FC Coarse and Fine Focus Block/Holder focus holder is for high magnification applications where precise fine focus adjustment is required. Rack and pinion mount allows smooth and precise focusing over 33mm of travel. Coarse and fine focus mechanism incorporates a slip clutch and tension adjustment. Fits 20mm diameter, 82mm long mounting post (FC11 adapter is required for mounting to the 71mm long posts on our S-4100, S-4200, and S-4500 stands). The 84.2mm diameter opening accepts all EM Series stereo bodies.