Backfocus??? I think mine does

msport said:

If at 25 mm the "worst" AF is achievable, what aperture would need
to be used to get the subject adequately within the DOF?

AX

Click to expand...

jdl said:

without knowing the exact location of
the autofocus sensor (hint: it's not the same size and shape as the
focus bracket that you see in the viewfinder, and it's not in the
center of the bracket, either)...

Click to expand...

Spannie said:

There's a lot of bashing of backfocusers going on here in the last
couple of days. Judging from my general everyday photos taken so
far, I am pretty sure my camera has backfocus problems like these:

http://www.pbase.com/image/28182695/original

http://www.pbase.com/image/28182726/original

I have about 500 more examples showing this tendency - on
everything I have taken at distances less than about 10 feet.

I've been reading this forum intensively over the last couple of
days, and it seems that for every picture or test to prove
back-focus, there are people who object to the test, settings, etc,
etc.

So I took the time last night to set up a test that should satisfy
all these issues that make some people here think that only morons
get back focus.

Some background about me: I've been using SLR's for 40+ years. I've
paid my way through engineering school with photography - Yes, I am
an engineer, and I know how focus works, DOF and all the other
things that effect image sharpness. I have always been a
perfectionist about sharpness. I know where I focus - and I know
when a photo is sharp or not. And I know the difference between
focus plane, DOF and camera shake.

Enought about this - here's my test target and set-up



Key points: The focus target is big enough to extend around the
center focus bracket. The target have enough contrast to ensure the
focus detecter will see it. The focus target is perpendicular to
the camera (alignments marks ensure this). The sharpness detection
lines are angled at 45 degrees to this.

Here's the complete test set-up:



Key points: The light was sufficient for the camera to NOT use the
fucus assist lamp. I made sure that the camera was lined up
perfectly with the focus target, using the alignment marks.
Auto-fucus was AF-S with the center bracket only. I made sure that
the focus target was perfectly centered in the focus bracket, and
the target extended completely around the focus bracket. I used the
timer at 2 seconds to prevent camera shake - as well as flash and
manual exposure of 1/250 sec.

I took over 150 shots at distances between 40cm (16") and 1.5m
(5'), with zoom between 25mm and 70mm. At each distance and zoom
setting, I took 8 shots as follows: 2 shots with triple AF (i.e.
half-press till it beeps then release it - repeat and press shutter
after the third time's beep); 2 shots where the focus was manually
turned closer before the shutter was pressed (i.e AF would move out
to focus); 2 shots where the focus was turned further manually
before the shutter was pressed (i.e. AF would move in closer to
focus); and finally 2 shots with Manual Focus.

Results: NOT ONE SINGLE PHOTO WHERE THE FOCUS PLANE IS IN THE DOF
AREA!!!! In some cases it was utterly appalling!!! Here's some
crops:

distance = 40cm - zoom = 70mm
Full image here: http://www.pbase.com/image/28182896/original



distance = 40cm - zoom = 25mm
Full image here: http://www.pbase.com/image/28182933/original



distance = 90cm - zoom = 70mm
Full image here: http://www.pbase.com/image/28183179/original



If there is any one with genuine questions, I'll be glad to answer
them. If you want to bash my back-focusing issue with MY camera,
trying to tell me that it does not exist, go right ahead - I will
simply ignore it.

--
Spannie

Click to expand...

msport said:

Min = 38 cm, shot taken at 40 CM...could that be a factor too?

It seems to me that you can apply some DOF formulas to see what
apertures could be used. Which was my point.

If you "try" F16 besides wide open, but not other apertures, you
can't really say you have to use F16 can you?

AX

Click to expand...

Mac Digitalist said:

jdl said:

without knowing the exact location of
the autofocus sensor (hint: it's not the same size and shape as the
focus bracket that you see in the viewfinder, and it's not in the
center of the bracket, either)...

Click to expand...

-------
Any idea where it is then?

•••••••••••••••••••••••••••••••••••
Just what on earth is a 'lense'?

Click to expand...

Jackrabbit said:

Spannie said:

There's a lot of bashing of backfocusers going on here in the last
couple of days. Judging from my general everyday photos taken so
far, I am pretty sure my camera has backfocus problems like these:

http://www.pbase.com/image/28182695/original

http://www.pbase.com/image/28182726/original

I have about 500 more examples showing this tendency - on
everything I have taken at distances less than about 10 feet.

I've been reading this forum intensively over the last couple of
days, and it seems that for every picture or test to prove
back-focus, there are people who object to the test, settings, etc,
etc.

So I took the time last night to set up a test that should satisfy
all these issues that make some people here think that only morons
get back focus.

Some background about me: I've been using SLR's for 40+ years. I've
paid my way through engineering school with photography - Yes, I am
an engineer, and I know how focus works, DOF and all the other
things that effect image sharpness. I have always been a
perfectionist about sharpness. I know where I focus - and I know
when a photo is sharp or not. And I know the difference between
focus plane, DOF and camera shake.

Enought about this - here's my test target and set-up



Key points: The focus target is big enough to extend around the
center focus bracket. The target have enough contrast to ensure the
focus detecter will see it. The focus target is perpendicular to
the camera (alignments marks ensure this). The sharpness detection
lines are angled at 45 degrees to this.

Here's the complete test set-up:



Key points: The light was sufficient for the camera to NOT use the
fucus assist lamp. I made sure that the camera was lined up
perfectly with the focus target, using the alignment marks.
Auto-fucus was AF-S with the center bracket only. I made sure that
the focus target was perfectly centered in the focus bracket, and
the target extended completely around the focus bracket. I used the
timer at 2 seconds to prevent camera shake - as well as flash and
manual exposure of 1/250 sec.

I took over 150 shots at distances between 40cm (16") and 1.5m
(5'), with zoom between 25mm and 70mm. At each distance and zoom
setting, I took 8 shots as follows: 2 shots with triple AF (i.e.
half-press till it beeps then release it - repeat and press shutter
after the third time's beep); 2 shots where the focus was manually
turned closer before the shutter was pressed (i.e AF would move out
to focus); 2 shots where the focus was turned further manually
before the shutter was pressed (i.e. AF would move in closer to
focus); and finally 2 shots with Manual Focus.

Results: NOT ONE SINGLE PHOTO WHERE THE FOCUS PLANE IS IN THE DOF
AREA!!!! In some cases it was utterly appalling!!! Here's some
crops:

distance = 40cm - zoom = 70mm
Full image here: http://www.pbase.com/image/28182896/original



distance = 40cm - zoom = 25mm
Full image here: http://www.pbase.com/image/28182933/original



distance = 90cm - zoom = 70mm
Full image here: http://www.pbase.com/image/28183179/original



If there is any one with genuine questions, I'll be glad to answer
them. If you want to bash my back-focusing issue with MY camera,
trying to tell me that it does not exist, go right ahead - I will
simply ignore it.

--
Spannie

Click to expand...

Would you be so kind as to E-Mail your chart to
[email protected] Thanks

Click to expand...

• McD.

John M. Polston said:

The problem is with the kit lens at least in my case. Now, whether
it's the lens or the lens parameters inside the camera which are a
little off, I don't know. Is this a huge problem in my case, NO
but if the other old lenses can focus good then the newer kit lens
should be able to if not better. Now I wish I had got just the
body and bought the 24-120VR instead.

Click to expand...

• McD.

John M. Polston said:

I think most if not all of the kit lenses suffer from BF and this
is the reason to not send it back for a replacement or a refund.

Click to expand...

• McD.

John M. Polston said:

Ok, I couldn't stand it and decided to do the test on my 3 lenses
which include the kit lens. The link below are the pics. My tests
are a little different in that they also include the different area
focus select points as you will notice in the photos. I decided
not to do the multi-point test on the 70-300G because I didn't feel
it necessary.

What I found was that the Kit Lens was Back Focussing most if not
all of the time but seemed to focus well on the Right-Focus Select
picture and pretty close on the Bottom Focus select but still a
little BF.

The other two lenses, 50mm-1.8 and the 70-300G were spot-on, which
was surprising as I thought the BF problem would lie in the camera
body.

http://www.pbase.com/johnpolston/back_focus

The problem is with the kit lens at least in my case. Now, whether
it's the lens or the lens parameters inside the camera which are a
little off, I don't know. Is this a huge problem in my case, NO
but if the other old lenses can focus good then the newer kit lens
should be able to if not better. Now I wish I had got just the
body and bought the 24-120VR instead.

This is not going to stop me from taking pictures with it.

--
John M. Polston
Atlanta, GA

Click to expand...

Mac Digitalist said:

John M. Polston said:

I think most if not all of the kit lenses suffer from BF and this
is the reason to not send it back for a replacement or a refund.

Click to expand...

-------
I have come across a few posts where people exchanged the lens,
tested the new one in the shop, and, guess what, no backfocus.
Throw it back at Nikon, I'd say. It might wake them up.

• McD.

•••••••••••••••••••••••••••••••••••
Just what on earth is a 'lense'?

Click to expand...

snriley said:

It's the kit lens! And I am not very happy that I spent $300 on it

• I could have bought something much nicer - shame on me for

following the recommendation of some of the reviewers!

Click to expand...