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Nikon 24-70 focus test

Surya Chataut , Jan 19, 2010; 02:15 p.m.

Hi, Did some focusing test with my Nikon 24-70 and it looks like its back focusing. 2mm / 6 mm is where the focus seems to be. Also do you think it should be sharper than what it is at 2mm/ 6mm?

http://www.flickr.com/photos/chataut/4283782755/sizes/l/

Details: 1/60 sec @ 2.8, 50mm, flash used, ISO 200, Camera Nikon D70s, tripod used, timer used, Matrix metering, Spot focusing.

Appreciate comments and ideas for a better test.
Thanks,
Surya

Responses

Les Berkley , Jan 19, 2010; 02:29 p.m.

Well peep my pixel, here we go again. Does this happen with other lenses? Does it happen at other focal lengths with this lens? What AF setting did you use--'spot' has no meaning. Is it doing this if you focus manually? Most importantly, I see that your lens is NOT positioned perpendicular to the test chart. Note the position of the near 30mm markings to the lower edge of the frame.

Surya Chataut , Jan 19, 2010; 02:49 p.m.

Les, if you are not a pixel peeper then that does not mean I should be just like you, right? Neways, test with 50mm/1.8 did not show the same issue. Spot does have meaning - meaning single area focus (as instructed by the focustestchart.com); I just wanted to be specific. The only thing I did not mention was - I used the auto focus functionality. The lens is NOT supposed to be perpendicular to the chart - http://focustestchart.com/chart.html

Les Berkley , Jan 19, 2010; 03:13 p.m.

Your chart is tilted. Look at the 30mm marks. You cannot judge sharpness when the chart is tilted. There is also some kind of shadow below the focus line, which looks as though the paper is crinkled. It has to be absolutely flat. Use manual focus and autofocus and check at several focal lengths. Don't use flash--you are adding an unnecessary variable. And there are already too many of those in your test.

You should not be like me. I am short and squat. You should also not pixel peep. It is an endless exercise in tail-chasing. Is it the lens? The autofocus? Take pictures. If the results fail to please you, and you honestly believe the lens to be at fault, send it to Nikon. When they test it, they will use an optical bench and a laser collimator. They will also test the lens' performance with autofocus. Then they will adjust it to spec.

Michael R. Freeman , Jan 19, 2010; 03:27 p.m.

Les is correct. Your chart is slightly skewed a few degrees clockwise. Also, if this is the entire image, you are not at 45 degrees to the chart (if you were the box would be centered). So any focus error will be exaggerated since you are at a shallower angle.

Repeat with a correctly aligned chart (use the viewfinder grid lines to assist) and at 45 degrees. Side lighting (from a window) would also be better than direct flash.

Surya Chataut , Jan 19, 2010; 03:41 p.m.

The reason I decided to do the test is because I was not very happy with some of my images. If I was a pixel peeper I would have done the test 1st hour of getting the lens and then returned/exchanged. I have had the lens for few months now and just decided to do the test after seeing some one my images.

Yes, this is a crop of the original image.

The paper was folded at that spot, so I will repeat the test with one that is not although 50/1.8 test does not show this issue (exact same positioning, down to the slight skew).

All said, I shall repeat the test with your suggestions. Appreciate the inputs.

Arash Hazeghi , Jan 19, 2010; 11:43 p.m.

Hi surya,
My impression is your lens/camera is slightly back-focus. I find the 24-70 AF to be pretty accurate although I have a D700 which makes a difference in this case. The newer cameras have AF fine tune feature which lets you calibrate the slight back and front focus issues, unfortunately with the older cameras you have to send them to Nikon for adjustment.
Here is a more accurate focus test method which uses moire interference pattern as opposed to simple separated lines, with this method you can check/calibrate AF down to single pixel limit but don't get too much occupied with it :)
Please follow the directions in this link http://www.komar.org/faq/camera/auto-focus-test/

Paul B. , Jan 20, 2010; 04:48 a.m.

I use this lens on my D3. It was slightly out of focus, and I calibrate'it on the camera at +15 . I was'nt also wery happy with the overall sharpness . After one year of use, the zoom ring rubber become loose and I was forced to send the lens to Nikon in order to change this rubber. They calibrate the lens (for free - also shipping was free) and now it's sharper than ever before and the fine tunning feature on my camera , is at "0".

Paul B. , Jan 20, 2010; 12:00 p.m.

"http://www.komar.org/faq/camera/auto-focus-test/"

Very interesting ! Thanks Arash !

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