Traditionally, lens focus mechanisms have been rather simple, just a cam which pushes the lens elements back and forth as the focus ring turns. Moving the lens assembly away from the film/sensor gives you a shorter focus distance.
In the Micro Four Thirds family of lenses, this mechanism is rather unusual. Only the two first pancake prime lenses, the Olympus 17mm f/2.8 and the Lumix G 20mm f/1.7 feature this type of mechanism, in which all the lens elements move during focus.
Most other lenses feature internal focus, meaning that only one or some of the lens elements inside the assembly move during focus. This has many advantages: It is usually more quiet, the lens can be more solid since there are no moving elements on the outside, and it is usually less noisy.
On the negative side, this type of focus mechanism can give you a change of effective focal length as the focus moves. This is not much of a problem for still photography, but if you are focusing during video recording, it can lead to what is called "focus breathing", as the image zooms in and out a bit as the focus jogs back and forth.
Showing posts with label focus noise. Show all posts
Showing posts with label focus noise. Show all posts
Saturday, 20 October 2012
Sunday, 17 July 2011
Focus noise compared
Focus noise can be distracting. If you are in a silent environment, noise from the autofocus will distract the people you try to photograph, and will potentially make you look stupid.
Most Micro Four Thirds lenses have internal focusing, meaning that some smaller lens elements inside the lens move to achieve focus. This is generally fast and silent.
To illustrate the difference in focus noise, I made some measurements using an Iphone. Now, I don't believe the Iphone is very well calibrated. So the absolute noise measurements are probably not too accurate. But the relative noise levels can be studied this way.
To measure the noise, I put various lenses on the Panasonic GH2, and put the camera in continuous autofocus mode, AFC. In this mode, half pressing the shutter will make the focus job back and forth continually. I pressed the shutter 3-5 times for about one second each time, to capture the noise level.
Here is a video showing the study:
The results:
Conclusions
The outcomes are mostly as expected. The Lumix G 20mm f/1.7 pancake lens is the odd man out in this test. Since it is the only Micro Four Thirds lens that features a traditional focus mechanism, and not internal focus, it is also the most slowly focusing and noisy. The lack of internal focus means that the whole focus assembly moves during focus. You can see this in the video.
Perhaps the only surprise in the test is the relatively loud focusing noise from the Lumix G HD 14-140 superzoom lens. This lens is marketed as a video optimized lens, and features fast and silent operation. I would speculate that the noise picked up is not only from the focusing, but also from the OIS unit, which is powered when half pressing the shutter. Also, since this is the largest lens, the sound comes from a source closer to the mobile phone picking up the noise. Hence, the sound reading should be expected to be more audible. So I would take the measurements from the 14-140mm lens with a grain of salt.
The Olympus ZD Four Thirds 50mm f/2 macro lens is not a contrast detection autofocus (CDAF) optimized lens, and therefore it is rather slow to focus. It also generates a lot of noise, since it moves large lens groups back and forth. This lens is mostly useful for studio work on Micro Four Thirds, I'd say, due to the very slow autofocus.
The final word is that most Micro Four Thirds lenses, except the 20mm pancake, focus very fast and virtually noiseless.
Another aspect is the noise from the aperture change. I have not measured this, but my experience is that this is rather noisy with all lenses, except the Lumix G HD 14-140 superzoom lens. The 14-140mm lens has an almost inaudible change of aperture.
I would have liked to test the Lumix G 14-42mm f/3.5-5.6 kit lens. However, I took my lens back to the store due to a bad aperture diaphragm. After more than two months, they have still not fixed it.
Most Micro Four Thirds lenses have internal focusing, meaning that some smaller lens elements inside the lens move to achieve focus. This is generally fast and silent.
To illustrate the difference in focus noise, I made some measurements using an Iphone. Now, I don't believe the Iphone is very well calibrated. So the absolute noise measurements are probably not too accurate. But the relative noise levels can be studied this way.
To measure the noise, I put various lenses on the Panasonic GH2, and put the camera in continuous autofocus mode, AFC. In this mode, half pressing the shutter will make the focus job back and forth continually. I pressed the shutter 3-5 times for about one second each time, to capture the noise level.
Here is a video showing the study:
The results:
| Lens | Measurements | Average |
Lumix G 8mm fisheye | 50 46 52 51 | 50 dB |
| Lumix G 14mm | 49 51 47 48 | 49 dB |
| Lumix G 20mm | 61 60 58 59 | 60 dB |
| Leica Lumix DG 45mm macro | 51 52 50 52 | 52 dB |
| Lumix G HD 14-140 | 55 62 65 62 61 60 | 61 dB |
| Lumix G 45-200 | 50 53 56 54 | 54 dB |
| Olympus ZD 4/3 50mm f/2 | 76 79 81 | 79 dB |
Conclusions
The outcomes are mostly as expected. The Lumix G 20mm f/1.7 pancake lens is the odd man out in this test. Since it is the only Micro Four Thirds lens that features a traditional focus mechanism, and not internal focus, it is also the most slowly focusing and noisy. The lack of internal focus means that the whole focus assembly moves during focus. You can see this in the video.
Perhaps the only surprise in the test is the relatively loud focusing noise from the Lumix G HD 14-140 superzoom lens. This lens is marketed as a video optimized lens, and features fast and silent operation. I would speculate that the noise picked up is not only from the focusing, but also from the OIS unit, which is powered when half pressing the shutter. Also, since this is the largest lens, the sound comes from a source closer to the mobile phone picking up the noise. Hence, the sound reading should be expected to be more audible. So I would take the measurements from the 14-140mm lens with a grain of salt.
The Olympus ZD Four Thirds 50mm f/2 macro lens is not a contrast detection autofocus (CDAF) optimized lens, and therefore it is rather slow to focus. It also generates a lot of noise, since it moves large lens groups back and forth. This lens is mostly useful for studio work on Micro Four Thirds, I'd say, due to the very slow autofocus.
The final word is that most Micro Four Thirds lenses, except the 20mm pancake, focus very fast and virtually noiseless.
Another aspect is the noise from the aperture change. I have not measured this, but my experience is that this is rather noisy with all lenses, except the Lumix G HD 14-140 superzoom lens. The 14-140mm lens has an almost inaudible change of aperture.
I would have liked to test the Lumix G 14-42mm f/3.5-5.6 kit lens. However, I took my lens back to the store due to a bad aperture diaphragm. After more than two months, they have still not fixed it.
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