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12-06-2013, 02:06 PM   #1
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Sigma 8-16, Pentax Bodies & FL less than 10mm

I happened to be reading a recent post this morning about the Sigma 8-16. It was about the inability of Pentax bodies to record focal length values derived from the lens' interface when below 10mm.There are several threads on this since the lens was introduced in February 2010. So its been almost 3 years now. Questions have been generated across pretty much the entire line of bodies K7 through the most recent K3. No support.

When you call Pentax you receive the following response .....
QuoteQuote:
Pentax does not make any lenses with a focal length shorter than 10mm so why would you think that this would an issue with Pentax bodies. We test our lenses and they work, and we are not responsible for other brands. They then directed me to call Sigma - since it was their lens.
OK, I'll play along on this charade - so I called Sigma's Technical Support line....
They answered, wonder gentleman who listened intently. He wanted to go and get a Pentax body along with the lens and test it out for himself, so I was put on hold. Unfortunately we were disconnected about 5 minutes later - and now every one is at their annual Christmas party. So it will have to wait until Monday.
I took today off, so I was pawing through the entrails of this problem with my K5 (firmware version 1.14) and the most current copy of PhotoMe, I find that:
  • 8-16 @ 8mm reports at ---8mm on the K5's rear panel in image review with the information panel set to report everything it can.
  • 8-16 @ 10mm - 16mm reports as expected
  • Any M42, K or M lens with SR enabled, and entering 8mm as a focal length will report as expected on the rear panel.
Loading the images and using PhotoME you come up with:
  • 8-16 @ 8mm reports at ---0mm in the focal length fields. The lens reports as type 8 18, so the body is able to interface with the lens correctly.
  • 8-16 @ 10mm - 16mm - the correct expected value in the focal length fields. The lens again reports as type 8 18, so the body is able to interface with the lens correctly.
  • Any M42, K or M lens with SR enabled, and entering 8mm as a focal length will display the entered focal length in the EXIF focal length field.
All of this points to the Pentax bodies' firmware. Why the 10mm threshold - probably some scaling range that worked for Pentax lenses and when values are out of range, they just leave the focal length EXIF field zero filled.

So, Pentax - why the goat rope with your customers? This is just being nothing but being disingenuous on Pentax's part. Are you calling your cu$tomer stupid? Gee, it can't be our body - must be the other company's [crappy] lenses - go give them a call and by the way - don't call us back. No they did not actually say that - but that was the attitude that was effectively conveyed....

Is this an earth shattering problem - no. Its an annoyance, that actually should be fixed - especially its been reported for 3 years now. There are workarounds that allow you to insert a specified FL into the images EXIF. This is probably 30 minutes worth of actual work. I will admit that you guys will probably spend another day or two, in regression testing all the A, F, FA and DA lenses.

Customer Service....



12-06-2013, 02:25 PM   #2
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If Pentax previously cannot fix this bug, may be Ricoh can?

A bit annoying, but I have learn to live with it.
12-06-2013, 02:30 PM   #3
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Apparently the K-3 is the same so there's no relief there either. I have heard that the 8-16mm is no longer made in K-mount too. Perhaps a response from Sigma to Pentax intransigence in this matter?
12-06-2013, 02:43 PM   #4
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It's not something that's ever bothered me. I just don't need that information, knowing it's less than 10 is good enough for me.

12-06-2013, 03:25 PM   #5
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It wouldn't matter so much in the bush but it would in the city.

Last edited by bossa; 12-06-2013 at 04:41 PM.
12-06-2013, 05:08 PM   #6
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Its the principal of the thing. The irritation - and more specifically just the plain attitude. The implication that the problem is with the lens and the body was just fine. I guess I should just be happy that I do not have a Pentax lens with SDM - what problem? I don't see any problem? What do you mean there is a problem?


12-07-2013, 06:17 AM   #7
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QuoteOriginally posted by interested_observer Quote
I happened to be reading a recent post this morning about the Sigma 8-16. It was about the inability of Pentax bodies to record focal l
All of this points to the Pentax bodies' firmware. Why the 10mm threshold - probably some scaling range that worked for Pentax lenses and when values are out of range, they just leave the focal length EXIF field zero filled.

I do not think so.
I suspect that the problem is in the comminication protocol between the lens and the camera.
The focal lengths are probably not communicated in plain numeric values, but with codes which stand for a numeric value.
This communication protocol could be dating from the F series (late 1980's).
There may not even be a code for values below 10mm.
Changing camera firmware does not help, you need to adapt a new communication protocol, and that may give problems with existing camera's and lenses.
12-07-2013, 09:34 AM   #8
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QuoteOriginally posted by glasbak Quote
I do not think so.
I suspect that the problem is in the comminication protocol between the lens and the camera.
The focal lengths are probably not communicated in plain numeric values, but with codes which stand for a numeric value.
This communication protocol could be dating from the F series (late 1980's).
There may not even be a code for values below 10mm.
Changing camera firmware does not help, you need to adapt a new communication protocol, and that may give problems with existing camera's and lenses.
I agree with you - essentially that is what I posted, its a form of scaling. There is a single pin connection that provides a serial data stream that contains in part the focal length information per Bdimitrov.The KAF mount is an extension of the KA mount which provides the aperture information.Sigma would have had to reverse engineered this (if it was not available), in order to make any of their AF lenses comparable. Within this serial stream (sequence) would contain a field for the focal length, in which the contents would represent the current focal length. This would have needed to support a range of values, the bottom of which Pentax is indicating is 10mm. It appears that Sigma has found a way to logically extend the range to some degree that would be fully comparable with the contents of the field.



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