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Backfocus "problem"

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David SL said:
if you do a search on "D70 backfocus" you'll find exactly 1 thread
(posted by davidxl on 3/25) with the subject line before last
Friday (Phil's review)...after that nothing until Phil's review and
then suddenly quite a few sprouted up. It is a fact that the
complaints have multiplied since the review as the original poster
asserted.
Click to expand...
-------
Errrm... what is your point?
  • McD.
•••••••••••••••••••••••••••••••••••
Just what on earth is a 'lense'?
 
Mac Digitalist said:
David SL said:
if you do a search on "D70 backfocus" you'll find exactly 1 thread
(posted by davidxl on 3/25) with the subject line before last
Friday (Phil's review)...after that nothing until Phil's review and
then suddenly quite a few sprouted up. It is a fact that the
complaints have multiplied since the review as the original poster
asserted.
Click to expand...
-------
Errrm... what is your point?
Click to expand...
Errrm... I believe his point is clear, and is the same as mine. The backfocus "problem" was extremely rare until Phil's review pointed it out, and now suddenly everyone and their dog has this horrible problem. Again, I'm not saying the problem doesn't exist in a few samples, which is true of any camera, and any lense, from any manufacturer - all I'm saying is that there are many many reasons for photos to be out of focus, and more often than not it is the photographer, not the camera, at the root of the problem. And, as Thom Hogan pointed out (read his reply in this thread, it's very enlightening), it may not necessarily be the result of poor technique, but simply a matter of not understanding what the autofocus sensor is "seeing".

--
Jeff

http://www.photo.net/photodb/member-photos?include=all&user_id=403266
 
Thanks for the thorough explanation. I have one question
Thom Hogan said:
What the heck am I talking about? Well, the AF sensors in Nikon
bodies don't align with the AF sensor shapes and sizes in the
viewfinder. Moreover, the central sensor, which appears to be under
test here, uses an auxiliary sensor at lower light levels, which
further shifts the location vis-a-vis the viewfinder. Thus, it's
quite possible that part of the AF sensor was seeing something Phil
didn't expect it to. But we won't know without more info form Phil.
Click to expand...
Then how do we know where the sensors are located? If we know this, then we will be able get the camera to focus exactly where we want it to, right?

--
spiny
 
Hi

I've been reading this forum for weeks and the combined one before the forum was split and the main thing I've noticed is that a lot of people are instantly jumped on when they complain of a problem. Comments such as you don't know how to use it, it's normal just get over it or report it to Nikon not us, etc. don't really encourage anyone to complain of anything which hasn't been thoroughly documented or found in a review.

It may be as you say that people have suddenly found a scapegoat for their own limitations but it could equally be true that they didn't want to risk the abuse until they had an informed opinion to back them up.

Personally I hope the former is true. I'm looking forward to getting my D70 and eventually starting to get shots of the calibre I've seen here over the past weeks.

--
Russell
D5 http://homepage.ntlworld.com/russell.whyman1
D7i http://www.russellwhyman.co.uk
 
I totally agree , remember the "green cast" , seems to have gone the way of the do-do bird , I understand the moire thing and it is a difficult one but back focus that is USer error IMO

J
 
davexl said:
Can you elaborate further on the cleaning issue causing focussing
errors?
Click to expand...
If the sensor area at the bottom of the mirror box gets dust and hairs and junk in it, autofocusing is compromised. I've found that I need to have my bodies professionally cleaned about once every 18 months or so (but remember, I drag them through worst case environments).
davexl said:
I have backfocus issues with my 80-200 F2.8. I noticed it after my
first shoot at the zoo, and since tripod tests and test charts have
shown consistent backfocus with this lens only. 60mm macro lens and
others seem fine - although 200mm f2.8 is far less forgiving than a
12-24mm!
Click to expand...
It's not unusual to see some variance in how lenses perform on AF, especially older lenses with mass. Some background: AF on the current bodies works on what I'll call "contrast anticipation." The sensors build a pattern of increasing/decreasing contrast and the camera's CPU tries to guess where the peak will be and stop the lens focusing at the peak. For that to be precise the lens focusing speed has to be precise. AF-S lenses generally focus more consistently and "tighter" than older screwdrive lenses. And some bodies (the D2h) have newer detection algorithms that help, too. In the Nikon world, the F5 had the worst algorithms, the F100 through D100 better, the D2h the best. On the flip side, the F5 had the best screwdrive mechanics, the other bodies less so. Canon bodies have similiar issues, but I'm not well enough versed to tell you which things are strongest/weakest in which Canon bodies.

Back in the mid 90's (it was after the F5 came out), Popular Photography did an "expose" on the problem, showing--if memory serves--that MF was always more accurate than AF, that AF was not perfectly consistent from focus to focus, that the direction in which focus was being achieved (back to front, front to back) can make a difference, and a host of other things. I believe Canon was slightly more consistent at the time than Nikon (possibly due to the silent wave motors in the lenses). Things have gotten better since then, but AF is not perfect, nor perfectly repeatable.

--
Thom Hogan
author, Nikon Field Guide & Nikon Flash Guide
author, Complete Guides to the Nikon D100, D1, D1h, & D1x and Fujifilm S2
http://www.bythom.com
 
spiny said:
Then how do we know where the sensors are located? If we know this,
then we will be able get the camera to focus exactly where we want
it to, right?
Click to expand...
The first issue of my DSLR Report newsletter (now out of print) had this info and how to test for it. Once I've got my site moved to the new server I'll be working at getting that article updated and posted.

--
Thom Hogan
author, Nikon Field Guide & Nikon Flash Guide
author, Complete Guides to the Nikon D100, D1, D1h, & D1x and Fujifilm S2
http://www.bythom.com
 
Forrest said:
Mention "back focus" or "front focus" in the Canon SLR forum, and
you'll have a hot-thread on your hands in no time. Thousands of
people all over the world were shooting rulers like there was no
tomorrow when the 10D came out.
Click to expand...
 
jdl said:
I know I'm going to get flamed for this, but here goes....has
anybody else noticed that nobody had any backfocus problems until
Phil mentioned it in his review....and now suddenly EVERYBODY has
HORRIBLE backfocus problems? Could it be the power of suggestion
at work here? There is a great tendency to blame the camera for
bad pictures, and when a well respected reviewer mentions a
possible focus problem, it makes it even easier to blame the
camera. Are you people REALLY sure you have a backfocus issue, or
could it maybe just be possible that you moved the camera after you
focused, or your subject moved, or you focused on the wrong spot to
begin with, or your TRIPOD MOUNTED camera moved when you pressed
the shutter release (you ARE using a tripod for your "tests",
right?) Just a thought.

I've seen lots of people complain about backfocus problems,
followed by a series of "test shots" of their cat, or child. Cats
move. Children move. Cameras not mounted on tripods move. People
have noses, and if you focus on the nose, the eyes will be out of
focus. Etc. There are many reasons why a photo can be out of
focus. Backfocus is just one of them. It is a poor carpenter who
blames his tools.

Food for thought. Flame away.
Click to expand...
 
I've taken more than 600 photos with the D70 already (both "test" images and actual wedding photos). Out of all my D70 pics a total of TWO had what can be described as backfocus. One of those photos had back focus because the subject moved forward an instant before I took the photo (after I had already locked the autofocus on his previous position). I'm not sure what caused the backfocus in the other image ... but I suspect it was OPERATOR error (translation: my mistake and NOT a problem with the camera).

When the Canon 10D came out many, MANY 10D newbies claimed that the camera had a serious focus problem and would not focus as it should. The reality is that there was probably a small batch of 10Ds (probably less than 100) that had a problem, but most of the people complaining about focus problems with the 10D didn't have bad cameras ... they were just bad photographers wanting to blame the equipment.
jdl said:
I know I'm going to get flamed for this, but here goes....has
anybody else noticed that nobody had any backfocus problems until
Phil mentioned it in his review....and now suddenly EVERYBODY has
HORRIBLE backfocus problems? Could it be the power of suggestion
at work here? There is a great tendency to blame the camera for
bad pictures, and when a well respected reviewer mentions a
possible focus problem, it makes it even easier to blame the
camera. Are you people REALLY sure you have a backfocus issue, or
could it maybe just be possible that you moved the camera after you
focused, or your subject moved, or you focused on the wrong spot to
begin with, or your TRIPOD MOUNTED camera moved when you pressed
the shutter release (you ARE using a tripod for your "tests",
right?) Just a thought.

I've seen lots of people complain about backfocus problems,
followed by a series of "test shots" of their cat, or child. Cats
move. Children move. Cameras not mounted on tripods move. People
have noses, and if you focus on the nose, the eyes will be out of
focus. Etc. There are many reasons why a photo can be out of
focus. Backfocus is just one of them. It is a poor carpenter who
blames his tools.

Food for thought. Flame away.
Click to expand...
 
I'll wait for the update. Thanks. I couldn't access you site yesterday but I can now. Guess it was the DNS propagation thing.
Thom Hogan said:
spiny said:
Then how do we know where the sensors are located? If we know this,
then we will be able get the camera to focus exactly where we want
it to, right?
Click to expand...
The first issue of my DSLR Report newsletter (now out of print) had
this info and how to test for it. Once I've got my site moved to
the new server I'll be working at getting that article updated and
posted.

--
Thom Hogan
author, Nikon Field Guide & Nikon Flash Guide
author, Complete Guides to the Nikon D100, D1, D1h, & D1x and
Fujifilm S2
http://www.bythom.com
Click to expand...
--
spiny
 
. . . posting here and get on with the D70 eBook ;-)
  • McD.
•••••••••••••••••••••••••••••••••••
Just what on earth is a 'lense'?
 
and it's even a lens some call to be soft.
Focus set to the 15cm mark

Sun from right, (wireless) flash from left to avoid as many shadows as possible.
Exif are included.

Chris

 
Dave, after Thoms comments did you find and read this
http://www.bythom.com/autofocus.htm

Thom says:

"Do you know where they are? The brackets in the viewfinder are not the size and shape of the actual autofocus sensors. Put the camera in Dynamic Area AF, select each sensor individually, and find a place where you have a near, sharp edge that can be placed against a far background (like a pole for a street sign). Activate autofocus and watch where the edge snaps into focus relative to the bracket. Note that in low light the cross-hatched autofocus sensors (center on CAM900 cameras, left/center/right on CAM1300 cameras) shift down and to one side (it varies, unfortunately), and are wider! Now, with that knowledge in place, does the camera focus every time now?"

The D70, of course, has a CAM900 sensor.

So, until the update, that's all I can find on this, but intend to subscribe once the dust (cough) has settled on his new servers ;-)

--
Nikon D70
 
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