Focus at different apertures

This is an exercise to assess the impact of varying the aperture whilst keeping the camera focussed onto the same point.

I have used the same set up as in the previous exercise which related to shifting the focus point for a fixed aperture.  I chose to do this because in the previous exercise my biggest complaint with the photographs was that the very wide aperture had caused the non-focussed blocks to become too much out of focus.  I wanted to see and show the effect of a narrower aperture.

The exercise called for drawing a circle round the in-focus items.  With the blocks overlapping each other, using a circle meant that I was encompassing out of focus blocks within my in-focus circle.  Instead I have drawn a green square along the table top that the pictures were taken on.  If the square were lying on the table (I didn’t adjust its perspective to make it look like it is) then the range of in focus blocks would be those at the distance of the square.

The pictures were taken at f2.8, f22 and f9.  The point of focus for all pictures was the block that sun and purple quarter circle drawn on it.

At f2.8, only the row of blocks that align to the point of focus block are within the depth of filed.

At f22, the focus area comes forward by a row and extends back by 3 rows.  So the depth of field has increased considerably and has extended further back than it has come forwards.

At f9, the focus area has come forward slightly but no by enough to encompass the next row forward.  The depth of field has gone back by enough to encompass at least another row, possibly two rows.  So again the depth has extended further back than it has come forwards.

The fact that depth of field extended further back than it comes forwards is a useful point to remember when choosing where to place focus points and set apertures.

f9

f22

f2.8