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05-03-2013, 02:15 PM   #1
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K-5 Focus Calibration - Sigma lenses

I'm looking for some advice, and I hope I'm in the right forum. I recently purchased a K-5, and two Sigma lenses - an 18-135 and a 24-70 2.8. I set the lens focus calibration using FocusTune, which works fine with the K-5 (I was glad to find it, having used Reikan FoCal with the Nikon D7000 that I used to own).

Using live view, both lenses are very sharp at maximum aperture. In fact the Sigma 24-70 is significantly sharper than two Tamron 28-75 f:2.8 lenses that I compared it against. The problem is that one lens has significant front focus issues, while the other back focuses. In fact, the 18-125 could only achieve correct focus calibration using the Debug mode method of expanding the AF calibration range by offsetting the zero point on the AF calibration scale to +40. Unfortunately, when the camera is set up that way, the 24-70's ideal calibration setting is more than -10.

So, I have some options -

1. Send the lenses to Sigma, where I will have to pay to have the 18-125 calibrated. The 24-70 is new, and would presumably be calibrated for free.

2. Leave the camera in debug mode, and shift the base calibration range when I change lenses. I don't know if there is a reason why I shouldn't do this.

3. Sell the 18-125 and buy another lens.

Any thoughts?

By the way, I love the k-5 - it's very solid and the image quality is great.


Thanks.

05-03-2013, 03:29 PM   #2
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I'd just get rid of the Sigma lens unless you really need an all in one lens. The Pentax 18-135 would be a good alternative to it.

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05-03-2013, 03:43 PM   #3
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You seem to have missed this item from the FocusTune instructions:

QuoteQuote:
Do not shoot in Live View mode
Camera Settings Best Practices - Apr 26 - MTD Product Info Center
05-03-2013, 04:46 PM   #4
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QuoteOriginally posted by rawr Quote
You seem to have missed this item from the FocusTune instructions:


Camera Settings Best Practices - Apr 26 - MTD Product Info Center
I didn't set the lenses up using FocusTune in live view mode - I'm not sure where you got the idea that I did.

The 18-135 Pentax would be an option to replace the Sigma 18-125, although reviews suggest that the 18-135 is a pretty mediocre lens, while the 18-135 Sigma that I have is sharp at maximum aperture.

I want an f:2.8 lens for indoor work, and 24-70 or 28-75 is the right range for the kind of shooting that I do, so I'm sure I'll keep either the Tamron or the Sigma. By the way, an alternative would be to keep the Tamron, although it's not as sharp as the Sigma, since the Tamron I'm looking at doesn't have significant back or front focus issues.

05-03-2013, 05:14 PM   #5
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QuoteOriginally posted by johnbachel Quote
The 18-135 Pentax would be an option to replace the Sigma 18-125, although reviews suggest that the 18-135 is a pretty mediocre lens
Mediocre?

https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/179869-da-18-1...at-can-do.html
05-03-2013, 05:16 PM   #6
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Thanks - Nice pictures. The only thing I had seen about the 18-135 was the photozone review, which wasn't positive.
05-03-2013, 05:20 PM   #7
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QuoteOriginally posted by johnbachel Quote
Thanks - Nice pictures. The only thing I had seen about the 18-135 was the photozone review, which wasn't positive.
That is why I wanted you to see that thread. There has also been long discussions on that specific review also. They might have just had a bad copy which can happen with any lens.

I know this is kind of off topic for you, but wanted to be sure you get the right information in helping with your decision.
05-03-2013, 09:40 PM   #8
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If you are very satisfied with the optical qualities from each of your lenses then I would recommend- send them off to Sigma for calibration to a Master Lens. Having them consistent with each other should solve your problem.

Then if the AF Fine Adjust of your K5 is not capable to accommodate the Sigma adjusted lenses, you should have Pentax Service calibrate your K5 to nominal using their Master Lens.

Actually if you want to try to spare the cost for the non-warranty Sigma... send both the single lens (under warranty) and the K5 (if under warranty) off for their separate nominal calibrations. Then see where the non-warranty lens ends up before considering to send it in.

05-03-2013, 11:44 PM   #9
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QuoteOriginally posted by johnbachel Quote
I didn't set the lenses up using FocusTune in live view mode - I'm not sure where you got the idea that I did.
QuoteOriginally posted by johnbachel Quote
Using live view, both lenses are very sharp at maximum aperture.
That's where I got the impression you ran your tests using live view.

QuoteOriginally posted by One3rdEV Quote
send both
Indeed. No lens and body combination in the world will share the same tolerances. To get everything 'right', you need lens and body adjusted together, inconvenient as it may be.
05-09-2013, 09:41 PM   #10
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QuoteOriginally posted by stormtech Quote
They might have just had a bad copy which can happen with any lens.
FWIW, PZ contacted Pentax and received confirmation that the copy wasn't bad.

The 18-135 just isn't that strong at long settings.

Thanks for the pointer to the samples thread.
The lens certainly got very nice bokeh.
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