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Navigating the Numbers : Understanding iPhone Camera Specs

I'm tackling the sometimes confusing world of iPhone camera specs and third-party iPhone lenses.

Today, I'm tackling the sometimes confusing world of iPhone camera specs and third-party iPhone lenses. I'll write about exciting technical aspects of iPhone photography, such as focal lengths, crop factors, and lens capabilities. My post focuses on the iPhone 11 Pro, but with some Googlefoo, you can look up your pocket camera information.

Understanding Focal Lengths and Crop Factors

I'll start with the basics. The iPhone 11 Pro boasts three different cameras, each with a unique focal length. But here's where the misunderstanding begins: Apple gives these focal lengths in 35mm full-frame equivalent terms. So, when the Photos app shows information for a lens like the "Telephoto", it's not the actual physical length but how it compares to the traditional 35mm camera system. However, Apple's technical literature does not mention this. I'll wait while you visit Apple's website to read the technical specs for iPhone 15 Pro, iPhone 14 Pro, or iPhone 11 Pro. As a photographer and someone who understands physics, I assumed the focal length was quoted in full-frame terms. However, Apple's technical literature must mention this explicitly.

Screenshot from iOS Photos App
Screenshot from iOS Photos App · 15 January 2024 ·

The physical focal length of the iPhone 11 Pro's cameras are listed in the table below, along with their crop factor. I also calculated the crop factors for each iPhone 11 Pro camera based on their sensor sizes. This number is important; it helps us understand how the iPhone's sensor size affects the field of view compared to a full-frame1 camera.

Camera Lens (Physical Focal Length) Sensor Size (mm) Crop Factor 35mm Full-Frame Equivalent Focal Length
Telephoto 6mm 4.15 x 3.11 8.34 50.04mm
Wide 4.25mm 5.88 x 4.42 5.88 24.99mm
Ultra-Wide 1.54mm 3.96 x 2.97 8.74 13.46mm

This table shows the conversion of the physical focal lengths to their 35mm full-frame equivalents based on each camera's crop factor. Using the telephoto lens as an example, multiply the physical focal length of 6mm by the crop factor of 8.34 to get a 35mm full-frame equivalent of 50.04mm. In the iOS Photos app, this is shown as 52mm. The sensor sizes I found online may be wrong.

Adobe Lightroom reveals the information that Apple seems intent on hiding away. I redid the table above using the information reported in Adobe Lightroom and removed the possibly inaccurate sensor dimensions.

Camera Lens (Physical Focal Length) 35mm Full-Frame Equivalent Focal Length Crop Factor
Telephoto 6mm 52mm 8.67
Wide 4.25mm 26mm 6.12
Ultra-Wide 1.54mm 13mm 8.44
Adobe Lightroom EXIF
Adobe Lightroom EXIF

With its 136mm full-frame equivalent focal length, the ultra-wide lens is ideal for capturing wide landscapes or architectural scenes where I want to fit more into the frame. The wide lens, at 26mm, is versatile for everyday photography, including street scenes and portraits, offering a natural perspective. With a 52mm equivalent, the "short" telephoto lens helps you get closer to distant subjects for portrait photography, where I want to focus on the subject with a somewhat blurred background.

Third-party Lens Magic

Now that I have a basis for understanding the iPhone's technical specs, let's talk about a third-party "lens" like the Moment 58mm Tele Mobile Lens. I have read positive reviews about Moment mobile lenses and was touched by a bit of G.A.S.2, I dropped in on their website to look around. Moment, unfortunately, assumes I know that this 58mm focal length is achieved with the iPhone's "default" 4.25mm camera (26mm FF FOV). That confusion is, in fact, what prompted me to write this blog post. In my opinion, the "58mm" name is a distraction and a misnomer.

Moment 58mm Tele Mobile Lens
Moment 58mm Tele Mobile Lens

An optical multiplier is a lens attachment that increases the effective focal length of a camera lens, allowing for closer magnification of distant subjects without compromising image quality. According to the information on the Moment website, the Moment 58mm Tele Mobile Lens is a "~2X" optical multiplier. So, when used on the native 4.25mm, 6mm and 1.54mm lenses on the iPhone, we get different focal lengths and fields of view.

Here's how it breaks down:

Camera Physical Focal Length With Moment 2X Multiplier 35mm FF FOV
Telephoto 6mm 12mm 104mm
Wide 4.25mm 8.50mm 52mm
Ultra-Wide 1.54mm 3.08mm 26mm

I found a link on Reddit that explains the expected focal lengths. I also received an email from Moment explaining that the multiplier is 1.75. With that revised information and assuming it's correct, here's what I think I know about using a Moment lens with an iPhone 11 Pro. So "~2X" means "1.75x". That’s technically correct.

Camera Physical Focal Length With Moment 1.75X Multiplier 35mm FF FOV
Telephoto 6mm 10.5mm 91mm
Wide 4.25mm 7.44mm 45.5mm
Ultra-Wide 1.54mm 2.7mm 22.75mm

Why This Matters

Understanding these specifications is important for photographers like myself who want to make the most of their pocket cameras. Knowing the crop factors and how the Moment lens alters the field of view, I can make informed decisions about my photography purchases.

Now that I understand that the Moment lenses are just optical multipliers, I can see how they open up new possibilities. They enhance the iPhone's capabilities, offering versatility for casual snapshots or skilled compositions.

I think the 45.5mmm FF equivalent focal length is nearly perfect for street and general photography. The 91mm FF equivalent focal length is an excellent focal length for portraits.

Final Thoughts

Photography is an art and a science. We blend technical knowledge with creative vision. Whether you're a professional photographer or a hobbyist, understanding your tools can transform how you capture the world around you.

  1. Apple. (n.d.). iPhone 11 Pro - Technical Specifications. Retrieved from https://support.apple.com/kb/SP805?locale=en_US
  2. Reddit user drunk_caterpillar. (2019, September 28). Gate dimensions of individual iPhone 11 Pro sensors with comparisons to traditional film formats. Retrieved from https://www.reddit.com/r/cinematography/comments/dadfas/gate_dimensions_of_individual_iphone_11_pro/
  1. Full-frame refers to a digital camera sensor size that matches the 36mm x 24mm dimensions of traditional 35mm film, frequently used as a standard for comparing different camera sensor sizes ?
  2. G.A.S., or Gear Acquisition Syndrome, refers to the urge to continuously acquire new equipment or gear, often driven by the belief that it will improve one's skills or results, typically seen in hobbies like photography or music. ?

iPhone Photography: A Workflow Guide

My workflow guide details how I use Halide Mark II for RAW captures, Adobe Lightroom Classic for advanced editing, and Luminar Neo for creative touches, enhancing my iPhone 11 Pro photography.

As an avid photographer, I'm constantly exploring ways to enhance my craft, especially when using a device as accessible and powerful as the iPhone. In this post, I'll share my refined workflow for post-processing iPhone photographs, leveraging the capabilities of apps like Halide, Adobe Lightroom Classic, and Luminar Neo. I think my approach combines the ease of mobile photography with more involved editing techniques.

Halide has recently become my favourite app for capturing images with my iPhone 11 Pro. The current version, Halide Mark II, offers advanced RAW shooting capabilities, allowing me to capture more detail and dynamic range. Halide provides manual exposure, ISO, focus, and white balance controls, enabling greater post-processing flexibility and higher-quality images than standard HEIC or JPEGs.

Kingston Mill Historic District
Kingston Grist Mill, Kingston Mill Historic District · January 6, 2020 · Apple iPhone 11 Pro · iPhone 11 Pro 6mm f/2

Luminar Neo offers AI-driven editing tools, customisable presets, and layer-based adjustments, catering to beginners and professionals for creative and efficient photograph enhancements.

I have used Adobe Lightroom in all its iterations since about 2003. I currently use Adobe Lightroom Classic via the Adobe Creative Cloud Photography subscription. I get access to both Lightroom Classic and Photoshop. Adobe Lightroom Classic is a comprehensive photo editing and cataloguing software. It offers advanced editing tools, colour grading, batch processing, and RAW file support. Key features include non-destructive editing, lens and camera-based corrections, detailed organisation, and robust preset capabilities, catering to professional photographers and photography enthusiasts.

Avalon Beach, Seven Mile Island
Avalon Beach, Seven Mile Island · August 23, 2023 · Apple iPhone 11 Pro · iPhone 11 Pro 6mm f/2

1. Capturing the Perfect Shot with Halide Mark II

Shoot in RAW1 Format: The Halide Mark II app for iPhone offers robust RAW photography features. RAW images preserve more details, particularly in highlights and shadows, generally display more colour detail, and are sharper than JPEGs. However, can they be grainier in low light or night settings? The first step in my workflow is using Halide Mark II to capture RAW images. In the settings, I can choose between RAW+HEIC, RAW, and HEIC options. HEIC captures a processed file, while RAW+ HEIC captures both a HEIC and a RAW image. I have Halide Mark II set to capture RAW images. Halide Mark II uses the DNG format for RAW. This format retains all the data from the sensor, providing a wide range of possibilities during editing. RAW image capture is also the fastest capture mode in Halide Mark II.

Sourland Mountain Spirits
March 21, 2021 · Apple iPhone 11 Pro · iPhone 11 Pro 6mm f/2

Lens Selection: Depending on the scene, I switch between the 6mm f/2 lens for a tighter frame (great for portraits) and the 4.25mm f/1.8 for wider angles, capturing landscapes or urban settings. The 6mm lens, with its tighter field of view, is perfect for portraits and detailed shots, offering a more focused perspective. The 4.25mm lens, on the other hand, captures more expansive scenes, making it ideal for landscapes and architectural photography. Both lenses provide superb image quality, but I prefer the 6mm f/2 for landscape and cityscape photographs.

Aperture: ƒ/1.8
Exposure Range: 1⁄71000 - 1s
Native ISO Range: 32 - 3072
Focal Length: 4.25mm (26mm FF FOV)
Image Size: 4032 x 3024
Autofocus Systems: Contrast, Phase
Flash: Yes

Aperture: ƒ/2.0
Exposure Range: 1⁄45000 - 1s
Native ISO Range: 21 - 2016
Focal Length: 6mm (51mm FF FOV)
Image Size: 4032 x 3024
Autofocus Systems: Contrast, None, Phase
Flash: Yes

In the Photos app, Apple labels the lenses by their full frame equivalent focal length: Ultra Wide Camera — 13mm ƒ/2.4; Wide Camera — 26mm ƒ/1.8; Telephoto Camera — 52mm ƒ/2. In Adobe Lightroom, Adobe labels the lenses by their native focal length: iPhone 11 Pro back camera 1.54mm f/2.4, iPhone 11 Pro back camera 4.25mm f/1.8, iPhone 11 Pro back camera 6mm f/2.

Apple labels the iPhone 11 Pro lenses by their full-frame equivalent focal length to give users a more familiar reference point, as full-frame measurements are commonly understood in photography. This helps in comparing the field of view with 35mm DSLR cameras. On the other hand, Adobe labels them by their native focal length, which is more technically accurate for the sensor size of the iPhone. This approach precisely measures the lens itself, disregarding sensor size or full-frame equivalency, which aligns more with technical standards in digital imaging.

Low ISO for Reduced Noise: In automatic mode, the Halide Mark II app automatically chooses the optimal combination of ISO and shutter speed. However, there are some tricky situations where you may override those settings. I strive to keep the ISO as low as possible, reducing grain and preserving image quality. The high end of the range is too noisy to produce usable images, even with noise reduction in Adobe Lightroom. Higher ISO settings are reserved for low-light situations where it's unavoidable. I set Halide Mark II to manual mode to adjust the ISO manually.

Wind blowing the leaves, Blue Spring Road
Wind blowing the leaves, Blue Spring Road · Thursday 15 October 2020 · Apple iPhone 11 Pro at 4.0 sec, · iPhone 11 Pro 6mm f/2

Manual Mode for Precision: Manual mode has become my go-to in challenging lighting or when I want more creative control over the shot. In Halide Mark II, I use the manual mode to gain control over ISO and shutter speed. To set the ISO, I swipe left or right on the ISO button to adjust the iPhone's sensitivity to light. For the shutter speed, I swipe on the shutter speed button to determine how long the detector is exposed to sunlight. This control is crucial, especially in challenging lighting conditions, as it lets me balance the ISO and shutter speed to achieve the desired exposure, whether capturing fast-moving subjects or shooting in low light, ensuring the best possible image quality.

Squash Soup
Squash Soup · February 15, 2020 · Apple iPhone 11 Pro · iPhone 11 Pro 6mm f/2

2. Initial Edits in Adobe Lightroom

Choosing the Right Adobe Profile: Depending on my subject, I select an Adobe profile—Landscape, Neutral, or Portrait—to start the editing process on the right note. Adobe Lightroom profiles apply foundational colour and tone adjustments, offering a starting point for further editing and styling.

Balanced White Balance: Adobe Lightroom's Auto white balance corrects image colours based on lighting conditions for a natural and balanced colour tone. I initially set the white balance to Auto. Then, I make fine adjustments to ensure the colours in my photo are as true to my vision as possible.

April 22, 2020 · Apple iPhone 11 Pro · iPhone 11 Pro 6mm f/2

Auto Adjustments as a Baseline: Adobe Lightroom's "Auto" tone automatically adjusts exposure, contrast, and other settings for an optimal balance in the image. The Auto setting provides a quick start to adjusting exposure, contrast, and other basics. I then tweak the shadows and highlights to suit my imagination.

Source Brewing
Source Brewing · December 16, 2020 · Apple iPhone 11 Pro · iPhone 11 Pro 4.25mm f/1.8

Enhance with Noise Reduction: Adobe Lightroom's Denoise AI reduces noise while preserving details, particularly useful in low-light conditions. I use the Raw Details feature if my image is exposed at low ISO. The Raw Details feature enhances the sharpness and clarity of RAW images, allowing for finer control over texture and edge definition, thus significantly improving image quality without adding unwanted artefacts.

July 4, 2021 · Apple iPhone 11 Pro · iPhone 11 Pro 6mm f/2

Lens Corrections: Adobe Lightroom offers Lens Corrections profiles for the iPhone 11 Pro, automatically compensating for common optical issues like distortion, chromatic aberration, and vignetting. When I import photos taken with the iPhone 11 Pro, Lightroom detects the specific lens used – wide, ultra-wide, or telephoto – and applies tailored corrections based on the lens's characteristics. This feature ensures that images look more natural and appropriate to what the eye sees, improving general image quality. It's useful for architectural and landscape photography, where straight lines and accurate colour rendition are essential.

September 1, 2022 · Apple iPhone 11 Pro · iPhone 11 Pro 6mm f/2

3. Elevating the Image with Luminar Neo

Applying a Personal Touch: Once I complete all the basic edits, I import the image with the Raw Details enhancements into Luminar Neo. In Luminar Neo, I apply the long exposure preset from the "Easy Landscape Collection". This step is where creativity comes into play, using advanced tools to give the photo a unique character. I usually set the slider to 43% with this preset as a starting point for further changes via the "Edit" menu.

November 20, 2023 · Apple iPhone 11 Pro · iPhone 11 Pro 6mm f/2

4. The Finishing Touches

Cropping for Composition: The final step often involves cropping the image to enhance its composition, focusing on the subject, or ensuring it adheres to the rule of thirds.

5. Optional Advanced Steps

I sometimes engage in local adjustments. The key is to enhance the image without overdoing it.

Conclusion

This workflow has consistently provided me with high-quality results, balancing iPhone photography's quick and intuitive nature with the depth and precision of experienced post-processing. Whether you're a seasoned photographer or just starting, I hope this guide inspires you to explore the potential of your iPhone camera and bring your creative visions to life.

  1. On iPhone 12 Pro and later Pro models with iOS 14.3 or later, you can take photos in Apple ProRAW. Halide Mark II provides this functionality for previous models. ↩

Ed25519 Keys for SSH

A technical article detailing how I switched my SSH login on a remote Linux server to use Ed25519 keys.

I changed my SSH login to my remote Linux server to use Ed25519 keys. This is one of the few technical articles I wrote this year. Writing these articles helps me better understand the technologies I use.

Ed25519 is a widely used public-key signature algorithm based on elliptic curve cryptography (ECC). It was designed by Daniel J. Bernstein, Niels Duif, Tanja Lange, Peter Schwabe, and Bo-Yin Yang. The "ed" in its name stands for the Edwards curve, which is the elliptic curve used in the algorithm.

Ed25519 is designed to provide high security while maintaining excellent performance. It offers 128-bit security, which means it is resistant to known cryptographic attacks. The algorithm is specifically optimised for speed, making it efficient for various applications.

Ed25519 is based on the twisted Edwards curve called Curve25519, which Daniel J. Bernstein also developed. The choice of this curve offers several advantages, including resistance against certain types of side-channel attacks and efficient implementation across different platforms.

Ed25519 uses elliptic curve key pairs for signing and verification. Key generation involves selecting a random 256-bit secret scalar, which is used to compute the corresponding public key. The secret scalar should be generated using a cryptographically secure random number generator.

To create a signature using Ed25519, the signer uses their secret scalar and the message they want to sign. The algorithm applies a series of mathematical operations to produce a 64-byte signature. This signature can be verified using the corresponding public key.

Signature verification involves using the signer's public key, the received message, and the signature. The verification process applies a set of mathematical operations to confirm the authenticity and integrity of the message. If the verification is successful, the signature is valid, and the message hasn't been tampered with.

Ed25519 has gained significant adoption in various domains, including cryptography libraries, protocols, and applications. It is commonly used for secure communications, digital signatures, key exchange, and other cryptographic operations. Many popular libraries and frameworks, such as OpenSSL, libsodium, and GnuPG, support Ed25519.

Ed25519 offers advantages over older signature algorithms like RSA and DSA. It has shorter key lengths, making it more efficient in terms of computation and storage. Additionally, Ed25519 is resistant to many types of attacks, including those based on side-channel information leakage.

Ed25519 has been widely recognised as a reliable and secure signature algorithm and has found extensive use in various cryptographic applications due to its performance and security characteristics.

To generate an Ed25519 key pair on macOS for logging into my Linux server, I followed these steps:

  1. Open the Terminal application on macOS.
  2. The ssh-keygen command generates the Ed25519 key pair. In the Terminal, type the following command:ssh-keygen -t ed25519 -f linux_server_key
  3. This command generates a new Ed25519 key pair with the specified filename (linux_server_key in this example).
  4. You will be prompted to provide a passphrase for the key pair. I recommend entering a strong passphrase to protect your private key. Press Enter if you want to leave it empty (not recommended).
  5. Two files will be generated in the current directory: linux_server_key (private key) and linux_server_key.pub (public key).
  6. Copy the public key to your Linux server. I used the ssh-copy-id command to copy the public key to the server. In the Terminal, type the following command:ssh-copy-id -i linux_server_key.pub username@server_ip
  7. Replace username with your username on the Linux server and server_ip with the IP address or hostname of the Linux server. This command will copy the public key to the appropriate location on the server and enable key-based authentication.
  8. If the ssh-copy-id command is not available on your macOS, you can manually copy the contents of the linux_server_key.pub file and append it to the ~/.ssh/authorized_keys file on the Linux server.
  9. Once the public key is copied, you can use SSH to log in to the Linux server using your private key. In the Terminal, type the following command: ssh -i linux_server_key username@server_ip
  10. Replace username with your username on the Linux server and server_ip with the IP address or hostname of the Linux server. This command will use the specified private key for authentication when connecting to the server.
  11. If you set a passphrase for the private key, you will be prompted to enter it before establishing the SSH connection.

That's it! You have now generated an Ed25519 key pair on macOS and configured it to log into a Linux server using SSH.