How To Test Camera Lenses? Only 2 Simple Steps For Testing

Step 1: Inspecting the Lens

When we eagerly unwrap a brand-new camera lens, we expect perfection. And most of the time, that’s exactly what we get. However, from our experience of opening countless lens packages, we’ve come to realize that not all of them are flawless. Approximately 2% of new lenses require exchanging, either due to factory quality control issues or rough handling during transportation. The likelihood of encountering problems varies depending on the brand and complexity of the lens. Autofocus zoom lenses with image stabilization, for instance, are more prone to issues compared to manual focus prime lenses.

That’s why it’s crucial to conduct a basic inspection as soon as you get your hands on a lens. This is especially true for used lenses. In this article, we will guide you on How to Test Camera Lenses to ensure you make the most informed decision.

1. Lens Barrel Examination

Before diving into optical testing, it’s essential to perform some hands-on checks to ensure the lens is in optimal condition. The lens barrel consists of multiple cylinders joined together. Pay close attention to the following aspects as you gently move, rotate, and extend different parts of the lens:

  • Are any pieces loosely hanging off?
  • Is the filter ring movable?
  • Are all the screw holes filled with screws, including those at the lens mount?
  • Does the internal barrel, if present, slide back and forth smoothly when zooming and focusing?
  • Does the front ring easily accept a filter? This is particularly important when dealing with used lenses, but we have also encountered new lenses with poor threads.

While examining the lens barrel, gently shake it to check for any loose screws inside. Keep in mind that lenses with vibration-reducing or image stabilization features may exhibit some trembling when shaken. Don’t be alarmed by this.

2. Focusing Mechanism Evaluation

Although we’ll address accuracy in the next step, it’s essential to assess the focusing mechanism first. Even if you primarily rely on autofocus, switch the lens to manual focus and move the focusing ring back and forth a few times.

Consider the following points during this evaluation:

  • Does the focusing ring move smoothly without any catches or a gritty feeling? Take note of whether the front element, back element, or internal group moves while focusing (neither the front nor rear elements should move during focusing).
  • Does the front element rotate during focus movement, making it challenging to use polarizing filters? Or does it remain stationary while moving?
  • Is there proper rotation of the distance scale as you turn the focus ring?
  • Is the manual focus ring continuously engaged, or does it have a clutch or a switch? Mount the lens on your camera, engage autofocus, and repeat the process.
  • Does autofocus operate smoothly?
  • Do the focus motors of your other lenses make similar noises?

Before proceeding, perform autofocus on a nearby object and then quickly switch to a subject at an extreme distance. Observe the time it takes for the lens to adjust focus. While a slow autofocus system may not be a hindrance when capturing macros or portraits, it can become a dealbreaker for sports or street photography.

3. Zoom Mechanism Check

Ensure that the zoom mechanism moves smoothly in and out. If the lens extends by stretching the front element or an internal barrel, carefully inspect for any areas of resistance or unexpected catches. Additionally, ensure that any extending barrels have clean interiors free from scratches that may cause friction during zooming. The barrel should not feel loose; it should remain stable when extended.

If the front element doesn’t stretch during zooming, pay attention to the movement of the back element. In some cases, when zooming, the back element may shift into and out of the barrel as part of the zoom mechanism. This is important because rear element zooms often have focal lengths that differ from the promised specifications when focusing on close objects. For example, a lens advertised as 300mm may only function as 240mm when focused 9 feet away.

4. Internal Components and Glass

Carefully examine the front and rear elements, not just through them, for any blemishes or coating flaws. While issues with the front element are generally insignificant, problems with the rear element such as scratches or coating flaws can significantly impact image quality. While adjusting the focus and zoom rings, look through the lens to spot any abnormalities. It’s normal to find a small amount of dust inside the lens, even if it’s fresh from the factory. However, be alert for damaged internal elements, loose screws, or foreign objects like metal fragments or pieces of cloth that may have unintentionally made their way into the lens.

5. Installation Process Assessment

As you mount and unmount the lens on various cameras, ask yourself the following questions:

  • Does the lens attach smoothly and securely?
  • When properly attached, does it feel sturdy without any looseness?
  • Is the locking pin latching on securely when you press the camera’s dismount button? Does it release without difficulty?

Step 2: Testing for Front- and Back-Focus

Before proceeding with any other tests, it’s crucial to ensure that the lens focuses accurately. This step applies to autofocus lenses as well as manual focus lenses because the viewfinder and sensor calibration may not be perfectly aligned in your camera. In our experience, “focus confirmation” devices often prove to be less reliable than regular autofocus.

1. Preparing for Depth of Field and Focus Testing

To accurately test focus, you’ll need a surface marked with indicators and positioned at an angle relative to the focus point. While not essential, we recommend using a LensAlign Pro for its convenience and precision. For close-range testing, a ruler or yardstick placed at an angle to a designated focus target will suffice. For distant testing, the material of the target (such as a wooden fence or chain-link fence) is less important.

While computer-generated targets are useful for autofocus micro-adjustment, they lack the necessary details for comprehensive lens testing.

2. Focus Accuracy Evaluation

Choose one focus point for accuracy testing (preferably the center point unless a specific reason calls for a different choice). Start by testing the lens at its widest aperture, then repeat the process with the aperture slightly stopped down.

The procedure is as follows: autofocus on the center point while aiming at the test target, and visually determine where the ruler or diagonal line indicates the sharpest focus. The two should be closely aligned. Keep the following points in mind:

  • Each lens has a unique ability to focus at different distances, so test from various distances.
  • The focus of a zoom lens may slightly vary between its minimum and maximum zoom ranges.

Conclusion:

By following these two simple steps to test camera lenses, you’ll be equipped with the essential knowledge required before making a camera purchase. We hope this article has provided valuable insights into How to Test Camera Lenses. Thank you for reading!

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