I have a job making a video about a woman's paintings . I want to be able to go in as close as brushstrokes if possible.

The only available sources are slides that were taken of the paintings about 10 years ago and the paintings are in unavailable.

A book was made about her work and those slides were the basis of the reproductions in the book.
The Printer (in China) sent her some good looking proofs that are around 4x6 as well.
So my possible sources are the 4x6 proofs or the original slides.

Someone else already scanned the proofs into 3039 x 1936 (pixels) TIFFs,
I've been editing with those, but figure a higher resolution scan might allow me to go closer.
So I went a local photo shop photo and a guy there scanned them to his Max resolution (roughly 15,000 x 11000 pixels.)
I figured the those scans would be sharper, but they seems much softer .

At first I thought this might just be an illusion in the computer because the file was so large it might be downsampling.
However when I reduced the image size in Photoshop it still looked soft,.

I have a lot of questions about what is the best way to get these slides digitized.
- Might my big files be fine but I just don't know how to work with them?
- Did the photo shop do an inferior job maybe due to using the wrong gesrthe wrong gear,
- What's the best place to have this done professionally in San Francisco

The problem might be that the proofs were printed at a low DPI (perhaps more for checking the color fidelity) in which case a high resolution scan can not improve on that level. Depending on the camera used, there could be good resolution in the slides themselves, so even a desktop scanner scan of the slides might be able to improve on the tiffs.

I've used a Spiratone variable bellows slide duplicator, connected to my Canon 5Dmii. The duplicator has mounts for all major brand DSLRs. Insert the slide in the front, point it towards a light source, then take a picture. I've digitized thousands of slides this way. The quality is good, I've been very happy with the results.

If you're going to scan the proofs yourself, make sure you scan it 300dpi minimum. More is better.