The 100x Fairy Tale: Focal Lengths and Optical Zoom in Smartphones Explained

Contents:

Note: As this article is very technical, you will find a short tl;dr with the most important learnings at the end of each section.

Basis: Angle of View, Focal Length, and Equivalent Focal Length

To understand what a specific optical zoom means on a smartphone, we first need to look at focal lengths. The focal length of a lens is the distance between the lens and its focal point. Therefore, an optical system with a very long focal length focuses light very far behind the lens. Thus, a long focal length means a small angle of view or, colloquially, a “strong zoom”.

Unfortunately, the focal length is not solely related to the angle of view. The size of the image sensor behind the optics also plays a very important role. A smaller image sensor would record a correspondingly smaller image section with the same lens, and “thus have more zoom”.

Different sizes of sensors in smartphones

To calculate the image sensor out of the equation and compare different cameras against each other, there is a so-called aspect ratio or crop factor. The form factor is defined as “one” for a 35mm or full-frame sensor. The crop factor now simply describes the ratio of the full-frame diagonal to the diagonal of the respective image sensor.

If you now multiply the actual focal length of a lens by the image sensor’s crop factor, you get the focal length of the lens in the 35mm equivalent. It is also this information that is mainly found in the data sheets of smartphone manufacturers. That makes sense, because the equivalent focal length is directly proportional to the angle of view and therefore provides a comparable value across all smartphones and cameras.

Focal lengths and their angles of view

Focal length in 35mm equivalent diagonal viewing angle
12 millimeters 122.0 degrees
24 millimeters 84.1 degrees
50 millimeters 46.8 degrees
85 millimeters 28.6 degrees
105 millimeters 23.3 degrees

Pro Tip: Almost all cameras save all kinds of information about the settings used in the EXIF ​​data of JPEG photos. The actual focal length is always found here, and never the focal length in the 35mm equivalent. This is exciting for datasheet sleuths – if you know the equivalent focal length, the relationship to the actual focal length allows conclusions to be drawn about sensor size. While the data sheets like to keep it a secret, the manufacturers do reveal at this point what ridiculously small sensors are in their smartphone cameras.

tl; doctor: To compare the “zoom” of different cameras, the focal length is given in the 35mm equivalent, because it correlates directly with the angle of view. The 24-millimeter equivalent in 35mm is the same for all cameras.

What does optical zoom mean on smartphones?

A focal length in the 35mm equivalent now defines exactly how large a certain object is reflected on the sensor at a certain distance from the camera. An optical zoom now means that the camera is optically capable of different angles of view or image sizes by varying the focal length.

AndroidPIT realme x3 superzoom image quality camera zoom

A digital zoom, on the other hand, is nothing more than cropping the photo using software, which reduces the angle of view or increases the focal length. Compared to the uncropped photo, this of course means a loss of resolution. It doesn’t really matter if the cut is done using Photoshop (middle) or “Hybrid-Zoom” (right). / © NextPit

To clarify the range of focal lengths or the flexibility of a lens, the relationship between the smallest and largest focal length has become common in photography. An optical system with 25 to 100 millimeters has a quadruple optical zoom – or had.

Because the marketing departments of smartphone manufacturers have thrown away all established conventions in photography. Instead, he cheerfully writes some nonsense on the data sheet: the main thing is that it is something other than the competition, and the “stupid customer” will buy it anyway, right?

What does 30x optical zoom mean?

The first smartphones with two cameras used to have a double optical zoom: the focal lengths of the two lenses were around 25 and 50 millimeters. Then came increasingly powerful telephoto sensors, and at some point double zoom became a “5x” in the camera app. When the ultra wide angle of LG smartphones made its way into the broad mass of smartphones, the gigantic angle of view was referred to everywhere as “0.5x” or “0.6x”, that is, as 0.5x , so to speak. camera.

The Samsung Galaxy S20 Ultra, for example, optically displays equivalent focal lengths of 13 millimeters to 103 millimeters and thus has around eight times optical zoom. Interestingly, this value is nowhere to be found. Depending on your goodwill, you may see this as an oversight on the part of marketing departments, or as deliberate and systematic simplification to foist on potential buyers features that don’t deliver on their promises.

AndroidPIT samsung galaxy s20 ultra review 24

I’m sorry, but that’s just stupid. / © NextPit

tl; doctor: A triple optical zoom means that the largest focal length of the camera system divided by the smallest focal length equals exactly three. The Samsung Galaxy S20 Ultra has an 8x optical zoom.

100x and that hybrid zoom shit

So where does the “100x” come from, which a Galaxy S20 Ultra proudly sports on the case? For 100x optical zoom, a smartphone would now have to cover a focal length range of 13 to 1300 millimeters in 35mm equivalent, and it would probably be THAT big and expensive.

The answer to the question “From where?” 100x is simple: from the imagination of Samsung product managers. Unlike “real” camera optical zooms, this “100x” has absolutely no bearing on the optical capabilities of the camera system. Instead, the Samsung Pi has chosen a fantasy value as the upper limit for the camera.

After years of educational work by tech journalists burned the term “digital zoom,” “hybrid zoom” or “spatial zoom” are the next sows to be fueled by the marketing village. Regardless of the name, this means nothing more than: This is a digital zoom once the maximum optical focal length has been reached.

zombies

Is the image quality at 100x to run away? To hell with it, the main thing is that you can write it great on the case. The 100x image looks cloudy even in postage stamp format here in the collage. Trust me, you won’t want to see it bigger. / © NextPit

Whether there’s a 60x, 100x, or soon 200x hybrid zoom in the datasheet doesn’t say anything about image quality; at best, something about the seriousness of the manufacturer. If you really want to know how close a smartphone can get while maintaining reasonable image quality, three values ​​are important:

  1. The focal length of the telephoto lens in 35mm equivalent
  2. The image sensor under this telephoto lens
  3. The light intensity of the telephoto lens

the Telephoto focal length in 35mm equivalent it tells you how well the smartphone can zoom in on distant subjects through optical magnification. If the ratio of fairy tale magnification to optical magnification gets too far, the cell phone has to digitally zoom, and the image quality suffers.

Here it comes Image sensor below the telephoto lens comes into play: the larger this image sensor, the more light it captures and the better the image quality. A very large image sensor not only offers better photos with through-the-lens optical magnification, but also offers more scope for digital zoom.

Finally, the Luminous intensity or telephoto aperture A role. The aperture describes the amount of light the sensor has available for the photo. In general, more light means less noise and less risk of blurring. In particular, smartphone cameras have lenses that are notoriously weak.

Camera AndroidPIT Honor 30 Plus

Periscope lenses are modern: the Honor 30 Pro+ also has a lens with a very long focal length. However, the “50x zoom” in the case does not justify it. / © NextPit

You can read these three aspects in the data sheet. Along with the quality of the camera algorithms, which is difficult to quantify, they are largely responsible for image quality.

Keep reading: Aperture in the cell phone camera: what is the use of F1.7 in the smartphone?

Digital vs Optical Zoom: Sometimes Better Than Its Reputation

However, the three points above also indicate cases where a digital zoom may be superior to its optical counterpart. With the Samsung Galaxy S20, for example, there was a huge outcry in the tech realm. Samsung advertises the smartphone with a “3x hybrid optical zoom”. The 64-megapixel “telephoto” actually only has 1.06x optical zoom compared to the main camera, with the remainder being 2.94x. hybrid poop digital. That’s as bold as it is stupid, and rightly so it backfired.

Because while the shitstorm was predictable, the Samsung Galaxy S20’s digital zoom is probably better than some optical zooms. Because the 64-megapixel sensor is really big at 1/1.72-inch and offers an area of ​​around 40mmtwo. If we now divide the sensor into nine equal-sized rectangles and consider the central area as a separate sensor, we end up with the 1/4.4-inch sensor in terms of sensor size that Huawei uses in its P20 Pro, admittedly somewhat outdated. It’s worth taking a close look at.

AndroidPIT Samsung S20 rear camera

It’s got some “gourmet duck” cat food: of the triple “Hybrid Optical Zoom” in the S20+, only two percent is optical, the rest happens digitally. / © NextPit

tl; doctor: A very large digital zoom sensor can produce better results than a small optical zoom sensor. The sensor decides! However, in most cases, optical zoom will have an advantage.

Keep reading: Exmor, Isocell & Co.: This is why the image sensor in the smartphone is so important!

Buying tip: the best smartphone with optical zoom

Which smartphone has the best optical zoom? Our previous tests actually point to the aforementioned Samsung Galaxy S20 Ultra.

However: this has nothing to do with the 100x in the datasheet. Rather, Samsung has installed a large image sensor that still captures enough light despite the small aperture. By the way, there is no need to wait for usable photos at a hundred times magnification: from about 10x the fun is over quickly, the rest is at best a party joke.

If you are really looking for an all-rounder for smartphone photography, take a look at the following article.

Keep reading: The best camera smartphones: the perfect snapshots for your pocket