seeking some advice regarding a purchase

Started Sep 23, 2012 | Discussions thread
antoineb Veteran Member • Posts: 6,648
Wich "science" please? ;-)

let's talk science then: you are probably aware than on a DSLR:

  • the AF chip receives ONLY light that goes through a narrow semi transparent area in the main mirror, and then needs to be reflected by a secondary tiny mirror

  • as a result the incoming light goes through an f8 aperture - it makes no difference for the AF whether you're using a lens with a large aperture (such as my superb Nikkor 85mm f1.4) or a cheap lens with a small aperture

  • the AF chip itself is tiny, no larger than then tiny imaging sensors in compact cameras

  • finally for the AF to work, you need for two DIFFERENT optical paths (the one from lens to semi-transparent area of mirror, to 2nd smaller mirror, to AF chip - and the one from lens to imaging sensor) to be made to coincide exactly

on the other hand on a mirrorless system, whether compact or interchangeable lens:

  • the AF is done with the main imaging sensor, which in the cheapest compacts is about the size of the AF chips on DSLRs, and in more expensive compacts or mirrorless systems, is MUCH larger than the AF chips on DSLRs

  • the AF is done using ALL the incoming light vs. just whatever part manages to get it via a tiny semi-transparent are

  • there is no need to make two different optical paths coincide

If you want to be scientific and care to read reviews, you'll find that many DSLRs, apart from the most expensive ones, will cease to be able to AF in light levels where compacts still AF fine.

In the case of my Nikon D7k:

  • its Live View AF will cease to function in still decent light levels, where any of my compacts still does great

  • its PDAF will fail in low light levels, unless the very strong AF-assist light is on

 antoineb's gear list:antoineb's gear list
Panasonic Lumix DMC-FZ8 Panasonic Lumix DMC-FZ18 Panasonic Lumix DMC-ZS7 Olympus TG-610 Nikon D7000 +5 more
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