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Old 03-30-2013, 11:30 PM
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FenceFurniture FenceFurniture is offline
Join Date: Sep 2012
Location: Close as dammit to Sydney, Oz
Posts: 137

Here we have two pics taken with the widest aperture my camera has (f3.5) and the narrowest (f8).
The focusing point has not changed (the little timber stop on the rule)
The camera position has not changed
The zoom lens is set for the same focal length

The pic on the left is at f8, and has a reasonably good (large in this case) DOF, whereas the pic on the left is a much shallower DOF. On the left you can quite easily read the 200 mm mark (although it's not properly sharp), but on the right the 200 mm is just a blur (smear).

However, at the top they are both reasonably similar, even though the right is a little more out of focus(and bear with me on the sharpness - forum restrictions on pic size have diminished that).

In this next picture, the aperture is still wide open at f3.5 (like on the right, above), but I have gone to a wide angle zoom position (and that is the ONLY thing that has changed)
The focusing point has not changed (the little timber stop on the rule)
The camera position has not changed

But unlike the picture on the right (at the same wide aperture) everything in the whole room is in pretty good focus (not critically sharp)

What to do if you canít get enough Depth of Field?
This is where the miracle of Digital photography comes to the fore, and Iím going to talk mainly from a perspective of posting pictures on the forum (where the maximum width is 800 pixels).

If you are already at minimum aperture, and canít get the DOF that you want, there is a very nice little work around Ė move the camera back (still using the same focal length) and crop the pic later, but BEFORE you resize it for posting. To do this you need to shoot at a higher resolution than 800 pixels wide, of course. This works an absolute treat because of the third point above Ė the greater the distance away the greater the DOF (with the same focal length).

In other words, because you are restricted to 800 pixels wide, you can shoot at (say) 1600 pixels wide, and crop the extraneous part(s) of the pic off and still get the required resolution.

Itís true that you can achieve a greater DOF by moving in closer to the subject with a shorter focal length (but itís a trade off), but the biggest problem with this is ending up with a wide angled perspective where the subject will get narrower as it recedes from the camera, so that your box with itís nice parallel sides will look quite ridiculous.

This technique is actually the equivalent of using a smaller sensor (Point 4) which gives a greater DOF.

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