of many occasions when converging produces confusion rather than clarity.


I was day tripping across southern NSW and came across this railway bridge at Harden Murrumburrah.  I’d been keeping an eye out for converging lines and found a few.  None seemed suitable for experimenting with the auto focus point.  It had already been a long day, but finally this congregation of converging lines appeared in the viewfinder. They fit the theme so well.

Turns out, I didn’t need to play with the auto focus point to capture the idea of confusion.  The site did it for me.  Convergences heading in different directions.  So, to let the site have its say, the best choice was to set the auto focus to full.  I don’t know if a mid-range aperture (f/9) was the right choice?

I tried shifting the focus point and shortening the depth of field, but neither was satisfactory.

Railway bridge 3 Railway bridge 2


To really understand the impact of repositioning the auto focus point and playing with the depth of field, I think I need a more detailed exepriment.  Perhaps with a matrix showing many combinations of the two to use as a shooting guide.  And a tripod.  I can then stick the results up on a board and review them.


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