Saturday, January 12, 2013

Does the Nikon D5200 Have a Focus Issue "Like the D7000"?




Pocket Lint just published their early impression of the Nikon D5200, leading with the story that they found focusing with the optical viewfinder to be less accurate than with Live View. They're also wondering if it's the same "issue" that early D7000 adopters faced.  Having said that, they were pleased with the sensor output, but I doubt that's what's going to get people's attention...

First, it's not that I'm skeptical of missed-autofocus claims, as some people genuinely do have trouble with phase detection autofocus, but as I've mentioned before, it's not a real "issue" in the same way that the the left-sided AF sensor alignment issue was real for the D800. One is a genuine product defect, the other is product idiosyncrasy. There is still a skill and experience aspect to using PD autofocus, which is why it's so easy for some people to dismiss mis-focusing claims (occasionally rudely, I might add). PD autofocus is not so much a push button process as it is user aid: there is still an element of user control and decision making to it. An analogy would be GPS maps: today's electronic apps (even the Apple maps...) are astonishingly sophisticated and rich sets of data... but once you enter in your mapping parameters, you as the navigator still have to decide if the map is taking you where you want to go. Most of the time, the map is reliable enough that you can operate on autopilot... leading to occasional disastrous results. But it goes without saying, to master the art of photography, the machine should be on autopilot, not the user.


With the D5200, the extra resolution will accentuate focus errors.. but this only applies if you are viewing images at the pixel level. If you are viewing image from a D5100 and a D5200 at the same viewing magnification (100% on your monitor), however, the difference in focus tolerance isn't a factor. Another potentially compounding factor is that the D5200 inherits Nikon's 39-point AF unit. As I've mentioned in my D7000 review, the nomenclature of the AF unit suggests that this the individual AF sensors in the D7000, D5200 and D60 are the largest in Nikon's line up. So if you combine lots of resolution with a sensitive but possibly less specific AF unit, you could have a camera that requires more attention to focus.

But, that's not what I'm seeing in Pocket Lint's samples. I'm referencing their eyeglass shot, here and here. The Live View sample is near perfect, with the point of focus roughly on the left bridge (in the image, right side). Pocket Lint isn't too specific about their setup, but I'll assume that these are crops, as they would need a macro lens to focus this close. If you look at the example that was focused with the optical viewfinder, you see that it isn't as crisp... but look closely: even if there is not one very sharp region there is still a region that is sharper than all the other regions. Yep, it's still the right bridge. So if the point of focus is in the same place in both pictures, why is one crisper than the other?

Mirror slap.

That's my guess anyway. The D7000 is known to have a stronger mirror slap than the cameras before; that might be happening here as well. You don't get mirror slap in Live View, because the mirror is already up and out of the way. (Earlier Nikon cameras like the D3x did experience mirror slap in Live View though). This is what I think Pocket Lint is seeing, because the point of focus is the same as the contrast-detect AF shot, but the decrease in contrast is relatively uniform across the whole PD AF sample... which is what you would expect with camera movement during exposure.

Of course, none of this is new to experienced shooters. Live View is the new manual focus; if you want to focus on something precisely, Live View gives the best and most user friendly results. Experienced shooters also know to watch out for mirror slap, especially at certain shutter speeds... though in most situations it's easy to forget and the results aren't as critical. These may be legitimate issues with the D5200, but the samples used here don't give very clear answers. However, forum folk are probably bracing themselves for another onslaught of "camera X backfocuses"...

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