In this post, we will look into the issues surrounding the focusing of the lenses. Contrary to the conclusion of some big camera testing site, the focusing of the NX10 raises some concerns.
Focus Locking
First, it is about the focus-locking speed which ranges from fast to okay to mediocre to sluggish depending on the lighting situations, the lenses and the AF area in use.
Just as the Pany's lenses for the GF-1, the focusing speed of NX10's lenses still lags behind as compared with those made for the regular DSLRs. Actually, the focusing speed cannot be called slow under decent lighting conditions but are not as fast as we would like. As discussed yesterday, there is an explanation for this performance. While the regular DSLRs are fitted with a dedicated module to do the algorithm for focusing, the MFTs and the the the likes of NX10 put this additional burden on the imaging sensor, hence the slower focusing speed.
Simply put, under good lighting conditions, the three lenses identify the focus as fast as the GF-1 which is almost instantly. But for subjects a wee bit flatter in texture or less contrasty under either good or especially low lighting conditions, all three lenses hunt and lock the focus only after repeated attempts. To be fair, however, this phenomenon has also been found in GF-1 and GXR. The issue is less obvious with GF-1 and more serious with the A12 50mm lens in Macro mode.
The speed of NX10's three lenses in locking a focus is, in terms of a scale of 1 to 5 stars, 3½ stars in general. You will be happy working with the lenses but not necessarily satisfied in terms of the focusing speed on some occasions. Let's look at some examples.
This shot was made using the long zoom lens in a slightly under-lit indoor area as suggested by the exposure combo. The lens was aimed to the rim of the mirror as circled. The focus was locked roughly after six unsuccessful ones
For this shot, the farthest focal length of the long zoom lens was used to focus the man in some 30 feet away. He was standing outside the brightly lit sidewalk, and the contrast between the man and the bright background should have provided enough clue for the lens. However, the lens failed to lock the focus for four attempts.
Similar situations were not uncommon during the testing.
To further confirm the observations, comparison was made between my Minolta Dynax 7 film camera, GX200 and the NX10. The difference does not bother me under good lighting conditions. But, even under good lighting conditions, the NX10's three lenses more often fail to lock the focus for subjects of a flatter texture and a bit less contrast. However, the Minolta Dynax 7 locks the focus almost instantly.
The following is the comparison between the GX200 and the NX10's pancake:
A book with a smooth, slightly reflexive surface was used for the shot.
The GX200 (in non-Macro mode) locked the focus instantly.
The pancake lens of the NX10 refused to oblige. It locked the focus only after several failed attempts.
Now this less satisfactory focusing performance is an issue to veteran photographers who photographic themes are wider. The culprit is not in the lenses but the ability of the APS-C sensor in doing the calculations for the focusing.
All in all, the issue is less with the pancake lens, more with the 18-55mm ones and most prominently with the 50-200mm zoom lens.
Another Focusing Issue
All of the three lenses lock the focus comfortably when pointing to a closer subject, but not to a farther subject.
This can best be illustrated with an example. The "Big Mac" poster in the photo below was at three metres away and shot at 130mm with the long-range zoom lens, using the single-AF mode and multi-AF area. The focus was locked in a split of a second.
Now, the lens was pointed to the picture in the background which was 7 metres farther away:
The lens searched through the focal lengths in an attempt to locate the right focus before locking it (similar performance was found in GXR A12 33mm, especially when the Marco mode is turned on). This took the lens roughly 4 seconds before locking the focus.
Then, from the focused subject at the far end, point the lens back to the subject at that "Big Mac" poster. All of the three lenses locked the focus almost instantly.
Similar tests done with all the lenses reveal that the lag is more noticeable in proportion to the increase in the focal length of the lens being used: roughly 2 seconds for the pancake, 2 seconds/ 3 seconds at 18mm/ 55mm with the middle-range zoom lens and 5 seconds at 200mm with the long-range zoom lens.
This phenomenon may not be an issue in most occasions, but can become annoying and fatal to street and sports photography where scenes may present themselves just around the corner.
Defocused
Also, with the long-range zoom lenses, defocusing is sometimes obvious under some circumstances like people are moving across the scene. This shortcoming can be worked around by turning off the multi-AF area and activating just the centre focus sensor.
Here, the focus was lost when people walked across the frame at the time the shutter release was fully pressed (continuous AF NOT in used). Probably the AF is too sensitive which is not a sin. For sure, in difficult shooting situations, it is wise for the photographer to use the most suitable focusing strategy: pick a selectable AF point to overcame the problem; otherwise, focus manually.
In the next post, some conclusive remarks about the NX10 will be offered.
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