Using the Pentax-DA 1.4x AW AF TC with a A lens

**scc** · 08-26-2019, 10:49 AM

Hi all,
I was wondering about the camera body recognition of the presence of the DA rear converter using a A or A* lens. With my K7 body, after entering the resulting focal length of the A lens+TC, the body displays/records the max A lens aperture. This is not related to a specific lens as this behavior occurs with both my 85 f/1.4 and 300 f/2.8 A* lenses. Now the issue is not displaying/recording a wrong aperture but whether the exposure meter is tricked or not. If the camera doesn’t know that a TC is present, it should underexpose. This can be solved by using the EV compensation but is my guess correct?
Has anybody experience to share about that?
Thanks
Claudio

**marcusBMG** · 08-26-2019, 11:58 AM

There is no problem. The f stop on the lens is transmitted. The camera adjusts the shutter speed according to the f stop set. The real f stop is one stop more but that doesn't affect the exposure because the metering off wide open is also one stop more, its consistent. Any exposure compensation required is due to the idiosyncracies of the lens + camera, the scene being metered , the ambient light.

**scc** · 08-26-2019, 12:17 PM

Thanks, makes sense.
So the only drawback is the wrong f stop on the exif, as indicated in the in depth review.

Adam · 08-26-2019, 12:35 PM

I don't think the f stop in the exif is wrong, since the TC automatically calculates it for you.

Adam
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**marcusBMG** · 08-26-2019, 02:57 PM

OK I've just tried my DA 1.4x with my SMC-A 50mm 1.7. The camera displays the lens f-stops ie 1.7... etc. Without a chip and 7th contact (on/in the lens) that's what it does, it seems.

08-26-2019, 10:49 AM	#1
scc Loyal Site Supporter Join Date: Dec 2012 Posts: 165	Using the Pentax-DA 1.4x AW AF TC with a A lens Hi all, I was wondering about the camera body recognition of the presence of the DA rear converter using a A or A* lens. With my K7 body, after entering the resulting focal length of the A lens+TC, the body displays/records the max A lens aperture. This is not related to a specific lens as this behavior occurs with both my 85 f/1.4 and 300 f/2.8 A* lenses. Now the issue is not displaying/recording a wrong aperture but whether the exposure meter is tricked or not. If the camera doesn’t know that a TC is present, it should underexpose. This can be solved by using the EV compensation but is my guess correct? Has anybody experience to share about that? Thanks Claudio

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08-26-2019, 11:58 AM	#2
marcusBMG Site Supporter Join Date: Nov 2012 Location: North Wales Photos: Gallery \| Albums Posts: 2,870	There is no problem. The f stop on the lens is transmitted. The camera adjusts the shutter speed according to the f stop set. The real f stop is one stop more but that doesn't affect the exposure because the metering off wide open is also one stop more, its consistent. Any exposure compensation required is due to the idiosyncracies of the lens + camera, the scene being metered , the ambient light.

08-26-2019, 12:17 PM	#3
scc Loyal Site Supporter Join Date: Dec 2012 Posts: 165 Original Poster	Thanks, makes sense. So the only drawback is the wrong f stop on the exif, as indicated in the in depth review.

08-26-2019, 12:35 PM	#4
Adam Administrator Site Webmaster Join Date: Sep 2006 Location: Arizona Photos: Gallery \| Albums Posts: 51,608	I don't think the f stop in the exif is wrong, since the TC automatically calculates it for you. Adam PentaxForums.com Webmaster (Site Usage Guide \| Site Help \| My Photography) PentaxForums.com server and development costs are user-supported. You can help cover these costs by donating or purchasing one of our Pentax eBooks. Or, buy your photo gear from our affiliates, Adorama, B&H Photo, KEH, or Topaz Labs, and get FREE Marketplace access - click here to see how! Trusted Pentax retailers:

08-26-2019, 02:57 PM	#5
marcusBMG Site Supporter Join Date: Nov 2012 Location: North Wales Photos: Gallery \| Albums Posts: 2,870	OK I've just tried my DA 1.4x with my SMC-A 50mm 1.7. The camera displays the lens f-stops ie 1.7... etc. Without a chip and 7th contact (on/in the lens) that's what it does, it seems.