This may be something that is obvious for some, but I noticed how many starting photographers struggle when it comes to understanding the relationship between resolution, detail and shutter speed, and how these things effect each other. This article is for those photographers.
Recently I had a discussion about the effect of resolution on the minimum shutter speed. As the discussion evolved it became clear how resolution was not quite understood. For the photographer it seemed to be very difficult to grasp the concept on how small movements will be seen more easy when resolution increases. That is when I realized how something that was quite obvious for some, is not always so obvious for others. Reason enough to write an article about it, and explain the concept and the relationship with simple words and some animated GIFs I made.
About the Minimum Shutter Speed Rule
There is a minimum shutter speed that can be used without the risk of blurry images due to shake. This rule may be familiar for a lot of you. It states that 1 divided by the focal length is the minimum advised shutter speed. The focal length needs to be corrected with the crop factor of the sensor because the rule is based on the magnification of the image. The longer the focal length, the narrower the field of view. The narrower the field of view the larger the magnification factor. Small movements due to shake will be magnified equally.
This rule is visualized in the next two animated GIFs. The inset shows the movement with a standard lens, and a tele lens. While the physical movement is the same in both examples, the one with the tele lens will show the movement much better because it is magnified.
This is why photographing with a 50mm lens will need a minimum 1/50th shutter speed. Shooting with a 200mm lens, will need at least a shutter speed op 1/200 sec. This is with a full frame sensor. If you use a 1.5x crop sensor, you will need to correct the focal length. The 200mm lens on a crop sensor will have the field of view similar to a 300mm lens, thus it will require a minimum shutter speed of 1/300th.
This rule is ancient history, based on shooting 35mm negative film, as far as I remember. As you may know, the 35mm film is the same size as a full frame sensor. This rule is also more of a guideline because some people can hold a camera much more steady while others will have difficulties even with the shutter speed as calculated by this rule.
About the Resolution of a Sensor
We have come to an age where the digital sensor had significant higher resolution compared to the analog film. Let’s look at some basics to have a good understanding about resolution.
The resolution is determined by the amount of pixels on the sensor. When more pixels are placed on the same sensor, the more detail can be captured. That is obvious, I guess. More pixels on the same surface area means these pixels are closer to each other.
Let's imagine a sensor that can resolve details of 10mm at 1 meter distance. Objects that are 10mm in size, or larger, will be visible in the picture. Objects that are smaller won’t be visible. If an object is just 2mm in size, it cannot be resolved and will be invisible. If we increase the resolution of the sensor 10 times, it has more pixels. Because these pixels are 10 times closer to each other, it will resolve a detail of 2 mm at 1 meter distance. Suddenly the object that is 2mm in size will become visible.
For this comparison it is very important that we keep the sensor size the same. If we increase the sensor size, the increased amount of pixels will be located on a larger surface. It basically means that if we increase the sensor by a factor 2, and we increase the amount of pixels by 2, the resolution stays the same.
Increase Resolution and Minimum Shutter Speed Rule
Let’s step back for a moment, and look a the minimum shutter speed rule. For this example we use a 50mm lens, and the rule tells us 1/50 sec is fast enough to prevent visible camera shake. Now we look at the sensor again that can resolve details of 10mm at 1 meter distance. Let’s assume there is a movement of 10mm up and down due to camera shake. The movement is too small to be resolved by the sensor resolution and thus invisible. That is why the image will look sharp at 1/50 sec.
Next, we increase our resolution 4 times again. Suddenly we can resolve details that are 2mm in size instead of 10mm. Suddenly the camera shake of 10mm at 1/50 sec will become visible. The minimum shutter speed rule of 1/[focal length x crop factor] does not work anymore when resolution increases too much.
Where Is the Breaking Point and What Is the Solution?
Somewhere there is a breaking point where the minimum shutter speed rule doesn’t apply anymore. I haven’t found an exact number of pixels, but a lot of reading suggests it might be somewhere between 24 and 30 megapixels on a full frame sized sensor. If you do know the exact number, please share it in the comments.
The solution is a faster shutter speed when the pixel count on a full frame sensor exceeds 30 megapixels. In those occasions the minimum shutter speed must be 1 / [focal length x 2]. In our example of a 50mm lens the minimum shutter of 1/100 sec is advisable to prevent the camera shake to become visible.
When the resolution increases even more, like with the massive 102 megapixel Fujifilm GFX100 camera, even the 2x focal length might not be enough anymore. Perhaps you could divide the resolution by the 30 megapixels, which could be the breaking point as mentioned above. In that case you should use a 3x focal length in the minimum shutter speed rule when it comes to a 100 megapixel sensor.
How About Image Stabilization?
When your camera or lens has image stabilization, it will become much more easy to use longer shutter speeds than the rule tells us. This becomes increasingly convenient when using high pixels count sensors. It is possible to correct the minimum shutter speed by the amount of stops of the image stabilization. If your camera or lens can correct up to 4 stops, the minimum shutter speed of 1/100 sec will become something like 1/8 sec with a 50mm lens.
Nowadays image stabilization can reach up to five or six stops, like the Panasonic DC-S1. In that case you would shoot with a minimum shutter speed that is calculated and corrected with the amount stabilization. I still would recommend using a shutter speed according to the the old minimum shutter speed rule. Never forget, image stabilization only compensates vibrations and shake, not a moving subject.
I would love to hear if you know what the resolution breaking point is, or the corrected rule for high resolution sensors. Please share it in the comment below. You are also welcome to share your thoughts about reducing camera shake and the solution you have. I am looking forward to your comment.