I am constantly experimenting with better ways to photograph a highly reflective, compound curved, multi-angled, shiny surface to actually reveal some of the crytal structure that the human eye sees when examining a blade. Some blades are pretty simple. A wakizashi or tanto in a transparent sashikomi polish is fairly easy to photograph. You can either use a longer lens or bring the camera closer to the blade, and the curvature is such that a single light source generally does the trick. As soon as the blade length gets much past 2 shaku with even minimal sori, the inverse square law kicks in, and the light falls off rapidly at both ends, so the nakago and the kissaki are poorly lit.
Some years ago, I used a single, long fluorescent bulb as my light source. Great for short blades, but hopeless on long curved blades. So I went to two shorter (24 inch) fluorescent fixtures which I could arrange in a V-shape to match the sori of the blade. That was better but still not great. Even with shielding, there was enough ambient light that the blade reflected the camera on the shinogi ji. A blade polished in kesho simply showed the outline of the hamon with no detail at all of the activity in the blade.
Recently a photographer friend introduced me to light painting; using a moving point source of light to illuminate an object during a multi-second exposure in a dark room. I have been playing with this technique over the last few months and while the look is different than the standard sword photos we are used to, it reveals a lot of detail in the hamon. Essentially it uses the same process that we use when we study a blade. We move a point source of light along the blade in a dark room to bring out the crystalline structure of the blade.
This method has its problems too. First off, every blade is different and requires a new solution. So I now have a variety of small LED and incandescent flash lights to play with. I used this method on the two shinsakuto blades I recently posted and I am pleased with the amount of detail showing in the hamon, especially on the Koretada. I do not photoshop any of my blade photos except to crop them and adjust the exposure. What you see is what the camera sees. The joy of the digital camera and this new approach to lighting blades is that you can take 40 or 50 exposures fairly quickly, sort through them for the best four or five exposures, refine that timing and light path, and take another batch.
It is a pretty amazing lesson in the physics of light. Just as nie formations like inazuma can switch from shining silver to shining black as you rock a blade under a light, frequently one half of the blade would show bright silver ji and dark hamon and right at the center of curvature would flip to dark ji and bright hamon. The angle of the light path requires a bit of experimentation on each blade.