This is a redesign of my first version I posted a week or two ago. After being un-impressed with the cheap solar filter film I got on Amazon I ordered a sheet of BAADER solar film. When it arrived I found it to be much much thinner than the other film, similar to tissue paper. I knew that my last design would not hold onto this material, nor hold it taut. Thus the redesign.
I will look into designed a front cover for this in the coming weeks.
2X M3x12(or 14) screw.
6X M3x8(6 might work) flat head screw (flat head not required, just looks better).
I designed this so you're able to align your film onto a holding ring, and then install that ring inside the lens hood. I highly recommend you TEST this out on something cheap and similar to your solar film. If using the Baader film I'd recommend using a mylar "emergency blanket" as a test material to get the feel of installing a film.
You want the film to tight, but NOT STRETCHED. Stretching a solar film can lead to degradation of it's filtering properties. This could cause blindness, and damage your camera!
This is where I ordered my solar filter film.
This was my original design. Still may be useful for thicker solar films.
Supports will help the base part of the hood, but they shouldn't be necessary. If you don't use supports there will be a couple lines of extruded plastic hanging in air. Remove them before using.
A smaller layer height might be beneficial for the clamping rings. (0.15mm)
Rear cap prints OK at 0.2mm, at 0.34mm the overhangs suffer.
I have added some assembly instruction photos above to the photo album in case anything isn't clear. It also demonstrates a technique to minimize wrinkles. Since you'll be using a telephoto lens, and probably cropping after that, wrinkles around the outside don't matter much. Also, the BAADER film instructions say wrinkles don't affect the image clarity with their film (up to a point I'm sure).