where there’s smoke there’s forum fire
From 16 to around 62 or so the lens is very sharp and focus is spot on. From around 62-65 to 85 the lens is still very sharp but with a back focus problem?????? I have sent it in once. It still has the problem.
There is talk of softness at the long end with 16-85. Mine is not soft at the long end - just back focus problem.
Is this a known problem?
Maybe you just don't notice the back focus problem at the wider focal lenghts? Try sending BOTH the camera(s) AND the lense in for calibration. It could be the camera that needs adjustment.
Test it with another lens first before sending it off.
Seems really odd you could see any BF really. At 65mm the lens should be at almost f5.6 and your depth of field should be about 3-4 inches shooting at a subject at 5 feet away.
If it were me, I would set it up on a tripod, put a beer or pop bottle on a stool at a measured 5 feet away (from the hot shoe mount), set the body to "S" AF and single spot, focus on the cap, and use the timer to fire the shutter, and see what happens. If it is blurry I would add two more bottles stacked behind at a 45degree from the first one to see it it is back focusing. Still not working, stack two more with an aspirin bottle on top of the last bottle - either way you will need that for later.
Post sample shots of the problem. It is useless to speculate otherwise.
Sent the lens in again.
Here is the test I did before sending it in the first time: Camera on tripod. Single AF. Remote used to fire the camera. Target was plugs placed about one inch apart. I let the camera refocus every time. Target plug was the sharpest until about FL 65. After that it was the plug behind.
No problem with my 85 1.8 (pre D) - same test.
I hope Nikon Service find and fix the problem.
I just wanted to know if it was a common problem. Maybe at 5.6 there is not enough light for the camera to focus?
Sorry I deleted the test shots - I did a lot :-).
BTW I used a single focus point - the middle one.
Without photos it is really hard to tell.
There can be some natural shift with zooms but not much more than a 1/2". Mostly that comes into play when you are at it's max close-focus distance. A lot of times it is just eliminating variables to find the cause.
Only other ways to test that I would suggest:
Set iso to 200 (turn off auto iso)
Use shutter delay
Shine a flashlight on the target object.
Test 5 focal lengths. 16, 24, 50, 65, 85.
I usually test suspect lenses with a ruler and a standard hobby cutting mat from Walmart. The key is to use a vertical line (corner of a block for me) for the camera to lock on.
Tao: The idea behind Your setup = The idea behind mine. Only I used little finger sized targets instead of a ruler. I will steal your setup :-) It is simpler an does more.
Using your pic. "6" would come out the sharpest between 16 and 65. And "5" would be sharper from 65 to 85.
Thank you for your input.
FWIW, I've used Double A batteries for this test.
I line them up at flanking 45 degree angles and focus on the middle one, snap, then see where the focus actually falls.
As such:
(0)
___(0)
____^_(0)
I actually used batteries and crayons before as well. the only thing I found was that the focus shifts slightly with curved objects and that is why I cut a few blocks of wood. It can make a difference on Macro work and getting the DOF calculations. For any other application, just about anything works fine.
Henrik1963 said:
Tao: The idea behind Your setup = The idea behind mine. Only I used little finger sized targets instead of a ruler. I will steal your setup :-) It is simpler an does more.Using your pic. "6" would come out the sharpest between 16 and 65. And "5" would be sharper from 65 to 85.
Thank you for your input.
Steal away! I actually take a second ruler and line it up to the camera on the 6 as well. I should just break down and buy a lens align target but for now this works.
You might try sending it back in with the photos you take and notes of settings. I have found some techs get belligerent and that works to overcome it.
First: Thanks all for your input.
The lens went back for at second time. And they fixed it. I have now tested it - both at home shooting at targets and in the real world taking pics. The lens is now sharp all the way from 16 to 85.
They told me the issue was related to the way the lens sends info to the camera regarding focus.
Best regards
Glad to hear you got it fixed! And thanks for the follow up info - I hope it didn't take 3 months to get your lens back.
Interesting to hear it was the "chip" and nothing mechanical - haven't heard that in a really long time since the first D-lenses. I'll have to keep that in mind when testing new glass.
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