I have done a lab on resolution power of a telescope. a wire gauze was placed infront of sodium lamp and i used a telescope with adjustable vertical slit to look at it. i was bit confused with the theory .. 1) I was told to record the slit width when the vertical wires just cease to be seen. Do I take the record when it starts to disappear or when it fully disappears? It was really hard to tell the point where the dissapearance started. Any suggestions as to get more accurate data? 2) why would the vertical wires of the gauze disappear? I know the central maximum coinciding with first minimum but whats it got to do with the wires?? Is it because the light sources between the gauze wires coming together (max + min) cancelled out so that the vertical wires are hidden? 3) I measured the distance between wires (x) distance between gauze and the telescope (D) width of slit (a) and have equation angular separation α = λ/a how would I get the wavelength from the measurements so that I can compare the values with the real wavelength of sodium lamp (590nm) to see the validity of my experiment? I tried drawing the light source diagram and came up with tan(α) = x/D but when I do that, the wavelength I get is really off the true wavelength of 590nm.