Thanks for the response Jason. I think it's great that you are making modular diffusers, and it's always been inexplicable to me why the camera manufacturers have never looked into this. When I made my first cup diffuser it was quite ridiculous how I totally transformed the light from the very expensive Canon MT24EX with a simple vending machine/water cooler cup. It told me straight away that no one had ever really thought about macro lighting modification. This is what led me to do a big empirical investigation into how light actually works in the macro region, which is different than flash or continuous lighting theory than at normal distances. The important two elements are relative distances and the inverse square law, which means small differences in distance can create big differences in light intensity. Unfortunately the article/threads where I laid all this out are no longer on the internet, although there are still links in some blogs trying out these principles. And some is retrievable with caches from the past.
In my diagram blue stands for well distributed light with no hotspots. Red stands for a brighter part, but where highlights will not usually be blown, and yellow stands for an intense spot, where highlights are likely to be blown.
When I first came up with this proposed light modifier I'd not even been able to make a prototype because I couldn't find any suitable domes. I sort of live-blogged my search for them, and then developed them, which you can see on this archived web thread below. To access this archived thread click on the blog below, and click on the link "Concave Flash Diffuser Test".http://www.davidkennardphotography.com ...iffusers-comparison.xhtml
I was certainly aware of the need, ideally, for different thickness plastic to eliminate hot spots. However, what I'm surprised with is that no one really understood that the inverted plastic dome concave diffusers completely re-shape the light as they act like a lens. Therefore the light is re-distributed even though the thickness remains the same. Ideally the plastic of the dome would be thicker at the apex where it is nearest to the light source and thinnest furthest away. I outlined this at the time.
The reason I'm telling you this is that it would be possible with 3D printing to produce an ideal inverted dome. I don't think the dome would have to be that deep. There are a number of ways these domes could be implemented. Ideal the whole flash head and reflector design would be altered to accommodate it, and I can't believe how lazy Canon have been with their new MT26EX. It would be possible to design a much, much better macro flashgun from scratch. No new technology needed. It's just lazy to take reflectors and tubes designed for normal flashguns and to just shrink them down as in the twin flashes on the market.
As per diffusion gel it's very easy to just build up different layers so there are multiple thicknesses where the flash head is closest to the diffuser space, and it's thinnest at the edges as in your 3D printed diffuser face. My suggestion for diffuser gel was that you should be able to make a clip at the base for holding the diffuser gel. Then you can make different custom lengths for different purposes. I've already been doing this for many years with a modular design. I tend to used self-adhesive velcro for attachment, not being concerned with looking professional. I have different lengths because the longer diffusers can be difficult for photographing things like Springtails on flat surfaces. So you can use a short one. I also have it so I can use multiple layers depending on how much diffusion I want. The idea with the multiple layers with a gap is that the first layer diffuses and spreads the hotspot from the flash head, so by time the light hits the second or even third layer, there isn't much of a hotspot.
The only reason I haven't got round to 3D printing any is mastering CAD software. It's really overkill for the quite simple shapes I want to produce, and it's not really designed for just making simple shapes. Plus for the last few years I've had very poor concentration due to an anxiety condition I developed after the death of my sister. It makes learning anything new difficult at the moment. Also it's more difficult for me to do some of the more demanding macro photography I used to do. I had seen the potential of 3D printing for this years ago. As I said I think it's good that you are finally doing what should have been done for a long time ago.
Good luck with your designs and projects.