Joe, you've posted eta - time curves from a number of sources. Now consider d(eta)/dt. Where is d(eta)/dt almost flat?Joe Farina wrote:This works very well. I've found that exposure time is quite important for MBDCG. I used to think that because it was so slow (a typical exposure with HeNe for a 4 X 5 holo would be ~20 minutes), a couple minutes here or there wouldn't matter. But I used the shutter described above, to do a series of exposures varied by two minutes. And it turns out that two minutes over-exposure decreases the diffraction efficiency noticeably.
Considering the figures for the density chart, consider that the amount of illumination through an uniformly illuminated aperture is proportional to the aperture area, which in turn is proportional to the square radius of the aperture
L = k*A = k*pi*(r^2) = k'*r^2
Consider now that in order to double the amount of light through the aperture, the aperture area must now double. How much greater must the radius be in order to double the area of the aperture and so double the amount of light through the aperture?