Are you tempted to switch to Sony A7 or get one as well as your Fuji?

Started 9 months ago | Discussions thread
Krich13
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Re: Are you tempted to switch to Sony A7 or get one as well as your Fuji?
In reply to hexxthalion, 9 months ago

hexxthalion wrote:

Krich13 wrote:

hexxthalion wrote:

Krich13 wrote:

F/2.8-4 lens is f/2.8-4 regardless of film/sensor size

... and 18-55 mm lens is 18-55 regardless of film/sensor size.

However, if you convert the focal length for equivalent angle of view, you must also convert the aperture for the same depth of field and light gathering ability (e.g. to evaluate noise or signal-to noise performance (and convert ISO for equal shutter speed).

For instance:

18 mm f/2.8 lens on a crop x1.5 camera at ISO 200 would produce a shot virtually indistinguishable from (same angle of view, same DOF, same signal-to-noise -- if the sensors use similar technology, same shutter speed/motion blur and even the same diffraction limited resolution) as 27 mm f/4.2 lens on full frame camera at ISO 450 AFTER both shots are scaled (up/or downsized) to the same pixel dimensions.

That's all fine, but comparing Fuji's fast zoom to Sony's slow zoom is pointless - we're talking about the 'speed' of lens, or light gathering ability. So in real world where you'd use large aperture on the wide end would be probably under worse light - you wouldn't do it for shallow DoF.

This _is_ the light gathering ability: the total amount of light (or number of photons) delivered to the sensor. To the whole of the sensor, NOT amount of light _per_unit_area_. Sony lens is slower, but it captures nearly the same amount of light (more actually) as the "faster" Fuji lens -- and then spreads this light over a larger sensor. If you subdivide the larger sensor into the same NUMBER (not density) of pixels as a smaller sensor, each pixel will receive the same amount of light and provide the same signal-to noise ratio. If the larger sensor has more pixels, each pixel will end up noisier, but downsample the images to the same pixel size -- and their noise would turn out similar again.

In good light or bad, wide aperture or slow, wide end or tele-- use the conversion formula above and you will obtain similar results with full-frame and cropped sensors (or medium/large format for that matter, in that case use "crop factors" smaller than 1).

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