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08-18-2013, 10:01 PM   #1
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EXIF data excludes range of focal lengths

No matter where I set my zoom in the 43 to 46mm range the lens reports only one of two values: 42mm, or 47mm. It happens whether the focus is at infinity or not. I've heard a theory about the lens reporting focal length in steps, but I remembered that image stabilization requires an accurate value to work properly, so I assume the focal length should be measured precisely. The lens is a Pentax DA 18--55mm f3.5,5.6.
Is it a bad copy or what am I missing here?

08-18-2013, 10:29 PM   #2
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This is normal because of how short the throw is. The SR will work just fine as long as the FL reading isn't above the actual focal length, so it's not a bit deal.

Adam
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08-18-2013, 10:40 PM   #3
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QuoteOriginally posted by Schmidt Quote
No matter where I set my zoom in the 43 to 46mm range the lens reports only one of two values: 42mm, or 47mm. It happens whether the focus is at infinity or not. I've heard a theory about the lens reporting focal length in steps, but I remembered that image stabilization requires an accurate value to work properly, so I assume the focal length should be measured precisely. The lens is a Pentax DA 18--55mm f3.5,5.6.
Is it a bad copy or what am I missing here?
If you were to disassemble the lens you will probably find some hard coded copper tracks inside the lens which are used for focal length and distance reporting. See this link:

https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/211868-disasse...ro-no-hsm.html

and look at photo 10 for the focal length encoding on this Sigma lens. It covers a range of values. That way lens manufacturers don't need to return 46.275mm as a focal length.

Regards

Chris
08-18-2013, 11:21 PM   #4
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Thank you both, Adam & seventhdr. It was my ignorance of how FL is used by IS, and not the lens. That's good news to me! Someone once gave me a concise explaination but I was a bit skeptical since he said he'd never used that lens. Turns out he was right all along.
It's getting late so I'm going to get some rest now... That's an interesting pic, by the way, and I'm going to try and learn more about what those encodings mean. Very cool indeed.

08-19-2013, 10:37 AM   #5
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For your information, the focal lenghts reported by various lenses I could get my hands on here
08-19-2013, 01:09 PM   #6
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QuoteOriginally posted by glasbak Quote
For your information, the focal lenghts reported by various lenses I could get my hands on here
That chart appears to be accurate for my lens, except for the FL of 45mm.
08-23-2013, 11:13 AM   #7
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QuoteOriginally posted by Schmidt Quote
No matter where I set my zoom in the 43 to 46mm range the lens reports only one of two values: 42mm, or 47mm. I The lens is a Pentax DA 18--55mm f3.5,5.6.
No, that lens you are complaining about is not the DA 18-55 , but it is the DA 18-55 II.
08-23-2013, 01:04 PM   #8
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QuoteOriginally posted by glasbak Quote
No, that lens you are complaining about is not the DA 18-55 , but it is the DA 18-55 II.
Yep. I took it out for a whirl and absolutely love it! I'm assuming it's guaging correctly (thanks all for all the good info). I still have so much to learn bout the equipment. It's the weather resistant model, so I didn't worry too much when some rain drops began to fall on it.
The only reservation I have (totally unfair) is that its FL is limited to 55mm. I've read the reviews on the 18-135 and the 50-200, and the optics were panned. But there seem to be enough happy customers here to make me think otherwise. I am seriously considering one or the other - but that's in the future.

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