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The Sony A7r II has 42.4 (effective) Megapixels with a pixel area of 20.33µm2; and

the Sony A7s II has 12.2 (effective) Megapixels with a pixel area of 70.55µm2.

(both are FF camera's)

That is, A7r II has more pixels, whereas the A7s II has larger pixels.

Question.

I'm looking for a comprehensive list on what (dis)advantages larger pixels have over more pixles and vice versa, in general. The specific case of the A7r II vs A7s II can be used for explanation purposes.

List of Camera's with same sensor size and different number of pixels.

  • A7r II, 42.4 megapixels
  • Nikon D810, 36.3 megapixels
  • Canon 5D Mark IV, 30.4 megapixels
  • Nikon D610, 24 megapixels
  • Sony A7s II, 12.2 megapixels
  • Canon 1Ds, 11 megapixels

EDIT: This (old) part will be deleted later.

This is not a 'small' difference. How does this translate to usage? What is the possible 'aim' of Sony here? What can one do that the other can't, or at least not as good. Here is an obvious starting point:

  1. More pixels yield larger image, which is what you want if you're going to print large photos.
  2. ...

Why would you prefer one over the other? When just looking into the number of pixel and single pixel area.

onimoni
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    One thing to keep in mind is that these sensors and their associated electronics are not always exactly the same differing only in pixel densities. Often a manufacturer may put better electronics behind the "better/larger/pro" sensor. You really have to evaluate the camera's performance as a whole. – Mike Dixon Apr 07 '17 at 11:32
  • @MikeDixon True. My question is, is it possible to (theoretically) isolate the aspect of pixels, i.e. pixel size and pixel number, and talk about what that bring to the game. I personally found that quite difficult due to the strong relationship pixels have with other aspects regarding image quality. – onimoni Apr 07 '17 at 14:01
  • I'm looking for a comprehensive list... To what end? What is the actual thing that you're trying to understand? Are you basing a purchasing decision on this information? Doing a science project? How will you know if the list provided in an answer is comprehensive? – Caleb Apr 07 '17 at 14:18

3 Answers3

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Here's a somewhat lengthy article devoted to the differences between the cameras: Sony a7S II vs A7R II Test — Which One is Right for You?. What I got from the article, with respect to sensors, is that the difference is basically a matter of bigger pixels (a7S II) vs. more pixels (a7R II). The a7S II is said to give less noisy images at high ISO, but the a7R II gives you higher resolution images. There are a number of other differences, many of them related to video (different gamma options, rolling shutter differences, frame rate differences). Read the article for a full rundown.

Why would you prefer one over the other?

Resolution isn't everything. For some people, the a7S II's cleaner images and video improvements will be more important than the a7R II's higher resolution; for others, the a7R II's higher resolution and crop mode will be more important.

Caleb
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Many people prefer the A7s II over the A7r II for filming. The A7s II has a lot smaller Pixel-density therefore it has better low light performance. This is important for filming because you can't have a slower shutter speed than 1/25s (if you film in 25 fps). 12 Megapixels are enough if you use the camera only for filming. Another usage for this camera could be astrophotography.

The A7r II is good for stills. Compared to the huge amount of pixels it has still a very good low ISO performance. As you already pointed out, with 42 megapixels you have a lot of detail in your shots. This allows you to crop your image without loosing too much informations.

Michael C
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LordMcFungus
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You can always resize images from the higher resolution camera down to the same resolution/pixel size of the lower resolution camera. This also results in averaging the amount of noise in the image. Assuming both sensors use the same technology and processing, when images from the the 42MP sensor are downsized to 12MP the improvement in noise will also be very similar to that demonstrated by the 12MP camera. Of course downsizing to 12MP gives away the higher detail possible with the 42MP sensor.

You can't resize the images from the lower resolution camera to show the same amount of detail as the images from the higher resolution camera.

So why would anyone want the lower resolution camera?

Mainly for convenience.

If one only needs the lower resolution then it simplifies the workflow by eliminating the need to resize. It also reduces the size of the resulting files. This is especially an advantage when shooting video or bursts of still images, rather than when shooting a small number of still images one at a time. Smaller file sizes mean faster write times to the memory card and more images/minutes of video can be stored on the same size card.

If one looks carefully at the specifications of the two Sony cameras listed in the question, one also sees that the features and video recording options for the α7S II are more optimized for video recording while the α7r II is more optimized for still imaging.

Michael C
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