Saturday, May 13, 2017

Introducing the 'The Focus Bar'

In previous posts I introduced a 'new', Magic Lantern based, approach to landscape focusing; based on the idea of monitoring the optical, diffraction and total blurs at infinity.

This approach is simplicity itself, as all one needs to do is monitor the blur (provided in microns) and stop focusing when your blur criterion is reached.

For example, for full frame landscape photographers a total blur of, say, 30 microns is OK for screen presentation. If, however, you are seeking the best quality for printing, then a total blur goal at infinity of, say, 15 microns may be a better goal. But note blurs are related to image size and viewing distance.

Once your blur-focus condition at infinity is met, the script provides info on the near field depth of field position, that also meets the total blur criterion. Thus you know you have achieved your focus criterion from the near distance to infinity.

In this post I'm introducing (in beta) a new feature: a focus bar (see image below):

This 5D3 screen dump shows the landscape focus helper, with the new focus bar.

This version 'only' provides a visual feedback on the optical blur through the scene: although I plan to add in diffraction, ie so you can visualize total blur, in a later release.

The focus bar provides you a visual impression of the blur through the field, the red dot being the point of focus. This is important information for those seeking high quality images, as, unlike diffraction, optical blur changes through the depth of field.

The left hand distance is set at the HFD/4: as this script is for landscape photographers, ie unlikely to be seeking focus below HFD/4.

The right hand distance is a user variable and adjusted by a multiplier (from the script's menu). The multiplier is based on sensor-limited 'infinity' (which the script calculates), ie the distance where the optical (sic) blur is the same as the sensor pitch, or the size of single sensor site. That is about 6.3 microns on my 5D3.

The colours provide info on the optical blur through the scene, based on a menu selected 'unity blur', eg 30 microns was used above. The colours provide the following info:
  • Black: an optical blur equal or greater than the unity blur x a multiplier (1-9)
  • Grey: the blur between Black (above) and a unity blur (white)
  • Green: a blur between the unity value, eg 30 microns above, and half this
  • Yellow: a blur of less than half the unity blur, eg less than, say, 15 microns
  • The red dot is the focus point and this varies from HFD/4 to the limit identified above. If focus goes beyond the set limit, the red dot will be shown outside the focus bar, providing another piece of info to be used.
The script is available from the download area (right), ie HFD3. Currently this is a beta release and I welcome feedback.

No comments:

Post a Comment