Size comparison of FE 4/2470 on A7 vs Olympus 12-40 f2.8 on GX7

Started Feb 6, 2014 | Discussions thread
quezra Veteran Member • Posts: 3,915
Re: Ladies? - use of anthropomorphic language ...

viking79 wrote:

Lab D wrote:

forpetessake wrote:

Lab D wrote:

Maybe it is what you had on hand. FYI, The Panasonic would be a better lens to compare since it is also only 24-70mm and does not have the optics for a close up lens as the Sony doesn't either. You will find the Panasonic is smaller than the Olympus, but maybe that was not your point (since you left the hood one the Olympus).

As for understanding exposure think of lens apertures like this. A fat lady and a thin lady are laying on the beach. Who will get sun burnt faster? Answer: both will burn/tan the same despite the fat lady having 4x the skin area.

... in a technical discussion is a sign of immaturity.

Since you don't understand the technical language and insists on the analogies, here is one for you. If you have two pans under the rain and one has 4 times larger surface (representing sensors), which one will have the deepest water level? It will be the same level for both.

I've seen that analogy too. Weather forcasters use it all the time and will tell you the size of the pan doesn't matter for measuring the amount of rain one is getting.

This is what makes the analogy work well, you can get the same depth of rain in each pan (same f/stop), but the large pan collects more water. In terms of digital sensors, this means that the larger sensor collected more light for the same exposure. You can use trade offs of full frame sensors to make the larger sensor more flexible.

If a full frame camera has 16 MP and an m4/3 sensor has 16 MP. Each "pan" is 4 times as large on the full frame as each "pan" on the m4/3. So at the same exposure, each pan captured 4 times as much water sitting in the rain for the same amount of time and same intensity of rain. If you have more pixels which are the same size (say 64 MP on the Full frame), then your pixel level noise/detail will be similar, but your image level noise/detail will be greater on full frame since you had more pans in the rain you can combine them together or not to make a cleaner or more detailed image.

Full frame is just more flexible. You might or might not need that flexibility.

We are also assuming for the sake of equivalence that each full stop of aperture collects double the light. However with digital, particularly short flange distance sensors (i.e. mirrorless), this may not be the case:

DxOMark wrote:

“We have been very surprised,” explained Frédéric Guichard, chief scientist at DxO Labs, “to find out that some of the gain from wider lens openings seems to be offset by the present state of sensor technology. Our measurements all point in the same direction: as you go further than f/ 4 – to f /2 and wider, the accrued quantity of light falls marginally onto the sensor. A stronger and stronger part of this additional light is blocked or lost. I am therefore inclined to question the real benefit of faster lenses.”

This loss seems to increase when the pixel size decreases, as shown on the figure below.

Well worth clicking on the link to see the graph. As pixel size decreases (which is highly correlated with smaller sensors), the greater the light loss at wider apertures. This is why fast lenses - f1.2, f1.4 etc. are increasingly found to have T-stop values closer to f1.8. Even without measuring instruments, I can very clearly see that I do not get double the light stopping down from f1.4 to f1.2 with either of my Canon lenses when on a digital sensor. The Zeiss FE 55 combined with the A7R's micro-lens configuration might have been the first lens+camera combo that actually got round this problem, DxOMark awarding it the surprising score of T1.8.

The PanaLeica 25/1.4 may get you f2.8 DoF of a FF, but its T-stop is identical to the FE 55/1.8, meaning the f1.4 of this m4/3 lens is equal to the f1.8 of this FF lens. This means it has absolutely no advantage over the FF lens in any way (well aside from size or price or non-IQ related issues). I will be very surprised if we don't see a similar result with the new PanaLeica 42.5/1.2 - which will do well to have a T-stop value less than T1.6.

 quezra's gear list:quezra's gear list
Sony a7 Sony FE 55mm F1.8 Sony Vario-Tessar T* FE 16-35mm F4 ZA OSS Sony Alpha NEX-5N Panasonic Lumix DMC-GH3 +10 more
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