Possible D5100 focus issues

Started Sep 22, 2012 | Discussions thread
AluKd
Forum MemberPosts: 86Gear list
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Re: Possible D5100 focus issues
In reply to cerberusjf, Sep 22, 2012

cerberusjf wrote:

CDAF seems to be quite a bit sharper than PDAF. Also the lower part of the focus chart seems to be more out of focus than the top with the PDAF, whereas it all seems to be in focus with CDAF.

Took a brief look through your photographs and, indeed, the top of both images seems to be quite similar, but the bottom of the PDAF one gets increasingly worse. That's... weird. I mean, I can find a few reasons for it to happen, but if you didn't touch the camera between shots, all of them would apply equally to both PDAF and CDAF.

Was your camera completely, perfectly, perpendicular to the chart? Focus is a straight plane, and if the camera wasn't perfectly perpendicular, the focus plane would bisect the chart, rendering part of it in-focus and part out-of-focus. Again, this would apply to both AF methods.

If your lens has a misaligned element, it could change the geometry of the focus plane and achieve that effect, as well. That would mean ALL your photographs would exhibit this to some degree.

I don't know. That's really weird.

Of course there could be a problem with my technique and I wasn’t using a tripod. But I am not sure why these problems wouldn’t show with the CDAF too.

CDAF hunts back and forth until it finds optimal focus, so it will, theoretically, always have perfect focus. Obviously, if there's any problem extraneous to the focus system itself, the focus won't be as good.

 AluKd's gear list:AluKd's gear list
Nikon D5100 Nikon AF-S DX Nikkor 55-200mm f/4-5.6G VR Nikon AF-S DX Nikkor 18-55mm f/3.5-5.6G VR Nikon AF-S Nikkor 50mm f/1.8G Nikon AF-S Nikkor 85mm f/1.8G
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