Depth of Field Adapter on Steroids

ProfHankD wrote:

Tons o Glass 0 Class wrote:

He had the Fresnel lenses spaced away from the diffusion sandwich (yum) a little bit, and one of the Fresnel lenses looks to be moving with the lens section when he focuses, so at least with the way the rig was built, he still needed the sandwich. He mentioned that the Fresnel lenses' focal lengths should closely match the main lens to work best, maybe the extra spacing was needed to compensate for a slight mismatch?

I don't get that at all.

I can't quite wrap my head around what the light rays involved are doing and what they need to do. He explains some stuff half way through the video right after the sponsored content and illustrates it to a degree, but not enough for me to say "I get it." I'm going to continue grabbing at straws here hehe.

You don't want the Fresnels up against a plastic sheet because you'll get Newton's rings, but Fresnel lenses shouldn't be needed with a good diffuser... it's just that a good diffuser will make a much darker image. Basically, what he did is a lot like you'd find in the old rear-projection large-screen TVs. In any case, large Fresnel lenses are usually pretty pricey too, so I'm not sure how his budget worked... even ignoring the fact that I haven't seen a comparable lens for less than the total price he's claiming for the lens and all. I guess he's a really good shopper or just got very lucky?

Matt also built a DIY projector and that's where he got the idea to use the Fresnel lenses, so the rear-projection TV angle checks out hehe! I'll wait for his supply list, but yeah, his budget might not be able to be matched by anyone.

I'm playing with an online ray-tracing simulator to try to visualize things better and set up components like he describes:

A rough ray diagram of Matt's system for light rays that pass through the diffusion screen?

So... this diagram only illustrates rays that aren't dispersed by the diffusion material? And light focused on the diffusion screen could be seen by the lens+camera observer without the Fresnel lenses... So... if the Fresnel lenses are used in this manner, does the rig even need a focusing screen? If not, could you just use one Fresnel that is about half the focal length of the current two, placed right where the focusing screen was?

The whole system isn't doesn't quite behave like that of a system with a focal reducer as the observer's lens would never have an aperture wide enough to focus all the rays pointed at it - I feel like my lens+camera observer is problematic in this diagram...

I feel like I'm missing something (everything?)...