The Sigma SD15 vs. Sigma fp: A Hands-On Comparison From Sensor to Street

When Sigma launched the SD15 back in 2010, it was a niche marvel, heralding the unique Foveon X3 sensor technology into the APS-C DSLR market. Fast-forward nearly a decade, and the Sigma fp, announced in 2019, represents a radical reinvention - an ultra-compact, full-frame mirrorless camera packed with modern features yet stripped of a traditional viewfinder.

I've spent extensive hands-on time testing both cameras across multiple shooting disciplines, diving deep into their sensor technology, autofocus abilities, ergonomics, and workflow potential to give you an informed, practical comparison. Whether you're a dedicated Sigma enthusiast weighing a step up, or a photographer curious about Foveon's distinct image signature vs. a full-frame sensor, this guide aims to answer the tough questions.

Let’s unlock what these two very different Sigmas offer and where each excels.

Form Factor and Ergonomics: Big DSLR vs. Pocket-Friendly Powerhouse

Starting with the physical experience of handling these cameras, the SD15 is a classic mid-size DSLR, while the fp is a minimalistic rangefinder-style mirrorless. My first impression after hours balancing them in hand was how dramatically different their design philosophies are.

The SD15 measures a substantial 144x107x81mm and weighs 750g. In contrast, the fp shrinks this down to a svelte 113x70x45mm and 422g - nearly half the weight and considerably more pocketable.

The SD15 sports a traditional DSLR grip with ample buttons and a pentaprism optical viewfinder, lending confidence during prolonged handheld sessions. Its heft adds stability, especially when paired with larger SA-mount lenses. By comparison, the fp’s minimalist body - lacking a built-in viewfinder entirely - feels more like a photographer’s tool kit: stripped, lightweight, and ultra-versatile.

The control layout also reflects their eras and target users:

The SD15 features mechanically driven dials and buttons for shutter speed, ISO, exposure compensation, and mode selection - hardwired for quick tactile adjustments. The fp opts for a spartan, almost buttonless approach, relying on a high-resolution touchscreen and fewer physical controls. This drastically changes the shooting experience; some photographers love the fp’s clean slate for customization, whereas others might find it unintuitive without a dedicated viewfinder to maintain composure.

In real-world use, I find the SD15’s ergonomics better suited for traditional DSLR style shooting and longer sessions, while the fp is a versatile companion for travel, street, and hybrid photo/video shooters seeking compactness.

Sensor Technology and Image Quality: Foveon X3 vs. Full-Frame BSI CMOS

Arguably the heart of any camera is its sensor, and this is where these two Sigmas diverge radically.

The SD15 incorporates Sigma’s hallmark Foveon X3 APS-C sensor, measuring 20.7mm x 13.8mm with a peculiar triple-layer design capturing full RGB color information at every pixel location. This results in an effective resolution of about 5MP with unique color fidelity and detail rendition unmatched in typical Bayer sensors of that era.

By contrast, the Sigma fp’s sensor is a modern 35.9mm x 23.9mm full-frame BSI-CMOS sensor producing 25MP images, built on more conventional yet highly optimized technology with backside illumination for improved low light and dynamic range.

What does this mean in practice?
For static subjects and highly controlled lighting - think fine art or studio work - the SD15's Foveon sensor delivers astounding color depth (albeit at lower pixel counts) and microdetail. I’ve hand-tested prints where its images rival larger megapixel Bayer cameras in perceived sharpness, particularly in midtones and skin tone rendition. Yet, there's a tradeoff: its maximum ISO 1600 (3200 boosted) limits performance in low light, and the slower readout hampers burst shooting and video (none supported).

The Sigma fp’s full-frame sensor, meanwhile, offers high resolution, excellent ISO range up to 25600 (102400 boosted), and notably better dynamic range, all of which make it a much better all-rounder for challenging lighting and action. It produces images with classic full-frame "look" and better noise handling - essential for weddings, events, and landscape shooters shooting in variable conditions.

This contrast follows from their sensor sizes, pixel counts, and technology - two different design philosophies: unique color signature versus versatile high-res imaging.

Sharpness, Color, and Dynamic Range in Real-World Use

To put their image quality in context, I captured comparable scenes ranging from portrait close-ups to ultra-wide landscapes.

Some sample images from both cameras show clear distinctions:

Sigma SD15 front Sigma SD15 screen back Sigma fp front Sigma fp screen back

• Portraits: The SD15’s rendition of skin tones is rich and painterly, thanks largely to the Foveon sensor’s layered color capture. Bokeh from Sigma SA lenses maintains a soft, creamy quality but is limited by fewer native lenses and lack of autofocus speed. The fp, with its superior autofocus and full-frame sensor, better detects and locks onto eyes, yielding sharper, more reliable results in dynamic portrait sessions.

• Landscapes: The SD15's color depth shines here with nuanced tonality and fine texture, but resolution (2640x1760 max) limits large print sizes or detailed cropping. The fp's 25MP sensor delivers high resolution files (6000x4000) that handle aggressive crops and display far better shadow recovery.

• Dynamic Range: The fp's full-frame sensor is the clear winner, handling bright highlights and deep shadows with grace. My bracketed HDR testing confirms the fp extracts far more usable detail with less color banding, an advantage critical in high-contrast outdoor shooting.

In summary, the SD15 excels in color fidelity and sharpness per pixel in ideal conditions but is constrained by sensor resolution and high-ISO noise. The Sigma fp is a more flexible imaging tool, adept across wider ISO ranges, dynamic lighting, and demanding genres.

Autofocus and Speed: From Modest DSLRs to Agile Mirrorless

When I first picked up the SD15, I was struck by its contrast-detection autofocus system with phase assist, limited AF points, and modest continuous shooting rate of just 3fps. It’s a system designed for deliberate, composed shooting rather than fast action.

In contrast, the Sigma fp offers 49 AF points with contrast-based AF and eye detection, continuous autofocus, and an impressive 12fps burst speed. These features open up vastly broader creative possibilities - from capturing fleeting expressions to sports and wildlife.

However, it’s important to acknowledge that the fp lacks on-sensor phase detection which can result in less reliable tracking in some situations compared to today’s hybrid AF systems - but compared to the SD15, its autofocus is leagues ahead.

Despite those differences:

• Sports and wildlife photographers will find the fp’s autofocus and burst rate far more practical. The SD15 simply can’t keep pace with fast-moving subjects.
• Street and documentary shooters benefit from the fp’s silent shutter and swift responses. The SD15 is bulky and noisy in comparison.

The Viewing Experience: Optical vs. Screen-Only

A crucial consideration for real-world shooting is the viewfinder and LCD experience.

The SD15 provides a traditional pentaprism optical viewfinder with 96% coverage and 0.6x magnification, giving a clear, detailed view with minimal lag or delay. Though not offering 100% framing, it’s accurate enough for professional framing needs. The downside: the rear 3" fixed LCD has relatively low resolution (460k dots), making image review imperfect, especially under bright daylight.

The Sigma fp chooses not to include any form of viewfinder, relying solely on a 3.15" fixed touchscreen with 2100k dots. This means composing entirely on the LCD - a divisive choice. In my experience, it’s excellent for intimate, handheld shooting, live view autofocus, and video framing, but challenging under harsh sunlight or fast action where an EVF’s advantages are apparent.

If your workflow demands rapid, precise framing and viewing in bright conditions, the SD15’s optical viewfinder leads. If you prefer a modern, touchscreen-driven interface with focus peaking and digital magnification, the fp’s screen is a robust tool.

Lens Selection and Ecosystem: SA Mount Legacy vs. Leica L Mount

Lens choice defines much of what a camera can do, and Sigma’s strategy differs sharply between these two.

The SD15 uses the Sigma SA mount, a relatively niche ecosystem with about 76 lenses available, mostly prime and zoom lenses catering to traditional photography styles. These lenses deliver excellent image quality, many boasting classic optical designs, but the system lacks the variety and advanced AF lens selections found in dominant DSLR brands.

By contrast, the fp employs the more universal Leica L mount. This opens Sigma owners to a growing number of lenses from Panasonic, Leica, Sigma’s own Art series adapted for L mount, and third-party manufacturers. Currently, about 30 native L-mount lenses exist, but given the alliance with Leica and Panasonic, the fp gains access to dozens of high-performance lenses across focal lengths and apertures.

For photographers thinking long term, this translates to:

• SD15 owners benefit from a specialized, exclusive lens lineup with competitive primes but face limited AF and few weatherproof options.
• fp users enjoy a growing, diverse, and modern lens ecosystem supporting fast AF, stabilization, and weather sealing.

You should consider your current and future lens investments carefully when choosing between these cameras.

Battery Life and Storage: Endurance in the Field

Neither camera breaks records for battery life - typical of Sigma’s niche designs - but their differences mirror their body types.

The SD15 uses a proprietary battery with a modest life, generally sufficient for casual shooting but requiring spares in longer sessions. Storage relies on a single SD/SDHC card slot with no UHS-II support, limiting write speeds - an important consideration when processing large Foveon RAW files.

The fp employs the BP-51 battery and supports SD/SDHC/SDXC cards with UHS-II speed standards. While compact and efficient, the fp’s battery life is average for a mirrorless sensor with electronic VT displays, and power management is a known minor drawback for video shooters.

For extended travel or event work, both cameras benefit greatly from extra batteries and fast, large-capacity UHS-II cards for the fp.

Weather Resistance and Build Quality: Reliability Across Conditions

If your work involves rough outdoor conditions, weather sealing becomes critical.

The SD15 offers no environmental sealing. It’s a robust build but requires care to avoid dust and moisture ingress.

Interestingly, the fp includes environmental sealing, a substantial plus given its small form factor. Sigma’s engineering manages a weather-resistant chassis protecting against dust and light moisture - useful for outdoor portraits, landscapes, or event coverage.

This makes the fp better suited to the unpredictable realities of professional outdoor photography.

Video Capabilities: Sigma’s Leap Forward with the fp

A significant limitation of the SD15 is its lack of video recording capabilities whatsoever - a product of its 2010 DSLR mindset where stills were paramount.

The Sigma fp, in contrast, offers 4K UHD video at 30fps with the ability to record in MOV (H.264) using Linear PCM audio. It features a microphone and headphone jack for monitoring and audio input - critical for professional video workflows. The fp also supports time-lapse recording and has ISO sensitivity suited for low-light video production.

While it is not a dedicated video camera and lacks in-body stabilization, its compact cinema-friendly design has attracted filmmakers who pair it with gimbals and external recorders for profound versatility. Its ability to shoot raw video externally (with firmware or software upgrades) makes it a sort of “baby Cinema EOS” system in a tiny body.

For hybrid shooters wanting quality video and photos, the fp stands well ahead.

Practical Use Cases: Matching Cameras to Photographers

Drawing from hours testing and user feedback, here’s how the SD15 and fp stack up across popular photography genres.

Portrait Photography

• SD15: Excellent natural skin tone rendition, rich color depth from Foveon sensor. However, slow AF and limited native lenses reduce efficiency in fast-paced portrait sessions.
• fp: Superior autofocus with eye detection, better noise handling in low light, greater lens flexibility. Recommended for photographers needing speed and versatility.

Landscape Photography

• SD15: Unique color fidelity and detailed mid-tones shine. Limited resolution restricts print sizes beyond moderate formats.
• fp: High-res files and broader latitude for shadows and highlights, plus weather sealing, make it a more practical landscape tool.

Wildlife and Sports Photography

• SD15: Not designed for action; 3fps burst and slow AF limit use.
• fp: 12fps burst with faster AF supports action photography, though tracking isn’t best-in-class. Full-frame sensor errs favorably on image quality.

Street Photography

• SD15: Bulky and loud; less discreet.
• fp: Compact, quiet shutter, touchscreen focus - ideal for street shooters valuing portability and speed.

Macro Photography

• Neither camera has specialized macro modes or focus stacking (both no focus bracketing or stacking). Lens choice is crucial here: SD15’s larger lens selection may help, but fp’s modern sensor and better live view support give a practical edge.

Night and Astrophotography

• SD15’s lower native ISO caps usability.
• fp’s extended ISO range and better dynamic range provide substantial gains - critical for starscape clarity and reducing long exposure noise.

Video

• SD15: No video function.
• fp: 4K 30p with mic/headphone jacks, time-lapse. Solid for indie and pro filmmakers.

Travel Photography

• SD15: Heavier and bulkier.
• fp: Lightweight, small, versatile sensor and lens grouping, longer battery life per gram, preferred for wanderers.

Professional Use

• SD15: Limited by slower throughput, niche lens mount, outputs RAW, but less flexible.
• fp: Delivers Pro RAW & Adobe workflow compatibility, weather sealing, 4K, and audio ports - better for multi-disciplinary pros.

Connectivity and Workflow Integration

Neither camera features Wi-Fi, Bluetooth, or NFC connectivity, but the fp edges ahead with a USB port supporting faster transfers and modern card support (UHS-II).

The SD15’s USB 2.0 interface and older storage format slow file transfers considerably.

The fp’s RAW files integrate cleanly into Adobe Lightroom and Capture One workflows, whereas the SD15’s Foveon RAW can require specialized or slower converters. Those working in high-volume conditions likely prefer the fp’s streamlined pipeline.

Pricing and Value: What Does Your Investment Buy?

At launch and still today, the SD15 hovers around $1500, while the Sigma fp ranges closer to $2050.

Given the substantial difference in sensor size, features, and modern capabilities, the fp represents a higher-tier investment. But objectively, its video features, autofocus, and compactness provide much greater usability for a broader range of users.

If you prize color depth over speed and flexibility, and enjoy a DSLR-style experience, the SD15 remains compelling - especially at its current used market prices.

Final Thoughts: Which Sigma Fits Your Style?

The Sigma SD15 is a fascinating camera - a niche, almost artisanal tool for those who want exceptional color fidelity and unique image qualities from Foveon X3 technology in a DSLR form factor. It’s excellent for deliberate, studio, or landscape photographers who don’t require speed or video and enjoy the tactile DSLR experience.

The Sigma fp, meanwhile, is a bold leap into the future. It’s an ultra-compact, full-frame mirrorless powerhouse aimed at hybrid shooters, street photographers, travelers, and video creators who demand the latest tech paired with a small form factor. Its limitations - like no built-in viewfinder and moderate AF tracking - are offset by remarkable image quality, 4K video, and professional features.

My recommendation?

• Choose the SD15 if your priority is ultimate color depth with a classic DSLR feel and you shoot mostly stills in controlled conditions.
• Opt for the fp if you want a versatile, portable camera for mixed photography and video use, with a rich lens ecosystem and excellent high-ISO performance.

Both are remarkable cameras, but your workflow, shooting style, and future ambitions will dictate the best fit.

In the end, intimate hands-on experience reveals that while Sigma’s SD15 and fp share brand heritage, they serve divergent photographers and purposes. I encourage you to consider where you shoot, how you shoot, and what you value most before investing.

If you have further questions or want tailored suggestions based on your shooting scenarios, feel free to reach out.

Happy shooting!