GRAND VAN HEURCK MICROSCOPE (Davis Nosepiece Shutter)

c. 1910

Maker: W. WATSON & SONS LTD.

The 'Davis Shutter' is a nosepiece iris diaphragm. It can be used to increase the depth of focus, and also for dark field work, except with highest powers where a funnel stop would be preferred. It was first suggested by Dr Royston-Pigott in 1869 for erroneus purposes, however it was first noted for its usefullness for 'increasing penetration' as described above on page 262 of the JRMS of 1882. This stopping down of the aperture behind the objective, analagous to a higher F stop on a camera, would increase depth of field while reducing brightness and eventually, reducing resolution.