Oct 22, 2020 | iPhone

The Difference Between Optical Zoom and Digital Zoom on an iPhone 11 Pro

Ralph

Ralph

A lot of people don’t give it much thought, but there is a huge difference in quality between optical and digital zoom on an iPhone 11 Pro.

Is there much of a difference in image quality between optical zoom and digital zoom on an iPhone 11 Pro?  Yes!  There can be a huge, glaring obvious difference in image quality, or there might only be a slight difference.  First, let’s define what optical and digital zooms are, how they work, and then see examples of each.  By the end of this article, you will have a lot better understanding of the two and how to get the best image quality from your iPhone.

Optical zoom, what is it?

Traditionally, optical zoom in DSLR and mirrorless cameras used multiple glass elements that moved relative to each other to provide the zoom effect, increasing or decreasing as the zoom ring was adjusted.  The mechanism for how the lenses worked together is not as important an idea to understand, rather than simply that optical zoom is an effect of the glass or lens used to capture the image.  At any zoom range, the circle of light that covers the optical image sensor that produces the photograph is the same – all of the image sensor is used.

Glass lenses and prisms inside of a DSLR lens can zoom to many magnifications.  The image that reaches the sensor is still nice and sharp with abundant clarity throughout the entire range.  There is no image quality loss with the use of lenses to increase magnification, other than lens quality of course.  No lenses are absolutely perfect.

In an Apple iPhone 11 Pro, the optical zoom takes place by way of a different lens and camera sensor.  Essentially, switching from the 1x wide camera to the 2x telephoto is just that, a different camera with a different lens and image sensor.  Again, the main takeaway is that with optical zoom on an iPhone 11 Pro, you are using different cameras with different fixed focal lengths.

Digital Zoom, what is it?

Traditionally, with DSLR and mirrorless cameras a photo is taken and then later, perhaps in post production, the image will be cropped.  That is to say that a smaller than original portion of the image will be extracted and made to represent the full-size photo with the undesired portion discarded from the image.  That is to say, I took a photo and decided to “crop” only the center ½ of the image out.  I take that center ½ of the image and increase it in size until it is the same size as the original.  

The problem with this method is that the image sensor can only capture so much information for the image.  When you cut out half of the information captured by the image sensor, and then double that half of an image in size, there isn’t any more information to fill in the gaps.  The image after the crop has degraded in quality since there is now half as much information for the same area.  You just end up with a larger image with less detail.

The same effect happens on an iPhone 11 Pro once you increase the zoom of the image.  It all looks so seamless, but when you swipe the zoom wheel and go from 2x to 5x or 10x, all the iPhone is doing is digitally cropping in further and further on the image from the image sensor.  It all happens in real-time so it doesn’t seem like a big deal, but it is. The image degrades more and more the further past 2x you zoom.  By the time you get the iPhone 11 Pro to 10x digital zoom, you should be able to see the image degradation on the screen.

Being smart with digital zoom.

Keep in mind there are three lenses on the iPhone 11 Pro: a .5x super wide-angle, a 1x wide-angle, and a 2x telephoto.  That’s it, those are the three lenses on the device.  If you flip the zoom wheel to 1.5x, well guess what?  There isn’t a 1.5x lens.  What is actually happening is the iPhone is cropping the 1x wide-angle lens image and adding some detail from the 2x lens image.  It’s a lot of fancy software wizardry going on to create the image.  The image is still cropped from the 1x wide-angle lens and “enhanced” with information from the 2x telephoto lens.  That may sound like a great idea, but the image will likely be clearer by not using any digital zoom and sticking strictly with either the 1x wide-angle or the 2x telephoto lenses.

Since there are essentially no moving parts to the iPhone 11 Pro lenses, each lens produces the best clarity at exactly one focal length or magnification.  On the iPhone 11 Pro, optimal image quality can be found at 0.5 ultra-wide, 1x wide-angle, and 2x telephoto.  Any magnifications greater than or in between these will have some digital cropping and manipulation.  Only at those three magnification settings will the images be at their best, relying only on the lenses to provide light to the image sensor.

You will even notice this in the file size of the images you capture.  If you use no digital zoom, the file size of each photo taken will be about 12.2 megabytes, which is as expected from a 12-megapixel camera.  Using digital zoom, say to 4x zoom will result in a photo that is about 8 megabytes.  Since the photo was simply cropped, some of the information in the periphery was discarded, hence less information and less file size.  There is no way to get that missing information back, it has been lost.

Images before and after digital zoom, from an iPhone 11 Pro.

Here we have a shot taken at a renaissance festival. This shot was taken with an iPhone 11 Pro using the 2x telephoto lens. Notice that while the subjects on the field are well off in the distance the colors are good, the detail and sharpness are good and with little grain. The image shows good depth and separation between elements.

RenFest 2
image of RenFest jousting competition

Next, we have an image taken from exactly the same location but using the 2x telephoto with digital zoom to 5x. Notice how the detail is starting to be lost and the colors of the trees are starting to wash out. The image is beginning to lose depth as well. This is the furthest I would go with digital zoom as the image begins to fall apart at about this level.

RenFest Lady
Image of a lady on the field of a RenFest jousting competition.

Finally, we have our third image, taken using the 2x telephoto lens with digital zoom pushed all the way to 10x. The image degradation is obvious here. There is major detail loss on the field and on the lady in the red and gold dress. I wouldn’t even post this on social media.

The best way for me to capture these images would be to get up and walk closer to the subjects on the field. Bringing the camera closer would be much better than diving deep into the abyss of digital zoom.

Conclusion

The Apple iPhone 11 Pro is one of the best examples of photography from a mobile device.  The images that it captures can be sharp and vibrant with excellent dynamic range.  If the digital zoom is abused, rather poor image quality can result.

My advice, if you need to zoom past the 2x telephoto lens’s range, use your feet, and get closer if possible.  There is no substitute for simply bringing the camera closer to the subject for a better image.  Conversely, if your subject is smack dab in between the 1x wide angle lens and the 2x telephoto lens, again just move a little closer and use the 1x wide angle.  You could also move a little further back and just use the 2x telephoto and that is fine as well.  

Pro Tip!

Of the three cameras on the back of the iPhone 11 Pro, the 1x wide-angle seems to be the camera with the best image quality of the three.  It has the largest aperture of the three and, therefore, the most sensitive to light and typically produces the best image quality in lower light.  The camera is also stabilized to help reduce motion blur.

The 2x telephoto probably has the second-best image quality as it has only a slightly smaller aperture, so it is not quite as good in lower light.  It is also a stabilized lens to assist with motion blur.

The 0.5x super wide-angle lens has an even smaller aperture than the other lenses.  The super-wide camera does not have stabilization and while this may seem like an issue, it rarely is.  The camera lens is wide enough that little motion blur tends to happen or be visible.  The lack of stabilization on this camera tends to be more of an issue for video, rather than images.

Ralph

Ralph

Ralph is an avid photographer in his spare time. He spends a lot of his photography time shooting sports photos of his daughter, who plays softball and swims. He also has a keen interest in mobile photography.

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