hands-on review of the D7100

Started Mar 15, 2013 | Discussions thread
photoreddi Veteran Member • Posts: 7,850
Re: Resolution and AF Re: Very good hands-on review of the D7100

rhlpetrus wrote:

photoreddi wrote:

rhlpetrus wrote:

photoreddi wrote:

rhlpetrus wrote:


AF: that may be the most relevant aspect of this new camera. Have you tested the various points. Since its sensor is denser than the D800's and I have seen some problems with PDAF for extreme lateral points (mostly the leftmost AF point), I wonder if you have checked that.

If there are problems with PDAF at the extreme lateral AF point, that shouldn't have anything to do with the sensor density since the AF sensors are located off-sensor, below the mirror box IIRC. No?

Thanks for the good job, rather fast!

Yes, excellent job. If Thom Hogan needs to hire another assistant ...

YOu forget that people check AF accuracy at full res. The D7100's full res is 50% higher (pixels per unit area) than the D800's. What was ok at 12MP (D700) seems not to be ok at 36MP, the D7100's sensor density at FF would provide 54MP worth of pixels.

No, I've long been aware of the D7100's higher pixel density and have cautioned others to be aware of this when they're pixel peeping. But the AF sensors won't perform any better or any worse no matter what the sensor is that's in the camera or what its pixel pitch is because by design PD AF is not intended to produce perfect focus. This may have been acceptable with older, lower resolution sensors but with cameras like the D800 and D7100, for the best AF accuracy Live View's CD AF should be used.

I didn't say the Af sensors would work better or not, just that if you have more resolution available any variation shopuld be more easily perceived.

True, but most D7100 owners if not using a tripod would shoot using PDAF, not Live View's CDAF, and just making photographers aware of the way that higher resolution makes focus imperfections more apparent wouldn't really help them without mentioning that the problem isn't solely due to the higher resolution, but due to the limitations of PDAF's focusing accuracy and consistency. Live View's CDAF isn't perfect, but I've found that it routinely produces better focused images if good shooting technique is used (tripod, mirror up, remote release, etc.) Since that's not going to happen shooting hand held, I don't think that the D7100's full resolution will be realized for hand held shooting unless very fast shutter speeds are used.

But what your quotes show is that your concern about the problems of the D7100's focusing accuracy didn't start with any mention of its higher resolution sensor. Instead, you wrote "Since its sensor is denser than the D800's and I have seen some problems with PDAF for extreme lateral points (mostly the leftmost AF point), I wonder if you have checked that", and as my reply indicated, that shouldn't have anything to do with pixel density. Higher resolution may make focus errors more apparent, but the problems with the D800's left AF sensor alignment/calibration were so extreme, that focusing errors would be easily noticed even this problem had occurred with the D90's 12mp sensor. I see your point though, since even though I think that your response was incomplete, technically, it wasn't wrong.

Speaking of forgetting, you recently replied to one of my posts, trying to correct me, saying that when I wrote that the 18.5mm 1-Series lens had an f/1.8 aperture, that I was mistaken, that it had a maximum aperture of only f/2.8. I owned that f/1.8 lens and my reply to you included a photo of it and IIRC, a link to it on B&H's website. Did you not see that reply, or did you just forget to acknowledge your error?

I just missed it, sorry, last week I was on a trip and didn't check carefully my posts. My apologies.

Ok, no problem. We all miss things from time to time even if we're not on a trip. I think that DPR's forum software/forum server woes contribute to that too since at times it's almost impossible to check for replies when the forum software fails, as it did for about two full days a week or so ago.

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