Gerd Waloszek       

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Leica X Vario: Functional Issues - Autofocus (Real World)

Note: The AF issues discussed here refer to the case that the camera signaled a correct focus (green rectangle(s)). The case that the camera cannot find focus and indicates this with a red rectangle is another matter. This may occur, for example, because there are no contours in the focus field.

Introduction

In addition to my investigations into the conditions that cause AF issues, I screened my 2013 Leica X Vario photos in order to collect photos where the AF failed, together with identical or similar ones, in which it did not.

At the beginning of my journey with the Leica X Vario, I used more or less exclusively 11-point AF. Therefore, most of the photos with AF issues that I collected were taken with 11-point AF. In addition, there are also photos with 1-point AF, but none with spot AF. I did not include photos taken with manual focus that were focused incorrectly, because this was, of course, my fault (I included, however, a few shots with manual focus where AF was wrong, but where a similar manually focused photo was OK).

I included also a few photos where one might debate whether AF was distracted by objects in the foreground. This is a complex discussion because:

• The 9 AF fields are more at the center than in the periphery. This is the more so true for 1-point AF, which just should use the center of the image.
• But: Focus and exposure may have been determined by half-pressing the shutter; then the section may have been changed. Whether this was the case, cannot be determined in hindsight... Often, when I do so, I use a higher up target so that objects in the foreground should even be more unlikely to distract AF.

So, there is definitely a "gray zone" in all of this. Nonetheless, I still maintain that for most of the shots, AF, either 11-point or 1-point, missed the target. There are also spurious "infinity" errors, where the Exif data state that the distance was set at infinity where the focus object wasn't. As an example, in one scene, I have three photos with an Exif distance of infinity, but one of them is fuzzy (not caused by camera shake!). I was regrettably able to "replicate" such findings in 2015 (after the firmware update 1.1)...

Overview

Below, I present the overall "distance picture" for 11-point (41 scenes) and 1-point AF (14 scenes):

Figure 1: Distribution of Exif distance values for 41 scenes taken with 11-point AF; for the legend see below

Figure 2: Distribution of Exif distance values for 14 scenes taken with 1-point AF

Legend: red = fuzzy, yellow = slightly fuzzy, magenta = fuzzy while set to infinity

Note: For an estimated correspondence between Exif distance data and real distances, see page Manufacturer-Specific Exif Data.

Please note that in some cases, there are more photos behind the magenta "infinity" marker, but those "hidden" photos are not fuzzy (the fuzzy photos are instances of the "infinity" error).

To sum up, my Leica X Vario sample erratically and unpredictably focuses too closely. There is a lot of variation in the distance settings of similar photos, but this is not surprising because photos of the same scene are typically not identical. Furthermore, there are also a few "infinity errors," where the error lies in the Exif data contradict the resulting photo.

A Few Examples

The following examples illustrate scenes, in which AF errors occurred. They include 100% sections to provide an impression of the fuzziness.

11-Point AF

Overview	Detail (1:1 Section)
Exif distance: 2850, focal length: 46 mm. The focus is too close.
Exif distance: 65535 (infinity), focal length: 19.6 mm. This is an example of the "infinity error": The camera records to have selected infinity, but selected a short distance.
Exif distance: 3989, focal length: 39.7 mm. The focus is too close.
Exif distance: 4177, focal length: 46 mm. The focus is too close.

1-Point AF

Overview	Detail (1:1 Section)
Exif distance: 1900, focal length: 36.7 mm. The focus is too close.
Exif distance: 1900, focal length: 46 mm. The focus is too close, but 1-point AF should not be distracted by the girl in the left foreground.
Exif distance: 2672, focal length: 43.1 mm. The focus is too close, but 1-point AF should not be distracted by the objects in the foreground
Exif distance: 1034, focal length: 20.4 mm. The focus is too close.

2014: 1-Point AF

Here is a 1-point AF example from 2014 showing one version with too close focus and another one with correct focus; both photos were taken immediately in succession

Overview	Detail (1:1 Section)
Exif distance: 2600, focal length: 25.7 mm. The focus is too close
Exif distance: 65535 (infinity), focal length: 25.7 mm. The focus is OK

Preliminary Conclusions

Overall, my "collection" of real world photos does not point to a fundamental difference between 11-point and 1-point AF with respect to AF errors. In some cases, 11-point AF may have been distracted by foreground objects, but I tried to exclude such examples from my collection. I included a few samples where foreground objects are at the periphery and should not be considered by 11-point AF (but may have been...). I also found examples, where 1-point AF may have been distracted by foreground objects, although this shouldn't have been the case, either. But this is very speculative...

I found a lot of variation in the distance settings of similar photos, though, but this is not surprising because photos of the same scene are typically not identical.

All in all, except for the very few "infinity errors," there seems to be one common pattern in the AF errors that I have encountered: The camera unpredictably focuses too closelyy, never too far (while sending a "green" focus confirmation). The reasons for this behavior are still unknown to me. Sometimes, it seems to me as if - even for 1-point AF - the camera is actually looking "beyond" the focus fields and takes the periphery into account. But in some cases, there aren't any objects in the foreground...