"Sigma SD1 Merrill not good for scanning negatives/slides"

D Cox wrote:

I scanned all my B&W 35mm negs with the sdQH and the Olympus 80mm macro lens. That lens was designed for use in slide duplication.

If you are talking about the Olympus Zuiko Auto-1:1 Macro Lens 80mm f/4 , I have tested that lens myself on a Pentax K-1 and found it good, but neither as sharp as the Pentax FA 50mm f2.8 macro, nor the Nikon 60mm Micro Nikkor (on a Nikon D810). Vignetting was another problem with the Olympus lens. Don't get me wrong—you can get very nice results with this lens, but if you are trying to achieve the best possible results, you are better off with a modern Macro lens.

The Sigma 70mm Macro lens had outstanding reviews, and my own comparisons did confirm this.

Results seem fine to me. I saved DNG files to speed up processing.

When I tried a few 35mm colour slides, I wasn't so happy with the colour. The Sony NEX-5N seemed to give better colour, and it has the great advantage of a built-in HDR mode. 35mm slides are very high in contrast, and you really need HDR.

I haven't tried stitching any medium format negs. Something to try later.

Color depends on many things; a daylight-balanced high-CRI light source should give great results with transparencies. I have had no issues with colors when using the Sigma SD1 for slides.

No offense, but I don't believe you give justice to your color slides by scanning them with the NEX-5N. When I scanned with the Pentax K-1, I was just barely able to get all the detail out of the slides. That's a full-frame 36MP sensor, vs. the NEX-5N's 16MP APS-C sensor.

It is easy to prove whether you really get all the resolution from your slide by doing a "microscopic" shot with macro bellows. You basically "crop-in" as far as you can with macro bellows, and compare the detail of that shot with your fully-framed shot.

In the end it all depends on what your goal is—if you just want to archive your negatives/slides for screen presentation, a 12MP scan with some sharpening is probably good enough. But if you want to really squeeze out every bit of detail possible, going beyond 1:1 and stitching is the way to go.