In this review, we will be considering two digital cameras, the Sony a7S and the Sony a7R. We’ll bring you all the features, pros, and cons, of these two cameras.
If you don’t have the time to read all of it, then read through the comparison overview section. There you should find all the information you need to make the right purchasing decision.
Ever since the emergence of mirrorless cameras, different people have been moving from using DSLRs to using mirrorless cameras. While Nikon and Canon are the biggest players when it comes to DSLR cameras, Sony is the biggest player when it comes to mirrorless cameras.
So, if you’re looking to get a mirrorless camera, we will not be surprised if you’re stuck in between two Sony cameras. If at the end of this article, neither of these two cameras, Sony a7S and a7R , catches your fancy, click here to find other cameras that might do the job.
Sony a7S vs a7R – Comparison Overview
Looking at the overall features of these two products, they’re really good. They’re quite similar cameras and it is not a surprise, they both belong to the Sony Alpha series.
However, when we move from the similarities down to the unique features, we will find out that each of these cameras has strengths which the other doesn’t have.
For the Sony a7S, it is the video shooting capabilities. The camera has a slightly better continuous shooting rate that can shoot 4K video, and slow-motion videos.
On the other hand, the Sony a7R takes better still shots with its 36-megapixel sensor.
So, at the end of the day, picking either of these cameras- Sony a7S or a7R, depends on what you want to do with your camera. Looking at the price comparison ratio, the Sony a7S is a lot more affordable. So, if you want to shoot videos with your camera, this is more economical.
Sony a7S vs a7R – Comparison Of Key Features
|Announcement Date||4th June, 2014.||13th of February, 2014.|
|Maximum Screen Resolution||12 MP||36 MP|
|Iso||100 – 409,600||100 – 25,600|
|Continuous Shooting Rate||5 fps (Frames Per Second)||4 fps (Frames Per Second)|
|Video Resolution||3840 x 2160||1920 x 1080|
|Battery Life||340 shots||360 shots|
|Shoot Slow-Motion Videos||Yes||No|
Sony a7S vs a7R – Circumstances They Are Best Suited For
| The Sony a7S is a full-frame camera that belongs to the Alpha series. For a professional camera with this much quality, we have to say that this is some value for money. |
Because this camera was released some years back, its retail price has dropped significantly. Although this might not have been regarded as affordable when it was released, it sure is value for money, when you look at what new professional cameras cost these days.
| The Sony a7R is also a full-frame camera that belongs to Sony’s Alpha series. Released just months before the Sony a7S, this camera is slightly more expensive than the a7S. |
The price of this camera has also dropped significantly, as Sony makes newer cameras. If you want something with the quality of Sony, but you don’t have the money to get their latest flagships, these two cameras- Sony a7S and the a7R, are great options to get you into that ecosystem.
| Generally, the a7S is better for video. You can see this in its features. The biggest of this is that this camera is capable of shooting 4K video. It is also capable of shooting slow-motion videos, in real time. |
This, coupled with it’s continuous shooting rate, and general build, tells you that this camera is the better option if you do a lot of video.
| This camera can only shoot in HD (1920 x 1080). However, it does come with triple the maximum sensor resolution, available on the a7S. |
Although this does not mean a better camera overall, it does mean you get clearer, more detailed images with the Sony a7R.
If you make really large prints of your images, then you want the camera with more megapixels. This will make your images more detailed, and prevent them from getting pixelated.
| Another scenario people often want to check out is “low-lighting scenarios”. If you shoot in low-light, then ISO is your friend. |
Basically, the higher the ISO, the more sensitive your camera is to light, so, the clearer your pictures are in the dark.
The Sony a7S comes with a larger extended ISO. This simply means that this camera will take brighter photos in the dark than the Sony a7R.
| This camera is not the best for low-lighting scenarios, but it definitely is not the worst either. |
Later in this article, we would talk extensively about ISO settings and how it affects your images.
Finally, this camera is a bit lighter than the Sony a7S. So, if you want a lighter camera kit, this is what you want.
Common Features Of The Sony a7S And a7R
The following features are common to both the Sony a7S and a7R:
1. Mirrorless cameras
2. Electronic viewfinders
3. Wireless connection
4. Environmental Sealing
5. Articulating Screen
6. RAW Support
7. Microphone Port And Headphone Port
8. Face Detection Focus
9. AE Bracketing
In this section of this Sony a7S vs a7R comparison article, we would be looking at the features both of these cameras share. Being that both of these are Sony cameras, in the same series, you can tell that they would definitely come with a lot of similar features.
However, because they are different cameras, some of these similar features are used differently or come in different measures. For the purpose of the Sony a7S vs a7R comparison, we would be looking at those slight differences in features, where applicable.
Which is a mirrorless camera: Sony a7S or A7R?
Both the Sony a7S and the a7R are mirrorless cameras. Mirrorless cameras feature a single, removable lens and utilizes a digital display system in place of an optical viewfinder.
In DSLRs there is a mirror and a prism inside, which is used to send light from the camera’s lens to the optical viewfinder. The mechanism works thus:
The light on the camera gets into the camera through the camera’s lens and when the shutter button is not clicked, this light hits a mirror. The mirror then paths the light into two; one going upwards, and the other going downwards.
The light sent upwards then hits a prism which straightens it towards the viewfinder. On the other hand, the light sent downwards goes to a specific sensor responsible for autofocus.
In recent times, Sony has been focusing on creating some of the best mirrorless cameras you can possibly find out there, and Sony a7S and the a7R are no exceptions.
In a mirrorless camera, there is no mirror, prism, or specific autofocus sensor. The light passes through the camera’s lens and is sent straight to the camera’s electronic sensor.
This sensor then transfers that light to a digital image, which is then seen by the photographer through an LCD screen, or an electronic viewfinder.
Mirrorless cameras have become very popular, and the choice for many photographers, a lot of whom are switching from DSLRs. This is because mirrorless cameras do a lot of things better than DSLRs.
The points noted in this portion of the article are not aimed at discrediting the DSLR as there as still some things mirrorless cameras can’t do better than those.
What Do Mirrorless Cameras Do Better Than DSLRs?
We’ve talked a lot about mirrorless cameras, but that’s not enough if we don’t look at their benefits above the DSLRs. So, without further ado, let’s look at what mirrorless cameras do better than DSLRs:
If you google the picture of the first camera and imagine all cameras being like that today, we’re sure you would second guess buying a camera for yourself. It’s the same for phones, and for computers. As technology is improving, people are opting for smaller, more compact devices.
We are in the era of very flat, thin, laptops, slim phones with bezels, and even recently, foldable smartphones. All this is in a bit to make technology as easy to carry around as possible.
The same goes for cameras. The first aim of the mirrorless camera was to make a camera that delivered the same quality images and videos, in a much smaller package.
This was done by turning mechanical work into electrical work. Removing the mechanical parts like the mirror and prism, and giving their jobs to a single electronic sensor. This helped these companies to make smaller, equally efficient, cameras.
This is not to say that every single mirrorless camera out there is lightweight. However, if you compare a mirrorless camera with a similar DSLR camera, in terms of quality, the mirrorless camera would always be smaller and weigh less.
If you’re a travel photographer, a vlogger, you shoot events, or you generally just prefer a smaller kit, then mirrorless cameras are what you want.
This comes into play when taking fast-moving objects. Say you’re meant to take pictures of a sporting event, or perhaps you’re a wild-life photographer. If you shoot any fast-moving objects, then a continuous shooting rate is something you’ll really be interested in.
Mirrorless cameras generally have better continuous shooting rates than DSLR cameras. This is because mirrorless cameras do not have any moving parts.
In the DSLR, when the shutter button is clicked, the mirror has to flip upwards, to enable light to hit the camera’s film, directly. This is actually what causes the DSLRs famous shutter click sound.
With a mirrorless camera, the light already hits the electronic sensor, so once you hit the shutter button, it takes the picture.
However, this particular point is not exhibited in these two cameras- Sony a7S and a7R, as they both have, not so good continuous shooting rates. If you want to find this out, check the top-level professional cameras.
You would find that mirrorless cameras can go as far as 20 frames per second, while DSLRs usually don’t go beyond 15 frames per second.
Before mirrorless cameras, DSLRs where adored when it came to video shooting. The wide range of lenses and accessories available, as well as the full HD capture, are some of the reasons why they were really loved by videographers.
However, with the latest technology, mirrorless cameras are beginning to give them a serious run for their money. The first is the processing power of mirrorless cameras.
Because mirrorless cameras depend mainly on software than hardware, they come with immense processing power. This processing power affects the processing of videos, making them appear a lot sharper.
Another reason is the 4K video. The further the world advances, the clearer videos are getting. Everybody now wants to shoot in 4K. Although not all mirrorless cameras can shoot 4K, you have a better chance at finding one that fits your budget, than DSLRs.
To find a DSLR camera that shoots 4K video, you have to be ready to spend big bucks. However, to find a mirrorless camera that shoots 4K video, you don’t need to spend so much.
Finally, Sony, as well as other companies, are making a lot of different lenses and accessories for mirrorless cameras. As the days go by, this collection of options to choose from expands.
Different Options To Choose From Across All Prices
This is just a bonus for you. It is not a feature difference between mirrorless and DSLRs. Because mirrorless cameras belong to a growing market, there are a lot of players in the space.
If you want to get a good DSLR camera, you most likely have to choose between Canon and Nikon. This duopoly means that you have to get these cameras, regardless of their ridiculous prices, simply because there’s nothing better out there.
On the other hand, with mirrorless cameras, there are a lot of small brands fighting for your patronage. Because of this, the prices are a lot friendlier. You have companies like Panasonic and FujiFilm, making excellent mirrorless cameras that are really affordable.
Because of this, even the big brands like Sony, Canon, and Nikon, have to reduce the prices of their mirrorless cameras.
What Do Mirrorless Cameras Lack?
Just like we said earlier, there’s no need to throw away your DSLR. There are still one thing that DSLRs do a lot better than mirrorless cameras, and that’s battery life.
Because mirrorless cameras are made to be small and compact, they make use of smaller batteries. When it comes to batteries, the smaller they are, the lesser their capacity.
Added to this, mirrorless cameras depend on power for everything. The electronic sensor on a mirrorless camera is always on, so is the LCD screen, and sometimes, the viewfinder. All these features are power-draining features, which reduce the battery life of these cameras.
With a DSLR, the sensor doesn’t need to be on, unless the shutter button is clicked. Also, optical viewfinders do not require any power, and you can even see through them when the camera is turned off.
Generally, if you pitch a mirrorless camera with an equivalent DSLR, the DSLR can have up to three times the battery life of the mirrorless camera.
If you use a mirrorless camera, you’ll need to carry extra batteries with you all the time, so that the batteries don’t give up, halfway through your shoot, leaving you stranded.
Which uses an electronic viewfinder: Sony a7S or a7R?
Both the Sony a7S and the Sony a7R use an electronic viewfinder. One of the major reasons why people like mirrorless cameras is because of their electronic viewfinders.
However, not all mirrorless cameras use an electronic viewfinder. Some of them use only the LCD screen to preview the frame to the photographer.
The first benefit of electronic viewfinders is that you can use them even when the sun is out. With an LCD screen, it’s difficult to use outdoors when it’s sunny. The rays of the sun will bounce on the glass, obstructing your vision.
Now, comparing this to the optical viewfinder on a DSLR, is where you begin to see all of its uses and pros. In the most basic explanation, an electronic viewfinder sees a digital image, while an optical viewfinder sees light.
What this difference translates to is that with the electronic viewfinder, you get a live preview of what your image will turn out to be. You can see things like focus, exposure, ISO before the shutter button is clicked. This helps the photographer to get the rightly framed shot and also get the right settings to get the perfect shot.
With an optical viewfinder, all you can see is the frame of the shot. Things like exposure and ISO settings are lost to the photographer until the actual photo is taken. This is why beginners prefer mirrorless cameras as you can tweak and edit settings, see their outcome, before taking the picture.
If you still don’t understand the differences between an electronic viewfinder and an optical viewfinder, check out the video below:
Which has the wireless connection feature: Sony a7S or a7R?
Both the Sony a7S and the a7R have the ability to connect to the internet using the wireless connection feature. With this wireless connectivity, it is easy for you to communicate with other devices, transfer files, and stuff like that.
If you want a camera with which you can upload an image directly to the internet, then you really need to be looking at either of these cameras- Sony a7S and the a7R.
An added feature to this wireless connectivity is something called NFC (Near Field Communication). With this, your camera is able to connect and pair with compatible devices, once they are within range. Most of the time, people use this feature to connect their smartphones to the camera.
Once your smartphone is connected to your camera using this NFC feature, you can use your smartphone as a remote control for your camera. With your smartphone, navigating through your camera becomes very easy.
One shortcoming that both of these cameras possess is that neither of them provides a Bluetooth feature. Being that there are a lot of devices that are Bluetooth enabled, it would’ve been a lot easier to transfer files from your camera to your smartphone or PC, wirelessly.
Which has an environmental sealing: Sony a7S or a7R?
The Sony a7S and the a7R come with an environmental sealing that protects the camera body. The cameras are made with magnesium alloy frames.
With these frames, both of these cameras are moisture and dust resistant. Moisture and dust usually come as a result of rainfall and strong winds.
This is what allows you to keep shooting, even in tough weather conditions.
Which has an articulating screen: Sony a7S or a7R?
Both the Sony a7S and the a7R come with articulating/tilting screens. With an articulating screen, you can shoot with your camera from challenging angles. When shooting at certain angles, it is difficult for you to use the eye-level viewfinder.
In scenarios like this, having an articulating screen that can tilt well enough for you to see, is pretty good. However, if you’re shooting under the sun, you might want to get a small covering for the LCD screen. Doing this will protect the LCD screen from getting damaged by the rays of the sun.
Which has the RAW support feature: Sony a7S or a7R?
The Sony a7S and the a7R both have the RAW support feature. Shooting RAW images is something that a lot of photographers love to do. The difference between RAW and JPEG is in the name. RAW is an unprocessed and uncompressed version of an image captured by a digital camera.
If you’ve heard the phrase “I shoot RAW” and are probably wondering what it means, well, RAW is an image saving format.
Although all cameras capture images in RAW format, not all of them allow you to save it like that on your memory card. These two cameras allow you to do that. Saving images in RAW format gives you clearer, more detailed images.
Because the camera doesn’t compress it, you have a lot more information to work with, while editing, before finally converting to JPEG by yourself.
Microphone Port And Headphone Port
Which has a microphone and headphone port: Sony a7S or a7R?
Both the Sony a7S and a7R come with a microphone port and headphone port. These ones are pretty straightforward. With the microphone port, you can connect an external microphone to your camera.
This will allow you to record high-quality audio, straight into your camera. While recording this audio, you’ll need to listen to, and monitor, what the camera is recording. This is where the headphone port becomes relevant.
The headphone port enables you to connect your camera to a headphone. That way, you’ll be able to listen to what your camera is recording and also monitor the clip.
Face Detection Focus
Which has a face detection focus feature: Sony a7S or a7R?
Both the Sony a7S and the a7R have the face detection focus feature. This feature allows the camera to focus on a face, once the camera recognizes it in the frame. It is really helpful when taking portrait photos.
Which has the AE Bracketing feature: Sony a7S or a7R?
The Sony a7S and the a7R have the AE Bracketing feature. Exposure bracketing involves taking different photos of the same scene, with different exposure settings.
These settings usually range from underexposed, correctly exposed down to over-exposed, usually with equal differences.
With Auto Exposure Bracketing, all you need to do is to put in the different settings you want for the image. Once that is done, at the click of the shutter, these various images with various exposure settings are captured. It saves you the time of having to take one, check it out, and then change up and take another one.
Also, if one image still isn’t perfectly exposed, with exposure bracketing, you can merge different photos of the same scenery to form one image, which will be correctly exposed. This is called an HDR image.
Sony a7S – What Are The Unique Features?
The following are the unique features of the Sony a7S:
1. Shoots 4K Video
2. Shoots Slow-motion Video
Shoots 4K Video
One huge thing about the Sony a7S is that it shoots 4K video. The a7R, on the other hand, only shoots HD video. The highest resolution for the video you can shoot on this camera is 3840 x 2160.
This particular feature is one of two that make the Sony a7S a better overall camera than the Sony a7R.
At the end of the day, 4K video is not something that we can only talk about. So, to see what the 4K video shot by this camera looks like, check out the video below:
Shoots Slow-motion Video
There’s not a lot to talk about concerning this particular feature. The Sony a7S has a slow-motion feature that enables you to take live slow-motion videos.
Sony a7R – What Are The Unique Features?
The following is a unique feature of the Sony a7R:
Maximum Sensor Resolution Of 36 Megapixels
Maximum Sensor Resolution Of 36 Megapixels
Whenever people talk about the quality of the camera, they often refer to how many megapixels the camera can process. Most people, especially amateurs, think that the better camera is always the one that has a higher maximum sensor resolution.
That is true in some cases, but not all. Having a lot of megapixels is good for a camera in a lot of ways. However, some cameras can do a lot with not as much maximum sensor resolution.
So, what do high megapixels do?
Well, they create more detailed pictures. This detailing is most times not seen by the human eye on the surface of the image. However, it becomes much more evident when the print of the image is bigger. So, having more megapixels in your camera is very important if you have large prints of your images.
With the detailing that comes with 36 Megapixels, the image can be enlarged by a great percentage, without pixelating. To find out how well your image would do on large prints, you can zoom into them and see how well they look, whether or not they get pixelated.
There is one downside to having high megapixels, which we must point out. When you use high ISO settings, because of the detailing that this megapixel provides, there will be a lot of noise on your image.
So, if you’re one that likes to use high ISO in low-light scenes, you might want to get something with smaller megapixels.
Sony a7S – What Are The Unique Pros?
The following are the unique pros of the Sony a7S:
1. It has a 409,600 maximum ISO, which is way more than is available on the Sony a7R.
2. The continuous shooting rate of this camera is 1 more than the Sony a7R.
3. The Sony a7S is more affordable than the Sony a7R.
4. You can shoot 4K video with this camera.
Sony a7R – What Are The Unique Pros?
The following are the unique pros of the Sony a7R:
1. It has a weight of 465g, which is 24g lighter than the Sony a7R.
2. This camera has a maximum sensor resolution of 36 megapixels, which is simply, superb.
Sony a7S – What Are The Unique Cons?
The following are the unique cons of the Sony a7S:
1. This camera comes with only 12 megapixels, which is quite poor for a semi-pro camera.
2. The Sony a7S is not as lightweight as the Sony a7R.
Sony a7R – What Are The Unique Cons?
The following are the unique cons of the Sony a7R:
1. It cannot shoot 4K video.
2. It only has a continuous shooting rate of 4 frames per second.
3. The Sony a7R has a maximum ISO of 25,600.
Common Pros Of The Sony a7S And The a7R
|Good Wireless Connectivity|| Both of these cameras come with wireless connectivity. With this feature, these cameras connect wirelessly and are able to transfer files and communicate with other devices. |
Added to this, both of these cameras come with something called NFC (Near Field Communication). With this, your camera is able to pair with compatible devices and connect to them once they’re close enough.
|Same as the Sony a7S.|
|Shooting From Flexible Positions||Both these cameras- Sony a7S Vs a7R, come with articulating LCD screens. With this screen, you can shoot from flexible positions, positions where it’ll be difficult to use your viewfinder.||Same as the Sony a7S.|
|Both Come With A Viewfinder|| These cameras come with an electronic viewfinder. All the benefits of an electronic viewfinder are highlighted in a section up in this article. |
But basically, they help you frame your photos very well and give you a live preview of what your picture is going to come out looking like.
|Same as the Sony a7S.|
|Saves RAW Images|| With these cameras, you can save your images RAW. This helps you get clearer, more detailed images. |
Images that are saved in RAW format contain a lot more information because they are unedited and uncompressed.
|Same as the Sony a7S.|
|Comes With A Microphone Port||With the microphone port that comes with these cameras, you can record high-quality audio straight into your camera.||Same as the Sony a7S.|
|Comes With A Headphone Port|| The high-quality audio recorded by the external microphone needs to be monitored and controlled. |
This is where the headphone port is important. With a headphone port, you can connect your headphone to your camera. This headphone is what you use to monitor the audio, as it is being recorded.
|Same as the Sony a7S.|
|AE Bracketing|| With this feature, you can get the perfect exposure setting for all your photos. |
Also, you can get really good HDR photos with this feature.
|Same as the Sony a7S.|
Common Cons Of The Sony a7S And The a7R
|Neither Of These Cameras Comes With Image Stabilization|| Without image stabilization technology, videos taken by either of these two cameras might get shaky when the camera moves subtly. |
This shakiness will result might cause some of the footage to be blurry.
|Same as the Sony a7S.|
|No Built-In Flash||Neither of these cameras come with built-in flash. Without this feature, you have to carry your external flash everywhere you go. This is not very good for portability.||Same as the Sony a7S.|
|No Touchscreen Feature|| With a touchscreen feature, you would’ve been able to interact with your camera as you would, your smartphone. |
Without this feature, it’s quite difficult to navigate through the settings and menus of these cameras.
|Same as the Sony a7S.|
|No Built-In Bluetooth Feature|| Although both of these cameras come with wireless connectivity, they do not come with Bluetooth. |
Having Bluetooth would have made it a lot easier to transfer files to and from other devices that have Bluetooth.
|Same as the Sony a7S.|
|No GPS||Without a GPS feature, you don’t have the luxury of geotagging your photos.||Same as the Sony a7S.|
|There Is Only One Memory Card Slot||No storage flexibility.||Same as the Sony a7S.|
Sony a7S vs a7R – What Do People Think About Both?
|People who bought this camera really liked the general look and features of this camera. The price, though, made a lot of people think twice about buying this camera.||People who bought this camera were also happy with their purchase. However, not many people were able to afford this.|
| The continuous shooting rate of this camera is not very spectacular. However, it did the job. |
One thing people really loved about this camera, though, is its ability to shoot 4K video.
| One spectacular thing about this camera is its maximum sensor resolution. This camera comes with 36 megapixels, which is simply incredible. |
You can print really large pictures without worrying whether it will be pixelated.
Sony a7S vs a7R – What Do We Think?
Both of these cameras are quite similar. However, they each have their strengths. The Sony a7S is better for shooting videos, the Sony a7R is better for taking still photos.
|Get the Sony a7S now!||Get the Sony a7R now!|
Sony a7S vs a7r – Related FAQs
Is Sony a7S Full-Frame?
The Sony a7S is a full-frame camera. It features a 12.2MP Exmor CMOS sensor and BIONZ X image processor which enables an outstanding image and video quality. The Sony a7S also comes with low noise, extended sensitivity up to ISO 409600 and an expansive dynamic range.
Additionally, the Sony a7S places emphasis on its movie capturing abilities and this makes it a good choice for most videographers. Sony has always maintained that its main focus is videography and it doesn’t come as a surprise that the Sony a7S fits into this category.
What Does The “R” Stand for in Sony a7R?
The “R” in Sony a7R stands for resolution. Since the “R” represents resolution, the Sony a7R places emphasis on the best picture quality. The Sony a7R features a full-frame sensor although the anti-aliasing filter is lacking in the camera.
Most professional photographers go for this camera due to its durability while beginners go for it because of the easy interface. The camera is also good for both still images and videography and with its BIONZ X image processor, good image production is guaranteed.
What Does The “S” Stand for in Sony a7S?
The “S” in Sony a7S means sensitivity mastered. Consequently, the native sensitivity range of the Sony a7S is 100-102,400, and can also be expanded for video and still images up to ISO 409,600.
The Sony a7S comes with an outstanding JPEG image quality and a good dynamic range.
The camera has a silent shooting mode which could come in handy for some scenarios where the user might need to record without notice. The in-camera HDR and the sweep panorama mode also functions effectively.
Is Sony a7R Good for Video?
The Sony a7R is not good for video. However, the camera is a good choice for images due to its outstanding 12.2MP Exmor CMOS sensor and BIONZ X image processor. The a7R was not originally designed for recording videos as a first priority.
The Sony a7R is a good camera that gives enormous value for the price it’s being sold. At 407 grams, the camera can lay claim to being one of the world’s best full-frame sensor cameras.
The Sony a7R features an in-built 5-axis image stabilization system that comes in handy to stop the jitters that happen during recording.
What is The Recording Limit of The Sony a7S?
The Sony a7S has a recording limit of 29 minutes and 50 seconds. This is also the case with the Sony a7R as both cameras record outstanding videos within the accommodated timeframe. If you want to record video clips that are longer than 30 minutes then you have to use an HDMI-connection external recorder.
The HDMI-connection external recorder makes it easier to capture longer videos with the camera. If you learn how to effectively use this recorder, you will get the best out of the Sony a7S.
What’s The Difference Between Sony a7S and a7R?
The major difference between the Sony a7S and the a7r is the sensor. The sensor of the Sony a7S is 24 megapixels while the a7r boasts of 36 megapixels.
The Sony a7S has a super 35mm crop mode while the Sony a7R has 45mm crop mode. This gives the Sony a7R an edge in terms of image quality and rolling shutter performance.
Most professionals go for a7S because of the picture and video quality while the a7R offers good options in 4k full-frame mode.