Re: Canon 5D Sharpness Question
- From: "Edward Holt" <Edward_Holt@xxxxxxxxxxx>
- Date: Sun, 26 Feb 2006 15:53:28 -0000
"Douglas" <aliens@xxxxxxxxx> wrote in message
news:a25Lf.13973$yK1.10869@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx
"Edward Holt" <Edward_Holt@xxxxxxxxxxx> wrote in message
news:43fc9535$0$29565$da0feed9@xxxxxxxxxxxxxxxxx
:I bought a Canon 5D and a Canon 20mm lens at Christmas.
: I've recently bought a Canon 28mm F2.8 and a Canon 50mm F1.8 Mk 2.
:
: The quality of the picture with the 20mm is always great.
: The quality of the picture with both the 28mm and the 50mm is great
: sometimes and not great the other times which is very annoying.
:
: I don't think depth of field is an issue and it also happens when the
camera
: is on a tripod.
:
: I think the pictures taken with the 28mm and the 50mm are not focused
: correctly. I have set the camera to focus on the central point only. I
: really rely on the camera to focus due to the lack of split screen or
: Fresnel ring.
:
: Has anyone else experienced problems with autofocus?
: It could also be a case of me not using the camera correctly - it's a
lot
: more complex than SLRs made 20 years ago which I'm used to.
:
: I'm considering buying one of the replacement 3rd party focusing screens
: that do offer split screen or Fresnel ring to help me out.
:
:
5Ds are like all EOS cameras. They have an unusually small distance
between
the sensor and the real lens element. This is called the back focus area.
Because of this short distance, back focus on Canon SLRs is more prone to
be
incorrect from the factory than with other brands. The other Canon unique
focus issue is the anti alias filter they put over the sensor to stop
moiré
effect. this produces a permanently soft image which is only correctable
with the use of artificial sharpening after the shot. If you set the
sharpness in the camera, all it does is just perform the artificial
sharpening itself.
You need to see if the out of focus thing happens when manual focusing as
well as on auto focus. If you can manually focus the camera better than
the
auto focus, the back focus is off and needs to be re-calibrated by Canon.
Otherwise, it is not uncommon for Canon brand lenses to also need
calibration WITH the body to obtain correct focus all the time. These
errors
usually are not noticeable past about a metre (3 feet) distance.
The 1.8 Mk II lens is a long way from being a great lens as far as focus
reliability goes. Warranty claim time and take your lenses back too. The
adjustment is a simple one but unfortunately Canon refuse to release the
software to independent repairers do this. My 5D was away for over 3
weeks.
The 20D before it, 10 days and the EOS 3 before that, a week. Wouldn't you
think things would improve with time? The only Canon SLR I've had in the
past 4 years which didn't need back focus adjustments was a 10D. Oddly
this
is the camera everyone else reported focus errors with.
Other Canon models I've sent back for back focus repair include the A1 and
a
Video camera. Before you send the 5D back, do some exposure checks. They
also have a habit of not white balancing properly on auto and another
often
overlooked problem is their inability to meter for a 5 stop darker scene
after taking a picture in a bright scene. All these things are fixable
with
a warranty claim.
I've done some tests using centre auto focus point and all three lenses at
maximum aperture.
Camera shake was also ruled out by fast shutter speeds.
Manual focus at close distance at a focus test page (i.e. a flat object at
approx 50cm) on the 50mm lens is less accurate than auto focus.
I placed three cans of soup in a line, but staggered in distance to the
camera by the width of one can. I auto focused on the middle can.
I enlarge images from a 50mm f1.8, 28mm f2.8 and a 20mm f2.8 so that the
cans were all the same size.
The image quality from the 50mm and 20mm was equal even though the 20mm had
to be enlarged by a greater degree. The best quality was easily the 28mm.
What appears to be the case is that the camera has actually focused on the
can to the right of the one I had covered by the middle focus indicator.
Could it be that the focus indicator in the view finder and where the camera
actually focuses is slightly out?
.
- References:
- Canon 5D Sharpness Question
- From: Edward Holt
- Re: Canon 5D Sharpness Question
- From: Douglas
- Canon 5D Sharpness Question
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