What Is an ORF File? Olympus RAW Format, Explained
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 |
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.
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.
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.
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.
To actually develop the file — choose your own white balance, recover highlights, work the color — you need a RAW editor. RevelRaw 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.
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.
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.
Related reading: All RAW formats RevelRaw opens · RAF, Fujifilm's RAW · RW2, Panasonic's Lumix RAW · What is an ARW file?