Headline - DSLRs have imprecise focusing due to their mirrors

Started Apr 5, 2014 | Discussions thread
Midwest Forum Pro • Posts: 17,151
Re: Let's not go down a path...
1

peevee1 wrote:

There is no such thing as absolutely precise mechanical adjustment. If there are mechanically different paths to the imaging sensor and to the AF sensors, there WILL be discrepancies between them. Add to that mechanical discrepancies in the lens themselves which affect PDAF (it tells a lens where to focus but it does not mean the lens is going to do exactly that due to its own imperfections - which might even differ from FL to FL and by focus distance, so it is simply impossible to ever calibrate them perfectly for all FLs and distances and apertures even on the high-end bodies which support calibration). CDAF by design is looking for focus, no discrepancies matter - what the main sensor eventually sees is what you ultimately get.

What if you needed to use electronic scales when cooking - to measure flour or milk not just to the cup, but to the 1/100th of a gram, to get it perfect? Suppose it took you three hours make a recipe instead of half an hour, and in the end you could not taste the slightest difference? Would it be worth working in slow motion for that level of 'perfection'?

What if I worried about getting the focus better on this shot, but oops, the opportunity was lost to me long before the slow AF method went 'beep'? Personally, I can live with this - and it's better on my PC than it is in dpreviews compressed gallery storage. Incidentally, it was taken with a 10mp 2008 Canon Rebel XSi (450D) and a kit lens. This kid was riding full blast across my field of view and I had very little time for the camera to focus and get the shot. It did.

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