Alley in Pisa, Italy

by Lars Kotthoff

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I read the whole of How do you find out the "sweet spot" of a lens? — great question and answer, but it didn't discuss a potential homemade rig for finding the sharpness aperture of my lenses.

I recently attended a wedding and took some indoor and outdoor shots — flash was not allowed so I had to play around with ISO — this went ok and I mainly shot at 2.8-3.2 f on my Tamron SP 90 — might have been the wrong choice, but I wanted to get a shallow depth of field.

enter image description here

I'm pretty happy with this image (in fact on the day I reviewed it on my camera screen and I thought I had captured a great shot until I got it on my PC and zooming in on the eye — it's not sharp — I'm finding this a lot with the D7000) — there is a nice shallow depth of field, however it's not really as sharp as I would have liked.

Settings

  • Nikon D7000
  • Tamron SP90
  • ISO 640
  • Exposure 1/60 sec at f3.2

I moved to from a D60 to the D7000 in February (bit of a gap in taking photos due to breaking my leg) but having used the cam I'm not really getting the same results as I used to with the D60.

enter image description here

As you can see this shot looks a little 'Fuzzy'

Settings

  • Nikon D7000
  • Tamron SP90
  • ISO 640
  • Exposure 1/100 sec at f2.8

And this final image is, in my opinion, 'pin sharp'

enter image description here

Settings

  • Nikon D7000
  • Tamron SP90
  • ISO 640
  • Exposure 1/80 sec at f3.2

I guess my issue is that I'm finding the results from my D7000 to not be as good as when I was using my D60 — and I haven't changed my style or approach - e.g. I try to get the shutter speed to match focal length.

I have an owl experience my wife bought for me coming up and can't afford to have sharpness issues for that.

I would really like to achieve the type of sharpness that is found in this photo:

http://www.flickr.com/photos/mycameraobscura/4706010150/

With a nice depth of field — can anyone help me out?

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I have realised since writing this might be just a 'practice harder' related question –  Rob Aug 17 '12 at 7:30
    
Are you comparing apples to apples when you zoom in? Remember, the D60 is a 10mpix camera and your new one is 16mpix. Put the D7000 images at about 80% instead of 100% to compare at the same size. The D7000 may just demand more precision than you're used to. –  mattdm Aug 17 '12 at 13:24
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2 Answers 2

up vote 4 down vote accepted

The first photo is tack sharp -- it's just that the focus is in the wrong place. You want the eye to be sharp, but take a look at the hair just above the ear. It doesn't get any better than that. It's hard to tell at the posted resolution, but I'd bet the base of the lavalier mic in the second picture looks as sharp at a 100% crop as it appears in this reduced-resolution image.

I know the Tamron 90. It is sharp, sharp, sharp from wide-open to f/11 or so, where diffraction starts to take over. It is only just the tiniest bit better at f/4 than it is wide-open. The problem is that you are now working with a camera that has a high enough sensor resolution to show focus errors that would not have shown up as clearly on the D60.

As your comment indicates, it's a matter of practice. The first thing to do is to figure out exactly where the autofocus sensor areas really are (the indicators on the focusing screen are only approximate), so that you can better control where the focus falls. Once you can consistently get the camera to focus exactly where you want the sharpest detail, you'll get back to loving the lens again.

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Stan - thank you so much for your decerning eye on this one - So this gives me some things to work on - I might increase my spot focus to a ball of 9 - Im going to think more about shutter speed vs focal length and trial f/4 out on the Tam 90 again meny thanks! –  Rob Aug 17 '12 at 12:50
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I would recommend you to raise the ISO to lower the shutter speed. The old rule which says "Match shutter speed and focal lenght" come in handy here. So for a 90mm lens, you should aim to have a shutter speed of (crop factor x focal length), in this case, 90 x 1.5 ~ 135 => shutter speed around 1/135 or shorter. Since the lens also lack stabilization, this rule apply even more.

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Ah Ha! great suggestion! - I didnt know the crop factor affected that rule. –  Rob Aug 17 '12 at 12:46
    
To be clear, its actually "faster" shutter speed. 1/135 means 1/200 is good, 1/500 is better. Sometimes, you gotta use a strobe to get the light you need. –  Pat Farrell Aug 19 '12 at 22:33
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