I have a rig consisting of the GH4 with 30mm Lumix macro, on a home built copy stand.
Under the camera, I use an Essential Film Holder with guides for 35mm strip films, 120 strip films, and 35mm slides. The EFH includes an integral diffuser made of Perspex (we call it milk Plexiglas® here in the States).
The EFH is mounted in a 10" by 15" piece of half-inch thick black foam core “railroad board” ($8.00 for a 20x30 sheet at Hobby Lobby, in the framing area. This keeps it steady. There is a cutout under the negative holders for the light to come through. The EFH feet are simply friction-fit into 3/8" holes drilled in the railroad board.
Under the EFH on bottom of the railroad board is a Viltrox L-116t video light. I attached it directly to the board using strips of very strong Velcro® mounted to the rim of the light. I can still remove the light and use it for other purposes.
The board itself is raised on the sides and back by three inverted ‘L’-shaped legs made of 1x2 poplar. I left the front open for access to the on-off switch. The unit may be powered by AC adapter or an NP-550 video camera battery. I have both.
This setup is heavy enough and stable enough to stay where I put it. I can pull strips of film through, making exposure after exposure rather rapidly, without having to realign the holder each time.
Regarding exposure: After decades of duplicating slides and transparencies, I understand two things:
First, there is a NOMINAL exposure for the film base plus fog. You need at least that much to get a black from a B&W or color negative. You need no more than that when copying slides, to avoid highlight burnout. Getting there is a process of testing.
Second, white balance needs to be FIXED by using your camera’s custom, pre-set, or manual white balance tool. (Lumix calls it a “manual” white balance.) Ideally, that’s referenced to a clear piece of the film in use. That will be amber in the case of color negative film, due to the mask. If not, the next best thing is to manually white balance the light source itself, in Shutter Priority mode.
With the video light set to 4400K and 100% power, my current exposure for Kodachrome 64 slides is about 1/200 at f/5.6 at ISO 200. I have found f/4 to f/5.6 to be the absolute sharpest apertures on the Lumix 30mm f/2.8 Macro lens. At apertures smaller than f/5.6, on Micro 4/3, diffraction limiting of sharpness becomes a problem.
I NEVER use automatic exposure or automatic white balance when copying images from film. I will increase exposures for “thick” (overexposed) negatives and for “thick” (underexposed) slides. But since I’m recording raw files, the film exposure has to be off quite a bit to make me stray from my base exposure.
I have found that Lightroom can recover details in the shadows and highlights of Kodachrome films that no optical/chromogenic process can. Making inkjet prints from my old slides is a joy.
As for color negative films, I get the best results from film where I’m able to white balance on a blank negative. Even for black-and-white, I like to do that so the preview JPEGs embedded in the raw files look neutral. It’s irrational, I know, but that’s my habit…
If I knew how to attach images in this forum, I’d post some…