Some data on Oly "Focus Stacking"

Started May 24, 2016 | Discussions thread
OP lester11 Contributing Member • Posts: 596
Re: Some data on Oly "Focus Stacking"

In case it is useful, I've summarised some posts (mostly mine!) for folks who might be interested in the Olympus in-body focus stacking with the E-M1 (mark I).
When taking a focus stack the camera steps forward 2 and then steps back 5 from the start to give 8 frames which it automatically stacks and merges in-camera. So long as the images align and there is good focus overlap between the frames, the Oly in-camera merge of a focus stack is indistinguishable from a Photoshop or Helicon Focus merge.
Experiments with a merged stack in the E-M1 using the Oly 60 macro lens at f2.8, compared with a Photoshop align and blend of the same stack. Given in-focus overlaps in the frames, both Oly and PS give pleasing merges. The difference is in their artefacts. Oly gives superior stack alignment. On the other hand, Oly ghosting on high contrast edges is dreadful when pixel peeping. Photoshop is the opposite, terrific ghosting control, but oof bits all over the place. As good overlap reduces or disappears, the Oly merge fails to give a satisfactory result, while the PS blend does the best it can, pretty successfully.
Experiments comparing the Oly merged focus stack against the same merged stack in Photoshop using the 40-150 Pro at f2.8. Results broadly similar to using the 60 macro as reported in post 57716893.
Graphs with the Oly 60 mm macro lens and target at 500 mm using 2.8, 4.0, and 5.6 with differentials of 1, 2, 3, and 4. Bracket width is about 3 times DOF for diff=1, 4.5 times DOF for diff=2, and about 7 times DOF for diff=3.
Graphs for focus stacking using the 12-40 Pro at 30 mm, with a target distance of 500 mm. Differentials of 1 and 2 give overlapping focus frames, a differential of 3 gives steps pretty much the size of the DoF, and differentials of 4 and larger would leave quite large oof gaps (oof bands) in the stack.
Graphs for focus stacking with close macro subject distances of 200 mm and 250 mm with the Oly 60 macro lens. Testing every differential from 1 to 10 shows the step size is a constant proportion of the DoF at the given aperture. For example, with diff=3, the step size is pretty much half the DoF of each aperture setting.
Blur banding occurs when there is insufficient focus overlap between the stack frames.
Example snap of macro DoF. PhotoPills and other apps calculate DoF using subject to sensor distance.
jannefoo's "Focus stacking with Fiji/ImageJ and Enfuse". Tutorial on focus stacking using Enfuse freeware.
An Enfuse merge gives ghosting under good control and no oof bits from an inadequate alignment of the frames, but there are artefacts on high contrast edges, the result as good as either the Oly in-camera merge or the PS blend.

For Focus bracketing, we have the excellent:
Richard Turton's "Investigation of E-M1 Focus Bracketing". Graphs and formulae for focus step in bracketing. Some take-aways: depth of field is 3 times the minimum focus step. Focus Step (metres) = f-Number x (Focus Distance (metres) / 21.4)²

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 lester11's gear list:lester11's gear list
OM-1 Olympus M.Zuiko Digital ED 60mm F2.8 Macro Olympus 12-40mm F2.8 Pro Olympus 12-100mm F4.0 Olympus 25mm F1.2 +8 more
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