DoF Calc - Day 79

One of the most difficult areas to grasp within photography is the Depth of Field factor (DoF). Depth of Field refers to the range of distance that appears acceptably sharp. Four major factors influence the DoF - the camera model (type), focal length (lens model), aperture and distance to subject.

My subject is a withered flower placed on a table with a brick wall as a back drop. I want the brick wall to be out of focus and the complete flower to be in focus. Normally I would chose a high aperture (small f-value) like f/1.4. The distance from the camera to the flower is 0.5 meter. The distance from the flower to the wall is 3 meters. I'm using my Nikon D300 with a AF 50mm f/1.4 prime lens. If I add those parameters into a DoF calculator the following appears:

My DoF is only 0.005 meter - that is 0.5 cm! So roughly a few millimeters on each side of the focus point would be in focus.

Here is a photo where I used an aperture of f/6.3. From the enhanced section it is clear that only the first part of the "optimal focus area" is in focus.

What happens if I change the aperture to f/11?

The range that will appear sharp changes to 4.2 cm. A huge difference.

I used an aperture of f/10 for the photograph of the small flower at the top of this blog article and maintained acceptable sharpness. 

I use an app for the iPhone called DoF Calc.

You can find an "On line Depth of Field calculator" here.

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