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01-07-2011, 06:18 PM   #1
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P-TTL with Sigma 18-250mm HSM

Has anyone encounter problem when using P-TTL with Sigma 18-250 HSM lens? My photos will underexpose >F8 and overexpose <F8 when using K7 build in flash or Metz 58AF2 with P-TTL. It happen only with the 18-250 HSM or manual focus lens, and Pentax has clearly stated P-TTL will only work with auto focus lens. The K7 build in flash & Metz 58AF2 work well with DA lens in P-TTL mode. Sigma US haven't response to my inquiry so far.

01-08-2011, 08:50 AM   #2
elg
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I have Sigma 28-135mm f/3.8-5.6. In relation to flash photography on my K-x I'm getting similar results with it as with the DAL 18-55mm kit lens. I.e. correct exposure with built in flash and underexposure (in some situations) with Metz 48 AF-1.

I know - everything is different with my Set-up, but it is still P-TTL

Did you check the EXIF information of your photos - is camera able to correctly identify the lens?

Maybe because Sigma 18-250 HSM is a new lens it has some compatibility issues? I have read about some people posting their Sigma lenses back to to Sigma in order to get them re-chiped after hitting compatibility problems.
01-08-2011, 09:40 AM   #3
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Hi Elg,

Thanks for your info. My K7 can recognize the 18-250 HSM and able to move the Metz power head according to the zoom setting. EXIF also indicate the lens was closed to the f-stop I set and shutter speed was correct.

I forgot to mention my ist*DS2 does the same thing with 18-250 HSM. Since ist*DS2 cannot focus HSM, the lens become manual focus and will not work with P-TTL anyway. Other Forum members have mentioned K7 is better at P-TTL. Pentax US has told me if my DA lens works with K7 P-TTL but not HSM, it is clearly a problem with HSM. Metz.de was really good and replaced my 58AF2 through dealer to ensure it was not a defect. Have you contacted them to resolve your 48AF1/DA18-55 issue?

I am hoping Sigma US will get back to me soon, otherwise I will send it in to request a "re-chip" as you say.
01-10-2011, 01:29 PM   #4
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When has Pentax ever stated manual focus and P-TTL are incompatible?

Manual aperture (e.g. K/M series lenses, and A-series lenses with the aperture ring off of A) and P-TTL are indeed incompatible, but not manual focus.

I've never noticed any issues with my Sigma 18-250 in comparison to any other lens. I've had PLENTY of P-TTL issues with my AF-540FGZ until discovering the adjustment trimpot.

In general the K-5 seems a lot more consistent than my K20D with an adjusted 540.

However, I have found that my 18-250 will not focus in live view mode on the K-5. I've seen indications that the lens needs to be re-chipped (and newer 18-250s may already include focusing fixes for LV AF), but haven't contacted Sigma yet.

01-10-2011, 11:16 PM   #5
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Hi Entropy,

The auto focus requirement for P-TTL was pointed out to me by Pentax US and is stated on p.26 of the AF540FGZ manual. Glad to hear your K5 P-TTL works well with the 18-250 HSM. Please keep us posted on your K5 LV AF compatibility issue.
01-11-2011, 09:16 AM   #6
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QuoteOriginally posted by Entropy Quote
I've had PLENTY of P-TTL issues with my AF-540FGZ until discovering the adjustment trimpot.
Hi Entropy,

Where you found this adjustment trimpot in your flash? Did you have to disassemble the flash in order to access it? I wonder if my Metz 48 AF-1 could be adjusted in a similar way?

Thanks,
Erika
01-13-2011, 02:21 PM   #7
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QuoteOriginally posted by elg Quote
Hi Entropy,

Where you found this adjustment trimpot in your flash? Did you have to disassemble the flash in order to access it? I wonder if my Metz 48 AF-1 could be adjusted in a similar way?

Thanks,
Erika
https://www.pentaxforums.com/forums/pentax-camera-field-accessories/103779-in...x-flashes.html

Very accessible on the 540, as I understand it less so but still present with the 360, unknown for Metz.
01-15-2011, 05:56 PM   #8
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QuoteOriginally posted by Entropy Quote
Very accessible on the 540, as I understand it less so but still present with the 360, unknown for Metz.
Thanks for the information, Entropy.
I looked at my Metz 48 and I could not find anything on its surface, so it must be inside, if Metz has it at all.

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