Tuesday, 20 September 2011

Lens buyer's guide

So, you have a Micro Four Thirds camera? Now, what lenses should you buy?

Before trying to answer this question, let's take a step back and ask: Why would you need more lenses?

Compact cameras and interchangeable lens cameras

A user coming from the compact camera world may be confused by the apparent need for more lenses. Even fairly inexpensive compact cameras comprise a feature packed lens: A zoom range of 12x or more, starting at a very wide angle, macro functionality, and even pretty decent maximum aperture (a low f-value). All this in a small package.

When "upgrading" to a Micro Four Thirds camera with the kit lens, they may easily be disappointed. They now have a larger, more expensive camera, which only features a 3x zoom lens, starting at 28mm equivalent wide angle, and no macro functionality. How is this an upgrade at all?

The answer to this lies in the size of the imaging sensor. Compact cameras generally have a very small sensor, which allows the manufacturer to design very small lenses that have all the functionality most people would want. With a larger sensor, it is physically impossible to design a lens which does the same, at least within reasonable economical constraints.

So why don't all cameras have small sensors, so that the built-in lens can solve all the photographic needs of the user?

Thursday, 8 September 2011

Noise comparison, aperture change

I have previously compared the focus noise of various lenses. The conclusions from my analysis were hardly surprising, for example, the Lumix G 20mm f/1.7 pancake lens had a rather loud focus noise, due to the traditional focus assembly which moves all the lens groups back and forth.

The lenses with an internal focus mechanism generally featured lower noise, with the Panasonic Leica Lumix DG Macro-Elmarit 45mm f/2.8 1:1 Macro and Lumix G HD 14-140mm f/4-5.8 as exceptions. In the latter case, I believe the microphone was too close to the lens, giving biased results.

You could ask why worry about the aperture change noise. After all, the aperture is generally stopped down just before the shutter is released. And for all Micro Four Thirds cameras, the shutter noise is rather high. So the aperture noise is simply drowned by the shutter noise anyway.

However, there are times when you don't trigger the shutter. This could be when using the new high speed, low resolution mode of the Panasonic GH2. Or, quite simply, when recording videos.

Also, some time in the future, we are going to get cameras without mechanical shutters. When the global shutter technology is mature enough, we will see this in Micro Four Thirds cameras. Then, the only noise we will hear is the focus noise and aperture noise.

To measure the aperture change noise, I placed a mobile phone near the camera, running the "Decibel Ultra" app, to measure the noise level. While I don't trust the absolute measurement of the phone, I think it is good enough to look at the relative levels of noise.

The GH2, and many other Micro Four Thirds cameras, has the feature of stopping down the aperture to preview the depth of focus (DOF). This is very useful, especially for macro photography. I use this feature to toggle the aperture between maximum and f/7.1.

The test



Results

I have only noted down the peak decibel measurements. The results:

LensMeasurementsAverage

Lumix G 8mm fisheye
77 76 7777 dB
Lumix G 14mm79 7778 dB
Lumix G 20mm76 75 73 7675 dB
Leica Lumix DG 45mm macro80 82 81 8382 dB
Lumix G 45-20083 80 81 84 8382 dB
Lumix G 14-4275 76 75 7575 dB
Lumix G HD 14-14078 78 8179 dB

Conclusions

According to the marketing material, the HD designation of the Lumix G HD 14-140mm f/4-5.8 superzoom lens means that it should have fast autofocus, low noise autofocus, and near stepless low noise aperture.

After my analysis of the AF speed, the AF noise and now, the aperture noise, I cannot see that the lens is that special. It performs pretty much like the basic kit lens. What I haven't looked at, though is the aperture change, which is quoted as "near stepless". Accurate to 1/6 stop, is what I have seen quoted.

That said, the Lumix G HD 14-140mm f/4-5.8 zoom lens does have a softer sound when changing aperture.

In terms of aperture noise, the lenses appear to perform quite similar. And this is not strange: The aperture diaphragm mechanisms are probably rather similar between the lenses.