I have an incoherent light source that is of unknown size, and I was wondering about the possible methods to measure its size. The issue is that I am expecting it to be very small (few micrometers), and if I try to use a pinhole camera much smaller than the source size I will not gain enough light to actually resolve the image.
If I use a reasonable sized pinhole camera (50um) - I will only image the pinhole - not gaining any new information about the source itself.
Right now, I am thinking of calculating it by looking at how quickly the light intensity falls off when it passes a sharp absorbing feature such as a knife edge or a slit. If the source was infinitely small I assume what I would see would be a fall-off that would be approximately as long ('smudged') as the effective mean wavelength of the light. If the source is larger than the wavelength, then the speed at which the light intensity falls off at the edge should be approximately equal to the size of the light source (corrected for the magnification of the imaging system). I guess what I am essentially saying is that the image will be something like the source intensity spatial distribution convoluted with the transmission map, am I correct here?
Are there any methods of estimating the source size by looking at the image of the source through a pinhole that is larger than the source itself, or by looking at the image of the source passing through a slit (two knife edges)?
Are there any other simple ways one can measure or estimate the source size?
It's also worth mentioning that I am dealing with light that is approximately 0.1-0.01nm in wavelength.