TC micro AF adjustments on A900

[braeside]

I recently tried a Kenko 1.4X Teleplus Pro 300 DG (thanks David K) with my Sony 70-400G SSM on the A900.

It does autofocus with this, however I have noticed that micro AF adjustment required is -20. The lens on its own needs -5 AF adjust, which is pretty standard with nearly all of my lenses - my body seems to have this amount of backfocus as standard.

Can anyone explain why the AF adjust is so radically different with the TC fitted?

Thanks.

[Bengeo]

Can't answer your question David, but does the A900 'remember' the 70-400mm + 1.4x AF adjust setting and show it separate from the 70-400mm setting?

Andy

[braeside]

Can't answer your question David, but does the A900 'remember' the 70-400mm + 1.4x AF adjust setting and show it separate from the 70-400mm setting?

Andy

No it doesn't Andy. Of course the Kenko is a dumb TC with no chip, so the camera has no way of knowing if it is fitted or not. I have to remember to adjust the AF adjust setting myself when I use the TC.

I don't know if a real TC like the Sony or Minolta one would be detected and and allow an automatic separate AF setting or not.

[Bengeo]

The Sony and Minolta TCs won't autofocus with that lens so perhaps they wouldn't register? If you want to swap your A900 for my A700 I could try it!

Andy

[braeside]

Ah of course I forgot that Andy. It would be interesting to know if a fast zoom f/2.8 which would AF would store the AF micro adjust for the TC+lens combo though.

[01af]

I recently tried a Kenko 1.4X Teleplus Pro 300 DG (thanks David K) with my Sony 70-400 G SSM on the A900.

It does autofocus with this, however I have noticed that micro AF adjustment required is -20. The lens on its own needs -5 AF adjust [...]. Can anyone explain why the AF adjust is so radically different with the TC fitted?

You are using your camera and lens outside the specification with a 3rd-party accessory which explicitly circumvents the requirements for reliable AF function ... and then you're asking why it doesn't work as smoothly as normal? Doh ...

By the way, image stabilisation with your Kenko TC won't work as precisely as without, too.

I don't know if a real TC like the Sony or Minolta one would be detected and and allow an automatic separate AF setting or not.

It should but it doesn't, even though the Minolta TC of course is detected and aperture and focal length get adjusted in the camera display and in the EXIF data properly. Still, as far as AF micro adjustment goes, the lens + TC combo is treated just like the lens alone---i. e. the adjustment value for the lens with TC always is the same as for the same lens w/o TC. Oh well ...

-- Olaf

[braeside]

Just curious if others who use the Kenko 1.4X TC on the 70-400G see the same effect with AF adjust differences with and without the TC? - I accept that it is outside the specification in terms of working aperture, but it does AF and appears repeatably accurate once calibrated. Point noted about SSS, I have not found that a problem so far, maybe if I was using a 2X it would make a big difference.

I am wondering if the -5 general AF offset I have with my camera is causing this?- A sort of magnified offset effect when TC comes into play? - I could correct that by the DIY screw adjustment on the AF sensor, but maybe not risk it as it it still (just) in warranty. Other option would be to send camera in for recalibration of the AF system.

[braeside]

I just got my 135/1.8 back from repair today (it had the loose front ring assembly problem). I tried the Kenko 1.4X TC on that - excellent results in terms of IQ and AF. I need same AF adjust for the lens and the lens+TC (-12).

For travel I will probably settle on the 17-35mm Tamron, CZ 24-70mm and the CZ 135mm (+ 1.4X TC for longer telephoto 189mm @ F/2.5)

[David Kilpatrick]

Glad to hear the 1.4X works well on that. It is a pity they have never put chips in this design.

David

[braeside]

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Yes it works very well on the 135/1.8

Just back from a ferry trip to Bruges and used the 135/1.8 + TC combo for shots of the gannets near the Bass Rock.

This was with the lens at f/4.5 1/1500s ISO 320 on A900 with CAF. (Effectively f/6.7 at 189mm).

[aster]

Beautiful...

What a contrast and good amount of details from flying creatures and a wonderful blue sky!


Congratulations, they make good combination.

Yildiz

[David Kilpatrick]

ISO 320 is pretty amazing, isn't it? Even reduces the noise in blue skies compared to ISO 200. I work a lot at ISO 160, which is also a good setting, but every time I process an ISO 320 files I wonder why I bother to reduce the setting. ISO 320 seems to be perfectly OK even for the most highly detailed subjects.

David

[braeside]

Yes David, I have started to use ISO 320 a lot. I did have to lower the ISO on a couple of shots in Bruges to get a wide enough aperture in the bright sun even with 1/8000s.

I must say I don't have a lot of problems with noise even in low light at up to ISO 800 on the A900. Pixel peeping yes it can look noisy, but normal sized prints and full screen viewing are great.

Recently printed some A900 architectural photos at 24 x 36 inches on my Designjet and they are stunning.