A friend used this guy's setup to scan his slides. He bought inexpensive extension tubes for his camera so he didn't need to buy a macro lens.
https://youtu.be/iMO50AlGyrw
A few years back I scanned about 10,000 (high quality) slides I have, and about 5,000 negatives and perhaps 1,000 prints. After a lot of trial and error, it turns out the most high quality and at the same time nerve friendly way is to use professional scanning services, and I used ScanCafe. If you want good quality results, there are so many things to consider and so many things that can go wrong or not quite work out that I gladly invested the roughly 20 cents it costs per negative or slide in one of their frequent sales to have the pros do it.
Even if you succeed to get the image sharp, which is already hard with one of these YouTube gizmos or even a very good macro lens, the difficulty only starts there. Slides need very carefully calibrated color corrections to look great; taking a digital image of a slide usually ends up looking "pushed" and unnatural in skin tones and sky color, and these things are very hard to undo in Photoshop. It's even worse when trying to go negative to positive, there is much more to it than just reverting the colors, as each negative was made to work in the color print system which emphasizes certain colors strongly and de-emphasizes others, and this effect has to be carefully considered. Finally there is the fact that slides and to a lesser extent negatives have a much larger contrast range than regular photos and even the best monitors, and poor scanning overblows the brights and muddles the darks.
There are other aspects like digital dust and scratch removal, which basically all slides and negatives need even if they were well kept in storage, which good professional systems do in hardware by in essence taking a separate image of the dust only, you can look it up under "Digital ICE". All this has the potential to drive you nuts if you want good results. And finally there is just the speed; before I let the pros handle it, I even bought an automated slide scanner for around $1000 that does a whole tray at once, but it gingerly nibbles along and takes two hours for 50 slides before the tray has to be changed, only to yield results that still leave a lot to be desired. Fortunately at the time the slide scanner had a high resale value and I didn't lose much.
The professional slide scanning equipment does all that, in my case they used the "Nikon Super Coolscan 9000 ED" (sorry about the funky name, greetings from Japan) which comes with its own software and costs five figures to buy. It has great dedicated Nikon optics, great sensors, and the low level processing software is calibrated to the specific optics and sensor. It scans at 4000dpi (resulting in around 20 Megapixels for a typical slide or negative) and 16 bits color depth (regular monitors are 8, high dynamic range TVs are 10 or 12). That Nikon system is generally considered the best until you get beyond medium format and invest yet 10 times more and have to live with continuous routine maintenance needs. Many professional photographers used that in the time when they would still shoot film and then scan that for the best possible results.