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Focus issue with 35mm f1.8 lens

Saint Trickster

UK
23 posts

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Saint Trickster Registered since 18th Feb 2013
Wed 20-Feb-13 11:54 AM

Hello

First post so please be gentle.
I've just upgraded to a D7000 from my D5100 (not a massive upgrade but worthwhile to me nonetheless) and I've noticed an issue with the focussing at large apertures with my 35mm f1.8 lens.
Basically, if I focus using the viewfinder then my images when zoomed in are blurred.
But if I use the LCD and liveview to focus then the image is very sharp when zoomed in.
I need to do a more formal test with a tripod tonight but is this a common problem as I never encountered it with my D5100?

Many thanks


jec6613

Norwalk, US
1315 posts

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#1. "RE: Focus issue with 35mm f1.8 lens" | In response to Reply # 0

jec6613 Registered since 12th Feb 2013
Wed 20-Feb-13 11:07 AM | edited Wed 20-Feb-13 11:13 AM by jec6613

This can be an issue with any DSLR, and it means that the AF system may need to be adjusted.

There are two different focusing systems at play here: the phase detect AF (PDAF) system has an array of CCD sensors house inside of the mirror box of your DSLR, that measure distance to subject and then the processor sends a command to move the lens to that point. Pretty simple, it's what's used when looking through the viewfinder.

The second is a contrast detect (CDAF) system, which uses the main imaging sensor itself and powers the lens back and forth until the imaging sensor sees a sharp image, defined by crisp high contrast lines.

Because the CDAF system uses the sensor that is going to take the picture, it is very precise and is easily the more accurate system. However, it's much slower, doesn't allow tracking subject movement, and is generally a poor performer (other than nailing focus) on a DSLR. The PDAF system is fast and very accurate, to within 1/3 of your depth of field at maximum aperture, but because the system is physically separate from the main imager, it can be out of adjustment from it.

On your other lenses with smaller apertures, you never noticed it because much more was in focus, but no doubt they missed focus as well. Wide open on the 35 f/1.8 though, depending on the distance, your depth of field can be exceptionally thin and you can end up missing the target completely. If it's significant, the permanent solution is to have your D7000 serviced (it has known issues with not hitting focus), hopefully under a warranty, by somewhere that can fix the AF system. However, in the meantime, if you need to use the camera before you can get it out to service, simply make sure that you stop it down to f/2.8 or 3.5 or so and that way you won't see the AF misses.

Here's a good troubleshooting guide to your AF system, I suggest reading up on it (it's a bit out dated, as it doesn't list the D7000 which does have AF fine tune, but things haven't really changed that much): http://www.bythom.com/autofocus.htm

briantilley

Paignton, UK
30235 posts

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#2. "RE: Focus issue with 35mm f1.8 lens" | In response to Reply # 0

briantilley Gold Member Deep knowledge of bodies and lens; high level photography skills Donor Ribbon awarded for his support to the Fundraising Campaign 2014 Nikonian since 26th Jan 2003
Wed 20-Feb-13 11:25 AM

Welcome to Nikonians!

Whatever you may have read or heard, in general the D7000 does not suffer from faults in focusing

There are many possible explanations for what you are seeing, and it's not much use us speculating at this stage.

Testing more carefully with a tripod, a good AF target and decent lighting would be a good next step. You could post some examples and tell us more about your camera settings, then I'm sure we'll be able to make some suggestions.

Brian
Welsh Nikonian

Saint Trickster

UK
23 posts

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#3. "RE: Focus issue with 35mm f1.8 lens" | In response to Reply # 1

Saint Trickster Registered since 18th Feb 2013
Wed 20-Feb-13 07:02 PM

Hello again

Thank you both for the welcome and informative replies.
I did a little research into the D7000's apparent faults before the purchase and obviously the so called back focus issue came to the forefront, but I didn't want to jump on that bandwagon hence my initial question.
This evening I printed off a test chart and set up my D7000 on a tripod. Used single point focus and metering, widest aperture and VR off for all my lenses.
I had to dial in -13 in the AF fine tune for the 35mm f1.8 lens, -6 for my soon to be sold 55-200mm f4-5.6 and -2 for my 105mm f2.8 Micro lens.
I'm happy that I've been able to get the viewfinder focus really very close to that of the LCD liveview now in all of my lenses but am a little worried I've had to dial in such a large adjustment on the 35mm one.
I may consider returning the lens to amazon or would it be better to send the camera and lens back to Nikon do you think? Maybe I'm worrying unnecessarily, I'd much rather concentrate on using my equipment than worrying about its possible failings which are most likely negligible in comparison to my own.

Many thanks

N4TVC

Burke, US
109 posts

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#4. "RE: Focus issue with 35mm f1.8 lens" | In response to Reply # 0

N4TVC Registered since 15th Jul 2006
Wed 20-Feb-13 11:40 PM

Many here have had focus problems that Nikon admitted were off and readjusted under warranty. Just look at all the posts. If you are in doubt, best to let Nikon have a look at it. I suffered with mine for several months thinking I had all of a sudden forgotten how to shoot after 40 years in the business. When I finally realized there was indeed a problem with the camera, I sent it off to be fixed and adjusted. Nikon did so and quickly returned the camera. It is now, and has been for over a year, perfect.

Charles

EAPhoto

Asheboro, US
75 posts

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#5. "RE: Focus issue with 35mm f1.8 lens" | In response to Reply # 4

EAPhoto Registered since 16th Jan 2013
Thu 21-Feb-13 12:23 AM | edited Thu 21-Feb-13 12:24 AM by EAPhoto

I agree with Charles. If you are pretty seasoned as a photographer and know how to get results and are not getting them do not drive yourself insane with test after test. Not that testing is a bad thing, but use common sense and trust your judgement. Bad results from familiar shooting situations should tell you something. The whole process of getting my D7k readjusted took just under two weeks.

Visit my Nikonians gallery.

RLDubbya

US
553 posts

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#6. "RE: Focus issue with 35mm f1.8 lens" | In response to Reply # 3

RLDubbya Silver Member Nikonian since 24th Dec 2011
Thu 21-Feb-13 12:30 AM


>I may consider returning the lens to amazon or would it be
>better to send the camera and lens back to Nikon do you think?
>

I had to set fine tune to -18 for a brand new Sigma 24-70/2.8 about a year ago. I recently had to set fine tune to -18 for a Nikkor 14-24/2.8; had to set the fine tune on both my D7000 bodies for these two lenses. Other lenses are fine - the 70-200/2.8 VRII is perfect with no fine tune.

I've shot thousands of images with the Sigma since fine-tuning, and hundreds with the Nikkor. Never looked back. They're just numbers. My images are perfectly sharp now, that's all that matters to me.

Enjoy your camera!


Saint Trickster

UK
23 posts

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#7. "RE: Focus issue with 35mm f1.8 lens" | In response to Reply # 5

Saint Trickster Registered since 18th Feb 2013
Thu 21-Feb-13 11:04 AM

Many thanks for all of the replies.
I'll try and get some images put on the site tonight with and without the finetuning adjustment.
At the moment for piece of mind I think I might return the lens and camera to Nikon for them to evaluate, but am open to suggestions after I upload the images.

Thanks for your time, really appreciate it.

Saint Trickster

UK
23 posts

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#8. "RE: Focus issue with 35mm f1.8 lens" | In response to Reply # 7

Saint Trickster Registered since 18th Feb 2013
Thu 21-Feb-13 04:30 PM

Here's some pictures to explain the problem.
Not very good quality and the light was indifferent but it's the best I can do at the moment.

Liveview:

Click on image to view larger version


No Finetune:

Click on image to view larger version


-13 Finetune:

Click on image to view larger version


Focus was on the black and white squares.

Thanks

The only processing I've done is to convert from RAW to JPEG in Lightroom 4 and crop to size.

EAPhoto

Asheboro, US
75 posts

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#9. "RE: Focus issue with 35mm f1.8 lens" | In response to Reply # 8

EAPhoto Registered since 16th Jan 2013
Sat 23-Feb-13 01:54 PM | edited Sat 23-Feb-13 01:55 PM by EAPhoto

I am starting to see why some of the gurus on here can punch holes through and question user error into many of the posted test in these forums.

f1.8 does not give you much room for error.

Looking at these, I would not be satisfied with the camera performance barring any shooter error.

I was producing these same kind of results from different situations with my D7K. No matter the subject or the lens, the softness was always there. The difference is night and day since I got my camera back from Nikon.

Visit my Nikonians gallery.

Saint Trickster

UK
23 posts

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#10. "RE: Focus issue with 35mm f1.8 lens" | In response to Reply # 9

Saint Trickster Registered since 18th Feb 2013
Sat 23-Feb-13 03:04 PM

Thanks for the reply.
I think for my own piece of mind I'll return the lens and body to Nikon to see what they have to say.
I'll update the thread when I get them back.

newfoundlander61

Kingston, CA
32 posts

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#11. "RE: Focus issue with 35mm f1.8 lens" | In response to Reply # 10

newfoundlander61 Registered since 03rd Feb 2013
Sat 23-Feb-13 10:37 PM

Here is a good video.

http://www.youtube.com/watch?v=7zE50jCUPhM&hd=1

Saint Trickster

UK
23 posts

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#12. "RE: Focus issue with 35mm f1.8 lens" | In response to Reply # 10

Saint Trickster Registered since 18th Feb 2013
Mon 04-Mar-13 07:15 PM

Hi
Just a quick update.

Firstly, Nikon returned my camera and lens within a week so well done to them.

The associated paperwork said they'd done the following....
Clean lens elements and check infinity focus, check, clean and test.
Check and adjust the body to Nikon standard.
Reported focussing faults were identified and repaired.
All other functions checked, clean and test.

So the results.....
Much, much better.
Not perfect and still having to dial in -7 in the fine tune menu but now I'm happy with this adjustment that the focus is spot on.
I've not checked any charts as its not really my thing but did spend a couple of hours tonight taking loads of photo's until I found a really good AF adjustment.
The main thing is I'm happy and can go and enjoy my D7000.
My only other lens a 105mm f2.8 macro needed a -2 adjustment but that was very simple to do.
Now I need to make the decision of which lens I should get to compliment the 2 I already have, probably a used 17-55 or a Sigma 17-50 I should think.
Thank you for all of your input, really glad I joined up.
ST

G