New focus test

Here is an example of the problem

cnewman1 said:

cnewman1 said:

Just gave the test a go, for some reason my paper seems to come our
with a plue / purple tinge to it. I have tried changing the WB
without any luck. Any ideas what would cause this?

Thanks

Davids8 said:

I captured the image per instructions.
The opened it in PS where I have Focus Magic as a filter. This
filter works by analysing the out of focus pixels and shows a "Blur
Width in Pixels" I dont pretend to know the algorhythmn used and
I'm not sure it matters for this exercise. See the image at
http://www.pbase.com/image/30566546 .

You can move the red box to calculate the blur width within it.

Now what I did was to start below the "ideal" focus line (ie closer
to the lens) and "walk" the red box up the line and noted the
numbers. The test image shown is from this thread. This is not
ideal as the small size (and low PPI) makes the red box rather
larger than I'd like. I have done this on my own full size images
and the red box is about half the size.
As the image comes more into focus the the blurr width gets less.
Again the actual number is not of concern to me - rather the trend
of the numbers - do they go up or down.

Has anyone else tried this type of "objective" analysis?

David

Tim Jackson said:

STOP! If you don't care about focus / back focus / front focus then
move right along to another thread.

To those of you still here, I have once again updated my notorious
focus test chart document.

There's now a LOT more information included on the AF system:

+ How the AF system works
+ Why the test chart works (in spite of rumours to the contrary)
+ Simple exercises for you to try out yourself which will greatly
help you in your understanding of how the AF system works.

Find it here: http://md.co.za/d70

Tim
--
=============================
At the time of posting this message, the latest
focus test chart is V2.1 (Dated 24 June 2004)
Get it here: http://md.co.za/d70
=============================

Click to expand...

Click to expand...

Click to expand...

Click to expand...

Dear Tim,

You are doing a great job. In one of my e-mails I referred to you as Sir, and you wondered why; this is the reason.

We all love you, respect you and thank you.

Dr. Henry James.

Mikhail Bogdanov said:

all his efforts are towards stirring s...t up without posting any
real pictures.

Click to expand...

Try not to let it worry you too much sweety pie, I'm sure the day will get better as the hours go by.

Tim
--
=============================
At the time of posting this message, the latest
focus test chart is V2.1 (Dated 24 June 2004)
Get it here: http://md.co.za/d70
=============================

Thanks Henry. I appreciate that enormously.

I wish I understood the human psyche I little better. Messages like Mikhail's leave me lost for a sensible response.

I don't know what's really required. An enema perhaps?

Tim

BTW, Mikhail, as you must know, the idea than Canon (or anyone else) would be paying me is quite silly. However, if you know of anyone who IS willing to throw any money at me please let me know!

--
=============================
At the time of posting this message, the latest
focus test chart is V2.1 (Dated 24 June 2004)
Get it here: http://md.co.za/d70
=============================

You know Tim, it is but natural that some people will oppose you. It is human nature. Some people get a real kick out of it. So let it not upset you. Just do your work and enjoy it.

Dr. Henry James.

Hi Thomas,



The above pic clearly shows that depth of field is set back from the point of focus. Have a look, for example, at the two 20mm markers and the two 30mm markers. The ones behind the focus line and the ones in front of the focus line are not equally in/out of focus.

Having said that though, as far as I can see from this image, it looks like the focus line itself is just inside the area that is in focus and therefore you shouldn't notice any problems in practice. It's borderline and hard to tell from this downsized image.

Obviously, if you choose to, you could have Nikon adjust it so that it's spot on.



Here, if one looks at the "+" symbols on the cells, you can see the slight back focus.

Numbering the cells fro left to right, Compare the "+" symbol on cell number two that on cell number five.

You'll notice that the one on cell two is ever so slightly more in focus than the one on cell five.

For the cell two positions behind the focus cell to be more in focus than the the cell one position forward, the point of focus would need to be slightly behind the intended focus point (cell four).

It's hard to tell from this heavily downsized image but I suspect that the blue cell might be more in focus than the red one. If this is indeed the case then the back focus in this image might be considered too much to be acceptable for close-up work.

Tim
--
=============================
At the time of posting this message, the latest
focus test chart is V2.1 (Dated 24 June 2004)
Get it here: http://md.co.za/d70
=============================

Hi Tim,

Thank you very much for producing such a useful test target. I have run tests on three separate bodies and the same 70-200 VR F2.8 lens. One with very bad backfocus, one with moderate backfocus, and one spot on. I get very consistent results even with your previous test chart (v 2.00). The results from tests using your chart agree with results from my real-world photos and other tests. I started the tests using V 2.00 and no longer have access to the other cameras to repeat the tests using your latest chart.

I had been using a particular D70 for about a month and a half with a Nikkor 28-200G and the kit lens. Only minor backfocus was suspected -- nothing to worry about. However, I encountered bad backfocus with my new lens, a 70-200 F2.8 VR. Your test card (v 2.00) supported my suspicion and quantified the backfocus to be about 2.5 to 3 inches at 70 mm taken from about 6-7 feet. See the test shot below. (The crop only shows the upper portion of the chart.)



That result agrees quite nicely with my real world photos and other tests. The backfocus diminishes towards 200 mm. I can get fairly well focused photos at 200 mm, and your test confirms only mild backfocus at that setting. Just stopping down to F4.0 at 200 mm will yield sharp photos.

I have used two matched CareBears (tm) as an alternate test. The bears have distinct patterns and textures on them, various relief, plus a relatively flat area on their bellies containing a distinct design large enough to ensure the focus area is properly targeted. The bears are placed side by side with the peach colored bear placed two to three inches behind and to the side of the target blue bear. While this test does not accurately quantify the backfocus as does your test, it does support the results from your test.

When I mount the camera on a tripod and photograph these bears at 70 mm from about 10 ft away at F2.8 the front target bear is fuzzy while the rear bear is much better focused. The texture on the peach bear's belly is sharper than the target bear. (Cropped. The target area is noted by text added in post processing.)



Another shot taken from the side shows the depths involved. The aperture is stopped down to F4.5.



I have since had the opportunity to test this lens on two more bodies.

I needed to determine if the lens or the camera body caused the focus problem. I returned to the store with my camera, lens, tripod, test card and the bears. The manager allowed me to photograph the test chart and the bears using their demo D70 attached to my lens. The camera's LCD when zoomed in to review the photos indicated good focus. To be sure, I took the compact flash card home to take a closer look. The store's camera body nailed the focus on both the test chart and the target bear at 70 mm and F2.8. The in-store photos using the shop's camera body are below. Both have been cropped. Notice that the blue bear's belly is sharp and the texture on the belly pad is slightly sharper than the peach bear's belly. I purposefully aimed a bit higher to ensure the bear's foot was not in the focus area. If the focusing system caught the foot instead, any backfocus might be compensated.





Encouraged, I went back to the store. I explained what I found to the store manager. We made a deal which allowed me to exchange my camera kit for another new camera kit he had in stock -- even though the exchange period for my kit had expired some time ago. I took the new kit home and reran the tests. Unfortunately, the new camera body with the 70-200 VR lens has backfocus also. It's not as bad -- about 1.5 inches at 70 mm from about 6-7 feet. Here is a test shot at 70 mm.



I have a large live oak tree which makes a good test subject for backfocus as well. The bark has deep high contrast patterns. There is a sizable limb which from one side of the tree recedes up and away at an angle. I can target any portion of the limb and in every photo taken to date at 70 mm and F2.8 the target is out of focus and an arc extended above and to either side of the focus area in in sharp focus. This photo was taken with the new camera body handheld with VR on at 1/800 sec approximately 15 feet away. The photo is cropped and the focus area is marked with text added in post processing.



Also included is a profile shot of the tree limb. (taken last week with the old camera at F16)



It looks like I'm going to have to pack the body and lens and ship them to the Nikon service center. I passed this info and similar photos on the Nikon customer support who agreed that there was something wrong with the focusing system. Your test chart really helped.

Thanks again,
Steve

It looks like embedding the photos loses a lot of resolution. So here are the links to the pbase photos.

Focus test chart with first camera with VR lens

http://www.pbase.com/image/30648205

Bears using first camera and VR lens. The belly patch texture is more visible when viewed from PBASE

http://www.pbase.com/image/30649269

This is test chart using the Shop's demo camera. It looks like it has no backfocus at 70 mm.

http://www.pbase.com/image/30650681

The bears in the shop using the shop's camera body. The target bear is much better focused.

http://www.pbase.com/image/30651140

My new D70 with the same lens. Still some backfocus at 70 mm :-(

http://www.pbase.com/image/30658048

Finally the tree limb. Notice the arc around focus area which is sharp.

http://www.pbase.com/image/30657826

Steve

WHAT IS THE 1/3 AND 2/3 RULE? THANKS

djmckay said:

Tim, I like your tests and technical explanations.

In my case I found that some of my lenses focussed perfectly at
distances up to approx. 2 metres, but at 4 metres and beyond the
had terrible back focus.
So I think people should also check at longer focus distances.

I realise that the above seems very strange.
I have had a lifetime as a medical and general photographer and
would never have believed the above possible.

Also people should not forget the 1/3 in front 2/3 behind DOF rule.

My 80mm to 200mm f2.8D was the only lens that the camera focussed
well.
All tests were made at wide apertures.

It took me a long time to convince myself that the camera was at
fault, and not me.
I found a good quick test was to photograph my wifes face.
Her glasses and hair was plenty good enough for the auto focus
latch on to, but the focus was always about her ear or neck.

Focus good now after Nikon service.

Click to expand...

Please read this:

http://forums.dpreview.com/forums/read.asp?forum=1034&message=9303741

lrf said:

djmckay said:

Tim, I like your tests and technical explanations.

In my case I found that some of my lenses focussed perfectly at
distances up to approx. 2 metres, but at 4 metres and beyond the
had terrible back focus.
So I think people should also check at longer focus distances.

I realise that the above seems very strange.
I have had a lifetime as a medical and general photographer and
would never have believed the above possible.

Also people should not forget the 1/3 in front 2/3 behind DOF rule.

My 80mm to 200mm f2.8D was the only lens that the camera focussed
well.
All tests were made at wide apertures.

It took me a long time to convince myself that the camera was at
fault, and not me.
I found a good quick test was to photograph my wifes face.
Her glasses and hair was plenty good enough for the auto focus
latch on to, but the focus was always about her ear or neck.

Focus good now after Nikon service.

Click to expand...

Click to expand...

--
http://www.280dgamingclan.com/ThomasAdams/gallery/

Tim Jackson said:

STOP! If you don't care about focus / back focus / front focus then
move right along to another thread.

To those of you still here, I have once again updated my notorious
focus test chart document.

There's now a LOT more information included on the AF system:

+ How the AF system works
+ Why the test chart works (in spite of rumours to the contrary)
+ Simple exercises for you to try out yourself which will greatly
help you in your understanding of how the AF system works.

Find it here: http://md.co.za/d70

Tim

--Having owned my D70 or rather 2 D70's since April and shot hundreds of photo's I would say that the autofocus on these cameras are as good as the F100 and8008, and my F4s but to add the real point here unless necessity requires autofocus nearly all the good photographers I know use manual fous and I've not seen a problem there nor have my many friends who have purchased the D70. I hate to see these pseudo-engineers keep pickin fly do-do out of pepper. If you have a problem take it to your dealer.
=============================
At the time of posting this message, the latest
focus test chart is V2.1 (Dated 24 June 2004)
Get it here: http://md.co.za/d70
=============================

Click to expand...

--
Neil.K. Wollpert

Hi Steve,

Thanks very much for the feedback.

It's just such a pity that these things don't work right out the box the way they should.

It seems not to be a problem of "faulty" equipment but rather that it has been assembled/calibrated without the requisite amount of care being taken.

Glad you're getting yours sorted out though.

Tim

--
=============================
At the time of posting this message, the latest
focus test chart is V2.1 (Dated 24 June 2004)
Get it here: http://md.co.za/d70
=============================