Exercise 3. Focus at different apertures.


This exercise asks for three photographs to be taken from the same point, focusing mid-point, using a tripod to ensure the same frame is maintained and using minimum, maximum and medium aperture with exposure adjusted accordingly.
In order to also be able to compare the outcome with the previous exercise I opted to use the same gate as the subject. All were taken in manual mode with a focal length of 50mm and ISO 100. The blue square indicates the breadth of what I think is the extent of the area of sharpness although as I noted previously I don't have great faith in my visual acuity.

The first shot was taken with an aperture of f5.6  and  exposure of 1/40 sec. The blue square indicates the narrow area of sharpness resulting from the shallow depth of field.

The second shot was taken with an aperture of f36 and exposure of 1 sec. A greater depth of field is apparent.

The third shot was taken with an aperture of f14 and exposure of 1/5 sec.

I felt that this one lacked sharpness overall and was actually hard to distinguish from the previous one.

Reflection on Exercise 3. Focus at different apertures.

My first thoughts on looking at these photos were 'I must paint the gate and get the hedge cut'. Then I addressed the job in hand.

This exercise again demonstrates to me that using different apertures results in greater sharpness of either foreground, background or throughout the picture, with a corresponding change in depth of field. This is something to bear in mind when deciding whether I want a sharper or softer subject of focus in my images. From the photos illustrated here and in Exercise 2 I can clearly see the effects. But I still don't understand why different sized apertures effect outcomes other than lightness. I have more reading to do...

Aha! 

Reading through the Workbook again I found that the f stop number is calculated by 'dividing the lens focal length by the effective aperture'. And http://photography.about.com/od/takingpictures/ss/DOF_2.htm tells me 'Fstop settings represent a ratio derived from the size of the lens opening and focal length'. Apparently the size of the aperture affects the angle at which light strikes the film (or in my case the sensor) thereby creating changes in the depth of field. So even if I keep the focal length static my choice of aperture size (f stop) remains part of the equation that determines depth of field. Stupid me. It's obvious when you know!