omd:focus_stacking

automatic in-camera focus stacking function for greater depth of field on Olympus cameras

introduction

  • macrophotography of 3D subjects is problematic as the depth of field (DOF) is rarely deep enough to cover the whole subject, even when the aperture is stopped down to f/11-f/16
  • capturing a subject 1cm in length from head to tail in perfect focus is a feat that all insect photographers wish to accomplish but when shooting at 1:1 macro, depth of field may only be 0.5mm
  • stopping the aperture down too much looses image detail due to diffraction issues
  • an option to address this issue is to take a series of photos with slightly different focus points then in post-processing with Photoshop or similar, combine these images and only display the in focus areas from each - this is called focus stacking
  • now this is very tedious for most of use mere mortals so in 2015, Olympus kindly automated this procedure in-camera for their latest OM-D cameras as well as their Stylus TG-3 and TG-4 Tough cameras by including automatic focus bracketing and taking this a step further to automate the post-processing of these images in camera as “focus stacking” mode
  • it can also be used in landscapes with very close foregrounds!

www.ayton.id.au_gary_photo_images_focus_bracketing_stacking-1.jpg

The above image was supplied to me for publishing here by Olympus photographer Kim Holst who created these nice explanatory diagrams

focus bracket mode method for static subjects

  • from the menu, turn Bracketing on, select Focus Bracketing Mode, and set the number of shots and focus steps:
    • focus steps are available from 1 to 10
      • focus step refers to the amount of focus movement where 1 is the smallest setting (use 1 or 2 when shooting at wide aperture)
    • up to 999 shots can be set
      • you will need 100 shots for a 1cm subject at 1:1 macro wide open aperture and focus step of 1
      • if subject is 1-2cm, can get away with 50-70 shots with focus step of 2-3 and aperture of f/5.6-8
      • for live subjects further away, focus step of 3-4 and aperture of f/6.3 and 14-18 shots may work well

focus stacking mode for static subjects

how many "steps" differential to use?

  • the amount of focus bracket = number of shots chosen x no of steps chosen x size of focus step differential for a given aperture and focus distance (see below)
    • when using a 60mm macro lens:
      • a single Focus Step differential (metres) = f-Number x (Focus Distance subject-sensor (metres) / 21.4)²
      • at f/2.8-f/16, at 1m distance, the focus step differential is approx. 1/3rd of the DOF of a single shot, so you could probably set focus step to 2 or 3 (or 4 for very close subjects, or when using f/8-16 for more distant subjects > 5m away - even use 6 or more for distant subjects at f/16 > 10m away)
      • thus at 200mm focus distance, f/2.8, a step = 0.16mm, while at f/8, it equals 0.45mm
      • thus at 400mm focus distance, f/2.8, a step = 0.9mm, while at f/8, it equals 2.7mm
      • thus at 1m focus distance, f/2.8, a step = 7mm, while at f/8, it equals 20.5mm
  • examples:

  • for small fungi, try using f/4, focus differential of 3 and 8 shots which allows automatic focus stacking, but if you need more DOF and thus more images, use focus bracketing mode and stack the images using a computer and software such as Zerene Stacker or Helicon Focus

using focus stacking to give steeper DOF fall off with wide aperture lenses

  • sometimes you may wish to have a certain amount of DOF but then a steep fall off to create better subject delineation from the background
  • focus stacking can be of use to achieve this with static subjects

www.ayton.id.au_gary_photo_images_depth_of_field_-_single_exposure_vs._focus_bracketing-1.jpg

The above image was supplied to me for publishing here by Olympus photographer Kim Holst who created these nice explanatory diagrams

tutorials

omd/focus_stacking.txt · Last modified: 2017/10/31 15:27 by gary1