[quote:a06533ea0f]As I understand it, the only reason the 4:1 ratio is so commonly used is to make sure that the "signal" of the reference light is that much greater than the "noise" of the object light. [/quote:a06533ea0f]
Actually, it's a little more complicated. Isn't it always
In the early days of holography, they needed a very low grain size and a very high gamma. The also were very concerned about "linearity", which basically means that a sinusoidal signal in would translate to a sinusoidal signal out - much like amplifier theory. The only material available was an X- Ray film, which I believe is, or was, basically the Agfa 10E75 (Martin, am I right?). This was pre-bleach days because bleaches were particularly noisy and they felt that to get a good H2, they need a very good H1. These days bleaches are better, but you still occasionaly hear the "don't need to bleach" mantra. Anyhow, in their drive for linearity, they figured that if they could expose in the middle of the H-D curve, then they could afford to have the dynamic range of the object go up and down a little and still retain linearity. If you look at the HD curve for the 10E film series, you'll see that the middle of the H-D curve falls such that a 4:1 variation of the object would still keep you in the linear region and so the gamma would be constant. If you varied the dynamic range above 4:1, you'd end up in the top or bottom curve - the "S" bit of the curve - and lose linearity. The early papers talk a lot of linearity. By the way, anyone interested enough in the roots of present day customs would find a treasure trove of info reading the early papers of El-Sum, Pennington etc. Those who understood this taught their students simply to maintain a 4:1 ratio and all would be well. Tthey in turn taught their students and a methodology was formed. Today's emulsions don't need a 4:1. In fact, if you intend to bleach, the bleaching process is inherently non-linear and so the H-D curve is meaningless anyway. But 4:1 is still a good starting point. If you go beyond 4:1, 0.5:1, as in your example, you'll get noise - essentially a halo around the object. I've used this technique before, as have others. About three years ago, I shot an angelic figure. Since this was meant to be an angel in a manger scene , I shot the H1 at about 1:2 (twice as much object as reference) to deliberately get a glowing (non-existant) angel hovering above a manger scene.
By the way, this is not meant to disparage your discovery of the technique. Since you clearly did not know of earlier attempts in this direction, your discovery of the technique is every bit as original as anyone else's.
