TALBOT4206

138 Holborn Bars

March 10^th/41

My Dr Sir

We send you one of our metalic <sic> speculums, ¹ of about seven inches focus parallell <sic> rays; with an aperture of about five and a half inches (this aperture can be increased some considerably <sic> without materially increasing the aberation <sic> of the reflector) – The box in which this reflector is placed – is rather short, it being originally intended for a shorter focus reflector – It will however answer your purpose, but should you find that the scattered light be a source of annoyance, you will have but to increase the length, infront <sic> of the present aperture – say some six or eight inches – it would be well to blacken the interior, and also to put a proper diaphragm to the addition: if found as above – viz, scattered light troublesome – The focus glass you will find inside of the reflector box = In adjusting the focus the ground surface of the glass must be towards the operator – should the slide, which carries the plate-holder move too stiff <sic>, you can ease it to your pleasure – should you desire to remove the reflector – remove the screw from the hook, at the small door, the speculum can them be removed if desired – A few trials of the focus glass will enable you to place and remove your prepared material quickly; Should you find that the im<ages?> ² are formed too quickly – you can first adjust the focus, remove the glass, place a cut-off between the reflector and the filter, place your material in at a side door, after which (the filter having the proper expression) this cut-off could be removed the desired length of time, then closed; the material as acted upon, could be removed at pleasure

Your Very Respectfully

John Johnson

W^m H F Talbot <Esq>

Wm H. F. Talbot Esq^re
N^o 31 Sackville Street