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11-20-2018, 09:22 AM   #1
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How to cheat ibis about focal lenght?

Hi,
I own a sigma 300 2.8 with sigma 1.4 and 2x tc dg version
My cameras dont recognise the total focal lenght , 420 and 600, and it shows 300mm in the exif. So Ibis is not working at the right focal lenght. Is there any way to enter it manually? may be with tape in some pin beetween camera and lens? wich of them?
thanks in advance and sorry bad english,

Paco from Spain

11-20-2018, 09:35 AM   #2
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As far as I know if you disable lens communication you lose focal length reporting and autofocus. You may be able to do that and keep aperture automation by blocking pin 7 only. If you do the lens shouldn't be able to tell the camera focal length and you should get an opportunity to input focal length on power up.
11-20-2018, 09:36 AM   #3
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QuoteOriginally posted by pasorro Quote
Hi,
I own a sigma 300 2.8 with sigma 1.4 and 2x tc dg version
My cameras dont recognise the total focal lenght , 420 and 600, and it shows 300mm in the exif. So Ibis is not working at the right focal lenght. Is there any way to enter it manually? may be with tape in some pin beetween camera and lens? wich of them?
thanks in advance and sorry bad english,

Paco from Spain
Which camera are you using this lens with?
11-20-2018, 09:40 AM - 1 Like   #4
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It would be awesome if debug allowed us to set this so you could engage it via menu. Sigh.

11-20-2018, 09:49 AM   #5
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QuoteOriginally posted by UncleVanya Quote
It would be awesome if debug allowed us to set this so you could engage it via menu. Sigh.
I'd like to be able to manually input any focal length I'm using...
11-20-2018, 09:52 AM   #6
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K1 II and K3II

---------- Post added 11-20-2018 at 09:58 AM ----------

K1 II and K3II.
The same cameras and lens works fine with the pentax hd 1.4 tc, But not with sigmas TC s. I suposse sigma tcs was designed for the sigma 300 2.8, but there is something inside that tcs that not allow perfect comunication with camera.
11-20-2018, 10:06 AM   #7
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As I recall Pentax TCs will alter the signal from the lens to reflect the focal length and aperture changes. The Sigma TCs aren't playing ball with the same rules. Is there an can the firmware be updated on the lens and/or TCs?
11-20-2018, 10:07 AM   #8
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I'd be interested in a solution to this anomaly as well. I've got an older Sigma EX 70-200mm f/2.8 with matching 2x but the camera, K-5 or K-70, always reports 200mm (or less).


Which pin is "pin 7", that is to ask, does one count the pins clockwise or anti-clockwise when looking at the back of the lens (or, indeed when looking at the lens throat on the camera)?

11-20-2018, 10:33 AM   #9
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11-20-2018, 10:38 AM   #10
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Yes, only the fancier teleconverters have internal circuit boards that read the focal length and aperture of the attached lens, and then output adjusted data to the camera - with the mathematically correct new focal length and aperture.

More budget oriented converters simply transfer the pin data from the front to the back of the converter, unaltered. Everything usually worked just fine, especially on film SLRs - except that your exposure data still reflected the wrong aperture. Your 300mm 2.8 on a 2x still said it had a 2.8 maximum aperture. AF still worked, and you saved two or three hundred bucks on the converter, so....

But now that we have IBIS, it would be nice to have the system seeing the correct focal length input into the system. And it would be nice to see our EXIF data letting us know we were using a converter, and at what real-world aperture we were shooting at.

Let us know if you figure out a work-around to this issue.
11-20-2018, 11:31 AM   #11
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a firmware update to allow us to input the focal lenght will be great.
11-20-2018, 11:46 AM   #12
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The Qs have this already and I use it all the time. I would think that the firmware for the K1 II and K3 II could be upgraded unless there is some technical limitation in the larger format that prohibits it. Maybe there is someone on the forum who knows camera code that could answer that.
11-20-2018, 12:26 PM   #13
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QuoteOriginally posted by Cipher Quote
The Qs have this already and I use it all the time. I would think that the firmware for the K1 II and K3 II could be upgraded unless there is some technical limitation in the larger format that prohibits it. Maybe there is someone on the forum who knows camera code that could answer that.
My K-30 also has this, but it is disabled if the camera thinks it already knows about the lens.

My Q-7 behaves the same way, I was thinking all recent Pentax cameras would behave that way.
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11-20-2018, 12:38 PM - 1 Like   #14
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There is no way to spoof focal length to IBIS while retaining auto-focus. Masking the data contact to allow manual focal length entry results in the lens not being detected as AF.


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11-20-2018, 01:17 PM   #15
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QuoteOriginally posted by pasorro Quote
Hi,
I own a sigma 300 2.8 with sigma 1.4 and 2x tc dg version
My cameras dont recognise the total focal lenght , 420 and 600, and it shows 300mm in the exif. So Ibis is not working at the right focal lenght. Is there any way to enter it manually? may be with tape in some pin beetween camera and lens? wich of them?
thanks in advance and sorry bad english,

Paco from Spain
What are you shooting with this combination?

Any motion at all by the subject, and you would want a shutter speed of 1/500, so IBIS would be of minimal value anyway.

note: I've been told that a number "too small" is better than one "too large", so having the IBIS set for 300mm might be OK.
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