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

Started Feb 6, 2014 | Discussions thread
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viking79 Forum Pro • Posts: 14,136
Re: apples and oranges

joe6pack wrote:

viking79 wrote:

Dennis wrote:

Emacs23 wrote:

I bet 24-70 is better. Larger sensor — easier to design.

Since when ?

A7 has 4000 pixel high image and 24mm page height, or 2000 line pair high image and 24mm = 83 LP/mm.

E-M1 has 3456 and 13mm page height, or 133 lp/mm requirement.

Which do you think is harder to design a lens for? A sensor that requires 133 lp/mm or 83 lp/mm? Even A7R has only 103 lp/mm requirement.

To look at this another way, pretend I wanted to get a "16 MP" image out of the camera. For the E-M1 that would require 133 lp/mm, but a lens with only 68 lp/mm would be fine on A7 or A7R. This is very low and easy to design, where 133 lp/mm is getting exceedingly difficult and expensive.


Seems to me 68 and 133 difference is just 1 stop. Which is offset by the f-stop difference between F2.8 and F4. And then the Olympus has longer reach. Seems to me Olympus wins here

This is resolution, not f/stops or EV difference. Those are in one dimension, so you have to square them to think in terms of area. Pretend you used a 68 lp/mm lens for the full frame and a 133 lp/mm lens for 4/3", and both cameras had infinite number of pixels (more pixels than the lens resolved), you would resolve 16 MP image with either camera.

But if you had 133 lp/mm lenses on both cameras with infinite number of pixels, you would resolve 16 MP on the 4/3" camera, but 4 times that on the full frame, so 64 MP image.

So the doubling the linear resolution (lp/mm) is equivalent to a 4x improvement in terms of MP, so a 24 MP full frame will easily outresolve a 16 MP 4/3 camera, in part because it is more pixels, but mainly because it is a larger sensor which is less demanding on the glass. It would easily out resolve a 24 MP 4/3 sensor too.

What I am referring to here with these lp/mm numbers is what is demanded by the sensor to resolve all the pixels, not what each lens is capable of.  More realistically the m4/3 lens won't be good enough to out-resolve the sensor, but it isn't hard for a full frame lens to do so.  Look at DXO Mark's perceptual MP and compare between different sensor sizes.  Which one does best, even given similar sensor resolution?

Ease of design also needs to take into account the coverage area. All things including aperture being equal, it is easier to design a lens for a smaller sensor too.

I think ease of design has more to do with field of view and entrance pupil size (focal length / f-number). The easiest lens designs I have seen which are very good are large format lenses. They are very simple lenses and don't need very high resolution (since the sensor size, film, is measured in inches).

I think in general smaller sensors are harder to design lenses for, as you have to start getting excellent performance at very large apertures to make them any good.

Start looking at C-Mount lenses, and see how many you find that can resolve more than 100 lp/mm in the corners (most are 60 to 80 or so), and see how much they cost? They start costing a lot.

The perfect example of this is the Pentax Q. If you shoot RAW with the camera the images are generally unsharp in appearance because none of the lenses can resolve anywhere near the 12 MP of the 1/2.3" or 1/1.7" sensor, so you have to apply a lot of sharpening to the RAW data. The 1/1.7" sensor is probably going to be a lot better due to the larger size. With the original Q I was getting only about 6 MP of resolution out of a 12 MP sensor.


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