All About Lenses
WHY IS THE LENS IMPORTANT FOR FILM DIGITIZATION?
The lens is critical because it's primarily responsible for image quality across the frame. A good lens can capture sharp, clear images and minimize distortions, color fringing, ensuring the fine details in your film are preserved consistently from center to edge.
WHAT FEATURES SHOULD I LOOK FOR IN A DIGITIZATION LENS?
For film digitization, you want a lens with flat field focus to ensure edge-to-edge sharpness. A lens with a high resolving power will capture the fine details of your film. Also, consider a lens with low chromatic aberration to avoid color fringes on high contrast edges.
IS THERE A LIST OF LENSES RECOMMENDED FOR DIGITIZING?
Certainly there is. Richar Karash spent huge efforts to test the majority of lenses available today. That includes old vintage enlarger lenses, process lenses and lenses from all modern brands. The must-read Richard's article "How good a macro lens do you really need for dslr/mirrorless camera scanning?" is available here. The list is also available here.
CAN I ACTUALLY COMPARE LENSES MYSELF, HOW WOULD I DO IT?
CAN I USE MY CAMERA'S KIT LENS FOR FILM DIGITIZATION?
While you can use a kit lens for digitization, a specialized macro lens will often yield better results. Macro lenses have a flat field of focus and are optimized for close-up work, making them ideal for capturing the fine details of film negatives and slides. Kit lenses are typically zoom lenses and not really designed to work at required reproduction ratios.
HOW DOES FOCAL LENGTH AFFECT FILM DIGITIZATION?
Focal length affects the magnification and working distance in film digitization. A longer focal length will draw on the sensor a more uniform image of the film original, but at the expense of working distance. You'll need to experiment to find the balance that works for your setup. The rule of thumb is that effective focal length of the lens should be at least two times the diagonal size of the camera sensor. 70-80+ mm lenses are good for full-frame digital cameras, 50-60 mm lenses are good for APS-C cameras.
This is how setup looks like with Schneider Kreuznach Componon-S 100 mm lens at the working distance. The distance between sensor and film is 40 cm (2x2x100mm=40 cm). Of course this setup is very sensitive to vibration given relatively heavy lens sitting at the end of the long arm.
WHAT'S THE DIFFERENCE BETWEEN ENLARGER LENSES AND NORMAL CAMERA LENSES FOR FILM DIGITIZATION?
Enlarger lenses are designed for reproducing flat film negatives onto flat paper, so they are very good at providing flat field sharpness (when used close to the prescribed reproduction ratio range something like 1:4 to 1:20). However, they most likely do not have focusing mechanisms, have screw mount M39 or M42, aperture has to be set manually and they will need an adapter to fit on your camera. "Normal" camera lenses are more convenient to use and can provide excellent results, especially if they are fixed focal length true macro lenses and can focus to 1:1 scale without extension rings.
ARE ALL MACRO LENSES SUITABLE FOR FILM DIGITIZATION?
While all macro lenses are suitable for close-up work, not all are equally good for film digitization. Some may exhibit curvature of field, strong light fall-off or other aberrations that can affect the quality of the digitized image. It's best to research lens reviews or test a lens yourself before committing to buy.
HOW CAN I TEST THE SHARPNESS AND FLATNESS FEILD OF FOCUS OF MY DIGITIZATION LENS?
You can use various test targets (like Vlads Test Target various offerings) or charts with fine details and various contrast levels. Photograph the target with your digitization setup, then examine the image at 100% view on a computer screen to assess sharpness, contrast, uniformity and any lens aberrations/fringing.
SHOULD I WORRY ABOUT LENS COMPATIBILITY WITH MY CAMERA BODY?
It's crucial to ensure your lens and camera body are compatible at least on paper. The lens' distance to the sensor at required reproduction ratio should exceed the camera flange distance by at least 1-2 cm so there is a space for lens adapter. Ideally you would want to fully control the lens aperture and focusing from your camera. While adapters are available for many lens and camera combinations, they may not support all features. Thoroughly research lens compatibility before purchasing. Enlarger lenses always require some sort of adapter/extension rings/bellows. Keywords are focal length, flange distance, type of mount. If lens' mount is M39 or M42 and focal length 50 mm or above there is very high chance that adapter can be found, but double check nevertheless.