F. Craig Callahan wrote:
> With the AF motor disengaged, DEP can't work,
I think Norman Chappel suggested switching to MF AFTER determining the
focus point with DEP mode; the intent was to keep the camera from
refocusing after switching to Av mode.
Chip Louie wrote:
> This is getting silly! DEP cannot work if you are busy mucking up the
> exposure!
I don't really think the original poster's intent was to alter the
exposure, despite the choice of wording.
> The whole point of DEP mode is to use the camera's processor to set the
> aperture for the DOF you want,
I think the point of DEP mode is to determine the point of focus and the
MAXIMUM aperture that will render everything between the indicated points
of focus acceptably sharp.
> if you change the f/stop DEP cannot work,
I can't think of a situation where one would want to use a larger aperture
than the one selected by DEP mode, but I can see where one might want a
smaller aperture, perhaps as insurance, or perhaps simply to, in effect,
use a smaller circle of confusion than Canon's alleged 0.035 mm.
In essence, DEP mode simply does what could be accomplished manually in the
old days when MF lenses had decent DoF scales:
1. Focus on the far
2. Focus on the near
3. Using the lens DoF scale, find an aperture that places both points
within the DoF
4. Set a shutter speed that gives the correct exposure with the
selected aperture
One could, of course, use a smaller aperture than the one determined with
the DoF scale. Some of us have lamented that high-end EOS cameras have not
provided the flexibility that had always been available with manual-focus,
manual-exposure cameras.
> Shifting the exposure in (P)rogram mode allows you to change the shutter or
> aperture values but the EV remains the SAME!
Some of the older EOS cameras, such as the EOS 5/A2/A2E, offered the same
flexibility in DEP mode: changing the aperture simultaneously changed the
shutter to maintain the same exposure. This feature seems to have been
eliminated on most (perhaps all) of the current EOS cameras.
Perhaps describing selecting among several equivalent aperture/shutter
combinations in DEP mode as "program shift" (as has been the case for most
posts on this topic in the last several years) has been part of the
problem. In DEP mode, one isn't really overriding a "program," and, at
least with the EOS A2/A2E, the manual did not refer to this feature as
"program shift."
This topic has seemed to come up once or twice a year for the past 5 years,
and every time, it has been beaten to death. This most recent thread has
certainly set a new standard for drifting into la la land.
Jeff Conrad
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