Zoom Lenses for Camera Scanning: The Evidence is Blurry

Zoom lenses are often dismissed as “not ideal,” yet widely used in practice. Here’s what actually happens when you put one to the test...

Discussions about the usability of zoom lenses for camera scanning are common on film forums. While many people sense that zoom lenses are “not ideal,” there is still a widespread belief that kit lenses are good enough — or that the optical traits of zooms can even be used to emphasize the analog character of the image.

This article is meant to test that assumption directly. I set up a simple demonstration to show what to expect when using a zoom lens for camera scanning, and to describe the process in enough detail that anyone can repeat the steps and evaluate any lens they already have.

A deliberately simplified setup

For this purpose, I assembled a pared-down setup consisting of an LPL CSC-10 copy stand column, a Leofoto G2 3D geared head to control camera leveling, a set of extension tubes, a Canon R7 APS-C camera with an EF-to-RF adapter, a Canon EF-S 55–250 mm zoom lens, Vlads Test Target mounted in a slide mount, a small mirror, a glass riser sourced from Amazon, and a CS-Lite light source.

The setup is built from readily available parts. The goal is not to create a polished, production-ready scanning rig, but simply to see how the idea holds up in practice. I paid close attention to alignment — because even small deviations would immediately skew the results — and to basic vibration control. Stray light was not a major concern for this test, since dynamic range and contrast were not what I was trying to evaluate. I wanted the images to clearly illustrate the process, with all elements left exposed and easy to see.

Why a test target is necessary

Vlads test target is, by design, high-resolution, with excellent contrast and edge acuity. It was created to help film-scanning users working with either scanners or cameras. The classic USAF 1951 pattern is repeated ten times across the frame, making it easy to compare resolution in the center and in the corners, and to judge whether image quality is uniform across the image area. This is especially important for camera scanning with lenses that may exhibit different resolution in the center and at the edges.

For classic film scanners using moving linear sensors, there are typically no issues with resolution or uniformity across the frame. In those cases, the primary concern is whether the film holders are properly aligned and correctly positioned over the glass bed.

Using real photographic negatives for this kind of assessment can be misleading: grain, subject texture, and low contrast can easily mask lens optical flaws, as well as overly high or low optical density in different parts of the image.

Test parameters and scaling

The basic idea is simple: set the zoom lens to different focal lengths, pair each with the appropriate extension tube(s), and capture images of the test target. (Fig.1.)
I used EF extension tubes measuring 12, 20, and 36 mm. The camera sensor is APS-C, while the target is full-frame 24 × 36 mm (the GEPE full-frame slide mount does indeed have a true 24 × 36 mm opening). This means the lens needs to provide a scale factor of roughly 0.62 (22.3 / 36), rather than 1:1 as would be required with a full-frame sensor.

Testing at 55 mm: immediate failure

Let’s start at a focal length of 55 mm. For this run, I used a single 36 mm extension tube. (Fig. 1.)
I adjusted the distance between the lens (with the lens barrel fully retracted) and the film by rotating the LPL stand’s head knob, allowing the camera to slide along the column while trying to fill the viewfinder with the test target as cleanly as possible. Autofocus was disabled — it was completely useless in this scenario. I enabled the camera’s Focus Peaking feature and eventually settled on a combination of focal length and camera-to-film distance where the target reliably filled the viewfinder.

The camera reported a focal length of 55 mm, and a ruler measured approximately 265 mm from the film to the mark on the camera body denoting the sensor plane. Final adjustment was made using a macro focusing rail with the viewfinder set to 10× magnification. At that point, the center of the image in the viewfinder looked acceptable.

Switching back to a 1× view revealed the real result (Fig. 3.). At the wide-open aperture, only the central quarter of the image looked usable. Beyond that, the image quickly turned into a blurry, fuzzy mess. This was not entirely unexpected, so the next step was stopping down the aperture.

At f/8, the image did not improve (Fig. 4.): the center resolved only Group 1, Element 6 on the USAF 1951 target, while the corners remained completely unusable and exhibited severe color fringing. The fringing was so strong that the USAF pattern could not be read at all in the corners. Stopping down further to f/11 did not help.

Conclusion: at a 55 mm focal length, this zoom lens is completely unusable.

Establishing a reference point

Of course, it helps to establish a baseline — we need a known good reference image to compare against the zoom lens results.

I should have noted earlier that, for reference (Fig. 5.), I captured a set of images using a Sigma 50 mm f/2.8 DG Macro lens in EF mount (US$150 current street price). This is a well-regarded true macro lens and, for the price and ease of use, hard to beat. Although it exhibits slight pincushion distortion, image quality across the frame is very good on an APS-C–size sensor.

At f/8, there is no visible color fringing. Resolution reaches approximately 69 lp/mm in the center and 62 lp/mm at the corners and edges.

Incremental extension: small gains, big limits

The next configuration used a combination of 12 mm and 36 mm extension tubes. At a focal length of 79 mm and a sensor-to-film distance of approximately 320 mm (12.5 in), the results improved only marginally. The full set of files at all aperture settings is available online.

The following run, at a focal length of 84 mm, used 20 mm + 36 mm extension tubes, with a sensor-to-film distance of 343 mm (13.5 in). Again, there was still a great deal left to be desired.

A glimmer of hope at 109 mm

The final configuration used all available extension tubes — 12 + 20 + 36 mm, for a total of 68 mm of extension.

After finding the working position, the camera reported a focal length of 109 mm, and the measured distance from the glass surface to the sensor plane was approximately 420 mm (16.5 in). The target now filled the viewfinder neatly (Fig. 8.)

Procedural note: As before, a full series of images was captured using Canon’s tethering utility EOS v.3, with aperture settings ranging from wide open to f/19 and exposure compensation set to +1/3. Because this demo setup was not particularly vibration-proof, the ISO was set unusually high — ISO 1000 — to allow very short exposure times and minimize the risk of vibration-induced blur. For real scanning work, however, I strongly recommend using the lowest native ISO available, typically ISO 100, and a more robust rig.

At 109 mm, the lens behaved like a typical non-macro lens. Optimal sharpness in the center reached approximately Group 0, Element 1 on the USAF chart, corresponding to about 55 lp/mm. The best corner resolution reached Group −1, Element 5, or roughly 44 lp/mm.

While the center was relatively clean, a reddish fringing became increasingly visible toward the edges and corners. On a 2K phone screen the image might look acceptable; on a decent computer screen, the deficiencies are immediately obvious.

For black-and-white film, this configuration may be barely usable as a proof of concept. For color work, however, the chromatic haze is enough to confuse most negative-conversion software, making the results largely unusable.

Final assessment for this lens

In the end, I was able to identify at least one configuration that can be of limited use — but only just. The setup was not vibration-proof. With the camera hanging 420 mm (16.5 in) above the film, even minor external disturbances, such as traffic outside or a neighbor riding a stationary bike, can affect the result.

I see little point in testing additional focal lengths all the way up to the lens’s 250 mm limit. This exercise demonstrates clearly that this particular zoom lens is not a serious contender for camera scanning. That conclusion should not surprise anyone who has tried it before.

Closing note

The same simple methodology can be applied by anyone to any camera-and-lens combination — including fixed focus and macro lenses ,— and it is a very effective exercise for understanding how all the components of a camera-scanning setup actually work together. This is how say APO Rodagon 4/75 D2X or Sigma 70 mm Macro Art have been placed at the very top of list of best lenses for scanning film.

This article deliberately avoids generalizing beyond the specific lens tested. The intent is not to dismiss zoom lenses outright, but to provide a repeatable way to test whether a given lens is truly suitable for camera scanning — and to expose its limitations before valuable time is wasted on subpar scans.