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01-07-2015, 03:14 AM - 5 Likes   #1
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Sigma 17-70 "Contemporary": compatibility problems with Shake Reduction

I recently bought a Sigma 17-70 C and took lots of pictures with my K-5 II to decide whether I received a good copy that is worth keeping. The good news is that the lens delivered very nice image quality, AF was always spot on at all focal lenghts (I took my test shots at 17, 21, 31 and 70mm) and there was no sign of decentering or other optical or mechanical problems. However, I discovered a compatibility problem with Pentax’s Shake Reduction (SR) function that, much to my regret, left me no choice but to return this otherwise nice lens. Please read on...

The Problem:
It took me a while to figure this out - I first noticed that some shots at 17 and 21mm were not sharp. I first suspected optical problems, but further tests proved that the lens is generally very sharp there as well. If there, the unsharpness looked like it was caused by camera shake. What I failed to understand was how it was possible to have so much blurred pictures at 17 and 21mm while none taken at 31 and 70mm, even shot with the same shutter speed, showed any sign of it. Weird…
To provoke the issue I took a series of pictures at shutter speeds where SR really matters, e.g. 1/13 or 1/10 seconds at 17mm. Result: About 9 out of 10 images showed camera shake, some of them quite pronounced.
It looked like this (100% crop): http://i.imgur.com/m5CoJ03.jpg

Now it’s getting interesting! A cross-test with my DA 18-135 (@18) and DA 15 (also at 1/13 or 1/10 seconds) showed the opposite behaviour: 9 out of 10 images were pin-sharp, only 1 showed slight signs of camera shake. Back to the 17-70, this time with SR deactivated: Only about 5 out of 10 images were blurred, and to a lesser extent than with SR activated. This led me to the conclusion that somehow SR is actually making things worse at short focal lengths. But why is SR malfunctioning here? To find out, I took a closer look at the metadata of the images created by the lens.

To function correctly, Pentax’s SR needs to know the actual focal length of the lens. Reason: the longer the focal length, the bigger the countermovement of the sensor needs to be for a given amount of camera shake. Please note we’re dealing with two values here:

1. The “normal” focal length information that can be read with almost any image editor from the EXIF data.
2. The focal length used for the SR mechanism (this is found in the so-called “manufacturer notes” metadata).

Most of the time 1. and 2. will be identical, but a different value in 2. is needed e.g. for lenses with internal focusing whose actual focal length changes with focus distance. The SR mechanism always uses the 2. value.

Now the problem: The “normal” focal length information is transmitted by the 17-70 to the camera without issues, but the “SR focal length” is plain wrong at the short end. This can clearly be seen in the metadata, where “focal length” is always correct but “SR focal length” is wrong at shorter focal lengths (I tested 17 and 21mm; from 31mm upwards it seemed OK). See for yourself the metadata of three shots at 17 or 21 mm: http://imgur.com/a/EFjUt

While “normal” focal length is correctly reported as 17mm or 21mm for all, “SR focal length” can be any value from 31mm to 70mm(!). This obviously leads to a malfunctioning of the SR mechanism, which overcorrects the camera shake and thus blurs the image.
At longer focal lengths (31mm and above) both focal length values are identical in the metadata and SR seems to work correctly.

My guess is that Sigma forgot to ensure that this value is transmitted correctly. You have to remember that they do not officially licence the K-mount and rely on reverse-engeneering the communication protocols between lens and camera. It’s easy to forget a seemingly harmless value in the manufacturer notes. However, in this case it causes real damage and makes SR useless at shorter focal lengths. Even worse, it actually amplifies the camera shake (SA - Shake Amplification ) and leaves the user no option but to disable SR at these focal lengths.

By the way, you can also see the weird SR behaviour in action during Live View: The image seems somewhat “jerky” and panning movements look really strange at the short end. If you zoom beyond 28mm or so the behaviour goes back to normal.

I strongly suspect this is a general issue with all copies of this lens and probably affects all Pentax camera bodies with SR. Unfortunately, all the images I found on the web from other Pentax users of this lens had most of their metadata stripped (Adobe products regularly do this) and no longer contained the manufacturer notes which show the “SR focal length” value. So to confirm the issue it would be great if owners of the lens could test their copy in the 17-21mm range to find out if this issue applies to all copies of the lens (and to all cameras). You can check the “SR focal length” value (both for JPG and Raw files) with programs like PhotoMe, or just upload them somewhere and I can check for you. Thanks!

Possible Solutions/Workarounds:
For now, the only option is to deactivate SR at shorter focal lengths because it does not reduce but actually amplifies camera shake. This won’t cause motion blur at shorter shutter speeds like 1/100 or above (where you wouldn’t need SR anyway ), but at speeds where SR matters it will actually work against you...

The Next Steps:
I guess the only party that can truly solve this problem is Sigma. Hopefully it is fixable with a firmware update of the lens. But I fear this will probably be regarded as a minor issue (I disagree!) that only applies to their least important supported camera mount.
As soon as others confirm the problem with their copies of the lens, I will notify my local Sigma representatives (Sigma Germany) of this issue and point them to this thread, and I encourage you to do the same in your part of the world. Maybe then we’ll have a chance that Sigma HQ takes notice of this problem and will try to fix it.

I will update this thread if I receive any news from Sigma regarding this problem.

Please note that I cannot do any further tests with this lens as I returned my copy to the seller. I will happily buy a copy again as soon as Sigma resolves this problem, because otherwise I really liked the lens.

-----------------
UPDATE:
Believe it or not, Sigma has already addressed this issue and published a firmware update that is supposed to fix the SR misbehavior. Kudos to Sigma for this quick reaction and for caring about their customers!
Further Information: https://www.pentaxforums.com/articles/pentax-related-news/sigma-addresses-17-...ion-issue.html



Last edited by sTi; 01-26-2015 at 02:59 AM. Reason: Update
01-07-2015, 05:54 AM   #2
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I just received this lens yesterday and barely started putting it through it's paces. I'll have a chance on Friday or Saturday to check out the SR focal length issue and will report. Aperture doesn't provide that tiny minutiae in its EXIF reporting so does anyone have a recommended app for a Mac that will? I'm guessing Exiftool might work which I'll have to install.
01-07-2015, 06:22 AM   #3
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Interesting. I'll def check this with my Sigma 17-70.
01-07-2015, 06:44 AM   #4
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I interested in everyone's findings as I was seriously considering this lens.

01-07-2015, 07:00 AM   #5
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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.
01-07-2015, 07:37 AM   #6
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QuoteOriginally posted by MadMathMind Quote
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.
Thanks. Could you check a few more pictures in the 17-21mm range?
The focal length is reported by the lens (also older FA lenses do this). If you use a fully manual lens the camera asks you to input the focal length when switching on.
I'm not sure how the "SR focal length" value is determined. I see two possibilities:

  1. SR focal length value is stored in the LensROM. The lens reports this value alongside the "normal" focal length. If (in case of older lenses) the lens reports no additional value for SR focal length, the camera simply uses the normal focal length value. This should work well enough.
    => Possible cause of problem for 17-70 C: The lens reports wrong or confusing values at the short end that mess up SR.
  2. The lens always reports the focal length only and SR focal length is calculated by camera based on the Lens ID. This would mean all older bodies that no longer get firmware updates (think K-5, K-r ...) couldn't make use of the SR focal length parameter if a new lens gets released.
    => Possible cause of problem for 17-70 C: the camera does not know the true Lens ID (IIRC Sigma has used the same ID for different lenses in the past) and may calculate the SR value for a wrong lens. Maybe it thinks a 28-70 lens is attached, so it works OK for this range but SR is clueless what to do in the 17-27 range and uses a random number in the 28-70 range. This theory would fit with the behaviour I observed.
The teleconverter may be something of a special case that needs cameras to have a firmware update to work correctly. I don't think there have ever been firmware updates simply to get support for new regular lenses. By the way, teleconverter support was only added in v1.07.
01-07-2015, 07:38 AM   #7
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I'll take a look at my 17-70 shots with PhotoME. My 17-70c has been a superb performer and nothing has given me cause to check for such an issue. I'm shooting with a K5 with the original firmware.
01-07-2015, 07:52 AM   #8
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QuoteOriginally posted by MadMathMind Quote
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.

What happens if you update the firmware and rest the camera settings back to factory settings? That would eleminate any camera settings issues.

01-07-2015, 08:03 AM   #9
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I just checked a photo shot at 17mm and the OP is correct. The SR is reading the focal length wrong although the photo is sharp across the frame and was shot with a flash at 1/50. I haven't been able to find any slow shutter shots to check for sharpness because I haven't shot very many. I try to avoid those kind of shots because I have enough physical issues of my own that cause camera shake and also because the high ISO quality has improved so much that I find I don't need to shoot at those speeds. I suppose if you do a lot of shooting at slow shutter speeds and rely on the SR, it might be an issue.

Here's the SR data copied form PhotoME from one of my 17mm shots.

SR Result: stabilized
Shake Reduction (Setup): 7
Shutter Release Half Press Time: 4.25sec
SR Focal length: 45mm
01-07-2015, 09:58 AM   #10
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I just took 3 jpgs @ ISO 200 at 17mm. 19mm and 21mm. The SR was on and the shutter speed was about 1/15" for each. I downloaded Photome, but I am not seeing where the SR Focal Length is displayed in the interface.
01-07-2015, 10:25 AM   #11
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I have what I guess is the older Sigma 17-70 Macro 2.8-4 I bought 4-5 years back ( what is the difference with the new one?)
It has been one of my favorite lenses, no problems whatsoever at any range. I turn off the Pentax SR and use the Sigma Sr...it seems about one stop better.One of my first shots with it in 2010.

70mm F5 ISO 1600 K20D 1/25 Otie Squirrel....son of Otis, one of thousands!


Ashamed you had a problem, this is a great lens for general shooting.

Regards!
01-07-2015, 10:43 AM   #12
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Rupert - I think he was saying that the problem showed up most significantly between 17-21mm and was gone at about 31mm. Also, I think that he was talking about shutter speeds in the range of 1/15" or less.

Also, I wonder if this is a problem restricted to the Contemporary version of this specific lens, or is it a Sigma-wide problem.
01-07-2015, 10:58 AM   #13
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QuoteOriginally posted by Spodeworld Quote
I just took 3 jpgs @ ISO 200 at 17mm. 19mm and 21mm. The SR was on and the shutter speed was about 1/15" for each. I downloaded Photome, but I am not seeing where the SR Focal Length is displayed in the interface.
It's under the heading "manufacturer notes", there is lot of stuff there, you may have to scroll down quite a bit. It may be in a different place than in the example screenshot linked above because these were from a K-5II. If you upload one of the images I could locate it for you and post a screenshot. It would be nice to know whether the K3 is affected as well from this issue.
01-07-2015, 10:58 AM   #14
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QuoteOriginally posted by Spodeworld Quote
I just took 3 jpgs @ ISO 200 at 17mm. 19mm and 21mm. The SR was on and the shutter speed was about 1/15" for each. I downloaded Photome, but I am not seeing where the SR Focal Length is displayed in the interface.
It's in the section labeled Manufacturers Notes.

Since it's below 0 outside and I had no desire to get out and do anything, I spent a good while looking through my photos and reading the exif in PhotoME. My K5 regularly listed the SR Focal length as 45mm when I shot at 17mm. I began checking some other focal lengths and found similar results. There were also slightly off SR results at longer lengths but only by a couple of mm's and not enough to likely cause a problem. I also found some differences in other lenses too, but only by a very little. Then another problem surfaced. I went back and looked at some of the other data in those 17mm shots I checked earlier and they are now listing the SR length as 52mm!

Since these are all pretty sharp photos, I'm beginning to think this is a problem with PhotoME. Why would the data change? I also found instances where my DA 10-17 was listed as an "M" or "K" lens even though in other places in the data it is correctly listed as a DA. I think PhotoME isn't correctly reading the data. My AV software also has tried to block PhotoME as malware.

Rather than send a lens back, the real answer to all this is to follow the rules of photography and use a tripod if you want to shoot at slow shutter speeds. It's always a crap shoot under 1/30 and for longer lenses, the minimum is usually the focal length; don't try to shoot with a 200mm under 1/200, etc and even that is no guarantee.
01-07-2015, 11:12 AM   #15
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QuoteOriginally posted by Spodeworld Quote
Also, I wonder if this is a problem restricted to the Contemporary version of this specific lens,
What is the difference between this an my older 17-70? I took a few test shots at 17mm 1/15 in my dim office and they looked plenty good....my K5 original is not the best at low light shooting at slow speeds, but they appeared decent using the Sigma SR.

Regards!
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