New Theory : How AF Works On The D70 !

dilbertdroid2 said:

dilbertdroid2 said:

Someone has just posted a thread explaining how they fixed the
focus of his D70 with one lens, while the others were at home, and
the focus on those didn't change.

Click to expand...

Click to expand...

http://www.mwords.co.uk/pages/printers/index.html

dilbertdroid2 said:

What preposterous drivel. This zips right over to the "magic
bullet" theory that holds forth the idea that digicams have some
magical properties and are exempt from the laws of optics and
physics.

Click to expand...

The Olympus E-1 seems to work like this. What is so magical about it any way? Maybe your over-the-top response is "preposterous drivel" ?

dilbertdroid2 said:

The imaging chip is NOTHING more than an electronic piece of film.
It is either aligned in the correct image plane or it is not
aligned in the correct image plane. There are some peripheral
issues with imaging chips that can cause flare, color casts or loss
of contrast, but otherwise they must obey the same physical laws as
film.

Click to expand...

This is true, but does not appear to be the only factor, there is some electronic adjustment in the camera.

dilbertdroid2 said:

When I rejected three D70 bodies with severe backfocus, I ran
exactly the same test on an N80 film body with exactly the same
physical setup and exactly the same lenses. And the N80 performed
perfectly. In all my tests, with both film camera and D70 bodies,
the AF test was followed by a manual focus test, with the same
outcome. The imaging chip in the D70 bodies were simply not
aligned accurately.

Click to expand...

What does this prove, if anything at all ? The tables in all the D70's could have been incorrectly set up. But I am not denying that there is a physical factor involved as well - in fact, IMHO it is both, and that is why it is so confusing.

Anastigmat said:

What about those who use a manual focus lens and get back focus? I
still thnk that the back focus problem is a hardware problem, not a
software problem.

Click to expand...

IMO the adjustment takes place during MF as well. This has been borne out by users who do tests in MF and AF and get identical results.

Forget the printer link, just finger trouble !

But to get back to the point :

As for how the lookup table works, you have no idea what the camera does when you press the shutter. The mirror lifts, so you can't see anyway. IMHO the camera performs some adjustment based on table values at that point, and that this applies equally to AF and MF.

MF on this body is a random process in any event, because there is no ground glass or split screen. You can only go on the green dot, and then you can just as well use AF.

As for adjusting the nuts in the body, I think that this is dangerous because it could cause the body adjustment to be inconsistent with the table, ie it could well work for some lenses, but then it would be out for others.

Nikon somehow managed to get the camera tables / camera software calibration / camera hardware calibration / kit lens calibration messed up, and all these factors interacting are leading to almost random results from users, partly because it appears that in many cases more than one of the adjustment components are out. In my case both the body and the kit lens were misadjusted. I still haven't got the D70 to work properly, after it has been in to Nikon three times, and the kit lens is still in.

At present my D70, with far superior lenses, still can't produce an image sharper than a standard P&S.

Tailz said:

dilbertdroid2 said:

Jola233979 said:

Someone has just posted a thread explaining how they fixed the
focus of his D70 with one lens, while the others were at home, and
the focus on those didn't change.

Click to expand...

Click to expand...

http://www.mwords.co.uk/pages/printers/index.html

Jola233979 said:

What preposterous drivel. This zips right over to the "magic
bullet" theory that holds forth the idea that digicams have some
magical properties and are exempt from the laws of optics and
physics.

Click to expand...

The Olympus E-1 seems to work like this. What is so magical about
it any way? Maybe your over-the-top response is "preposterous
drivel" ?

Jola233979 said:

The imaging chip is NOTHING more than an electronic piece of film.
It is either aligned in the correct image plane or it is not
aligned in the correct image plane. There are some peripheral
issues with imaging chips that can cause flare, color casts or loss
of contrast, but otherwise they must obey the same physical laws as
film.

Click to expand...

This is true, but does not appear to be the only factor, there is
some electronic adjustment in the camera.

Jola233979 said:

When I rejected three D70 bodies with severe backfocus, I ran
exactly the same test on an N80 film body with exactly the same
physical setup and exactly the same lenses. And the N80 performed
perfectly. In all my tests, with both film camera and D70 bodies,
the AF test was followed by a manual focus test, with the same
outcome. The imaging chip in the D70 bodies were simply not
aligned accurately.

Click to expand...

What does this prove, if anything at all ? The tables in all the
D70's could have been incorrectly set up. But I am not denying
that there is a physical factor involved as well - in fact, IMHO it
is both, and that is why it is so confusing.

Click to expand...

Why would back focus suddenly be a problem on digital SLR's? People have used AF SLR's for decades without back focus issues. Why would the camera even need a table. Surely it's just measuring phase differences in the images that comes through the lens, via CCD sensors?

Hello,

Previously, I had backfocus with the kit lens and spot on focus with the 50mm. After the first recalibration, I had spot on focus with the kit lens and frontfocus with the 50mm.

Now my camera is back for yet another recalibration. The Nikon Service Center technician was very confident about being able to achieve perfect focus with both lenses. I cannot see it as possible unless there is a lens calibration table of some kind inside the camera. As soon as my camera comes back, I will be able to prove your theory right or wrong!

Regards
Thomas

Leo Hamulczyk said:

Why would back focus suddenly be a problem on digital SLR's? People
have used AF SLR's for decades without back focus issues.

Click to expand...

Times change, its all digital now. The camera is just a dedicated computer.

Leo Hamulczyk said:

Why would
the camera even need a table. Surely it's just measuring phase
differences in the images that comes through the lens, via CCD
sensors?

Click to expand...

It just establish a base level using the AF. Then it does adjustments to that to cater for a wide variety of lenses.

Pretty neat, if it works. You can have poor manufacturing tolerances on your lenses and yet have all of them focusing perfectly.

But Nikon clearly haven't got it all right yet.

First prize would be software that you can run on your PC to calibrate all of your lenses, even other brand lenses, to work spot-on with your camera. But don't hold your breath for this - they'll keep it in-house.

Last year I bought a Canon 10D. Focus was too soft (thanks for all the extra AA).
I returned the camera.

Last month I bought a D70. Loved the feature set and egonomics. Focus was off, especially manual.
I returned the camera.

I haven't been trying to upgrade from my prosumer solely for the privilege of schlepping multiple lenses and cleaning the sensor.

The price on these entry level dSLRs is OK, but their output is not.

Mimoid said:

Hello,

Previously, I had backfocus with the kit lens and spot on focus
with the 50mm. After the first recalibration, I had spot on focus
with the kit lens and frontfocus with the 50mm.

Now my camera is back for yet another recalibration. The Nikon
Service Center technician was very confident about being able to
achieve perfect focus with both lenses. I cannot see it as possible
unless there is a lens calibration table of some kind inside the
camera. As soon as my camera comes back, I will be able to prove
your theory right or wrong!

Regards
Thomas

Click to expand...

I'm starting to have doubts about the consumer dSLR's as well. I haven't found that I can get better pictures from the D70 than from my P&S digital. In fact the P&S images are sharper than the D70 pictures.

Maybe one should wait for a while.

larry reibstein said:

Last month I bought a D70. Loved the feature set and egonomics.
Focus was off, especially manual.
I returned the camera.

I haven't been trying to upgrade from my prosumer solely for the
privilege of schlepping multiple lenses and cleaning the sensor.

The price on these entry level dSLRs is OK, but their output is not.

Mimoid said:

Hello,

Previously, I had backfocus with the kit lens and spot on focus
with the 50mm. After the first recalibration, I had spot on focus
with the kit lens and frontfocus with the 50mm.

Now my camera is back for yet another recalibration. The Nikon
Service Center technician was very confident about being able to
achieve perfect focus with both lenses. I cannot see it as possible
unless there is a lens calibration table of some kind inside the
camera. As soon as my camera comes back, I will be able to prove
your theory right or wrong!

Regards
Thomas

Click to expand...

Click to expand...

None of them manuals cover the CAM900 modules sadly
I am trying to obtain a CAM900 manual (N80).

It was very interesting, they explain the adjustment of the mirror, where using some standard lens they focus at infinity and adjust so the focal planes for the viewfinder and metering etc are the same !! that statement means that mechanical mis-alignment is not really the issue here !!!

What I did find interesting in the Eeprom section, they had L1 - L9 positions and then other data - I assume L1 - L9 store some basic generic information about Nikon lenses , the other data storage areas must contain generic lens data or general AF correction factors such as a focal lenth, aperature lookup table.

I also found it very interesting that the N90 (a very old and basic camera in comparison to the D70) also stored in the Eeprom lookup tables for things like hyperfocal focus point information using aperature and focal length, then also I noticed exposure metering readings where adjusted using the aperature and focal length.

All very interesting but one thing which has totally baffled me - once the viewfinder, CCD, and AF/Meter sensors are all in the same focal plane. Should you not see the backfocus in the viewfinder?? The human eye is looking at maximum contrast in testing focus, so is the AF module (phase detection - which is more accurate than the human eye) so regardless of the lens the AF should hunt back and forth till maximum focus - confusing !!!

regards,
Tarkan

jdl said:

I'm not sure exactly what it all means, but it would appear that
there is indeed some sort of table stored on an EEPROM that
contains some sort of "adjustment data" related to the autofocus
system.

Interesting.

--
Jeff

http://www.photo.net/photodb/member-photos?include=all&user_id=403266

Tim Jackson said:

I spent a few hours trawling through those service manuals the
other day.

I'm glad I found them and they made for interesting "reading" but I
didn't really learn anything that could be useful in the context of
the D70 :-(

Tim
--

=============================
At the time of posting this message, the latest
focus test chart is V2.0 (Dated 12 June 2004)
Get it here: http://md.co.za/d70
=============================

Click to expand...

Click to expand...

--
A Nikon D70 Owner

tarkan said:

All very interesting but one thing which has totally baffled me -
once the viewfinder, CCD, and AF/Meter sensors are all in the same
focal plane. Should you not see the backfocus in the viewfinder??
The human eye is looking at maximum contrast in testing focus, so
is the AF module (phase detection - which is more accurate than the
human eye) so regardless of the lens the AF should hunt back and
forth till maximum focus - confusing !!!

Click to expand...

With all the problems that people have had, the AF has virtually always achieved sharp focus through the VF. I believe that some sort of focus adjustment, based on the table values or defaults, are made when the shutter is pressed and the mirror lifts. That's why you won't see the BF through the VF.

Less likely to be a lookup table in the lens, but what can go wrong in a lens is the data that is reported to the camera.

It is possible the lens is not reporting the correct focus point information (distance info) and even the focal length - this will have serious implications if the camera is using this information to adjust the AF !!

These are the only variables I can think of which would need adjusting or fixing in a lens.

Optically the camera in theory should keep adjusting the focus till hits a maximum.

Imagine this scenario, the lens is at focal length of 50mm, aperature f1.8, object you are trying to focus on is 1meter away. now you AF and the camera locks focus and thinks great I am on target - but the lens is reporting back focal length is 50mm and the focus point (distance information) is stating 1.3 meters, so the CAM900 which is very intelligent knows that using the DOF calculations thinks this is not right - so tries to correct the problem.

This is the only way I can explain why the AF module which only hunts for maximum focus then decides to backfocus slightly.

regards,
Tarkan

Robert Hoge said:

Just a thought here... Is it possible that the value we think is in
the lookup table is actually stored in the chip (eprom) in the lens
itself. It would seem to make more sense to have it there in the
"D" lenses so that the camera table would not have to be changed
when a new lens came out.
If so the camera table may only be a default table if the lens data
is not available. Then either the lens information is wrong,
missing, or lost in a bad connection to the camera, for those
people having BF problems.
Maybe??
Bob

Click to expand...

--
A Nikon D70 Owner

DOHHHH, I did think that yesterday !!! well DOF does not come in to play till the shutter is tripped, and I do think the Camera and AF is DOF aware !!

regards,
Tarkan

Tailz said:

tarkan said:

All very interesting but one thing which has totally baffled me -
once the viewfinder, CCD, and AF/Meter sensors are all in the same
focal plane. Should you not see the backfocus in the viewfinder??
The human eye is looking at maximum contrast in testing focus, so
is the AF module (phase detection - which is more accurate than the
human eye) so regardless of the lens the AF should hunt back and
forth till maximum focus - confusing !!!

Click to expand...

With all the problems that people have had, the AF has virtually
always achieved sharp focus through the VF. I believe that some
sort of focus adjustment, based on the table values or defaults,
are made when the shutter is pressed and the mirror lifts. That's
why you won't see the BF through the VF.

Click to expand...

--
A Nikon D70 Owner

Well said! Why buy a camera (at any price) if you can't get sharpness.

Tailz said:

Maybe one should wait for a while.

larry reibstein said:

Last month I bought a D70. Loved the feature set and egonomics.
Focus was off, especially manual.
I returned the camera.

I haven't been trying to upgrade from my prosumer solely for the
privilege of schlepping multiple lenses and cleaning the sensor.

The price on these entry level dSLRs is OK, but their output is not.

Mimoid said:

Hello,

Previously, I had backfocus with the kit lens and spot on focus
with the 50mm. After the first recalibration, I had spot on focus
with the kit lens and frontfocus with the 50mm.

Now my camera is back for yet another recalibration. The Nikon
Service Center technician was very confident about being able to
achieve perfect focus with both lenses. I cannot see it as possible
unless there is a lens calibration table of some kind inside the
camera. As soon as my camera comes back, I will be able to prove
your theory right or wrong!

Regards
Thomas

Click to expand...

Click to expand...

Click to expand...

tarkan said:

What I did find interesting in the Eeprom section, they had L1 - L9
positions and then other data - I assume L1 - L9 store some basic
generic information about Nikon lenses , the other data storage
areas must contain generic lens data or general AF correction
factors such as a focal lenth, aperature lookup table.

Click to expand...

Also interesting is in the N70/F70 service manual, in the "Inspection Standards" section for AF adjustment accuracy:

L0-L9.....+ - 90um (using offset value)
.............+ - 180um (using no offset value

Lxx........+ - 50 um (using offset value)
.............+ - 100 um (using no offset value)

What are L0-L9 and Lxx? Different lense types? Focal length ranges? Niikor/3rd party lenses? Curious.

And what does "using offset value" "using no offset value" mean?

--
Jeff

http://www.photo.net/photodb/member-photos?include=all&user_id=403266