You're looking at a lens – in a store, online, or on YouTube – and everywhere you see these letters and numbers: F/1.8, AF, STM, HFT-X, E-Mount. And you ask yourself: What does it all mean?
Don't worry, you're not alone. Lens manufacturers like to throw around abbreviations as if they were self-evident. But for beginners, it's often a mystery. Today, we're going to solve this mystery and explain in simple terms what the most important lens terms mean and why they're important to you.
The F-value: Perhaps the most important number on a lens
Let's start with what you'll encounter everywhere: the F-value, also called aperture or maximum aperture. On every lens, you'll find a designation like "F/1.8", "F/2.8", or "F/4". But what does that mean?
The F-value describes how large the opening in the lens is, through which light falls onto your camera's sensor. And now comes the part that confuses many at first: The smaller the number after the "F/", the larger the opening and the more light comes through.
An F/1.8 lens therefore has a larger opening than an F/4 lens. That sounds illogical at first – smaller number, larger opening? Yes, that's exactly how it is. The reason for this is mathematically somewhat complicated and not so important for beginners. Just remember: Small number = lots of light.
And why is that important? For three reasons. First: With a fast lens like F/1.8, you can also shoot in low light. In the evening, indoors, at dusk – the lens captures so much light that your pictures will still be bright and clear. You don't have to crank up the ISO value, which leads to grainy, noisy images.
Second: You get that beautiful blurred background that you know from professional photos. With a wide-open aperture like F/1.8, only a narrow area is in focus (for example, the face), while the background becomes soft and out of focus. This is called bokeh, and it simply looks great.
Third: A fast lens allows for shorter shutter speeds. This means your photos are less likely to be blurred because the camera captures the image faster. Especially important when shooting handheld or with moving subjects.
In short: An F/1.8 lens is significantly more versatile and powerful than one with F/4 or F/5.6. And the best part: With prime lenses, you can get F/1.8 at an affordable price. For zoom lenses, a similar aperture often costs many times more.
AF and MF: Automatic or manual focusing?
The next two letters you'll encounter again and again are AF and MF. AF stands for Autofocus, MF for Manual Focus. But what's the difference?
Autofocus means the camera focuses automatically. You press the shutter button halfway, the camera finds the correct focus point, and once everything is sharp, you press it all the way down. This is super practical for most situations – portraits, street photography, snapshots. You don't have to think, you just press the button, and the camera does the rest.
Modern autofocus is now really clever. Many cameras have face detection and eye-tracking – this means the camera automatically recognizes faces and focuses on the eyes. Perfect for portraits, because the eyes should always be sharp. This works for both photos and videos.
Manual Focus means: You focus yourself. On the lens, there's a ring you turn until the image is sharp. That sounds complicated and old-fashioned at first. But there are situations where manual focus is better. For example, in macro photography, where you want to precisely control which tiny area is sharp. Or in videos, where you want to gently shift between two planes of focus. Or in very low light, where autofocus sometimes struggles.
The good news: Most modern lenses have both. You can switch between AF and MF, depending on what you need. On many lenses, you'll find a small switch labeled "AF/MF" – this allows you to toggle between the two modes.
STM: The quiet autofocus motor
If you're looking at lenses, you'll sooner or later stumble upon the abbreviation STM. STM stands for "Stepping Motor". But what does that mean for you?
STM describes how the autofocus in the lens works. An STM motor is particularly quiet and precise. This is especially important if you're shooting videos. Imagine you're filming and the autofocus has to adjust during the recording. With an old, loud motor, you would hear the humming and whirring in the video. With an STM motor, the focus is practically silent.
STM also has advantages for photos: The focus is fast, precise, and works steplessly. This means it doesn't focus in small jumps, but smoothly and evenly. The result: You get consistently sharp images without the autofocus "pumping" or searching.
So, if you see a lens with STM, you know: The autofocus is modern, quiet, and well-suited for photos and videos.
FN-Button: Your shortcut to important functions
Many modern lenses have a small button labeled "FN" or "Fn". FN stands for "Function". But which function?
The great thing about the FN button: You can assign it yourself. In the camera settings, you define what should happen when you press this button. The possibilities are diverse. For example, you can set the FN button to:
- Lock the focus, even if you hold the shutter button halfway down
- Switch between different focus modes
- Activate the magnification, so you can focus very precisely manually
- Lock the exposure
- Call up certain camera settings
The FN button is therefore a freely programmable button directly on the lens. You don't have to rummage through menus or fiddle with the camera – you simply press the button on the lens and immediately access the function you need. Super practical when you need to work quickly.
ED and HR: The glass for better image quality
Now it gets a little more technical, but don't worry – we'll keep it simple. If you read a lens description, you'll sometimes find terms like "ED glass" or "HR element". But what does that mean?
ED stands for "Extra-low Dispersion". ED glass elements are special optical elements in the lens that reduce chromatic aberrations. Chromatic what? Simply put: Sometimes you see colored fringes on photos, especially at high-contrast edges – often purple or green. These are chromatic aberrations, also called color fringing. ED glass minimizes these color errors, making your images clearer and sharper.
HR stands for "High Refractive Index". HR elements are also special types of glass that correct certain color errors, especially magenta casts that can sometimes occur in certain lighting situations.
You don't need to understand in detail how these glasses work. The important thing is: If a lens has ED or HR elements, it means the manufacturer has made an effort to optimize image quality. You get sharper, clearer images with natural colors and minimal errors.
HFT-X: The coating against reflections
HFT-X stands for "High Fidelity Transfer – Extended" and describes the further development of the original Rollei HFT coating from the 1960s, which has now been specifically extended for modern sensors. In addition to significantly lower reflection (−42%), it is specifically optimized for modern sensors and ensures cleaner colors, more stable skin tones, and fewer spectral artifacts.
Mount: The connection between camera and lens
Now we come to a significant term: Mount. The mount is the connection between the camera and the lens. And here you have to be careful, because not every lens fits every camera.
The most common mounts for mirrorless cameras are:
Sony E-Mount: For all Sony Alpha cameras
Nikon Z-Mount: For Nikon's mirrorless Z-series
Canon RF-Mount: For Canon's mirrorless EOS R-series
Fuji X-Mount: For Fuji's X-series
Before buying a lens, you must make sure that the mount matches your camera. A Sony E-Mount lens will not work on a Nikon Z-camera – the connections are different. While adapters exist, it's best to buy the right lens for your camera directly.
However, the mount is not just a mechanical connection. It also transmits important data between the lens and camera: the aperture setting, focus information, all Exif data for your image management. A good mount connection ensures that the camera and lens work together perfectly.
EXIF Data: The invisible information in your photos
Speaking of data: Have you ever heard of EXIF data? EXIF stands for "Exchangeable Image File Format" and describes all the information stored in your image files.
When you take a photo, the camera not only saves the image but also a lot of additional information: Which lens was used? Which focal length? Which aperture? Which shutter speed? Which ISO value? On which date and at what time?
This EXIF data is super helpful. When you later look through your photos on your computer, you can precisely track what settings you used to shoot. This helps you learn.
Modern lenses automatically transmit this data to the camera. You don't have to set anything; it just happens in the background. And when you later open your photos in Lightroom or another image editing program, you'll see all this information at a glance.
Filter thread: For protection and creative effects
At the front of your lens, you'll often find a designation like "Ø 62 mm" or "Ø 77 mm". This is the filter thread. But what do you need it for?
You can screw filters onto this thread. The most common are:
UV filters: Protect the front element from scratches, dirt, and fingerprints. Many photographers permanently leave a UV filter on their lens, simply for protection.
Polarizing filters: Reduce reflections (for example, on water or glass) and make the sky a richer blue. Great for landscape photography.
ND filters: Neutral Density filters darken the image, allowing you to use long exposures even in bright light. Perfect for long exposures of waterfalls or clouds.
USB-C: Firmware updates made easy
A modern development in lenses is the USB-C port. Some lenses have a small USB-C port on the side. What for?
Through this port, you can perform firmware updates for your lens. Firmware is the software that runs in the lens and controls how the autofocus works, how the lens communicates with the camera, and so on. Just like with your smartphone or computer, there are sometimes updates that bring improvements or bug fixes.
With a USB-C connection, it's super easy: You connect the lens directly to your computer, download the new firmware, copy it to the lens – done. This often only takes 30 seconds. You don't need a special dock, no additional software, nothing. Just plug in the cable, install the update, done.
Full Frame and APS-C: Sensor size makes the difference
One last important term you should know: Full frame. Some lenses are designed for full-frame cameras, others for APS-C cameras. What's the difference?
Full-frame sensors are larger (36 x 24 mm) than APS-C sensors (approx. 24 x 16 mm). A full-frame lens completely covers the larger sensor. An APS-C lens is made for the smaller sensor and does not cover the entire full-frame sensor.
In practice, this means: A full-frame lens works on both full-frame and APS-C cameras. An APS-C lens only works on APS-C cameras (or on full-frame cameras in crop mode).
The good news: The Rollei 24mm, 35mm, and 85mm lenses are full-frame lenses. This means they work on all Sony E-Mount or Nikon Z-Mount cameras, whether full-frame or APS-C. So you're flexible if you ever change cameras.
All clear? Almost!
A lot of information. But now you know what all the letters and numbers on lenses mean. You don't have to memorize all the technical details. But it helps to understand the basic terms so you know what you're buying and why certain features are important to you. A fast aperture, a modern autofocus, good optical elements – all of that makes the difference between mediocre and really good photos.
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