NavList:

Frank you asked: Did any periscopic sextants provide a wide field "finder" capability? 

I know of no British periscopic sextant which had more than one field of view.  However, different sextants had different fields of view. The sextant in the Hermes accident was a KSH 0203 (also known as the RAF Mk1) which had a field of view of 7.5° and 4X magnification.  By the time the RAF MK2 came along they’d gone back to 2X magnification and a field of view of 12°.  The RAF Navigators “Bible”, AP1234, said of the RAF Mk2 at Part 1, Sect. 3, Chap. 5

……… The sextant has a field of view of 12° both in azimuth and elevation and a magnification factor of 2.  Because of the narrow field of view, the object to be observed has to be identified by setting its precomputed altitude and azimuth on the sextant.  The object should then appear approximately in the centre of the field of view.  Great care must still be taken however, to ensure that the object being observed is the required one, as the accuracy of the azimuth setting depends on the accuracy of with which the true heading of the aircraft is known.  If for any reason the heading set on the sextant is different from that which the aircraft is flying, the wrong object may be observed. 

The only British bubble sextants with a more than one field of view were the Hughes MkIXAM and BMs (M for magnifier).  These had a double eyepiece on a swivel bracket which could be pulled against a spring and rotated through 180° to give either the normal eyepiece or the twin-lens telescopic one.  All I could find on magnification was.  At one end of the bracket is a standard eyepiece and at the other end a simple twin lens telescope, having a magnification of two diameters.  This means that the diametrical field of view is halved and through it stars will appear four times as bright. I was issued with a MKIX BM during the first part of my training, but I can’t remember now which eyepiece I used.  I can remember them all being advertised for sale in “Flight Magazine” shortly after I handed it back for 12GBP each, but I never got round to buying one.  Regrets, regrets. Dave