Archibald wrote in post #19279798
The
quality of the light is determined by the diffusion. The
direction of the light is determined by the angle of the rig.
When I said you can shoot at 90 degrees, that was just an example. I was not suggesting you actually shoot at that angle. You should pick an angle that works for the photo you are shooting.
This grasshopper was partially front-lit by shooting with a rotated rig.
The shot below shows the angle it was shot at. So I rotated the image about 40°.
The directional effect is subtle because the light was heavily diffused.
A light that is camera mounted, at a relatively low angle, has a tendency to blow out the shadows. The light will end up looking soft because it is large compared to the subject, and to a certain degree because there are little to no shadows due to angle. But the light on that hopper is not diffused very well, and you can see it in the specular surfaces. They are acting like true mirrors and in some areas are returning the color of the light source, and not the color of the surface itself. In the specular areas you should see color and texture, and that is an indicator of the level of diffusion. In macro it is really easy to end up with a light that is soft/specular because there is very little room for the light from the flash to spread out before it hits the diffusion surface that the subject sees, so you end up with a hot spot in it. In a studio soft light = diffused light most of the time because studio modifiers are designed to let the light from the flash spread out before it hits the final diffusion surface -and in a studio you have room for it.
Here is an example of what I mean about color in the specular areas. Although the specular highlights are obvious (due to the angle of the light) there is color and texture in them. Also this series starts at 1x, the worst possible light due to the distance between the light and the subject being the greatest, to 3x with the light getting progressively better (due to the apparent light size principle) as the distance between the light and the subject drops.
I took that sequence to demonstrate the apparent light size principle and as a torture test -the angle between the light and the subject is terrible. At the angles that I normally shoot the specular highlights are almost unnoticeable due to how well the light is diffused. 2.5x:
IMAGE LINK: https://flic.kr/p/2me6pF9 22 Spot Ladybug by
John Kimbler, on Flickr
I am not saying your light should look like my light but I am saying that if you are concerned about the detail in your images then light quality is really important, and IMHO, it has a bigger impact on image quality than diffraction. I routinely see people wasting their time with triple digit focus stacks that have less detail than my single frames because their light quality is poor. Due to the short distances between the flash and the subject it is really easy to end up with a soft light source (large relative to the subject, so the shadows are soft) that is also acting like a point source (due to a hot spot in the diffusion surface that the subject sees). If the specular areas are returning the color of the light source, due to poor diffusion, then there will be quite a lot of detail that is simply being erased by the light. That detail is not being blown out, because it is not an issue of exposure and underexposing will not prevent the detail loss caused by the hot spot in the light source. You have to find a way to force the light from the flash to spread out, and not just block that light. I spent years experimenting with different materials, and in the end the only thing that worked for me is a 1/4 stop white China silk scrim fabric. The light from a twin flash is so intense that it blew right through every other material that I tried. Currently I am losing 1 and 1/4 stops with my diffusers when I compare them to the bare flash heads. One stop better than my old set.
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