Friday, September 18, 2020

DOFIS: perfect focus and exposure bracketing for photographers

Those that have been following my DOFIS developments will know that I’ve been evolving DOFIS to be the single script that I have running for all my EOS photography needs. That is, helping me achieve blur-informed, infinity focus, and carry out scene-informed, automatic/semi-auto/manual focus bracketing with ML or DOFIS advanced exposure bracketing.

Although DOFIS started off as a script to provide 'just' focus bracketing information, it has now evolved into a powerful tool for all photographers: and, dare I say, videograhers, where DOFIS can show you ‘correct’ relative or absolute DoFs.

Because of limitations within Lua, accessing the ML advanced (exposure) bracketing (AB) can only be accomplished via the semi auto focusing option, ie up until now you could not auto exposure bracket in full auto focus bracketing mode.

This restriction has been bothering me, hence I’ve now incorporated my own auto exposure bracketing scheme within DOFIS, which you can access in full focus bracketing mode, as well as when focus bracketing is switched off.

The new auto exposure bracketing option is based on exploiting two of Magic Lanterns most powerful photography features, namely, RAW-based auto ETTR and the RAW-based Ev-based spotmeter; and adapting the ideas of Ansel Adams and Fred Archer, from their film-based Zone System. 

Of course in digital photography we expose for the highlights and process (and potentially bracket) for the shadows; which is just the opposite of the classic Zone System rule for film photography, where we expose for the shadows and develop for the highlights.

To optimally use the new auto exposure bracketing feature, you need to enable the ML RAW Ev spotmeter in the Overlay menu, plus, ensure that Auto ETTR highlight ignore is set to 0, and that the two SNRs are OFF.

The following chart illustrates how the various exposure and focus bracketing options interact, noting that DOFIS allows you to exposure bracket without focus bracketing. 

The DOFIS auto exposure bracketing feature is based on a modification of the classic zone system, where the usual zone IX, ie where we would expect to see specular highlights etc, is the ML spotmeter zone 0 in DOFIS:

Thus the zone system’s 18% grey, zone V, where a camera normally tries to meter at 0Ev, can be assumed to be the ML spotmeter 'zone', -4E to -5Ev.

The updated DOFIS menu now looks like this:

Here we see four new menu items, related to exposure bracketing. The first menu item allows the user to enter the RAW EV (integer) spotmeter value from the shadow region of the image where you wish to see details. In DOFIS all you need to know is how many stops down from the highlights do you wish to place the shadows, eg -6Ev, say.

As an example, after ML ETTRing, we see the ML RAW EV spotmeter, in the area of the image we are interested in, reads -8.7Ev, so let’s say this is -9Ev. We wish to ensure this is two stops below middle grey, which in the normal zone system is zone III, thus we wish the shadow area to end up at -6Ev, ie zone III. We thus enter this value in the Shadow Ev in DOFIS.

The third menu item that controls the DOFIS exposure bracketing is the Ev delta value, ie the bracketing Ev step. A zero here, as above, switches the exposure bracketing off. Active values are 1 through to 4. A value of 4Ev giving you the option of carry out, so-called, zero noise bracketing. Typically one would use 1Ev or 2Ev steps, ie for tonal smoothness.

Finally, you can introduce a delay of 0, 1 or 2 seconds, after initiating the DOFIS exposure bracketing, ie, like focus bracketing, after pressing the trigger key that you have set in the script.

In future posts I aim to provide examples of how I’ve used the latest DOFIS script in the real world. Until then, as usual, I welcome feedback on this post and any hearing about other users' experiences with DOFIS.






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