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Forum: Pentax SLR Lens Discussion
03-23-2018, 09:39 AM
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FWIW, the discontinued lens is an earlier version from some years back, not the current "Contemporary" 17-70/2.8-4.
Steve
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Forum: Pentax SLR Lens Discussion
03-22-2018, 07:56 PM
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There were two issues addressed in the firmware update. One was a problem with AF and the other with the lens not reporting the proper focal length to the body. One can easily check to see if the second issue is a problem by monitoring the displayed FL in the EXIF or detailed review screen as compared to the position on the lens barrel. The value used by the SR system is not particularly sensitive as long as the FL is reasonably close.
FWIW, I have been shooting with the "C" version on the K-3 since Spring of 2014 with its original firmware and have not had any problem with SR at the wide end. I would expect that current production "C" version lenses will have the proper firmware version flashed, though that is difficult to assess without a dock. Perhaps a note to Sigma might provide the answer?
Steve
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Forum: Pentax SLR Lens Discussion
01-28-2015, 06:36 PM
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Be prepared for a very involved procedure. The calibration must be done for each combination of distance and focal length. Good luck.
Steve
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Forum: Pentax SLR Lens Discussion
01-27-2015, 03:43 PM
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When you do, could you also post the relevant exif?
Steve
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Forum: Pentax SLR Lens Discussion
01-23-2015, 03:45 PM
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My thoughts as well. As I commented above, I have not had issues with my lens, but will definitely explore having my firmware updated.
Steve
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Forum: Pentax SLR Lens Discussion
01-22-2015, 06:35 PM
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My take after exploring the Exif for dozens of images on two different cameras and multiple lenses is that SRFocalLength is not a reliable indicator of the focal length used by the SR system for its functionality. For the images I explored, is not unusual with manual focus or non-Pentax lenses for the value to vary from the true focal length present in other parts of the Exif. This is even true when the focal length information manually entered.
I do not believe this value is transmitted by the lens across the data pin.
Steve
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Forum: Pentax SLR Lens Discussion
01-22-2015, 06:11 PM
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A few notes regarding focal length, exif, Pentax maker notes, and exiftool
The exiftool focal length output requires some explanation. Here are a few notes:- Exif: The Exif specification defines the Exif.Image.FocalLength (tag 0x920a, aka Exif.Photo.FocalLength) as a rational number expressing the actual focal length of the lens in millimeters. The value is in the exif section of the exiftool output with the label "Focal Length".
- MakerNote: The exif specification allows for maker-specific data to be included in the Exif.Photo.MakerNote section (tag 0x927c in Exif IFD). The MakerNote section consists of binary data in proprietary format. Tools such as exiftool parse this binary data as a best guess of what it is and what it is used for. Probably the best way to characterize the MakerNote section as parsed is that it is "Reliable, though not accurate" (my apologies to the MLS disclaimer statement). To put it another way, these are the values, but what they mean might not be what we think they mean and how they are used by the camera is also a matter of conjecture. The authors of exiftool created multiple tag names to fit the data fields they have discovered. The full list is published on the exiftool Web site HERE.
- Pentax MakerNote FocalLength: The authors of exiftool created a Pentax-specific MakerNote tag called "FocalLength"
- Pentax MakerNote SRInfo tags: exiftool also supports a grouping of SR-related tags applicable to Pentax cameras other than the K-3. Within this grouping is a SRFocalLength tag
- Pentax MakerNote SRInfo2 tags: These are SR-related tags used by the K-3. The K-3 does not support a specific SRFocalLength tag as detectable by exiftool. This does not mean such a tag is not there, only that the developers were unable to find data to match.
- Pentax MakerNote LensInfo tags: The authors of exiftool created a Pentax-specific tag for this section also called "FocalLength". The LensInfo section documentation has a note indicating that some of the tags in this section required creative techniques to decipher.
- Exiftool Composite Tags: These are tags whose values are generated by exiftool based on values of other tags. The authors of exiftool chose to include a Composite tag called "Focal Length35efl" whose value is the calculated equivalent focal length in millimeters for 35mm format. The way this tag is displayed depends on the command line option used for exiftool.
For the K-3, Focal Length is found three different places in the Exiftool output. At 17mm on the Sigma 17-70c the output runs as follows:ExifIFD: 17
MakerNote(1): 17
MakerNote(2): 16.875
Which value corresponds to the focal length as passed by the lens through the data pin is anyone's guess.
On the K10D at 17mm, Focal Length is found three times and SRFocalLength once. The output runs as follows:ExifIFD: 17
MakerNote(1): 17
MakerNote(2) SRFocalLength: 66mm (!!!)
MakerNote(3): 16.9 Again, it is important to note that it is not known what value is passed by the lens to the camera or the purpose of the information as stored in the Exif. It is possible that the tag in question contains an unrelated dump of some part of working memory when an unknown lens model is mounted. As for the image in question, it is nicely sharp and may be viewed HERE*
I did a bit more look-see of archive images of the 17-70 on the K10D and noticed that the SRFocalLength values vary according to focus distance. At or near infinity, the value is close to or identical with the actual, depending on focal length. I suspect that the SRFocalLength value is a calculated setting used for internal calculation and not based directly on what is passed by the lens. That is pure conjecture complicated by the fact that for Pentax brand AF lenses, the SRFocalLength appears to always agree with the exif FocalLength. I checked for manually-entered focal length (Pentax K, M, A lenses) and found that the SRFocalLength for those too was seldom the value entered.
Is this enough of a mess yet?
Steve
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Forum: Pentax SLR Lens Discussion
01-22-2015, 11:26 AM
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To the OP:
I may have missed it, but did you provide evidence photos of this "issue"?
If not, please post and when you do, please don't post the full image. Instead give us comparative full-resolution crops (say 800px on the long axis) of a representative section for both the 17-70c and the DA 18-135 taken hand-held at the same aperture of the same subject at the same distance. I would suggest a center crop to give equal advantage to both lenses.
Steve
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Forum: Pentax SLR Lens Discussion
01-22-2015, 11:11 AM
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I have been using my 17-70c since April of last year and have not had problems with SR at any focal lengths on both the K10D and K-3. In fact, I have been very pleased with my hand-held results with this lens in general and have not had any problem with soft results.
The focal length reported to the camera (reported in the maker notes section of the exif) is consistent with indicated focal length on the lens barrel, not that it makes much difference. The SR system may tune to focal length, but the tuning is pretty rough. I shoot with a wide range of non-AF lenses where I have to input the focal length manually and as long as you are close to the actual, the SR does a good job.
As was noted on several other comments, SR is useful, but tripods are better when maximum sharpness is desirable.
To reiterate:
I have been using my 17-70c since April of last year and have not had problems with SR at any focal lengths.
Steve
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