@Digitizer My light is a custom built trichromatic RGB light, not an iPhone, and I scan with a Minolta 5400 scanner lens, in theory capable of 80 lp/mm, but my limit is around 60 lp/mm since I use a 24 MPix APSC sensor. My setup is described above:
I did some more tests and what is seen in the videos is actually NOT a by me detectable increase in resolution, but a reduction in the brightness due to the privacy screen, which reduces the “glow” around the highlights and gave the impression of increased definition. In my current setup, I hit the limit of the sensor, and I cannot detect an increase in resolution due to the privacy screen, nor due to the CS screen. I will correct this in my video posts above. I do think that an increase in collimation (light directionality) should increase the resolution, but with my current 24 MPix sensor, I cannot confirm it. I would therefore appreciate it if others could try a privacy screen and/or CS screen to see whether it is indeed a cheap solution to increase resolution, but for this at least 36 MPix are needed. With my 24 MPix, I hit around 60 lp/mm maximum and, hence, cannot confirm the effect myself. The actual shot files look as follows (legend in the top left corner) at 300%:
As you can see, also increasing the distance has no visible effect on the resolution, but it does cause a larger light fall-off in the corners.
Inspired (again) by @Alain_Oguse I tried a fully collimated light as well (on a shoe string…), using collimator lenses from an old enlarger, and a microscope lens stuck on a flash light to create a point source:
The last pic is simply shot with my phone on the screen that I use for scanning. I noticed the following with (ad-hoc) fully collimated light:
- It is extremely efficient with respect to light
- As also @Alain_Oguse found out, everything is in focus (DOF is huge: I struggle still explaining the optics reason for that) and in order to focus with a collimated light source, one has to add a diffuser for focusing, which is then removed for taking the picture. This explains why with collimated light one picks up more dust and scratches.
- One picks up EVERYTHING due to the huge DOF, and since the taking lens is focused on the point light, I also noticed whatever imperfections there are on the microscope lens. Not good.
Hence, imho, an ideal setup would start with a diffused light source, on which something is placed that makes the light more directional, to ensure that high contrast edges are better defined. Unfortunately, with my current 24 MPix sensor, I cannot verify whether this theory is indeed correct. A 36 MPix sensor is not available in APSC, so I would need to use a full-frame camera, at which point I start to significantly deviate from the magnification factor that my Minolta 5400 lens is designed for.
For now, I will simply stick the CS sheets on my diffused light source, since indeed each sheet does amplify the brightness by around 25% which is always a good thing.