'Hunting' and focus capture : 5300 vs. 7100

<p>HI,<br>

I've reviewed the line-up of 5300 vs. 7100 features, but I'm interested in primarily one feature: the ability of the camera to find a proper focus point, particularly in low light. Included in that category is a strobe lighting situation where the ambient light prior to the strobe ignition is fairly poor. In working with models, I find my 'old d5100' lacking in the ability to 'decide' on a focus point in these circumstances, resulting in the camera sounding like car tires trying to grip a surface with a few inches of snow, and frustration for me as well as the model. I'm assuming the d5300 is better in this task than the 5100, but is the 7100 noticeably better than the 5300? I'm assuming a lot of variables go into this issue, but if I use 1/60 sec. /800 ISO/ f 3.5 as a goal for accurate and reliable available light focusing, maybe that would be helpful. My hands--because of years of computer use--aren't that good to handhold below 1/60th (and maybe even 1/125th), but I don't want to rely on a tripod. Thanks.</p>

<p>Alan, it's primarily the AF detection range (in EV) that determines how dark it can be and still focus. The D7100 is -2EV, the D5100 is -1 EV and the D5300 is also -1EV. -2EV is one stop lower light than -1EV.</p>

<p>Then it comes down to the AF module and algorithms in the camera how fast it can focus in the dark, in other words how much it hunts.</p>

<p>Focusing ability has nothing to do with the exposure you select. It is lens dependent though.</p>

<p>All in all the D7100 is a cut above the others and can work with one stop less light.<br /> The D7200 is even better and works down to -3EV.</p>

<p>PS. You should stick to cross sensors when working in low light, not let the camera decide. On the D5100 that is the center AF point only. Sometimes it also helps to turn rotate the camera slightly to get it to lock onto something. Also try to focus on something that is high contrast.</p>

<p>The reason cameras have trouble with focus in low light is because the focusing sensor is really an image sensor and low light means more noise. So it has trouble focusing on edge where one side is a noisy black and the other is a noisy dark gray. If however it was white there would be less noise and mid gray it would be less noise and lot easier to focus, even if the light level is exactly the same.</p>

<p>I own both a D5100 and a D7100. The D7100 is absolutely better at AF. It's quick and spot on. My D7100 will even focus in moonlight! (Using f2.8 lenses.) So yes, the D7100 is absolutely better in low light focus than the D5xxx cameras.</p>

<p>Kent in SD</p>

<p>Interestingly timed posting!</p>

<p>I took my D5300 and D300 to an airshow recently and got more 'keepers' with my D300. The morning light wasn't great. What EV does the D300's AF module manage?</p>

<p>I'm tempted by the D7200 at the mo'...:-)</p>

<p>The D7100 has Advanced Multi-CAM 3500DX which is a newer version of the Multi-CAM 3500DX that was used in the D300. The Advanced version is more sensitive in low light (less hunting and more reliable focusing in low light) and officially supports AF with f/8 lenses with some of the focus points. In daylight the older versions work fine as well. The D7200 has the newest version, called Advanced Multi-CAM 3500DX II which has a slightly smaller focus point coverage but further increased sensitivity in low light.</p>

<p>The D5300 has an entirely different focus module (Multi-CAM 4800DX) which in my experience is more prone to hunting in low light and/or with fast primes, but my experience of that module is based on the D7000, not the D5300. I think the main motivation for Nikon to use this module is because it takes less space than the Multi-CAM 3500 and thus allows the camera to be a bit more compact. I believe this module has also been improved from its first versions but I'm unfamiliar with the details of its progress.</p>

<p>If your priority is in focusing in low light, then I think the D7200 would be the best choice in a DX camera but if your budget only allows D5300 or D7100, then I would recommend the D7100.</p>

<blockquote>

<p>I took my D5300 and D300 to an airshow recently and got more 'keepers' with my D300. The morning light wasn't great. What EV does the D300's AF module manage?</p>

</blockquote>

<p>D300 can focus down to -1EV so the same as the D5300. Your increased keeper rate was probably due to more suitable focusing algorithms and the AF module itself.</p>

<blockquote>

<p>The reason cameras have trouble with focus in low light is because the focusing sensor is really an image sensor and low light means more noise.</p>

</blockquote>

<p>mm There is not more noise outside of the camera, it is the sensor itself combined with the builtin signal amplifier which generate the noise. So the noise is the same no matter what EV-level. If the signal to noise ratio of the combined sensor and signal amplifier becomes lower ( Soless signal opposed to the same noise level) then it becomes harder to "see"the difference between noise and image information (lower contrast levels) . so it really comes down to the quality of the Sensor / Amplifier combo which determines the quality of information that the Af-processor is offerred to work with for determining the optimal focus position to feed to the lens.</p>

<p><em>So the noise is the same no matter what EV-level.</em></p>

<p>This isn't correct. The most important source of noise in photon detection is known as <em>photon shot noise</em>, which arises because photons arrive at the detector at random intervals. If you have only a little light coming in, there is greater variability in the number of detected photons from one time window to the next. If you have a lot of light coming in towards the sensor, then the number of photons detected becomes more precisely the same from time window to the next. The shot noise is the square root of the number of detected photons N, which gives a signal-to-noise ratio of sqrt(N). There is also noise due to thermal sources in the detector, and amplifier noise etc. but it is typical that the photon shot noise dominates. Not always though.</p>