Optimising Film Scans from Olympus micro 4/3 Cameras
One of the challenges with Olympus micro 4/3 cameras is the mind bogglingly large number of options and shooting modes. I use an E-M1 mark II with an Olympus 60mm macro lens to digitise 35mm negatives, but I have never really been sure what the optimum way to configure the camera was. This post is an attempt to put that right…
The Scanning Rig
My film scanning rig consists of a copy stand which makes a good rigid mount for the Olympus, along with a home-made light-box on top of which I can place a holder containing a strip of six negatives. The light-box is deep to ensure an even light, and I use a dark perspex cover with a cut-out so that only one negative is illuminated at a time, reducing the chance of lens flare.
Before starting scanning, I collimate the system by placing a flat mirror on the light-box so that the E-M1 can see the reflection of its own lens. The rig has two axis of freedom: the copy stand allows the camera to tilt side-to-side, while small wedges placed under the light box provide a front-to-back adjustment. The wedges work surprisingly well, and I prefer these to a full tripod head, which makes the camera rig too unwieldy to adjust precisely.
I use a film holder that originally came with an ancient PlusTek film scanner. It is not perfect, but it has thin plastic bars at each frame edge which help keep the film flat. An alternative would be to use some simple glass sheets, although this increases the problem of dust and can potentially lead to visual artifacts such as Newton’s Rings.
The main factors that could cause soft images with this setup are:
- failure to align the lens and negative planes accurately, causing the image edges to be out of focus
- film curvature, causing parts of the image to be out of focus
- lens focal plane curvature, causing parts of the image to be out of focus
- optical aberrations at the field edges from the macro lens
- camera shake and vibration
- auto focus errors
Fortunately, most Olympus cameras have a range of shooting options that can help both diagnose and resolve potential sources of softness…
Resolution and Sharpness Tests
For these tests I used four shooting configurations provided by the E-M1 mark II, and which are also supported by most recent Olympus cameras:
- “Anti-shock mode” (diamond symbol in the menus). This uses the mechanical shutter, but adds a delay prior to shooting to reduce shutter induced blur (“shutter shock”). For these tests, I used a 1s anti-shock delay.
- “Silent-shutter mode” (heart symbol in the menus). This uses a fully electronic shutter, so there should be no risk of shutter shock at all. On newer cameras such as the E-M1 mark II there is almost no penalty to using silent-shutter mode – the main risk being banding if a fast shutter speed is used with a modulated light source (such as most LED lamps or fluorescents). To avoid problems either use an incandescent light or simply avoid short exposure times.
- “High-Resolution Mode“. This is the Olympus’ most commonly cited party trick. The camera takes a set of nine images, moving the sensor fractionally as it does so. The images are then combined in-camera to generate a 50MP JPEG and 80MP RAW file. In theory, this should give the best possible image quality – although at these resolutions if you stop the lens down enough to increase depth of field you risk loosing sharpness due to diffraction.
- “Focus Stacking“. The traditional way of dealing with depth-of-field issues in macro photography is to take a set of images at slightly different focus positions and then use software to build a composite image, and this is one way to deal with a potential focal plane alignment issue. Usually, focus stacking is a lot of work – but fortunately some newer Olympus cameras can now perform an automatic focus stack in-camera. In this mode, the E-M1 takes a set of eight images at evenly spaced positions around the focus point.
The test negative was shot using an M7 and 21mm Super Elmar lens in bright daylight – a combination which should yield a razor sharp image from edge to edge. The film was Delta 100 developed in DD-X 1+4. For each shot a shutter delay of 8 to 12s was used to eliminate any vibration from the shutter button (you could also use a wireless remote or phone), and three separate images were taken to check for consistency, each being individually refocussed using the camera’s auto-focus system. The intention was to choose the sharpest image of the three, but it turned out that each set of three images were indistinguishable – Olympus’s auto focus is encouragingly reliable.
For the first set of tests, all the images were shot at f5.6 – pretty much the sweet spot for sharpness with the Olympus 60mm macro lens.
The negatives were processed in Capture One Pro 11.2 and three crops taken from the centre, mid-zone and far corner:
|Mode||Centre Crop||Mid crop||Corner Crop|
The first thing to note is that, other than the focus stack, pretty much all the images look good in the centre and are weak at the extreme corner. The weak corner area is a mainly caused by poor flatness in the film holder (depth of field here is a fraction of a mm), with the worst affected corner being that shown here.
The focus stack yields a 20MP JPEG, but as the file size shows there is considerable loss of detail compared to a single image. The in-camera stacking has also trimmed the edge of the frame and then re-scaled the image back to 20MP. The result is clearly the worst of the set by a significant margin, and a focus stack made manually would yield a much better result. Unfortunately this is not really practical for every frame of a 35mm film!
The two single-shot images look pretty much identical, so if using a non-continuous backlight it is safer to just use the mechanical shutter to avoid possible banding (remembering to configure an anti-shock delay).
The high-resolution images clearly resolve more detail in the centre and mid-areas than the single shot images, while the corner remains stubbonly blurry. The 80MP RAW file is very soft out of camera, and needs extensive and careful sharpening to match the 50MP JPEG output – and the only real advantage to keeping the RAW file is for colour film where you want to maximise dynamic range and colour noise.
The following screen shots show larger crops in Capture One, paired with the single-shot on the left vs the sharpened hi-res shot on the right. The improvement with high-resolution mode is clear, and attempts to adjust the sharpening of the single-shot mode are unable to close the gap:
Lastly, a series of images were made to compare high-resolution images, this time taken at different apertures. The choice of aperture gives a trade-off between increase depth of field (tolerance to film flatness issues) and softening due to diffraction:
The centre is good at all apertures, while f5.6 looks like an optimal trade-off between the diffraction softened f8 image and the poorer corner performance at wider apertures.
Capture One Pro 11 Sharpening Settings for Olympus High-Resolution RAW Files
All of the above high-resolution RAW images needed substantial sharpening in Capture One to optimise the image result, and much trial-and-error gave the following settings:
That sharpening value of 900 is not a mistake: the Olympus high-resolution RAW files are extremely soft out of camera and need an improbable degree of sharpening to match the (excellent) JPEG output. Using a large sharpening value with a small radius gave good results without problematic artefacts.
Lastly, the Olympus macro lens has a lot of Chromatic Aberration at the frame edges. Normally, just ticking the CA box in the lens corrections should resolve that – but I found that it actually made the CA worse. The work-around is to click the three dots next to the CA correction tool and select “Analyze”. Even though these are black-and-white images, removing the CA helped improve sharpness at the edge of the image field.
- for best resolution and dynamic range, use 80MP high-resolution RAW files taken at f5.6, and use heavy sharpening in Capture One
- for smaller files with no practical loss of resolution, the Olympus 50MP high-resolution JPEG output is excellent
- take great care to align the film plane with the plane of focus
Keep in mind that to see any differences between any of these methods takes a particularly extreme level of pixel peeping combined with a very sharp and very fine-grained film. Even the simplest single-shot approach exceeds the output possible with most dedicated film scanners.
But, for me, perhaps the most surprisingly result is just how much detail can be extracted from Delta 100 in 35mm format!