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12-22-2010, 03:14 PM   #1
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How do Front/Back focus issues show?

Looking at getting a Tamron 17-50mm f2 to replace my kit lens in the new year...

Some of the reviews for the lens (2008/09 not really mentioned in newer reviews) mention 'Front/Back Focussing' issues...

What are these issues? How do they show up in images?

Is it something that has been rectified in Tamrons later production runs? (post 2009...)

Is it something I need to worry about with my K-x? (Not sure if I can adjust for these issues like the K20/K7 can...?)

This seems to be the most sensible and cost effective upgrade to the 18-55mm f3.5/5.6 kit lens curently on the market in the UK and faster than the Pentax 16-45mm f4 which retails here at a similar price-point...

Any thoughts appreciated... Merry Christmas

12-22-2010, 03:22 PM - 1 Like   #2
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This will answer your question: Nikon D70 Focus Chart. This applies to all cameras, not just the Nikon D70. Here you can download the chart to do your own testing too.

It's not so much of a problem with the lens as it is a variance in production. That's why most of the newer Pentax cameras can dial in focus correction for individual lenses.

I considered the same lens, but ultimately thought the 16-45 would better suit my needs. I've also owned the DA* 16-50 and DA 17-70, but kept the 16-45. All of them are pretty decent lenses, including the Sigma 17-50.

Merry Christmas to you too.
12-22-2010, 03:44 PM   #3
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Cheers man... Very useful link... I've downloaded a copy of the chart... It explained the issue easily (which makes a nice change!!)

When you say "varience in production" is this something that's eradicated over time... or do these "variences" occur often?

The DA-16-50 and 17-70mm both retail at around twice the price in the UK and as yet I'm unable to find the Sigma 17-50 in a Pentax mount outside of France...
12-22-2010, 04:26 PM   #4
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I haven't used the Sigma or the Tamron, but I would guess they are very similar. Many people here use either of them and rate the lenses very high.

As far as production goes, from what I understand, a lens can pass quality control with very minor FF/BF issues. This is because it falls within an acceptable range at the production facility. My K10D needed a focus adjustment a couple years ago, but unfortunately I found this out the hard way, after a shoot full of OOF pictures from the FA 43. I calibrated it using that chart and haven't had a problem since. Here's a better explanation and a good read: LensRentals.com - "This lens is soft" and other myths

12-22-2010, 05:16 PM   #5
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QuoteOriginally posted by builttospill Quote
This will answer your question: Nikon D70 Focus Chart. This applies to all cameras, not just the Nikon D70. Here you can download the chart to do your own testing too.

It's not so much of a problem with the lens as it is a variance in production. That's why most of the newer Pentax cameras can dial in focus correction for individual lenses.

I considered the same lens, but ultimately thought the 16-45 would better suit my needs. I've also owned the DA* 16-50 and DA 17-70, but kept the 16-45. All of them are pretty decent lenses, including the Sigma 17-50.

Merry Christmas to you too.
Thank you very much for the link. I've been wondering if I have this problem and this will let me verify it!

Merry Christmas!
12-23-2010, 12:25 PM   #6
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First, it helps to be sure of the return/exchange policy before purchase. You can easily save a few pounds on the price, then burn it all if you have to pay postage on a return.

Second, if you're going to test, try to cover all the variables to make sure your results are good. Sometimes people get all excited about their terrible lens, when they've simply botched the test.

Third, use the lens in the real world too. By all means take shots at wide-open aperture and see if focus is where you thought it was. That puts perspective on test chart photos.
01-20-2011, 08:34 AM   #7
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QuoteOriginally posted by builttospill Quote
I haven't used the Sigma or the Tamron, but I would guess they are very similar. Many people here use either of them and rate the lenses very high.

As far as production goes, from what I understand, a lens can pass quality control with very minor FF/BF issues. This is because it falls within an acceptable range at the production facility. My K10D needed a focus adjustment a couple years ago, but unfortunately I found this out the hard way, after a shoot full of OOF pictures from the FA 43. I calibrated it using that chart and haven't had a problem since. Here's a better explanation and a good read: LensRentals.com - "This lens is soft" and other myths
Could you help me how to do the calibration? I'm having serious backfocus problems...
I have the 1.31 firmwire, and can not figure out how to deal with it

Thx!
01-20-2011, 11:02 AM   #8
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Sure. Take a look at this guy's blog. He very clearly walks you through testing your K10D and how to adjust it. I'm posting the link because he explains it better than I could: Photography Rulez: K10D Focus Error Adjustment

Once you've tested, do you know how to get into the debug mode and set the focus adjustment? If not, take a look here: https://www.pentaxforums.com/forums/pentax-dslr-discussion/27040-k10d-firmwar...tml#post276514

If you have any questions during the process please ask.

01-22-2011, 12:41 AM   #9
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Does pentax have any cameras yet with an auto focus adjustment?
01-22-2011, 12:42 AM   #10
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Nevermind the last question, I found the answer
01-24-2011, 06:28 AM   #11
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If your camera has live view, this is the place to go and the thing to do (imho)

AF microadjustment for the 1Ds mark III, 1D Mk3, 5D Mk2, 7D
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