Focusing issue?
- Thread starter dickelfan
- Start date
get_armbarred
Senior Member
Yea 1.8 is pretty wide open. Just a small increase in f stop should fix it.
Is there a formulation for that?
There are a lot of smartphone apps and online calculators, like this one.
PS. This is very instructive when you want to do macro photography. For example, using a 105 mm macro lens at the shortest focusing distance of 31 cm (parameters for Sigma 105), the depth of field at a modest f/5.6 is only... 0.1 cm! This is why people use very small apertures for macro. Still, closing the aperture to f/22 would increase the DOF to only 0.5 cm.
PS. This is very instructive when you want to do macro photography. For example, using a 105 mm macro lens at the shortest focusing distance of 31 cm (parameters for Sigma 105), the depth of field at a modest f/5.6 is only... 0.1 cm! This is why people use very small apertures for macro. Still, closing the aperture to f/22 would increase the DOF to only 0.5 cm.
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I use Photo Caddie on the phone.
Another good site on DOF is dofmaster.com
You can use a smaller aperture or move back a few inches (or centimeters). Guessing you were about 20 inches away, which gives a DOF of .55 inches. Changing to f/4 would more than double the DOF to 1.24 inches. Keeping the fast aperture of f/1.8 and moving back 10 inches increases the DOF to 1.27 inches.
The near depth of field or the portion between the focus point and the camera, at f/1.8 and 20 inches would be 0.27 inches, so that slight turn of the head was just enough to move the eye on the right into the soft blur.
It's still a very good shot though. Captures that something that the little ones have.
Another good site on DOF is dofmaster.com
You can use a smaller aperture or move back a few inches (or centimeters). Guessing you were about 20 inches away, which gives a DOF of .55 inches. Changing to f/4 would more than double the DOF to 1.24 inches. Keeping the fast aperture of f/1.8 and moving back 10 inches increases the DOF to 1.27 inches.
The near depth of field or the portion between the focus point and the camera, at f/1.8 and 20 inches would be 0.27 inches, so that slight turn of the head was just enough to move the eye on the right into the soft blur.
It's still a very good shot though. Captures that something that the little ones have.
BackdoorArts
Senior Member
Not sure if those apps are free, but I use TrueDoF-intro, which is free and handles every lens I have (you can't go bigger than a f/1.4 or smaller than f/32, but at those points who truly cares? just the folks who already know how small that is).
Yes at F1.8 the DOF is quite shallow. For getting both the eyes in focus, either take the shot square on, or increase the aperture to F4 (but then that will not have an out of focus background as with F1.8.