Nikon D7100 left focus issue

Started Apr 19, 2013 | Discussions thread
PepsiCan
Contributing MemberPosts: 736Gear list
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Re: still
In reply to Mako2011, Apr 23, 2013

Mako2011 wrote:

PepsiCan wrote:

lock wrote:

I can see a back focus on the left side picture with the 70-200, and what he should have done is take a series of 10 on both the left and right side to confirm the difference. That would rule out random error of the AF sensors. That is the only real thing he should have done to make his judgement more solid. Other than that, his pictures show more information pointing at a left af sensors issue than the opposite.

lock

And compare those shots against CDAF focussed shots taken in Live view. That would unambiguously rule out any lens issues.

You can still have lens issues that affect PDAF but are overcome by CDAF

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My opinions are my own and not those of DPR or its administration. They carry no 'special' value (except to me and Lacie of course)

Yes, but that is not why I say to test with CDAF. CDAF is a better reference against which to compare everything else than when you compare PDAF shots with each other. Once you have a reference, you can safely draw conclusions. When you compare two pictures both taken with PDAF, you cannot exclude the lens perse as the cause of a focus issue, so you do not know for sure whether the lens or the camera's focus system is the issue (although you will have a degree of likelyhood). With a CDAF reference any statements made will carry more weight because you're eliminating possibilities. And note that the CDAF test should be added to what Lock already described. It cannot proof much in itself.

My point is not that you cannot assert focus issues with PDAF-only tests. My point is that without also testing against CDAF you have a less strong case and you need to be cautious about the conclusions you draw. When you stake a claim on an internet forum, you need to be a bit more diligent in what you do. Misinformation is just as powerful as information. So, people will question the claim for all kinds of reasons. The tester may be a very competent person and he/she may be right. But readers can only validate that when the evidence is presented. And yes, that does sometimes mean you need to go a bit further to convince someone else than would be necessary to convince yourself.

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Canon PowerShot S95 Adobe Photoshop Lightroom 4 Nikon D7100 Nikon AF-S DX Nikkor 16-85mm f/3.5-5.6G ED VR Nikon AF-S DX Nikkor 35mm f/1.8G +5 more
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