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03-24-2014, 09:28 AM   #1
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Smudge at the sharpest point

Hi Snappers,

I am shooting with a Pentax K-r and I notice there is a small amount of smudge which appears even at the point of focus which sometime irritates.

I have attached a pic where in the nail was focused and when zoomed it got smudged. Name:  Smudge.jpg
Views: 239
Size:  55.5 KB

I need advise on how to eliminate that.

Thanks in advance.
Vivek.

03-24-2014, 09:34 AM   #2
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What lens was used? What aperture, and other settings?

How did you check that the focus to make sure it was accurate - did you manually focus in live-view?
03-24-2014, 09:38 AM   #3
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It doesn't look terrible at 100%, it just looks like you might have been shooting at a wider aperture. Looking at something at 400% is useless.

What lens were you using? What settings were you using?
03-24-2014, 09:41 AM   #4
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Without knowing the shutter speed it's hard to be sure... But this could also be due to a small amount of motion blur. Maybe small downward movement in the hand at the last instant before the exposure was complete?

Really need Basic settings to help rule out issues.

03-24-2014, 09:54 AM   #5
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QuoteOriginally posted by JinDesu Quote
What lens was used? What aperture, and other settings?

How did you check that the focus to make sure it was accurate - did you manually focus in live-view?
The settings used were

Focal Length : 55mm
Aperture : F/5
ISO : 800
Exposure : 1/100

I chose point focus and pointed exactly at the nail using autofocus. I clicked this pictures using Autofocus Continous option.

---------- Post added 03-24-14 at 10:26 PM ----------

QuoteOriginally posted by elliott Quote
It doesn't look terrible at 100%, it just looks like you might have been shooting at a wider aperture. Looking at something at 400% is useless.

What lens were you using? What settings were you using?

Below were the settings used.

Focal Length : 55mm
Aperture : F/5
ISO : 800
Exposure : 1/100

I am using the 18-55 Kit lens which came with the camera.
03-24-2014, 10:00 AM - 1 Like   #6
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Ooh, the wonders of the kit lens at 55mm wide open. And at close focus too.

This combination is the absolute worst you can do with the Pentax kit lens.

Av and f/8.
03-24-2014, 10:02 AM - 1 Like   #7
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The 18-55 is weak at the long end and wide open, so you're losing sharpness there. Try stopping down to about f8 and maybe backing off to 45mm or so.

Also, AF.C isn't ideal for this subject, it is meant for action and will release the shutter even if you lose focus. Use AF.S for this.
03-24-2014, 10:05 AM   #8
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QuoteOriginally posted by GryphonPhotoCat Quote
Without knowing the shutter speed it's hard to be sure... But this could also be due to a small amount of motion blur. Maybe small downward movement in the hand at the last instant before the exposure was complete?

Really need Basic settings to help rule out issues.
The exposure was 1/100 of a second. The above posted image was just a sample where in the smudge is very prominently visible. It happens when I capture a static object using a tripod.

03-24-2014, 10:19 AM   #9
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That actually is a bit better that I would expect from a kit lens, wide open, 55mm, and close up.. Other manufacturers wish their kit lenses would do that well with those settings.
03-24-2014, 10:27 AM   #10
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QuoteOriginally posted by sanvic15dj Quote
I need advise on how to eliminate that.
Looks like the glow you get when you ever so slightly miss focus when wide open. Stop down a click or two.
03-24-2014, 11:29 AM   #11
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The kit lens isn't a bad lens, but avoid shooting wide open. I stay at f/8 when at all possible with the kit.

If you want sharp at pixel level you need to get yourself a good prime lens, preferably a macro. And a camera without a lowpass filter...
03-24-2014, 11:55 AM   #12
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Did you focus, and then zoom afterward? Some lenses can't maintain exact focus while zooming.

Also, the main reason I keep my DA18-55 around is because of less sharpness. It's good for basic product photos, where you don't want every spec of dust or small scratch exaggerated to look much worse than it actually does in real life.
03-24-2014, 12:09 PM   #13
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QuoteOriginally posted by sanvic15dj Quote
The exposure was 1/100 of a second. The above posted image was just a sample where in the smudge is very prominently visible. It happens when I capture a static object using a tripod.
How did you focus? Auto focus? Or manually focusing with liveview at 16x digital zoom?

The bloom, as someone else said, looks like when you miss the focus by just a small margin.
Also, the 18-55 kit lens is not the sharpest lens out there - what you show is reasonable in expectation for that lens. You are shooting wide open at F5.6 and 55mm, when good performance is after 1 or 2 stops closed (F8/F11 in this case).

If you had a faster lens like a DA 50mm F1.8, you could shoot at F5.6 and get a much sharper image out of it.

Edit* actually - based on the skin just below the nail, I'm pretty sure you've front focused just a little bit. In addition, due to it being a zoom, the hood will not protect against stray light as well as the wide end of the lens. Thus at close focus and wide open, the lens will lack a bit of contrast and exaggerate the blooming. A solution to that would be to expose the image darker and bring it up in post process.
03-24-2014, 12:27 PM   #14
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QuoteOriginally posted by Parallax Quote
Other manufacturers wish their kit lenses would do that well with those settings.
Interesting... I've heard the exact opposite.
03-24-2014, 12:27 PM   #15
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Filter? Was there a filter on the lens?


Steve
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