Pentax AF 1.7x focus correction

snimcho · 09-29-2014, 08:41 AM

Hi all,

I'd like to use the 1.7x TC with SMC Pentax-M* 300mm F4. Currently the TC produces a little front focus. In the camera (k5iis) I can correct it +/- 10 but it remains a little bit in front of the target. In the menu it doesn't appear as a particular lens but the camera gives me the "Apply to all" correction.
The error is constant and I can confirm it by comparing to live view CAF result.
I wonder if it is possible the error to be corrected inside the TC as it is done with lenses. I suppose there is some electronics inside the TC. I can't find any disassembling info so I'm not sure what is inside... yet.
So, can someone put more light on that issue?

Also any other ideas how to avoid the FF will be appreciated.

Thanks

**jatrax** · 09-29-2014, 09:55 AM

I have a similar situation with mine on some lenses. I read a post somewhere that it could be adjusted so I sent it to Eric and asked him to look into it. He checked it over and returned it with the comment that there is no adjustment available on the 1.7x AF adapter. He also noted that on his test bench it was dead on to specification. So I suspect the problem is either the lens or the combination of using two film era optics with a digital camera.

snimcho · 09-30-2014, 03:26 AM

Thanks for the answer. I'm still curious if the device has any electronics and software inside but I don't see any tech. info about it. Anyway as Eric have said, I rather have to accept that the correction is not possible and to use it in live view when I like to have AF.
Actually the FF issue is visible on f4 but when I put the lens on f5.6 the error is minimal. On f8 it is hard to find.
Still interesting how the device is calibrated during production. Also it may be the optics that on some reasons produce different error with different lenses.

snimcho · 10-02-2014, 12:48 AM

I think I found a kind of solution. Through the debug menu (which I can enable thanks to pk_tether v0.7.0) I can get deeper AF correction. It will take some time because I have to set the correction first and then to clear it when I decide to change the lens. My intention is to use that combo for birds so I hope to do some real tests soon.

09-29-2014, 08:41 AM	#1
snimcho Forum Member Join Date: Sep 2014 Posts: 79	Pentax AF 1.7x focus correction Hi all, I'd like to use the 1.7x TC with SMC Pentax-M* 300mm F4. Currently the TC produces a little front focus. In the camera (k5iis) I can correct it +/- 10 but it remains a little bit in front of the target. In the menu it doesn't appear as a particular lens but the camera gives me the "Apply to all" correction. The error is constant and I can confirm it by comparing to live view CAF result. I wonder if it is possible the error to be corrected inside the TC as it is done with lenses. I suppose there is some electronics inside the TC. I can't find any disassembling info so I'm not sure what is inside... yet. So, can someone put more light on that issue? Also any other ideas how to avoid the FF will be appreciated. Thanks

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09-29-2014, 09:55 AM	#2
jatrax Site Supporter Join Date: May 2010 Location: Washington Cascades Photos: Gallery \| Albums Posts: 12,991	I have a similar situation with mine on some lenses. I read a post somewhere that it could be adjusted so I sent it to Eric and asked him to look into it. He checked it over and returned it with the comment that there is no adjustment available on the 1.7x AF adapter. He also noted that on his test bench it was dead on to specification. So I suspect the problem is either the lens or the combination of using two film era optics with a digital camera.

09-30-2014, 03:26 AM	#3
snimcho Forum Member Join Date: Sep 2014 Posts: 79 Original Poster	Thanks for the answer. I'm still curious if the device has any electronics and software inside but I don't see any tech. info about it. Anyway as Eric have said, I rather have to accept that the correction is not possible and to use it in live view when I like to have AF. Actually the FF issue is visible on f4 but when I put the lens on f5.6 the error is minimal. On f8 it is hard to find. Still interesting how the device is calibrated during production. Also it may be the optics that on some reasons produce different error with different lenses.

10-02-2014, 12:48 AM	#4
snimcho Forum Member Join Date: Sep 2014 Posts: 79 Original Poster	I think I found a kind of solution. Through the debug menu (which I can enable thanks to pk_tether v0.7.0) I can get deeper AF correction. It will take some time because I have to set the correction first and then to clear it when I decide to change the lens. My intention is to use that combo for birds so I hope to do some real tests soon.