Explain the basic principle of Stadia Method.

Let us consider the external focusing type of telescope and let us consider the line of sight to be horizontal. Let,

`f=`focal length of the object glass.

`i=`stadia hair interval `=ab`

`S=`Staff intercept

`=AB`

`c=`siatance from O to the vertical axis of the instrument

`d=`distance from O to the staff

`d'=`distance from O to the plane of the diaphragm

`D=`horizontal axis from the vertical axis to the staff.

Now, from triangle AOB and aOb, we have,

`d/d'=u/v=S/i`.......(i)

Again, from lens formula, we have,

`1/f=1/u+1/v`

Multiplying both sides by `uf`, we get,

`(uf)/f=(uf)/u+(uf)/v`

or, `u=(uf)/v+f`....(ii)

Now, from (i) and (ii), we get,

`u=f+f/(i/S)`

`=f+(fS)/i`

Adding a constant `c` on both sides, we get,

`u+c=(fS)/i+(f+c)`

Again from figure,

`D=u+c`

Thus,`D=(fS)/i=(f+c)

Also, let `K=f/i` and `C=f+c`,

then the above expressio....

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