The concept of front focus means that when the focusing point was being targeted, the lens overshot ahead and the depth of field was shifted. As a rule, SLRs with high-aperture optics suffer from this. This is a closed loop system with direct feedback, which does not require adjustment, since the maximum contrast on the matrix will correspond to the maximum sharpness of the image in focus. SLR cameras have separate focus sensors, so this system needs alignment. Errors and reveal front focus.
It is necessary
- - paper;
- - Printer;
- - a computer;
- - Internet connection;
- - camera;
- - tripod.
Instructions
Step 1
To test front focus, use a special scale with a "sight". You can do it yourself - download the scale on the Internet, print it on a printer, stick it on cardboard and make cuts for stability. Place the camera on a table or tripod. Set white balance on a piece of paper and one-shot autofocus.
Step 2
Take pictures at the widest aperture. Disable the Image Stabilizer, if equipped. Select the central focus point in the camera and direct the camera so that the plane of the focusing "sight" is perpendicular to the optical axis of the lens.
Step 3
Choose a distance so that the scale divisions fall into the frame - use them to evaluate the work of afthofocus. The focusing mark on the viewfinder should not leave the target with a small margin. Set a margin according to the size of the mark itself, because the sensor units are slightly larger than indicated by the mark on the viewfinder. If a sharper detail is behind the mark, but in the sensor area, then the camera will focus on this contrasting object.
Step 4
Test autofocus. Bring focus to one edge, aim at the target, take a picture. Bring focus to the other end, aim, take a picture. Repeat several times. Switch to manual mode, release focus and rotate the focus wheel manually until focus is confirmed, take a picture.
Step 5
If the lens did not hit the point. See the amount of DOF offset and the lens miss rate by taking a few shots. A small miss is considered normal. If the focus point is systematically out of range, then there is a front focus. It is not only the lens that can miss, but the camera itself. Therefore, if autofocus is blurry, consider alignment.
