= Slit-limited resolving power of a grating
{title2=$R=m\lambda f_{\rm coll}/(xd\cos\alpha)$}
A slit of width $x$ at the focus of a <collimator> subtends $x/f_{\rm coll}$. Its projected width is $x f_{\rm cam}\cos\alpha/(f_{\rm coll}\cos\beta)$. Dividing this width by the <grating dispersion> gives $\Delta\lambda=xd\cos\alpha/(mf_{\rm coll})$. Thus the <spectral resolving power> is $R=m\lambda f_{\rm coll}/(xd\cos\alpha)$. Omitting the anamorphic factor gives a denominator $\cos\beta$ instead; these agree in the <Littrow configuration>.
Back to article page
