DSLR scanning curved negatives

Some of my 40 year old 35mm negatives are curved along the entire length of the film and at the cut ends giving me 2 way distortion - films are either cut into 4 or 6 images per strip.
My negative holders, which are adequate for non curved strips, can’t hold the film firmly flat along the strip. I’ve been looking for alternatives and the Kaiser filmstrip holder for Dia_duplicator 6506 claims to hold strip perfectly flat. Anyone have any experience with this?
Apart from the skier, can anyone suggest any other alternative? I had read that old curly negatives can be “straightened” by putting them in an enclosed area with a humidifier but don’t want to risk my negatives if that advice is wrong.

Humidifying the film can flatten it, but the gelatin used to hold the crystals might get sticky, which is not what I’d want.

How about putting the film under a sheet of glass? Be sure to get gallery grade glass, it reduces reflexions and distortions that you might get from cheap window glass.

I’ve seen a guy using a wet-mount technique. You’ll find some info on petapixel too…

Thanks for your suggestion. I had been considering laying glass on top but previous advice somewhere on this site suggests you shouldn’t do that because of Newton’s rings. Does gallery grade glass prevent them? Wet-mount increases the risk of Newton’s rings I think.

I had worked with glass and never had any newton rings. The bigger problem is dust. I’ve never wet mounted any negatives so far. It looks like too much effort for digitizing lots of negatives. It might be the best possibility though - if the picture is worth it.

You can use anti-Newton glass or acrylic to sandwich the negative. That’s the standard process with a Screen Cezanne scanner. Another option is that you can wet-mount the film to a glass sheet using mylar and Kami, Lumina, or Gamosol scanning fluid.

I had some very curled up 2¼X¼ negatives a customer had brought me to copy, I had an old negative carrier from a Besler 4x5 enlarger that worked great to hold them while I copied them. Just a thought. Should be able to find one on ebay, it would be a kind of slow process but should work to hold them flat.