DSLR scanning of negs, Epson negative holders VS Lomography holder

I have started to use my Nikon D600 with a 60mm macro lens on a copy stand and a Logan florescent tube light box. Presently I'm using LR and Negative Lab Pro to convert the B&W and color negs. I have a bunch of Epson negative holders from my 4990 scanner that I have used, but was wondering if the 120 holder from Lomography would keep the negative flatter. It seems that most of the You Tube tutorials use this Lomography holder. Also, is the light source critical. I seem to get pretty even light with my Logan. So far I am pleased with my results but would appreciate other opinions on this process.
I also have an older but very usable Bowens Illumatron that I have started to use for 35mm slide and negative digitizing and like this setup very well, and would appreciate comments from members who use this Bowens setup.

For the past several years, I've been using a DSLR -- and now a mirrorless Sony -- to dupe my 35mm images. My Sony NEX 7 has a 24.3 mp sensor, which delivers 4000 x 6000 pixel images -- same resolution as the better Nikon CoolScans. I find 24.3 mp is sufficient for all the film emulsions I've used. I can resolve Kodachrome 64 grain easily.

The rig I cobbled together uses a Nikon AIs Micro-Nikkor 55mm f/2.8 at its heart. I've attached a slide stage to it using an extension, and I've used an assortment of extensions behind the lens to achieve almost exactly 1:1 magnification with my APS-C Sony. If I had a full frame camera, I'd just use a set of bellows with a slide copy attachment. Most slide copy attachments also have a film stage, so digitizing film strips is also easy. For my rig, I have a film stage that I can use in place of my slide stage.

I also own an Epson 4990. My 4990's medium format holder does a decent job of keeping the film flat, I think. I also own an Epson 3170 -- which also scans medium format, so I have a holder from that scanner as well. Anyway, what I have always done when duping my slides and negatives is to set the lens at f/8 so that there is enough depth of field dialed in to eliminate any problems that might be caused by the film's surface being less than flat.

To dupe medium format, I have a light box that I built for originally viewing slides, but now it gets more use duping medium format images. I have a couple of fluorescent strips inside the box currently, but I'm thinking about replacing them with an array of LEDs. The advantage to LEDs is they put out a pure white light, whereas fluorescents put out some sort of funky green light -- even those supposedly corrected to imitate natural light. My camera does an ok job of white balance correction, but I'd just as soon not have to rely on it.

Michael,
I too have questioned my light source and ordered a Huion L4S light box. It is LED, very thin and light but a little too blue in the color temp of the LEDs from what I read. It was pretty cheap, $35, so I will give it a try and get back to you.
Robert

f/8 doesn't give you "depth of field" in micro/macro... depth of focus is the issue. not the same....what you need is fine focusing. f/8 gives you a lens's optimum detail resolution, not depth of focus. Bellows are focusing hassles, better to use something with a helical.

The best possible light is a strobe of some sort. Nikon scanner's advantage over any lens is it's lack of lens. Lenses lose detail, scanners don't suffer that.

I use my enlarger neg carriers on a light box. It's easy to do a custom white balance before doing any copying.