The focal length of a lens is the (focal) distance from the centre nodal point of the lens to the film/sensor plane when focussing on an object @infinity.
Focussing on a closer object requires this (focal) distance to increase.
For an object to be captured lifesize the proportion of focal distance to image distance needs to be 2f-2f
A conventional lens's proportion of focal distance to subject distance is low wheres as a macro setup is the opposite in as much as the focal distance is relatively high in proportion to the subject distance.
As the lens is relatively long to the subject the DOF is narrow, therefore in order to capture enough detail a smaller aperture is required, and this in turn limits the amount of light to the sensor, so long exposures and or flash is required to light the subject. Long exposures and exaggerated lateral camera movement/shake necessitates the use of a tripod and where possible remote shutter release as well as mirror up mode .
There are several ways of adapting the camera to suit for macro
1) Close up lens.... lowest quality option .. but inexpensive, basically a magnifying glass (rated in diopters )
2) Extension tubes.. Magnification is calculated by image size/original size ie 1:1 2:1 etc
use formula to determine what extension tube length is required
3)Macro lens.. specifically designed for close up work
We were given the task of taking two macro shots. One using the extension tubes on an SLR and one using the Hasselblads, the image sizes needed to be 1:1 and 2:1.
Using the formula V=(m+1)f we needed to calculate the length of extension tube required to effectively shoot our images at a magnification ratio of 1:1 and 1:2 ratio
Where V=total focal distance (lens length + extension tube) There fore to work out tubes length just subtract lens length.
We came up with needing 50mm for 1:1 and 25mm for 1:2
..These are the shots we got
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