# Crop Factor, Low Light and Aperture with m4/3 lenses?

Started Jun 15, 2014 | Discussions thread
Re: Handevision Ibelux ?

Truthiness wrote:

texinwien wrote:

Truthiness wrote:

I wasn't talking about SNR of the signal of such, but about the image as rendered by the lens, before anything sensor does.

and when less enlargement is needed, the lens is stressed less,

What does "the lens is stressed less" mean? Is that accepted optics terminology? Do you have some links to authoritative sources that talk about this in more detail?

I have something better than that - logic:

If you want to produce a 20 cm by 30 cm picture (600 cm^2) from a full frame system where the lens draws you an image of 36 mm by 24 mm, you need to enlarge the image the lens draws to 6940% of the original size, 69 times larger the size the lens draws).

If you system has for example 17.3 mm by 13 mm as in m43 and you want to print the same size (600cm^2), you need to enlarge the image by 26700%, 267 times larger the size the lens draws.

The more you need to enlarge the image, the better quality the image lens draws needs to be for one to get the result one wishes.

If you use the very same lens on both these systems, the aberrations of the lens will be more visible due to the larger enlargement on the system with the smaller image sensor.

Here's a logical thought experiment. Perhaps you could tell me how it fits in with the logic you've provided above:

The above logic of mine should be perfect. Or what in it is not? Please point out something. Happy to learn.

1. We attach an FF lens to an ideal 16MP FF camera and take a photo of a static scene.

Ok.

2. We attach the same FF lens to an ideal 16MP m43 camera via a optically perfect speedbooster and take a photo of the same static scene.

The problem in this though experiment is that you add a perfect optical instrument to the system. What this does is that it perfectly downsizes the image drawn by the lens from 43mm diagonal to 21.6mm, thus you can duplicate the 43mm siized image diagonal perfectly as well.

You might just as well use say that if by magic we manage downsize the image drawn by the lens perfectly by a factor of million, we would not need any better lens to get to the same output size with the same optical quality

Without the perfect idealized speedbooster you can not enlarge from 21.6mm diagonal to 43mmm diagonal without the imperfections of the lens becoming more visible.

(Of course the images will be different for different formats regardless, but this is not the point.)

It is not a necessary to rely on thought experiments although the one provided by texinwien is a perfectly valid one. As a matter of fact, it is a well-known law of optics that geometric aberrations scale. In other words, you can take a lens design for FF, scale it down to an MFT lens, and the lens will resolve just as well in line pairs per image diagonal and twice as well in line pairs per millimeter as long as diffraction is not a problem.

Anders W's gear list:Anders W's gear list
Panasonic Lumix DMC-G1 Olympus OM-D E-M5 Olympus E-M1 Panasonic Lumix G Vario 14-45mm F3.5-5.6 ASPH OIS Panasonic Lumix G Vario 7-14mm F4 ASPH +28 more
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