No, which is why I originally never said a thing about circle of confusion. You wanted to know why the DoF calculators were giving different numbers.
DoF is easy:
1) distance to subject
2) focal length of lens
3) aperture
Easy peasy.
cheapest Camera that will do depth of field
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No, which is why I originally never said a thing about circle of confusion. You wanted to know why the DoF calculators were giving different numbers.
DoF is easy:
1) distance to subject
2) focal length of lens
3) aperture
Easy peasy.
Soldato
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This is untrue, DoF remains the same if the focal distance between the subject and background remain the same, regardless if the focal distance between the subject and the camera changes, i.e. focal length. FoV however is directly related to focal length.
I don't either!
Glad it wasn't only me.
DP, thank you for your patience with me. Over the last few days I've been doing more reading and thinking more about it to wrap my head around it.
I knew focal length, aperture and focal distance being the makeup of DoF, but the rest of your treatise takes a bit more grasping.
DP, thank you for your patience with me. Over the last few days I've been doing more reading and thinking more about it to wrap my head around it.
I knew focal length, aperture and focal distance being the makeup of DoF, but the rest of your treatise takes a bit more grasping.
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Or the simple explanation ... This background is near and small ... that one is far away and large.
Soldato
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Sorry i'll explain with more detail
If we were to take a photo of a non moving subject (a sign post for example) one at 50mm & the other at 200mm, but adjust your distance from the sign so the subject fills the frame in both photo's, the only thing that changes is the field of view. The depth of field decreasing on the 200mm photo is just an optical illusion from the field of view decreasing. Because of the tighter field of view, the background appears closer giving the impression of a more out of focus area.
Sorry i'll explain with more detail
If we were to take a photo of a non moving subject (a sign post for example) one at 50mm & the other at 200mm, but adjust your distance from the sign so the subject fills the frame in both photo's, the only thing that changes is the field of view. The depth of field decreasing on the 200mm photo is just an optical illusion from the field of view decreasing. Because of the tighter field of view, the background appears closer giving the impression of a more out of focus area.
I see what you are saying but feel it needs some clarification.
When you increase the focal length from 50mm to 200m you do actually reduce the Depth of Focus, it isn't an optical illusion. However, since you have also moved backwards to keep the subject the same size in the frame the increased subject distance has increased the depth of focus. The two have exactly cancelled each other out.
The 2 images will look very different due to perspective - which is what you are getting at. The longer lens has a much narrower field of view, so effectively a smaller area of the background is stretched over entire frame compared with a shorter focal length. This makes the background much smoother, increases subject separation, and looks like the depth of focus is reduced even when it isn't (since the background looks more blurred). The opposite is true for wide angle lens compared with 50mm, a very wide area of background is compressed and squeezed into the background of the frame, creating a busier more nervous background.
This does raise a useful teaching point. Most people want a shallow Depth of Focus so that they can separate the subject from the background better. Depth of focus is 1 tool to do that, but perspective is another, often more powerful tool. You get a much better subject separation and isolation using a 200mm lens than a 50mm prime, even if the 50mm prime is over a stop faster.
This leads to a second point. People often want shallow DoF in order to generate Bokeh. However, Bokeh describes the quality of the out of focus rendering, not the actual depth of focus. A fast prime can have very bad bokeh shot wide open at f/1.4, a slower lens shot at f/5.6 can have beautiful Bokeh. Bokeh can also be improved by increasing the distance form the subject to the background, avoiding high contrast background, stopping down a little and using longer lenses.
I think this pretyy much covers everything related to DoF!
Soldato
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I see what you are saying but feel it needs some clarification.
When you increase the focal length from 50mm to 200m you do actually reduce the Depth of Focus, it isn't an optical illusion. However, since you have also moved backwards to keep the subject the same size in the frame the increased subject distance has increased the depth of focus. The two have exactly cancelled each other out.
The 2 images will look very different due to perspective - which is what you are getting at. The longer lens has a much narrower field of view, so effectively a smaller area of the background is stretched over entire frame compared with a shorter focal length. This makes the background much smoother, increases subject separation, and looks like the depth of focus is reduced even when it isn't (since the background looks more blurred). The opposite is true for wide angle lens compared with 50mm, a very wide area of background is compressed and squeezed into the background of the frame, creating a busier more nervous background.
This does raise a useful teaching point. Most people want a shallow Depth of Focus so that they can separate the subject from the background better. Depth of focus is 1 tool to do that, but perspective is another, often more powerful tool. You get a much better subject separation and isolation using a 200mm lens than a 50mm prime, even if the 50mm prime is over a stop faster.
This leads to a second point. People often want shallow DoF in order to generate Bokeh. However, Bokeh describes the quality of the out of focus rendering, not the actual depth of focus. A fast prime can have very bad bokeh shot wide open at f/1.4, a slower lens shot at f/5.6 can have beautiful Bokeh. Bokeh can also be improved by increasing the distance form the subject to the background, avoiding high contrast background, stopping down a little and using longer lenses.
I think this pretty much covers everything related to DoF!
Bang on that, i was finding it hard to explain! Sensor size has an impact on DoF too
It's amazing how bokeh can differ from same specification lenses, or similar at least. My old AF-S 80-200 2.8 had absolutely stunning bokeh, super smooth, how ever im not that impressed with the AF-S 70-200 2.8!
One thing though..
Could you not argue that DoField is related to DoFocus then, rather than focal length? In regards to the same test, but not keeping the subject fill the frame. If you take a photo at 50mm, a candid portrait for example from 5ft away (head & shoulders) and then take another photo from 20ft away (full body) at 50mm, the DoField would be considerably more out of focus on the close shot despite focal length not changing, only focus distance.