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Focusing issue....

portrayal22

Greentown, US
10 posts

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portrayal22 Registered since 27th Oct 2010
Wed 26-Jun-13 01:57 PM

Ok, I have no idea what I am doing wrong. I shoot in either M or AP and after getting the exposure correct I focus on the eyes of my subject. The little green light shows up solid in my viewfinder and "my" camera tells me I am in focus. Later when I look at the photos, even though it is mostly focused, I am unable to actually find that sweet spot. The images are just not as sharp as I want them to be. Can anyone give me any advice or suggestions on how to find that sweet spot of my lens?

I usually shoot with a 24-70 2.8 lens at f7.1 to f8.

Thanks!!

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elec164

US
2600 posts

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#1. "RE: Focusing issue...." | In response to Reply # 0

elec164 Silver Member Nikonian since 15th Jan 2009
Wed 26-Jun-13 02:40 PM

Personally I find the lens evaluations at slrgear.com useful. Using their interactive blur index chart seems to give a good idea of how the lens performs at various f-stops and focal lengths.

According to their review, that lens should perform very well from f/4 to f/11.

That aside I would ask how you are evaluating for sharpness. Reason being is that at f/8 the projected diffraction spot size is around 10 microns. With an 8x12 print there is about 8.5x enlargement making the diffraction spot about 85 microns which is under the average eye sight resolution. But at 100% view on a monitor with a resolution of 93 PPI it results in about a 32x enlargement making the diffraction spot size 320 microns or well above the average eyesight resolution. So an 8x12 print at average viewing distance and eyesight the focus plane should look fairly sharp. But on a monitor at 100% view I would think you will start to see the effects of diffraction.

At least I hope I calculated all this correctly.

Pete

Pete

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BR

Glen Mills, US
542 posts

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#2. "RE: Focusing issue...." | In response to Reply # 0

BR Registered since 17th Nov 2006
Fri 28-Jun-13 08:22 PM

What shutter speeds are you using? With or without VR? Is your subject moving?

Barry

JosephK

Seattle, WA, US
7109 posts

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#3. "RE: Focusing issue...." | In response to Reply # 0

JosephK Silver Member Fellow Ribbon awarded for his excellent and frequent contributions and sharing his in-depth knowledge and experience with the community in the Nikonians spirit. Nikonian since 17th Apr 2006
Fri 28-Jun-13 11:18 PM

>Ok, I have no idea what I am doing wrong. I shoot in either M
>or AP and after getting the exposure correct I focus on the
>eyes of my subject. The little green light shows up solid in
>my viewfinder and "my" camera tells me I am in
>focus. Later when I look at the photos, even though it is
>mostly focused, I am unable to actually find that sweet spot.
>The images are just not as sharp as I want them to be. Can
>anyone give me any advice or suggestions on how to find that
>sweet spot of my lens?
>
>I usually shoot with a 24-70 2.8 lens at f7.1 to f8.

Well, f/8-ish should be giving you lots of depth of field, so that is probably not the problem.

However, at f/8 if indoors then your shutter speeds could be low enough to start worrying about motion blur, both camera and subject.

Another aspect is your post-processing settings regarding sharpening.

It is highly doubtful that the problem is related to any sweet spot of the lens. Can you post an example or two, unedited with all the EXIF data intact? That way we will see what you are seeing.

---------+---------+---------+---------+---------+
Joseph K
Seattle, WA, USA

D700, D200, D70S, 24-70mm f/2.8, VR 70-200mm f/2.8 II,
50mm f/1.4 D, 70-300mm f/4.5-5.6 VR, 18-70mm f/3.5-4.5 DX

gheck58

Aliso Viejo, US
2911 posts

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#4. "RE: Focusing issue...." | In response to Reply # 3

gheck58 Silver Member Nikonian since 26th Dec 2003
Tue 02-Jul-13 08:28 PM

I'm not discounting that there may be a lens issue but it sounds like either a shutter speed or hand holding technique issue. Have you tried another lens under the same conditions first? The 24-70 is pretty heavy and if you are shooting at lower shutter speeds you need to hold it still. Also, try cranking up the ISO if you need too to get a shutter speed over 1/250 and see what happens.

Hecky

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DinoCardelli

Plantation, US
236 posts

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#5. "RE: Focusing issue...." | In response to Reply # 0

DinoCardelli Registered since 19th Oct 2010
Tue 02-Jul-13 09:30 PM

Can you post a picture with the EXIF data?

Do you have the same problem when shooting in Apeture?

Also, you didn't mention what 24-70 you are using? Newer model? Older ?

DC

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MEMcD

US
31632 posts

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#6. "RE: Focusing issue...." | In response to Reply # 0

MEMcD Moderator In depth knowledge in various areas Nikonian since 24th Dec 2007
Fri 05-Jul-13 02:57 PM

Hi Nita,

What AF mode are you using: AF-C, or AF-S?

What AF Area mode are you using: Single point, Dynamic Area, or Auto Area AF?

What shutter speed are you using?

Again, uploading a sample image with the Exif data intact would be helpful to diagnose the problem.

Best Regards,
Marty

G