D800 fine focus adjust 🤔

Started 4 months ago | Discussions thread
ericbowles
ericbowles Contributing Member • Posts: 853
Re: D800 fine focus adjust 🤔

Giovanni_1968 wrote:

Leonard Shepherd wrote:

Assuming you used a D800 more efficient central cross type sensor on an eye - there is no reason why - with a suitable for good AF cross type subject - AF should not still be good.

Comparing a good AF subject (presuming a cross type AF point was used) to an about as bad as you can get AF subject is a bit like comparing a good apple to a rotten orange.

I have no way of checking - but presume the repairer checked AF was good with a sensible AF subject before shipping your D800 back to you.

Tomorrow I will try and repeat the test but the fact remains that before repair it worked much better, actually never failing and always with the same shooting style which is very basic, S-AF on the central point, as simple as that.

My concern is that the guys didn't check it properly, I left them the camera and my 50/1.4 to test it and it is still not accurate, it doesn't matter target, tripod bla bla bla, that's not how I shoot not how a camera is used most of the times, in real life it doesn't focus the way it did...

Thank you for your concern

I think the reference to using a tripod is because you want to eliminate variables.  The test target needs to be aligned correctly or your frame edges are going to show front or back focus that is caused by misalignment.  The LensAlign system has two options for alignment - a mirror or a cutout circle and dot.  The other thing you need is a good focus target.  There are some targets that provide inconsistent results, and you want a target that has a high level of consistency.  Just because you shoot handheld does not mean

I have a couple of lenses that I start with in my testing because I know they produce consistent results.  I start with a known lens and camera combination, validate that combination, then move to testing.

You have to remember the objective.  There are a lot of things you can test.  You can test to fine tune.  You can test AF speed.  You can test AF accuracy.  You can test performance of different AF sensors.  You can test sharpness.  You can test handheld technique.  With any test you have a distribution of results.  That means with a perfect setup and perfect testing, you will have focus errors - even with LiveView focus.  T

You mention this issue started after repair.  Have you blown out the bottom of the mirror box where the AF sensor is located?  It's very common for a little debris on the AF sensor at the bottom of the mirror box to cause inconsistent focus errors.

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Eric Bowles
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