Some help please is my Sensor Alignment off?

[Highlandsnapper]

I have been having problems with my A700 since last summer with out of focus shots that i would have swore were virtually unmissable! (well almost)

So after some home tests i found i had slight back focus which i adjusted myself, and all seemed well and good, but i had been shooting mainly at close ranges and usually with a smaller aperture.

Then with my Sigma 120-400mm HSM i was getting very mixed results, some pin sharp some so out of focus all i got was mush ! Was it camera shake, i really dont think so i was using shutter speeds upto and over 1/1000 with same results. The last failure was the last straw.Four deer crossing a field 50yards in front of me, walking i might add. Nothing behind them but sky (was an incline) not a single shot in focus using my manfrotto monopod.

Today i went out my pretty solid Video Tripod mounted lens to tripod (Sigma 120-400mm HSM) 2sec mlu with virtually all shots slightly off, this is where i noticed that some of the shots appar to be sharper on the top 3/4 right hand side of virtually all the shots? Then i remembered a shot i did at my brothers wedding where the left was oof while the right side seemed fine.

Could the 3 Hex screws have vibrated loose after i did the AF adjustment or is there an alignment issue with my sensor?
The included shots are the largest the host provides. Someone tell me iam not imagining this please.

Top & Bottom Image with Tamron 17-50mm Middle image with Sigma 120-400mm HSM

[Highlandsnapper]

As before shot on a tripod with MUL with my Sigma 120-400HSM.

Spot focus on the right hand wooden post of the gate.
I know its overexposed etc. etc. but i was not interested in that by this point.
Ment to be wide open slipped up @ f6.3 here 1/500 sec ISO-200, result = mush.

Full shot


Centre 100% Crop (focus area)


Top Right seems to be to only part of the image that is remotely in focus.


So what would you guess D.K lens or camera or both?

[Chris Malcolm]

It's very hard to disentangle focus problems in ordinary shots, there are too may things going on, and which might be going on. You should carefully photograph some test patterns where what is going wrong is quite clearly shown.

By the way, the hex AF adjusting screws only adjust the AF sensor plane position and orientation. They do not affect the image plane. Differential focus between sides is more often a decentred lens. If it happens with all lenses it needn't be the sensor misaligned, it could the mount has got bent to one side.

[KevinBarrett]

I agree, at least with your Tamron, there doesn't seem to be a focus problem, but either a decentered lens or a misalignment between sensor and lens.

[Highlandsnapper]

Yeah i know the 3 hex screw only adjust the AF module, what i was wondering is, if they have moved (as they seem very loose) and the spot location was actually now up in the right corner.Or is there a sensor misalignent problem or a combination of both?

The Shot at the wedding is the only one i can remember or see that has that strange focus issue.

The trouble with the sigma 120-400mm i have found, i think.
It seems not to be able to focus properly at or near infinity. The distance scale stops @ 40meters. From there to infinity it misses badly most of the time, large high contrast object or not.

Not sure what to do about this.