New Nikon should equal the NEX 7 in IQ (but with lens MP)

Started Sep 20, 2011 | Discussions thread
ProfHankD Veteran Member • Posts: 4,965
Re: Nikon 1 is different enough

viking79 wrote:

The idea of equivalent focal length is entirely confusing. They should have never used it, but manufacturers were trying to help people adjust to smaller sensor sizes (at the same time giving them effectively smaller aperture lenses). Full frame almost always has cheaper and lighter lenses for the light gathering ability. Look at large format film cameras (like 8x10" image area). They have very small lenses with very small depth of field.

Equivalent focal length is just another way to express diagonal view angle, and it is used because it is more intuitive once "everybody" is used to a particular format, i.e., 135 frames. I only find it confusing for rectangular formats that have very different aspect ratios (e.g., square formats or 16X9). As we, and basic physics, all agree, aperture and focal length are entirely unaffected by crop.

As I commented earlier, the claim that a lens with a larger f/number (we really should be saying t/number here) and correspondingly greater coverage can deliver the same total number of photons to the focal plane is valid, but I wouldn't call that "light gathering ability." Your claim that the total photon count is what matters for film (large format or otherwise) is exponentially wrong -- remember reciprocity failure ? Individual silver halide particles are most like digital energy threshold detectors and too little energy does absolutely nothing.

Ironically, the sensors in digital cameras are generally nearly linear analog photon counters . Thus, the "total photon count" argument is approximately valid for them, but variations in quantum efficiency, leakage, etc., often favor the sensors with higher sales volume (generally APS-C and smaller) because they get correspondingly better tweaking of the design, fab processes, etc.

As for large-format lenses being small, by what measure? The ones I have are HUGE in use -- e.g., my APO Goerz needs something like 2 feet of bellows between it and a sheet of 4"X5" film to give me roughly the view angle of a 135mm! Yeah, the glass is often proportionately quite small, but that's for cost reasons. Correcting a fast lens for a large coverage area would require too much glass, and the depth of complex designs tends to cause internal vignetting that would limit coverage.

As for DOF, well, that's a whole other can of worms. DOF requires rules for determining the allowable "circle of confusion" -- which is not something people generally agree on.

In summary, as optics and sensors get better, smaller tends to win because it's cheaper to use less material. Yeah, I'd like nothing better than to see Sony make a commodity-priced FF NEX with sensor steady-shot that shoots movies better than a Red One and is a programmable computational photography device. My research work is trying to make things like that happen -- I've wanted something like that ever since I built a 30MP video wall driven by a Linux cluster supercomputer in 1996 . However, smaller sensor cameras have some real advantages, and fast, physically small, telephoto view angle lenses head the list. Of course, personally, I prefer ultra-wides.

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