Four influencing image quality factors of digital cameras

Introduction

In marketing, it is popular to have short and easy messages. Those short messages allow reaching a big target group, as nobody has to study the topic in depth. In the case of photography is this message “the bigger the sensor, the better the image quality.

At the time the first 35mm sensors, with the size of 36x24mm2, arrived in the market the manufactures called this format full-frame sensor. This name suggests to the end-user that this is the biggest available sensor and a clear statement, that the user buys the best available quality. In this communication, it is not mentioned that the sensor is only one of in total of four components, which are relevant for image quality

Beside the sensor three additional components are essentially important for the image quality. Lens, image stabilisation and image processor. How those components influence the image quality I will show with simple examples. I hope my thoughts demonstrate, that in photography sensor size is not the only value which the user should monitor to make the correct decision, if they plan to buy a camera.

The lens

Factors influenced by lens

  • Sharpness
  • Resolution
  • Contrast

The lens is the first element of the image quality chain and therefore the most important. In case your lens is not able to deliver details to the sensor, it is impossible that the result can show the details in the result. Due to the sensor specification, the lens requirements in digital photography are much higher than in analog times. Light rays, for example, should reach the sensor straight. Otherwise light rays which should reach i.e. the red pixel could reach the blue or green pixel. This would cause issues in colour processing, which should be avoided.
In analog time i.e. a 50mm F1.2 lens had 7 lens elements (Minolta Rokkor), today a modern 50mm F1.4 lens (Sony Planar T*FE 50mm F1.4 ZA) has 12 lens elements nearly twice as many. This value shows how big the development in lens technology has been since digital times started. As the lens is the most important element for image quality that some of the photographers invest most of their money in an expensive camera and not in the lens. In case the budget makes this decision necessary personally I would make it vice versa. In the end, you would keep the lens much longer as the camera.

The sensor

Factors influenced by the sensor

  • Sharpness
  • Image noise
  • dynamic range
  • resolution

After the lens, the sensor is the second element in the image quality chain. It has an influence on noise performance, dynamic range, and resolution, which means it influences the sharpness of an image. The sensor size influences the image noise and dynamic range only indirectly, but more in detail now.

Image noise / Dynamic range

If you want to look at the influence of the sensor size on the image noise you first have to make sure that technology improvements do not affect the result. Fortunately, I had a Sony Alpha 6000 and a Sony A7II available. Both cameras were introduced in 2014, so it can be assumed that the sensor manufacturing technology is the same. Also, both cameras have an identical number of pixels with 6000×4000 pixels. To find out how the results differ, I took a picture with both cameras, with the same lens and the same settings. The result looks like this.

Alpha 6000, ISO 25600
A7 II, ISO 25600

Even in the preview, you can see that the A7 II has a larger dynamic range than the Alpha 6000. This is especially noticeable in the mouth. If you look at an enlarged section, it quickly becomes clear that the A7 II is less noisy.

Alpha 6000, ISO 25600
A7 II, ISO 25600

It seems that the connection between sensor size and lower noise is confirmed and therefore most of the testers stop at this point with the comparison. But is really the truth? As the A7II as a function with which you can switch the area from 35mm format to APS-C format. In case the sensor size would have an effect this should be visible in images taken in this way. Let’s take a look at the comparison pictures.

A7 II APS-C setting, ISO 25600
A7 II 35mm format, ISO 25600

As you can see the dynamic range is identical in both images, but what is the image noise.

A7 II APS-C setting, ISO 25600
A7 II 35mm format, ISO 25600

Also, the noise is identical. Sensor size could not be the reason, that the noise performance of the Alpha 6000 higher is than the one of the A7 II.
The reason is the pixel size itself. As the Sony Alpha 6000 has the same pixel count on a smaller sensor area, the pixel itself is smaller, or in other words: the pixel density is higher. It isn’t as easy as it looks. The sensor size is no parameter for more or less noise performance, this has to be seen in conjunction with the pixel count.
The pixel size of an APS-C camera with 24 million pixels is equal to the pixel size of a 35mm format camera with 54 million pixels. Would I compare those cameras the noise performance would be identical.

M.Zuiko Digital ED 100-400mm F5-6.3 IS

Blue tit at take of

In summer Olympus introduced the M.Zuiko Digital ED 100-400mm F5-6.3 IS and I had the opportunity to use it. After I made the first images, I have been very impressed by the image quality. Even though it is “only” a standard lens and not out of the Pro category image quality is on a very high level. Autofocus speed and accuracy is superb. Technical Details you can find on many websites, therefore I would like to skip them here. I intend to share the experiences I made with the lens.

Speed

With a starting F value of 5-6.3, the lens is not the fastest and in case of bad light, you have to increase sensitivity in the camera. I used the E-M1 Mark III together with the lens and used sensitivities up to 6400 ISO and satisfied with all my results. In case you don’t have to shoot fast-moving objects in bad light conditions the lens is more than usable. Compared to faster lenses, which are more expensive and heavier, you will have only disadvantages in case of bad light conditions.

Focal length range

With a focal length range of 100-400mm, it is ideal for wildlife photography and especially bird photography. The angle of view is equivalent to a 200-800mm lens for the 35mm format. Also, the MC-14 and MC-20 teleconverter are compatible. In case you combine it with the MC-20 the equivalent field of view is up to 1600mm. That supports you in shooting images from long distances, which is especially helpful when you are shooting shy animals. Sharpness and resolution in conjunction with the MC-20 and MC-14 are very high. The only disadvantage is that you lose 1 (in case of MC-14) or 2 (in case of MC-20) f-stops light sensitivity when you are using the converters, therefore even more light is needed or you have to increase sensitivity in-camera even more than without converters.

Macro capabilities

Besides the outstanding tele lens performance, the lens has also a very short minimum focus distance. Due to that function, the lens can be used also for macro photography. As the shallow depth of field depends also on focus distance this enables you also to separate your objects from the background with nice bokeh. Here some images I made with a short focusing distance.

Image stabilisation

The lens has. a built-in image stabilization, but in opposite to the M.Zuiko Digital ED 300mm F4 IS PRO it doesn’t support Sync-IS, which enables the system to use lens and camera stabilization together. Therefore the stabilization effect is not as big. However, In case you are using the lens in conjunction with an Olympus camera you get a better image quality when you are using lens and camera stabilization. Then the lens compensates for yaw and pitch movements and the camera is taking care of rotation, which is caused mainly when you are pressing the shutter release.

Conclusion

In case you are looking for a long focal length for a fair price the M.Zuiko Digital ED 100-400mm F5-6.3 IS is a perfect fit. The additional macro capabilities and compatibility with the teleconverters the lens offers additional benefit and makes the lens very universal. The only drop of bitterness is the speed of the lens, which makes it difficult to use the lens in bad light conditions. On the other hand, a fast lens is much more expensive.