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12-01-2013, 11:15 PM   #1
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Do I have serious backfocus or am I missing something?

Hi,

I got my K-30 with 18-135 lens two weeks ago and I noticed that when I take pictures of my dogs at 135 mm I almost always get the tail in focus but not the face. I have now found different focus charts and tried them out. As far as I can tell there is serious backfocus and even with setting the focus adjustment to its max value it gets only slightly better.

Can the camera be really that bad or am I doing something wrong? I am attaching the images to this message.

1. 18-135 at 18mm
2. 18-135 at 135mm
3. 18-135 at 18mm different chart
4. 18-135 at 135mm
5. 55-300 at 62.5mm
6. 55-300 at 120mm

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12-01-2013, 11:38 PM   #2
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When using these test charts, you need to be very careful and ensure that the camera is aligned with the chart. Any misalignment can lead to confusing results (the 2nd chart isn't straight so the two scales don't match up). Be sure that there's plenty of ambient light, too.

Also, are you using the central AF point only? If you have the camera set to auto-11 it might sometimes focus on something other than what you're pointing at directly.

If the above charts were shot with a -10 AF adjustment, I'd say you probably don't have any back focus. But it's hard to say based on the above shots...

I'm sure you already know this, but here's the full testing procedure. It might be worthwhile to get one of these pro test charts to settle the matter once and for all!
Fixing Front and Back Focus - LensAlign MkII - PentaxForums.com

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12-01-2013, 11:55 PM   #3
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One of the first things I did after I got my K5-II was to set the autofocus to spot rather than multi point. I reckon I get far more predictable results. I put the centre of the frame on the point I want in focus, half press the shutter button to get a focus lock, and then recompose and fully press the button to take the shot. My 18-135 seems to hit the focus bang on every time using this method.

I used to do basically the same thing with the split prism manual focus on my K2.
12-02-2013, 02:23 AM   #4
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+1 for the spot focus. I change all of my cameras to center only focus. I can recompose the shot after I've selected what to focus on.

Different temperature light sources will also change your focus plane.

12-02-2013, 10:28 AM   #5
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I had spot focus turned on. I also tried approaching the focus point from different directions but the result was always the same. I'd be very curious to see how the results look for other cameras. Unfortunately I don't know anybody who has another Pentax or even DSLR.
I guess I'll try over the weekend in good daylight and then make a decision whether to send it back or not.
12-02-2013, 10:31 AM   #6
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QuoteOriginally posted by Adam Quote

Also, are you using the central AF point only? If you have the camera set to auto-11 it might sometimes focus on something other than what you're pointing at directly.

If the above charts were shot with a -10 AF adjustment, I'd say you probably don't have any back focus. But it's hard to say based on the above shots...
The pictures I posted were made with neutral AF adjustment. Cranking it up all to 10 made things a bit better but if anything there was still back focus. I can't get the camera to front focus even if I go to the maximum adjustment,
12-03-2013, 11:08 PM   #7
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So, where's the dog?
12-04-2013, 07:24 PM   #8
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Looking at your chart photos, none of them seem very well lined up. In order for the charts to work properly they have to be perfectly flat, and aligned centrally and horizontally with the camera.

With the Regex ones, did you test to make sure the AF can't lock onto the grey part of the chart? It may be that the AF isn't actually locking onto the black bit in the middle of the chart. There are a number of different charts with different shades of the grey bits. Sometimes you will need the very lightest one for some cameras with very sensitive AF.

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