# What Is an ORF File? Olympus RAW Format, Explained

> An ORF file is Olympus RAW Format, unchanged from E-System DSLRs to the OM-1. What's inside one, which cameras write it, and free ways to open it on a Mac.

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Published July 24, 2026 · Daniel Tello · RevelRaw

An ORF file is **Olympus RAW Format** — the RAW file written by Olympus and OM System cameras, from the OM-D E-M line and PEN bodies to the OM-1, OM-3 and OM-5, and even the Tough compacts that shoot RAW. It is not a finished picture. It holds the reading from every photosite on the sensor at the instant of exposure, plus the camera's metadata and embedded JPEG previews, in a single `.ORF` file. That makes it your digital negative: the whole photograph, before any decisions about how it should look were locked in.

The company behind it changed names — Olympus became OM System in 2021 — but the format carried on unchanged. A file from an old E-M5 and a file from an OM-1 are both `.ORF`, and your editor treats them exactly the same way. Here's what's inside one, and how to work with it on a Mac.

## ORF at a glance

|  |  |
| --- | --- |
| Full name | Olympus RAW Format |
| Extension | `.ORF` |
| Written by | Olympus and OM System bodies — the OM-D E-M line, PEN line, OM-1/OM-3/OM-5, and Tough compacts with RAW |
| What it holds | Unprocessed sensor data (typically 12-bit), EXIF metadata, your Picture Mode setting, embedded JPEG previews |
| Typical size | Roughly 15–25 MB from the ~20 MP Micro Four Thirds sensors; High Res Shot ORFs run far larger |
| High Res Shot | Composites multiple frames into a single 50–80 MP ORF |
| Opens with | macOS Preview and Photos, and RAW editors such as RevelRaw, Lightroom or Capture One |

## Which cameras write ORF files

Four eras of cameras, one extension. Olympus started writing ORF in the early 2000s, on the E-10 and E-20 and its RAW-capable Camedia compacts, and never switched:

- **E-System DSLRs (2003–2010).** The Four Thirds era, from the original E-1 through the pro E-3 and E-5 down to the compact E-4xx and E-6xx models.
- **PEN (2009 on).** The E-P1 opened Olympus's Micro Four Thirds chapter, and every RAW-shooting PEN since — E-P, E-PL, E-PM, up to the current E-P7 — writes ORF.
- **OM-D (2012 on).** The E-M5 started the family; the E-M1, E-M5 and E-M10 generations carried it through the 2010s. The Tough compacts joined in 2015, when the TG-4 became the first of the waterproof line to shoot RAW.
- **OM System (2022 on).** The OM-1 and OM-1 Mark II, the OM-5 and OM-5 Mark II, and the OM-3 all keep the format under the new name.

That last handover is the one photographers actually search for. Olympus sold its camera business in 2020, the brand became OM System in 2021, and the file format did not change with it. There is no separate "OM RAW": an OM-1 writes the same `.ORF` structure an E-M5 wrote a decade earlier, so archives from both brands sort together and any editor on our [Olympus and OM System page](https://revelraw.com/om-system.md) reads the lot. The one per-camera wrinkle is decoder support — software still has to learn each new body's files individually, which is why a months-old OM System camera can sit unreadable in Photos while files from a format more than twenty years old open everywhere else.

## What's actually inside an ORF file

A camera sensor doesn't record a picture. Each photosite records how much light hit it through a single-color filter — red, green or blue — arranged in a mosaic. An ORF file stores those readings as they came off the sensor:

- **The mosaic sensor data.** One brightness value per photosite, typically at 12-bit precision. No white balance, no sharpening, no Picture Mode has been applied yet — turning the mosaic into a viewable photograph is the job of your RAW editor.
- **Metadata.** Camera body, lens, exposure settings, and the Picture Mode you had dialed in. Editors read this to know how to interpret the data; nothing in it is baked into the pixels.
- **Embedded JPEG previews.** The camera develops previews with its own processing and tucks them inside the ORF. That's what you see on the camera's screen and in Finder thumbnails — which is why a RAW file can look one way as a thumbnail and another once an editor opens the real data.

## Art Filters and Picture Modes ride along as metadata

Olympus put Art Filters on the E-30 in 2008 and they have been a signature of the system ever since — Dramatic Tone, Grainy Film and Pin Hole sit in the same menu as the everyday Picture Modes such as Vivid, Natural and Monochrome. Shoot JPEG and the camera cooks the chosen look into the pixels for good. Shoot RAW and that same choice is only written into the ORF's metadata; the sensor data underneath stays exactly as the light arrived.

The camera does apply the filter to the JPEG previews it embeds in the file, and that sets up a small ambush. A Grainy Film frame looks the part on the camera's screen and in Finder, then opens as a straight color photograph in Lightroom, Capture One or RevelRaw, because the editor has swapped the stylized preview for its own render of the untouched sensor data. Only OM Workspace, the free app from the camera's maker, reads the tag and reproduces the camera's rendering — and it is also the only place you can move a shot from one Art Filter to another after the fact.

For everyone else this is good news about the file: the ORF stays a clean negative. A Monochrome Picture Mode has not discarded the color, and a Dramatic Tone experiment has not cost you the ordinary version of the frame — the look is a note on the file, and a third-party editor simply starts without it. When an Art Filter *is* the picture, shoot RAW+JPEG so the camera's render survives next to the negative.

## Small files, big negatives

One of ORF's quiet virtues is size. Micro Four Thirds sensors sit around 20 MP, so a typical ORF lands at roughly 15–25 MB — a fraction of what many full-frame RAW files weigh. Cards last longer, imports finish sooner, and a decade of shooting fits on a drive that doesn't make you wince. You give up nothing that matters for editing: the file is still the complete negative. The honest flip side of the small sensor is that it gathers less light per exposure, so high-ISO ORFs lean harder on your editor's denoising than full-frame files do — worth weighing when you choose one.

Then there's the exception. High Res Shot modes composite multiple frames into one much larger image, and the resulting ORFs land in the 50–80 MP range — files several times the usual size, with detail to match. Same extension, same workflow; your editor simply gets a lot more to work with. On recent bodies each composite also arrives with a companion file ending in `.ORI`, a plain single frame from the same sequence that most software ignores; what it's for, and how to open it, is covered in [our ORF opening guide](https://revelraw.com/blog/how-to-open-orf-files-on-mac.md).

## How to open ORF files on a Mac

macOS ships with RAW support for most Olympus and OM System bodies, so the basics are already on your Mac: Preview opens ORF files with a double-click, and Photos imports them. Two caveats. First, files from a just-released camera can fail to open until Apple ships a RAW update for that body — the file isn't broken; your software just hasn't met that camera yet. Second, Preview only shows you a develop of the RAW; it isn't an editor. For the full rundown — which bodies macOS covers, where OM Workspace fits, and what to do while a new camera waits for support — see [how to open ORF files on a Mac](https://revelraw.com/blog/how-to-open-orf-files-on-mac.md).

To actually develop the file — choose your own white balance, recover highlights, work the color — you need a RAW editor. [RevelRaw](https://revelraw.com/index.md) is built around Sony Alpha, but it opens Olympus and OM System ORF files all the same — drag one in or pick it from File > Open, and AI scene detection ranks 40+ presets against your photo, with the standard fine-tune controls on top. Everything runs on your Mac; no file ever leaves it. The big subscriptions — Lightroom, Capture One — read ORF as well.

## How to convert ORF to JPEG

For a quick conversion with no editing, Preview can do it: open the ORF, then File > Export, choose JPEG, and set the quality. For a conversion that's actually developed — your exposure, your color — open the file in a RAW editor and export. RevelRaw exports JPEG, PNG, TIFF and HEIF, with platform presets for Instagram, print and web. Either way, keep the ORF afterwards: it's the negative, and every JPEG is just one interpretation of it. Our guide to [converting RAW to JPEG on a Mac](https://revelraw.com/blog/convert-raw-to-jpeg-mac.md) walks through each app step by step.

## FAQ

### What does ORF stand for?

Olympus RAW Format — the RAW file from Olympus and OM System cameras: unprocessed sensor data, metadata and embedded previews in one `.ORF` file.

### Do OM System cameras still write ORF files?

Yes. The brand changed in 2021; the format didn't. An E-M5 file and an OM-1 file are both `.ORF`, and editors treat them the same.

### How do I open an ORF file on a Mac?

Double-click it: Preview handles files from most Olympus and OM System bodies. Files from a just-released camera may need to wait for a macOS RAW update. To develop rather than just view the file, use a RAW editor such as RevelRaw.

### Why are some ORF files so much larger than others?

A normal ORF runs roughly 15–25 MB. High Res Shot modes composite several frames into one 50–80 MP image, so those ORFs take up several times the space.

### Do Art Filters change the RAW data in an ORF file?

No. An Art Filter or Picture Mode is applied to the camera's JPEGs and to the previews embedded in the ORF, and recorded in the file's metadata — the sensor data underneath is untouched. Only OM Workspace re-creates the camera's rendering; other editors open the unfiltered negative.

### Can RevelRaw open ORF files?

Yes. Drag an ORF in and it opens like any other RAW — presets, scene detection and fine-tune controls all work. Exports go out as JPEG, PNG, TIFF or HEIF.

**See what's really in your ORF files.** Download RevelRaw, drop one in, and watch it ranked against 40+ presets in seconds — with one full-quality export on the house. [Get it on the Mac App Store](https://apps.apple.com/app/apple-store/id6773942240?pt=120914369&ct=Blog&mt=8) (requires macOS 26 or later).

Related reading: [Olympus and OM System RAW editing on a Mac](https://revelraw.com/om-system.md) · [How to open ORF files on a Mac](https://revelraw.com/blog/how-to-open-orf-files-on-mac.md) · [All RAW formats RevelRaw opens](https://revelraw.com/formats.md) · [RAF, Fujifilm's RAW](https://revelraw.com/blog/what-is-a-raf-file.md) · [RW2, Panasonic's Lumix RAW](https://revelraw.com/blog/what-is-an-rw2-file.md) · [What is an ARW file?](https://revelraw.com/blog/what-is-an-arw-file.md) · [What is a NEF file?](https://revelraw.com/blog/what-is-a-nef-file.md) · [What is a CR2 file?](https://revelraw.com/blog/what-is-a-cr2-file.md)