>The problem with high reproduction ratios and small lens apertures is
diffraction of light through the diaphram. The light rays no longer all
converge at a point, making precise focus impossible. Too small an aperture
does nothing for DoF and kills the sharpness of the details over the whole
image. Its better to reduce the reproduction ratio for a given focal length
lens and gain DoF that way, or use a shorter focal length lens, increasing
the reproduction ratio and gaining DoF because less extension is required.
That's why a range of macro lenses, from 20mm to 135mm, is needed (at least
that's my personal rationalization <g>). However, it doesn't take too long
before DoF is hopelessly small no matter what you do, so you do your best to
arrange your subject angle to as thin a plane as possible anyway.
>
>John P
Very true. If magnification is gained by extension alone. If it is gained by
supplimentaries (reversing lenses etc), the diffraction is less. Diffraction
increases with extension.
Foxy
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