The overall strip marking allows users to set up their scanning rig precisely to capture the desired frame.

The test strip features a 50% raster that covers the entire strip.

This raster consists of transparent and opaque squares with extremely high edge contrast (acutance). While the human eye perceives the grid as a uniform gray color, a camera can easily resolve these square elements. Observing the shape and sharpness of the squares on a computer screen provides crucial information about the quality of the scanning setup. Users can immediately determine if the captured image is sharp and if sharpness varies between the center and the edges or corners of the frame.

Here's an example of how the image might look if the corner is out of focus:

There is also a simple procedure to check the evenness of illumination and the presence of light fall-off:

1. Place the strip in the film holder and center it properly based on the markings on the strip and the holder's opening.

2. Turn on the camera and observe the frame. Use the focus peaking feature (if available) to focus the lens. Move the camera up and down and adjust the focus to capture the desired part of the image. The markings allow users to clearly see what parts of the image will be captured and whether the film holder is oriented properly.

3. Capture the image. Tethered capture is highly recommended to avoid camera shake and to speed up picture transfer to the computer.

4. Use any available software to examine the picture at 100% magnification on a computer screen. Start by reviewing the center.

5. If the center is not sharp and clear, repeat focusing and adjust exposure until the center looks perfect.

6. If the center appears smudged, it indicates the shutter speed is not fast enough to "freeze" the image or the rig is prone to external vibration. Address the vibration issue and proceed.

7. Once the grid is sharp and has proper contrast, review the frame sides and corners.

If one side or corner is noticeably less sharp than the other, the misalignment between the camera sensor and the test target film plane is likely the cause. Adjust the camera and film holder positions until all corners and edges are similarly sharp.

If the corners and edges are similarly sharp but not as sharp as the center, the lens may be the issue. Try shooting at different aperture openings to see if this helps. Most lenses perform best at F/8 or ±1 stop. If the problem persists, consider using a different lens.

Once the captured image is uniformly sharp across the frame, the most complex and labor-intensive part of scanning rig tuning is complete. You can now replace the test target with your film and start scanning.

Uneven lighting used to illuminate the original film can cause issues, separate from the quality of the light color-wise. The core idea is similar to the technique invented 130 years ago for reproducing photographs in print media. Max Levy patented the use of halftone screens to rasterize continuous-tone images into a grid of varying-sized dots. We will use the Levels tool in Photoshop or Lightroom to reveal which individual squares in the grid have different brightness and/or sharpness.

Capture the image of the test target with the raster as usual. Then, in software like Lightroom, apply curves to the image to increase contrast to an extreme level.

Once highlights and midtones are eliminated, the grid elements with brightness differences become easily observable. In the brightest areas, black grid elements surrounded by brighter elements will bleed light into darker squares, making black elements relatively smaller and revealing areas with higher brightness. The operator must adjust the backlight to even out the intensity across the frame. Uneven illumination is the most common cause of color casts and odd colors when negatives are inverted and light is not uniform across the frame. Pay attention to the holder edges, as they can affect nearby film areas through shadows and light dispersion, and take appropriate countermeasures.

Q&A

Q: Do I need both a "35 mm alignment strip" and a 35 mm test target with USAF 1951 patterns, or can I use just one? 

A: You may want Vlad's Test Targets with USAF 1951 patterns if you want to determine the resolution in lines per mm your scanning rig allows. They can help quantify resolution differences between the center and corners or compare different lenses. If you don't need lp/mm numbers and trust your eyes while reviewing test images, the alignment strip will suffice. Additionally, the strip allows for analyzing back illumination uniformity.

Q: The alignment strip doesn't have actual perforations (sprocket holes). How does that affect film holders with drives for 35 mm film? 

A: While it's true that there are no real perforations, the strips have been tested with VALOI Advancer and Digitaliza+ drives. However, I cannot confirm which holders require perforations to advance film.

Q: Do Type 120 and 4x5 Vlad's Test Targets have the features described above? 

A: Yes, they do! Type 120 and 4x5 Vlad's Test Targets are made using the same laser technology and media. They feature a raster covering almost all areas between USAF 1951 targets, allowing for the same techniques described above.