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Forum: Pentax SLR Lens Discussion
01-23-2015, 10:16 PM
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Wow. I wonder what was wrong with the lens.
What's interesting is that the flaw was discovered through the SR focal length parameter, even though we can conclude that the lens cannot transmit this parameter. I suspect that there was another glitch in this lens's firmware for the Pentax mount. The Canon and Nikon mounts feature OS, but that was removed from the Pentax mount (and the price not lowered....). Guessing somehow, the removal of that feature caused an issue somewhere.
My other two Sigma lenses don't have OS in any mount. I have not had this issue with them, so I'm really leaning toward the lens having some bug that resulted from removal of OS and a failure to make all the necessary changes in the lens firmware. The fact that the fix was issued so fast means it was something really, really simple. It's like someone forgot to remove a few lines of code somewhere.
---------- Post added 01-23-15 at 11:18 PM ----------
It was, but the SR focal length will differ from the actual focal length for manual lenses, which transmit nothing, so the camera couldn't know the lens is internally focusing. It was deemed that this hypothesis wasn't the explanation either. We never quite figured it out.
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Forum: Pentax SLR Lens Discussion
01-22-2015, 09:52 PM
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I reached this conclusion a couple pages ago, based on the bold statement. I noticed this as well.
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Forum: Pentax SLR Lens Discussion
01-21-2015, 07:03 PM
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Well, to be fair, you probably wouldn't have noticed the issue yourself were it not for this thread. Many people here had the lens for months before anyone noticed; there wasn't a single complaint here before this thread. Obviously, there is an issue, but it only comes up in very limited circumstances: the shortest focal lengths with slow shutter speeds. If you're over 1/30 or so, you probably won't see any effect. I can tell that you won't see an issue if you're at "good" shutter speeds, as you can see in this set:
https://www.flickr.com/photos/127442034@N03/sets/72157648971006462/
Here's 1/50 at 19mm: https://www.flickr.com/photos/127442034@N03/15013565523/in/set-72157648971006462
Now, it's understandable that you may not want to purchase a lens that has a known issue. But what are your alternatives? The new 16-85 may be a good one, but it is quite a bit slower throughough its range. The 17-70 Pentax has SDM and all the issues that have plagued it (no definitive proof they are fixed). Think about that a bit. I never noticed an issue because I just avoided the combination that causes it. Well, I guess I did notice the issue but didn't know why. I just knew to avoid it; and 98% of the time, it's not hard to do so. Just something to consider.
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Forum: Pentax SLR Lens Discussion
01-10-2015, 07:23 PM
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But we know that's not quite it either because my M lens, which transmits nothing through its missing electrical contacts, gave me a SR focal length of 204. That's not even an input option (I told it 200mm). I can't believe the camera is measuring the focal length of the lens--if it could do that, then we'd never need to input any FL to being with.
It only seems to be this lens. And then only certain ranges of focal length. My Sigma 18-35 has its SR parameters correct, as does the Sigma 70-200 II I have.
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Forum: Pentax SLR Lens Discussion
01-10-2015, 05:07 PM
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Yes. But if you're saying the lens sends these numbers...
focal length
aperture
...
SR focal length
I don't believe it because why in 1985 or whatever would there be a parameter called SR focal length? And actually, this SR focal length cannot come from the lens. I just checked it on a 200mm lens M series lens. I had input 200mm as the focal length into the camera. It lists the SR focal length as...204mm. Now where did it get that if the lens transmits absolutely no information? There's no option for 204mm. And 200mm is a possibility because I've gotten that with my Sigma 70-200 before.
So, I conclude that the SR focal length parameter is calculated by the camera from the actual focal length and....something else. But what? Clearly, the lens itself doesn't play a role in the process because if it did, we should get the same number for an M lens that the camera was told--or we'd get nothing at all and stabilization wouldn't work for pre-F series lenses. But it does work. So...what on earth does the camera do to get this parameter?
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Forum: Pentax SLR Lens Discussion
01-10-2015, 12:14 PM
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I don't think it can come directly from the lens. If it does, then the Pentax engineers had remarkable prophetic vision in to 1980s to include a parameter in lenses for something that wouldn't be developed for 20 years. More likely, the camera assembles this value from some collection of information provided by the lens.
It doesn't simply match with the actual focal length if the parameter is missing. I have different values for my F series 70-210 lens, which shouldn't be providing any SR parameter since it's 25 years old. The camera has to be creating this value from some combination of focal length, focusing distance, etc.
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Forum: Pentax SLR Lens Discussion
01-10-2015, 11:59 AM
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If this were the case, then SR wouldn't work with any wide angle lens. As I can confirm with the Sigma 18-35 and others with the Pentax 18-135, this is not the case.
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Forum: Pentax SLR Lens Discussion
01-09-2015, 06:21 AM
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I no longer own the lens. If they want information or ask me to do something, I can't. I'd worry they'd see this as wasting time and not take listen to serious requests.
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Forum: Pentax SLR Lens Discussion
01-08-2015, 09:50 PM
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I have two other Sigma lenses that do not display this issue. My 70-200mm HSM II (a bit older, I think around 2009 or 2010) is always within a couple mm of the reported focal length. That makes sense that the two not be 100% identical because if they always are, then why both having two separate parameters?
I checked about 10 of my images with the Sigma 18-35 f/1.8. Those were 100% identical. Now, this is a lens that has been reported to have major focus issues (which I have not seen to nearly the extent of what others have), which are most assuredly something miscommunicating between the lens and body.
If the issue is in the lens, it seems to be unique to the 17-70. I never noticed the issue because I avoided those low shutter speeds. Come to think of it, I think I did so because the pictures didn't come out so well. I had always assumed that 1/10 is just too slow, even with shake reduction. But I am able to hold the 18-35 at the wide end at that shutter speed and have even gone down as low as 1/6 with limited success. (Anything slower....forget it.)
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Forum: Pentax SLR Lens Discussion
01-07-2015, 05:16 PM
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Some of my 17-70 shots are reported correctly. Many are not. About 33% of the ones I tried were correct. All the others were wrong. I only looked at 17-21mm for the most part, but quick checks on longer ones looked right. Then I decided to try out some other lenses:
Pentax DA35 f/2.4: Had SR focal lengths of 35, 36, 37
Pentax F50 f/1.7: 52mm across the board (most had SR turned off, whoops, and I no longer have this lens)
Pentax F 70-210 f/4-5.6: Consistently higher than actual. Had a 188 for actual 180, 121 for 118, etc. Doesn't seem to be too big a deal.
Pentax FA77 Limited: All looked correct at 77mm
Pentax DA*300: SR focal length of 292 across the board
Sigma 18-35 f/1.8 Art: All correct
Sigma 70-200 HSM II: Mostly all correct; had a 105 for an FL of 106, and a 188 when actual was 200, but otherwise all matched
In short, this is very bizarre. How would it be 1-2mm too high? Zoom lenses aren't always at the FL they claim, but if the lens were just giving the wrong numbers, then how would the camera get these random numbers? Seems like the camera is measuring something to cook up these numbers, but what?
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Forum: Pentax SLR Lens Discussion
01-07-2015, 07:00 AM
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I had this lens for nearly a year and did not have issues with it. I will look at a few images and see what's up. I looked at one shot at 17mm and according to PhotoME, that's what it lists the SR shake reduction as.
This is the first time I have heard of SR focal length in the metadata. Shouldn't that be something that is set by the camera and not the lens? Lots of automatic lenses that work just fine with shake reduction were designed long before it was ever cooked up. If an FA lens were expected to send that information for SR to work properly---which it can't because SR wasn't even a concept in the 1990s, then SR would obviously be unusable with any FA lens. Since that's not the case, SR focal length has to be something that the camera is calculating itself.
Here's a thought: you are running firmware v1.06. I'm one behind. Most notably, I don't have the firmware that supports the focal length changing HD DA 1.4x TC. I wonder if that made any changes that somehow messed up the communication. I strongly suspect that the TC lets the camera do the focal length and aperture updates. If it were in the TC itself, there would be no need for new firmware because it would work like any other lens.
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