Vespa series lenses are adjusted for back focus according to standards before leaving the factory. However, the flange distance of different cameras may vary slightly when leaving the factory. In order to facilitate matching with different cameras and achieve the best imaging results, back focus adjustment is required.

1. Preparation

Step 1: Save the target for shooting. You can use the "Siemens Star Chart", or use other black-and-white, high-contrast shooting targets;

Tips: You can go to "DZOFILM Official Website - Support - Download Center - Tools - Back Focus Adjustment Lens - Back Focus Adjustment Star Chart" to download (Click here to jump);

Step 2: Install the lens onto the camera or camcorder;

Step 3: Set the lens to the maximum aperture;

Step 4: Place the shooting target about 1.5 meters away from the camera imaging plane, and adjust its position to the center of the screen.

2. Back Focus Adjustment

Step 1: Rotate the zoom ring to the longest focal length end, then rotate the focus ring to the clearest state of the screen, and note down the focus scale value S1;

Step 2: Rotate the zoom ring to the widest angle end, then rotate the focus ring to the clearest state of the screen, and note down the focus scale value S2;

Step 3: Compare S2 and S1. If S2 is less than S1, you need to increase the back focus shims; if S2 is greater than S1, you need to decrease the back focus shims;

Tips: The adjustment amount of shims is related to the rotation angle of the focus ring corresponding to the difference between S1 and S2. The greater the rotation angle, the more shims need to be adjusted, and vice versa;

Step 4: Repeat steps 1-2 until S2 equals S1, indicating that the lens is in a parfocal state, and the back focus adjustment is complete.

Place the shooting target about 1.5m away from the "Φ" mark on the camera imaging screen, and position the shooting target in the center of the screen.

Example:

Taking the CATTA zoom 35-80mm as an example, assuming the lens zooms to the 80 end and focuses to the clearest state of the screen, the focus scale value is 1.5m, then zoom the lens to the 35 end, refocus to the clearest state of the screen, and the focus scale value is 1.4m, which is smaller than 1.5m. Refer to the "Back Focus Shim Adjustment Reference Table" below, increase the back focus shims by 0.12mm, and reconfirm. When the screen is clearest at both the 80 end and 35 end, the focus scale values are both at 1.5m, indicating that the lens is in a parfocal state, and the back focus adjustment is complete. 

Tip: For the back focus shim adjustment value, "+" means to increase shims, and "-" means to decrease shims.