Sony claims they can not repair BF on 70-200G !

[lock]

After having had a discussion with a rep. of the repair service about the BF on the 70-200g, I wanted to send it in again. But the rep. said, they can only adjust for BF in the body. This means I have to accept a compromize because BF only shows up in the 70-135 mm range. And I will lose my A700 body for the next 6 weeks as well.

I have checked the body with a non-F/2.8 lens covering the 70-200 range as well. Camera and lens are spot on. Below 70 mm the cam is also very good ( with two different lenses, one of which is F/2.. So the BF problem does seem to arise from the body, but from lens itself.

So my question is: Is there nothing Sony can do but adjusting the body, and with that, compromizing the AF of the lens itself and of others ? Or should they be able to repair the lens too ?

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[David Kilpatrick]

Try checking the 70-200mm using the edge AF sensors not the centre. If the f/2.8 sensor is giving BF when the others are not, they may be able to adjust this - or you may simply find that the solve the problem, you need to switch to using wide area focus or a fixed f/5.6 sensor (any one of the others except the centre).

David

[lock]

David, then do you agree with the Sony rep that they cannot fix the BF by correcting the lens ?

I think I tested two already, but I will redo this this evening. But these sensor are not cross type and may not be as fast as the central one..

[David Kilpatrick]

They can't correct BF which happens at a range of focal lengths like this. I notice the same thing slightly on my new Sigma HSM 70-200mm - at medium focal lengths, it is tending to backfocus slightly. But overall I am not sure yet whether to use the A900 correction and pull the focus forward. My A700 had a general tendency to backfocus and I corrected the body. I think that if they correct the body, they do two things - first, they adjust the sensor position and calibrate. Then the replace the lens tables with a neutral set that does not correct lenses as much.

This is likely to improve your performance. It's very possible the combination of a slightly out of adjustment sensor/AF sensor/mirror setup, and the resulting calibration offset table stored in your camera, will disagree with some lenses at some settings. If they set the whole thing up again properly, it may cure all the problems and not put other lenses out of true.

David

[lock]

I checked four sensors (left/right/bottom/top) and the central one and all behave the same at 70 mm. Taken at a distance of about 6.3 feet, pictures at the 45 degree LEGO plate with objects stacked on it as a circle and with a small clown dead in middle, the focus is about 5/6 cm's backward. This is a similar to the results found with the three boxes tests, using the horizontal plane.

So they might adjust all the hardware, and then try to find the best software to go with the problems the lens is causing ? Why don't they just try to adjust the internal arrangement of the lenses ?

[Winston]

Do you get the same result at all apertures?

[lock]

I did check more apertures yes. But I did not go as far as F/4 cause I bought the 70-200G because of it's low light and thin DOF capabilities. Otherwise I could just put my Tamron 55-200 on it and sell the G-lens...

[David Kilpatrick]

OK, a sensible suggestion would be to visit the place you bought the lens, if possible, and take some shots on another A700. Or try to meet someone with the same combination of gear and test it - see whether it really is the lens, or the body. If the lens focuses wrongly on all Sony bodies, then there may be a fault with the lens. If it focuses correctly on another A700 body, then adjustment of your body should fix the problem.

David

[lock]

Easier said than done...Sony A700 isn't the most popular camera over here.

This is what I will do. I will bring in both body and the lens. They can have go at both of them. If they decide they do not need the body afterall, I will have them send it back to me.
But if it doesn't work out, I will contact Sony Japan. I just do not wish to accept any compromise with such a lens price.

[lock]

Sony is willing to help me out. They offered to adjust the lens if possible, by adjusting the body AF (more or less the way David said). If it does not work well ( too much BF/FF compromise along the 70-200 range), they will send it to Gödöllö - Hungary . There they do adjust this type of lens, if neccesary.
To compensate, they will adjust the kitlens as well ( , and check if the two Tamrons still do the job..The latter was more or less my limit. They work well now, so ruining that would not be a good deal to me.


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