autofocus & peaking manual focus

<p>How does f/stop affect focusing accuracy? I'm using an NEX 6.</p>

 

<p>For most body/lens combinations, changing the f/stop merely affects the depth of field. Focus capture is independent of f/stop provided there is sufficient light for the sensor circuitry to do its job.</p>

<p>It might depend on the camera and conditions. I can't speak for NEX in particular but it is conceivable that in brighter light it may not necessarily be wide open when in live view, and it may not use the same aperture setting while composing/focusing as when capturing the image. Theoretically if it was stopped down a bit it might make identifying the precise plane of focus slightly more difficult -- the visible band with focus peaking may be a little broader and less distinct?</p>

<p>This said, if you're shooting with an adapted lens, you probably have full control over the aperture so can opt for focusing with the most light and narrowest depth-of-field, or focusing with the lens stopped down to shooting aperture which might make identifying the point of sharpest focus a little harder but allow previewing the increased DoF when stopped down (including any focus shift).</p>

<p>Robert,<br>

The other posters correctly pointed out that focusing accuracy is really independent of f/stop. I might add that using a mid-range aperture such as f/5.6 to f/8 usually gives the sharpest images, so based on the resulting print, you could say that the "<em>apparent</em>" focusing accuracy of the system is improved as you stop down, but only to a point, given diffraction. Smaller apertures (f/16-f/32) gives greater depth of field at a given subject distance, but again, diffraction takes a toll on image sharpness regardless of the "accuracy" of focus. Conversely, you can have a highly accurate focusing system when using the same lens at its maximum aperture (wide open), say, f/2.8, but only have a very small plane in focus, especially the closer the subject is. Focusing accuracy is dependent more on the camera's AF system, mirror/box (if a DSLR) and sensor alignment, and lens element alignment. Many DSLRs have an "AF Adjustment" option that lets you "tweak" any "front" or "back" focus for a given lens. Of course, mirrorless systems like your NEX 6 has no need of this since it has no mirror, and focus is determined directly off the sensor! Good luck with your NEX 6! </p>

<blockquote>

<p>"f/stop <strong>merely</strong> affects the depth of field" <em><strong>Stephen L.</strong></em></p>

</blockquote>

<p>Not so with the Electronic Viewfinder NEX cameras.<br />Using manual focus, your NEX with it's wonderful EVF, not only adjusts for focus shift and the gain/intensity immediately, but it's actually capable of "seeing" a sharp & contrast rich lens !</p>

<p>So if a lens is a bit soft wide open, the "focus <em>peaking</em>" is<strong> less</strong> apparent. But when stopped down (in most every case), the lens performance increases; with this, the <strong>evf NEX</strong> will become <strong>alive with "<em>peaking</em>"</strong>.<br /> Accordingly as edge performance becomes better, focusing of objects at the edge (without having to re-compose) becomes possible/easy...</p>

On the NEX-7 with very low light and a manual lens stopped down the EVF image can be grainy. Also with a lot of depth

of field, the focus peaking can show pretty much all edges in focus which is hard to focus exactly where you want it. But

those are very minor problems. Also don't forget focus magnification which can allow you to focus by eye a lot better than

you could normally do and with a button reprogram you can click to mag, focus and click out quickly and easily.