Peter Hancock wrote:
> Does anyone know why Canon has dropped the depth mode from their digital
> SLRs?
The "official" explanation, at least from Canon USA, is that the Depth AE
algorithm required considerable firmware space that was needed for other
features, and apparently Depth AE wasn't perceived as very popular (If you
recall, some years ago it was widely derided by the photo press as an
"amateur" feature. I shall decline further comment on this ...).
You're not the only one unhappy with the elimination of Depth AE--this was
the topic of several recent threads in the EOS forum on photo.net. You
might want to check there for a few others' thoughts.
> ... the full manual depth system of my old 100, which was one of the
> reasons I originally bought into the Canon system.
The Depth AE on the EOS 5 and the EOS-1n was a big factor in my changing to
Canon 10 years ago; DoF control with Nikon AF lenses was nearly impossible.
> I just looked to see what they've put on the 5D, and the answer
> is nothing at all.
The EOS-1D Mk II in April 2004 was the first to eliminate Depth AE. With
the EOS-1Ds Mk II, EOS-1D Mk II N, and EOS-5D having followed suit, the
future of Depth AE is not looking bright.
> Is the theory that you don't need it because you can
> check the image after you've taken it?
One never knows, but this would seem utter nonsense.
1. You'd need to be tethered to a monitor to make the assessment (I
suppose you could zoom to different parts of the image with the
camera's LCD if time were no object).
2. As you mention, you'd still need an iterative process to get things
sharp, which seems silly since DoF has been easy to control with
DoF scales on manual-focus lenses from almost the first days of 35
mm SLRs and rangefinders. It's now difficult to set with an $8k
DSLR ...
The calculations required are
u = 2 x u_n x u_f / (u_n + u_f)
N = f^2 / c x (u_f - u_n) / (u_f x (u_n - f) + u_n x (u_f - f))
where
u = Focus distance
u_n = Near limit of DoF
u_f = Far Limit of DoF
N = F-number
f = Focal length
c = Circle of confusion
You'd need some means of getting accurate distance measurements; the AF
lens distance scales certainly won't provide it, but a laser rangefinder
(such as a Bushnell) might do the job. The calculations are more than I
care to deal with in the field, but I suppose a PDA could solve that.
The procedure might go something like this:
1. Measure the near distance
2. Measure the far distance
3. Calculate the focus distance and f-number
4. Use the rangefinder to locate an object at the focus distance
5. Focus the camera on that object
6. Set the f-number
7. Take the picture! (if the Sun hasn't set)
This assumes, of course, that the lens is unit focusing, which most aren't.
Gimme a break ...
> I wonder whether they could firmware update the 10D to give it full manual
> depth mode?
My guess is that they could, and last year, I posed this question to Canon
USA, who forwarded it, along with my other comments, to Canon Japan. Canon
Japan have yet to comment ... and I'm not holding my breath.
The best I can suggest is to write a letter to Canon; the two of us aren't
going to change things, but if everyone who has bemoaned the demise of Depth
AE were to write to Canon, they just might listen.
Jeff Conrad
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