Film scanning with a digital camera.

The usual reason for copying slides and negatives with a digital camera is to get high resolutions, higher than you get from a slide/negative copier. Then most people print out these scans at 8"x10" or smaller or simply display them on their computer or TV.

A 14 Mp digital image from this cheap JPG scanner look great on my 49" 1080p TV or on my monitors. Higher resolution simply isn't necessary for most uses.

eBay - 14MP/22MP HD Photo 35mm 135mm Negative Film Scanner Slide to Digital File Scan

Scanning B&W negatives or color slides that still have good color works well but you really don't need 20Mp or higher images.

When photographing color negatives you have to contend with the orange base color and with fading. Some color slides also exhibit color changes or fading.

If you copy a color negative with a flash and the camera set at the Flash WB setting and the orange base color will screw up the dynamic range for all three of the RGB channels. Correcting for the base color is relatively simple but none of the RGB histograms will be full range. Using an 80A filter as D Cox said will help with the base color but you will have to increase the exposures if you use the filter.

If the negative is faded things are even worse.

Even after correcting for the base color you will find lots of problems with the RGB histograms. None of them will be full scale and they can all be at very different positions on the scale. You now have a digital image with three different dynamic ranges, one for each of the three RGB images, and almost certainly one or more of the histograms will be less than 1/2 of the scale. Expanding all RGB histograms to full scale helps the color but doesn't recover the real dynamic range.

Here is an example of a scan of a faded color negative after removing the base color. Check out the blue histogram.

If I stretch out the B channel to match the R and G channels I get better colors but I still get a poor quality image because of the lack of dynamic range in the B channel.

Basically it is extremely difficult to get an image with good color from the a digital image taken with a digital camera.

With a proper scanner you can correct the colors as part of the scan so that each of the RGB channels of the digital file has a full dynamic range. A good scanner will even correct for the base color of a color negative.

The way this is done is that the time spent scanning each of the three RGB color channels can be varied so that a full dynamic range can be acquired for each channel.

The color results with a proper scanner still aren't perfect, but they will be the best you can get from a faded color negative.

VueScan software is great for this purpose if it can be used with your scanner. Unfortunately it can't be used with my cheap 35mm scanner but the scanner's built-in software will automatically remove the base color and allow RGB channel corrections during scanning.

VueScan Scanner Software for Windows, Mac OS X and Linux