A transparency film is much higher contrast than a properly exposed and processed negative, color negatives being especially flat or low contrast. Slide film is designed to have a high gamma or slope in its contrast curve. To scan with the best results, you want to scan to a linear gamma/contrast, and not introduce any further gamma/contrast in your capture and processing. I use Capture One and under “Base Characteristics” for the ICC profile for your camera, you should choose “Linear Response.” You will get a capture processing that is truly linear and it will have significantly better highlight and shadow detail than any other curve chosen. Having linear as your base setup, then test and set your correct exposure. I am not aware you can use a linear gamma with Camera Raw, but I have not used it since PS6, so others correct me. As of PS6 Camera Raw, even the “Linear” point curve does not give a linear response. Camera Raw ALWAYS introduces a built-in LUT gamma “correction” for the camera used and in my experience this LUT cannot be turned off. There are other raw processors I have not used that may have a truly linear response, so check out your favorite for this capability. I have no affiliation with Capture One but my experience with it is that it’s tethering is easy and reliable, and its color engine is superb. I make digital scans with it and my Nikon D850 that are extremely high quality and faithful to the original.
If you’re familiar with using the terminal, you could get a copy of DCRAW and use it to create a TIFF with custom gamma.
Due to the high density differences of modern slide film, a possibility to get better definition would be to capture two to three shots, exposed with the same aperture, but with different exposure times and then combine those shots with Lightroom’s HDR merge function.
Post a link to a few of the .raf files and I can try to see what we can do…
I’ve had to do the multiple exposure and blend technique for focus when I used a less than stellar lens, and could not get sharp grain center to corner. I don’t recommend doing a three exposure blend for focus unless absolutely necessary (really curly film) as the software can create merging inconsistencies with visible grain, an in and out of focus look. As for HDR blending, it could be worth a try with a really difficult slide, but you will almost never need to do that if you can get a linear-processed capture. It’s better, more predictable and much faster in post to get it all in one shot, both focus and tonal scale.
The camera profiles included with Negative Lab Pro are true linear profiles. So it should be exactly what you are looking for to get a more neutral starting point on your slide digitization.
In your case, you can use the profiles as a starting place for editing your slides (without the need to use the Negative Lab Pro plugin itself). Just open up the “profile browser” in Lightroom Classic by clicking the “four boxes” button to the right of the profile name. You should then find the “Negative Lab v2.3” profile. If you want to make it easier to find this profile, you can also click the “star” icon by that profile, and then in the future, it will show up in the main profile dropdown list.