I'm using a 28-105mm lens which has a minimum aperture of f/3.5
I've used a different set of subjects to the earlier exercise to make it more interesting in terms of images and my learning
Image 1:
I've positioned where I have 4 trees and have ensured the camera is at aperture priority. I've set the aperture to f/4.2 the widest aperture the lens will allow and have focused on the centre tree, the one leaning slightly left to right. The camera has selected 1/30 sec shutter speed, I'm on a tripod so will guarantee a sharper image than hand held
From this image the tree in front and behind the subject tree remain out of sharp focus, so is the foliage in front and behind though I do note the grass level with the tree is also in sharper focus. There is a gap of about 3-4 feet between the trees so clearly the depth of field at this focal length for this aperture is less than 6-8 feet.
Image 2:
I've set the aperture for this second image to f/9 and I note the camera has set a shutter speed of 1/8 second to get the same exposure. This is because the the aperture is now smaller letting in less light so the shutter will now stay open a bit longer to compensate. In this image for first tree, second and third trees are all in focus, as is the foliage between the first and third tree. This now suggests the depth of field at f/9 is at least equal to or greater than 6-8 feet and all 3 trees are in sharper focus, particularly the first and third which were not at the wider aperture. I think the depth of field is actually greater than this since the tree with ivy is now also in sharper focus which is at least 15 feet away. I suspect the depth of field stretches farther back
Image 3:
The aperture for this image is at the maximum of f/29. Whilst the depth of field appears similar to that at f/9 the image is distinctly softer than image 2. I think this is likely a result of using a zoom lens at its maximum aperture where the lens does not perform at its best. performing some on-line research when using a zoom lens lens aberrations can occur at their maximum and minimum apertures are are often best used 1 or 2 stops / aperture setting above / below their maximum to avoid these aberrations and ensure sharper focus for the depth of field required. However I also note that at an aperture of f/29 the camera has set a shutter speed of 1 second. Though the camera is on a tripod the could have been vibration / wind etc which may have contributed also to the softer focus
Exercise Learnings:
a) A wide aperture will give a narrow depth of field. This depth of field appears to be dependent on the focal length of the lens and the distance from subject to camera
b) Using a narrower aperture (larger f number) will require a longer shutter speed to expose the image correctly / the same as if using a wider aperture
c) Creative use of the depth of field (DOF) can be used when creating images, combined with manual focus the element in focus and the DOF can be well controlled (Exercise 2 demonstrated this using a set aperture)
d) DOF calculators can be bought to assist with DOF calculations. This can be very helpful in ensuring the image visualised is that created. I've identified this when looking to check my DOF estimates with actuals.
e) Zoom lenses will not always give the best image results when used at their minimum and maximum apertures
f) longer shutter speeds increase the risk of camera shake. In this instance I should have used a remote shutter release for all images on the tripod but particularly image 3
g) I think I should probably have used a different subject for this exercise to better demonstrate focus with different apertures. However I have learnt / reminded myself about some key aspects (as mentioned in the learnings above) so this exercise has proved valuable to me
The key in progressing through these exercises is not not only to learn aspects of photography but to put them into practise so to assist in creating the final image that one has visualised.
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