Just to generalize, the following seem to be the most important factors when picking a light source for scanning film with your digital camera:
(BTW, these factors are true whether you are using Negative Lab Pro to convert your negative film scans, or something else!)
1. You want a High CRI (Color Rendering Index)
The Color Rendering Index (CRI) is a scale from 0 to 100 percent indicating how accurate a “given” light source is at rendering color when compared to a “reference” light source. The higher the CRI, the better the color rendering ability
When digitizing negative film with a digital camera, having a high CRI light source is VERY important. The the differences in colors within the orange mask are incredibly small, so if your light source is not able to pick them up, there isn’t really anything you can do in post to correct for it.
Here’s a good video showing some examples of the effect of having a high CRI on color reproduction.
If the light source you are looking at for scanning film negatives doesn’t have a CRI listed, I would consider this a BIG RED FLAG.
2. Good separation of color channels in Spectral Sensitivity Curves
This is a subject that Nate Weatherly has looked into more than I have, but makes a lot of sense.
The paper that was traditional used in darkroom prints of color negative film had narrow bands of receptivity to red, green and blue, that were clearly separated. This is particularly true of the red channel, where modern digital cameras sensors are sensitive across a broader spectrum of red wavelengths (including yellow/orangish light).
(graph credit to Nate Weatherly)
Basically, all this means that modern digital camera sensors will pick up more interference with the orange mask than photo paper would.
The ideal solution to this is to have a light source that produces distinct, narrow bands of red, green and blue light, that are in a similar range to photo paper spectral sensitivity.
I haven’t seen too much written about this outside the private Negative Lab Pro users facebook group, but examples of seen are extremely compelling.
3. You want Even Illumination and Predictable Results
This is a bit tougher to quantize. Also, there are things you can do in your set up to help with this.
Using a Kaiser Slimlite Plano, I’ve never had any issues with even illumination, and the results are the same every time.
In my experience, it is very difficult to get perfectly even illumination if you are not using a professional LED light table solution (for example, a home-built led table, flash setup, old tungsten light table, etc)
Even pre-built setups can have some issues…
Here’s a look at a Portra-Trace LED light table that was giving a users poor results. To the naked eye, it appeared to be even lighting, but by taking a photo the led table directly (and then added contrast to approximate the contrast during a negative conversion process), you can see it is terribly uneven!
This is one of the biggest issues I see with the files that users of Negative Lab Pro send to me…
If you convert your negative notice “orange blobs”, particularly around the borders of your film, it is probably a light source issue
Having the predictability is why I prefer using a LED light table instead of some of the other options (like flash) where I would expect a higher level of variance between setups - but I’m sure with the right steps, you can make a non-LED light table solution work quite well.
4. Also consider how “collimated” or diffused the light source is in your setup
Collimated light is when the beams of light are being emitted parallel to each other. The opposite of collimated light is diffused light, where the beams are scattered and non-parallel.
Collimated light has two effects when DSLR scanning a film negative:
- Collimated light produces sharper looking scans (whereas diffuse light will produce softer scans)
- Collimated light produces more contrast in scans
Which is better? Well, it’s really a matter of opinion and the debate has been going on for a while (in a darkroom setting, you can choose between using a condenser head (for collimated light) or a diffusion head.)
But I would say this:
- If you like the sharpness and detail you see in drum scanners or dedicated film scanner (like Nikon Coolscans), try to get a more collimated light source.
- If you prefer the “softness” of a traditional fine-art print, go for a more diffused light source
So, which light source should I get?
I’ll let members of the community jump in, but here are my personal observations based on my own experiments and files users have sent me:
Recommended LED Panels:
- Kaiser Slimlite Plano (CRI = 95, very even)
- iPhone or iPad, especially newer models with OLED (must elevate film off surface!). While the reported CRI is not high, it has spectral sensitivity curves more similar to film paper, resulting in less color interference from the orange mask. It is also a more “collimated” source of light, meaning it will produce sharper results than diffuse light sources.
- Any modern Samsung Galaxy/Galaxy Note s7, s8, s9, pixel 3, etc
- Walimex Pro LED (CRI = 90)
NOT Recommended LED Panels:
- Huion tracing tablet (unlisted CRI)
- Artograph light pads (unlisted CRI, although reportedly ~80 CRI)
- Porta-Trace (observed unevenness)
Other options worth exploring (not LED panel)
- Flash with a UV filter
- Solux 4700k Daylight Halogen bulb
- GE Reveal or Chromalux tungsten light bulb with a CTB gel or an 80a filter.