Tuesday, 24 December 2013

Are Panasonic fooling us?

The new ultra compact Lumix GM1 is marketed with a record breaking 1/16000s maximum shutter speed. That surely sounds impressive. The camera also has a brand new shutter module, using a stepper motor rather than a conventional spring actuated shutter curtain.

But is this an improvement? Let's compare the specifications with other similar cameras:

CameraLumix GM1Lumix GX7Lumix GH3Olympus OM-D E-M1Nikon 1 V2
Maximum shutter (mechanical)1/500s1/8000s1/4000s1/8000s1/4000s
Flash sync speed1/50s1/320s1/160s1/320s1/250s
Maximum shutter (electronic shutter)1/16000s1/8000s1/4000sNone1/16000s
Electronic shutter readout speed1/10s?1/10s?1/10sNone1/80s
Flash sync speed (electronic shutter)Not possibleNot possibleNot possibleNone1/60s
Body



Mechanical shutter


Starting from the top, we see the mechanical shutter maximum shutters speed. Both the Lumix GX7 and Olympus OM-D E-M1 have the newer, updated shutter modules, capable of 1/8000s shutter speed.

This can come handy for outdoor photos at a large aperture, when you want to have a thin depth of focus (DoF), even on a sunny day. Without a fast shutter speed, you need to use an ND filter to achieve the same. The Lumix GM1 only rates at 1/500s, which is quite poor. Of course, you could always use the electronic shutter, which is faster, more about that later.

The flash sync speed is the fastest shutter speed in which the curtain is fully open. For the flash to fire, the sensor must be fully exposed, meaning that the first front curtain must have opened completely, before the rear shutter starts closing. Hence, the flash sync speed is essentially the speed of the shutter curtains. A flash sync speed of 1/160s means that the curtains open (or close) fully in 1/160s (or slightly faster).

Again, we see that the Lumix GX7 and Olympus OM-D E-M1 have the fastest shutter units, capable of a 1/320s flash sync speed. This is good for fill flash on a sunny day, when you don't want to stop down the aperture, probably to keep the depth of focus (DoF) short. Without a fast flash sync speed, you again need to use an ND filter.

Alternatively, you can use the "high speed sync" mode, found on most flash units, e.g., Lumix FL360 or Olympus FL-600R. This allows you to use the flash with a faster shutter speed than the flash sync speed. This is achieved by having the flash unit fire several flashes as the shutter curtains move across the sensor. This works well, but drains the flash power reserve much faster. The maximum flash effect is also significantly reduced in this mode.

Electronic shutter


The electronic shutter is an innovation first introduced to the Micro Four Thirds world with the Lumix G5 in 2012. In this mode, the sensor is read out sequentially, row for row, replacing the need for a mechanical shutter.

However, there is a big downside. The sensor takes around 1/10s to read out fully, top to bottom. This is analogous to the flash sync speed with a mechanical shutter. You could compare it with the speed of the curtain as it moves across the sensor. The important thing to realize here is that the electronic shutter readout speed (1/10s) is much slower than the flash sync speed (1/320s).

What does this mean in practice? The slow readout speed causes significant rolling shutter artefacts. I have written about it here and here, using two different methods to measure the sensor readout speed with the GH3.

Some reports indicate that the electronic shutter readout speed of the Lumix GM1 is faster than 1/10s. Some indicate it could be around 1/15s or 1/20s. However, this is still very slow, and will still give you serious rolling shutter effects.

The Nikon 1 system is largely based on electronic shutters. The compact J and S series cameras don't even have any mechanical shutters at all. The first batch Nikon 1 J1 had a sensor readout speed of 1/60s, while the later Nikon 1 J3 ups it to 1/80s.

So the cheap, entry level Nikon 1 J3 has an electronic shutter readout speed (1/80s) which is faster than the mechanical shutter curtain of the premium Lumix GM1 camera (1/50s). This is hardly impressive at all.

The Lumix GM1 has an electronic shutter speed that maxes out at 1/16000s, sounding very impressive. However, any shutter speed faster than 1/500s is done with the electronic shutter, which is barely usable due to rolling shutter artefacts.

And when using the mechanical shutter, the curtain moves rather slowly, at 1/50s. This could give you rolling shutter artefacts, if you photograph objects moving fast.

Still, the Lumix GM1 is an impressively compact camera, and it does look and feel very well. However, if you are very critical, you could say that the GM1 looks like a one trick pony, with compactness being the one trick.

The Lumix GX7, on the other hand, has a newer, traditional shutter unit, and is capable of an 1/320s flash sync speed, which is quite respectable. Then again, the shutter is said to make a fair amount of noise, compared with other cameras.

Smaller lenses, smaller apertures


Another way in which the Panasonic specifications are a bit misleading is the aperture range of kit zoom lenses.

Panasonic recently launched their third tele zoom lens, the Lumix G 45-150mm f/4-5.6. It is impressively compact considering the specifications:

LensLumix G 45-200Lumix X 45-175Lumix G 45-150
Max aperturef/4-5.6f/4-5.6f/4-5.6
AnnouncedSep 12, 2008Aug 26, 2011Jul 18, 2012
Length100mm90mm73mm
Diameter70mm62mm62mm
Weight380g210g200g
Filter thread52mm46mm52mm
Front lens element diameter37mm32mm27mm

So, how can Panasonic design a smaller lens with a smaller front lens diameter, and still retain the same aperture range, f/4-5.6? The answer is simple: They cheat.

Well, "cheat" may be a bit too strong word, as the aperture range is indeed f/4-5.6 for all of them. But what the specifications don't tell you, is that the aperture between the short and long ends is different. This diagram sums up my point:



If you took the average aperture over the focal length range, then you would see that the newer lenses have a smaller average aperture. Hence, while the specifications look the same, the smaller lenses are giving you a smaller aperture on average. I guess there is no way to avoid this: Panasonic cannot cheat the laws of physics. If they make a smaller lens, then the aperture must be smaller.

The same also goes for the kit zoom lenses. Here are the four kit zoom lenses from Panasonic:

Lumix LensG 14-45mmG 14-42mmX PZ 14-42mmG 14-42 II
Year released2008201020112013
Length60mm64mm27mm49mm
Diameter60mm61mm61mm56mm
Weight195g165g95g110g
Filter thread52mm52mm37mm46mm
Front lens element diameter45mm30mm21mm25mm

I only have the two in the middle, but for them, we again see a clear correspondence between the front lens diameter and the aperture range:



The most recent kit zoom lens is remarkably compact, and has a very small front lens element. With this in mind, I would guess that the aperture is not linearly decreasing as you zoom, but looks more like the Lumix X PZ 14-42mm in the diagram above.

So, is this a problem? Based on my own experience, I tend to use the zoom lenses the most in the very short or long end. And in those positions, I get the aperture from the specifications, so there is no change. However, when using the lenses somewhere between the short and long ends, the newer and smaller lenses will give a smaller aperture.

But the difference is not huge. At the very most, it is one half stop. But mostly far less than this. So I think few users will notice any change.

On the other hand, the size of the lenses is important to many people. After all, if size was not important, why would we stick with the Micro Four Thirds format? For example, the Sony NEX system cameras are not a lot larger, but feature a larger APS-C sensor. It is the lenses, though, where the main difference in size is. And this is where Panasonic can make a difference. The cameras cannot be made significantly smaller, given that there must be some grip surface and a screen. But, as they have demonstrated, the lenses can be miniaturized even further. That is one way to differentiate themselves from the competition.

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