What causes front- or back-focus in a lens and camera body combination?
Asked 9/9/2012
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Sometimes a specific lens and camera body need AF microadjustment to focus accurately. I understand this is often due to normal manufacturing variation, but which parts of the lens or camera are usually responsible for front- or back-focus? In other words, what components or tolerances affect where the focal plane ends up relative to the sensor?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
13y ago
2 Answers
3
It can be any number of different things. It all comes down to the tolerences that consumer cameras are built to.
Typical suspects would include:
- Lens Element locations
- Flange-to-film distance
- Sensor location
- Focus sensor
It is all about the location of the focal plane as outlined here: What is back-focusing?
Originally by user4892. Source · Licensed CC BY-SA 4.0
user4892
13y ago
0
Generated from our catalog & community — verify before relying on it.
Front- or back-focus usually comes from tolerances in the autofocus and optical/mechanical alignment of the camera-lens system, not just one single part. The main factors are:
- lens element positioning/alignment
- flange-to-sensor (or film) distance
- sensor position
- autofocus sensor position/calibration
All of these affect where the focal plane actually falls. If the AF system thinks focus is correct but the focal plane lands in front of or behind the imaging sensor, you see front- or back-focus.
That’s why one lens may focus perfectly on one body but need microadjustment on another: both are built within tolerance, but their small deviations can add up. AF microadjustment compensates for that combined error.
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