GFX Technologies #4 - The Story of GFX Shutter Design

Everyone knows that the GFX 50S is a mirrorless camera. The GFX 50S is a 51.4MP camera. GF lenses are designed with the future in mind and can cope with resolutions up to 100MP. A mirrorless structure helps to achieve better image quality in several ways: there is more freedom as pertains to lens design, more precise focusing on the sensor surface, and finally no mirror shock.

The mirror shock is a huge factor that affects image quality. If the camera was created with a mirror, we estimate as much as 30% deterioration in resolution would be inevitable. Mirror shock leaves that much of an impact, especially for a medium format system.

Although it does not leave as big of an impact as the mirror shock, there is another element that causes shock inside a camera body: a focal plane shutter. Every time you press the shutter button, you feel the slight sensation. This is one way for photographers to know that the shutter has been released. But the shock is minimized to have minimum effect on the image quality. 

Our shutter design is actually all about shock absorption. Firstly, because we recognize that the shutter design affects image quality. Secondly, because we recognized that the shutter design affects overall durability. As mentioned on this X-Pro2 story, it is also about the sound and feel of the shutter. It is interesting to know that not all shocks are the same. Shutter speed affects how the shutter is released. Hence, the image quality, durability, and shutter sounds also change. When the shutter unit is designed, countless variations of settings are taken into account and we test them one by one. Many photographers are keen to learn the sensor and processor generations, but there are not that many that talk about the shutter unit designs. But truth be told, we put as much cost and labor into designing the shutter unit as other major design elements. 

For example, shutter unit pieces are not mass-produced during the development phase, so some parts are handmade one by one. This leads to a cost that is 30 times higher than the final product. We test them until they break, one after another in order to get feedback. We need to test in various environments and need to know its performance and weaknesses.

"As much as 30 units were broken before we landed on the final shutter design," said one designer. "In order to any make claims of 150,000 actuations or weather-resistance to -10°C, we actually needed to put it all to the test and confirm our claims."

There are two generations X Series shutter units. The GFX shutter blades are four times bigger than that of the X Series. It also needs to move as fast as 1/4000 sec. The spring tension and shock impact is 10 times bigger as a result.

The shutter design for GFX 50S was a challenging task. We overcame the difficulties with three approaches.

Firstly, rigid and tough metal parts are used. To achieve a lightweight body, plastic parts were considered. Carbon was another option. But we learned that these were not optimal for the shutter unit. Plastic is not tough enough for a medium format. Carbon is vulnerable to shock and is easy to break. We sought the best balance of strength and lightness. The broken 30 shutter units guided us to our conclusion. 

Secondly, we implemented a shock absorption mechanism. The shutter blades generate the greatest power when the first blade (that is, the front curtain) moves. When the moving arm comes to the lower end of the frame, its power is transmitted as shock to the inside of the camera. There is cushioning material within the shutter unit so that shock will not be transmitted.

However, there is still a shock that cannot be completely absorbed within the shutter unit. Therefore, a method of attaching the shutter unit to the casing is devised. Cushioning material is placed on the mounted part. You can imagine it as suspending the shutter inside the camera. We are careful not to transmit the generated impact to the sensor or the optics. This is the third approach.

You may think "why not use electronic front curtain shutter? Other cameras do this!" The answer is both "Yes" and "No".

The electronic front curtain shutter reduces shutter shock. It is particularly useful for shutter speeds from 1/15 to 1/60 sec. The electronic shutter closes first, and then the mechanical shutter closes in the rear.  Front curtain is the most powerful, so the shock is minimized. This is very efficient mechanism. 

But if the shutter speed is any faster, the story is a bit different.

Starting around from 1/125 sec, mechanical front and rear curtains move simultaneously while maintaining a constant distance.  This is also true if electronic front rear curtain is used. The electronic shutter on the sensor is followed by the mechanical rear curtain shutter. 

The decisive difference is that the electronic front curtain and mechanical rear curtain do not go on the same path. If the mechanical shutter is used for both front and rear curtains, they go on the same path. The gap between the electronic and mechanical results in undesired vignetting and blurred images for fast shutter speed. This is why GFX 50S automatically switches to mechanical shutter starting at 1/640 sec.

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