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Forum: Pentax SLR Lens Discussion
07-20-2015, 06:43 AM
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The Sigma 18-35 Art is crazy sharp - but... It took me two copies to get a good one for AF, and others report never getting one. If you're willing to take the chance, when this lens gets it right it's second to none!
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Forum: Digital Processing, Software, and Printing
03-02-2015, 06:00 PM
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ASP is much better with its auto exposure. Lightroom too often over exposes and you have no control over it. On the other hand, there are times when ASP can't match Lightroom output, and file handling is better in Lightroom. ASP doesn't have nearly as many lens profiles, and custom profiles don't always work. ASP is faster - at lot! And I really like being able to click on the slider and have it move 10 each time. If I could only have one, it would have to be Lightroom. But ASP is so cheap, you can skip two trips to McDonalds and own it.
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Forum: Pentax SLR Lens Discussion
01-29-2015, 01:39 PM
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Just finished updating the firmware for the 17-70 (v1.01), and calibrating the focus. It's not that hard.
This is how I did the auto-focus adjustment. You don't have to take a single picture during this process. Using a tripod, aim your camera perpendicular to a flat surface with contrasty edges for each of the 4 distances. Use live view to focus at 17mm. Switch to contrast and watch where the lens moves to focus. If it doesn't - yippie! If it's short (near) then you'll have to add a positive number for calibration. If the lens goes long you'll have to put in a negative number for that zone. Write it down. Do this for all sixteen combinations of zoom and distance, then dock up your lens and put in the offsets. It won't take you long to figure out if a 2 is too much or too little, and you'll get a sense of how to adjust them all.
If you're only using one camera, it would make sense to me to put the AF Fine Adjust to zero before you start.
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Forum: Pentax SLR Lens Discussion
01-23-2015, 05:37 PM
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I've had 2 copies of the 17-50, and couldn't get either one to focus consistently with either a K-7, or K-5IIs. I've had the 17-70 C for about 8 months now, and have nothing bad to say about it. After nearly 25,000 pictures I'm still impressed with how it performs, especially on the K-3.
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Forum: Pentax SLR Lens Discussion
01-22-2015, 08:14 AM
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Is it coincidence that the problem is from 17mm to about 24mm, which is exactly where the lens changes from f2.8 to f3.0, and that the problem also shows up at about 40mm to 70mm, where the lens changes from f3.5 to f4.0. Seems odd to me that the aperture extremes exactly match the errors in the SR focal length.
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Forum: Pentax SLR Lens Discussion
01-22-2015, 07:44 AM
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Focal Length is always correct in the EXIF, which adds to the mystery. Why would the focal length be right, and the SR focal length be different? There's some other kind of math going on here.
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Forum: Pentax SLR Lens Discussion
01-22-2015, 06:41 AM
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If I might add that with my copy of the 17-70 C, not only are the SR focal length values different than the focal length values from 17mm to 24mm, they're different as well from about 40mm up. Where (and how) these values are calculated seems to be a mystery, but the actual focal length is always correct, regardless of body (k7, k5, k3), and that for sure comes from the lens. Also, the SR FL numbers seem to be missing in the EXIF data for the K-3, but that could be a problem with exiftool.
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