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

Started Jun 15, 2014 | Discussions thread
Re: Handevision Ibelux ?
1

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.

See below.

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.

If your logic doesn't survive a platonic thought experiment, what sort of logic is it?

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 said earlier:

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

What we have seen here is that it's not really the enlargement that is the issue.

Although we don't have any perfect physical speedboosters, we have some pretty good ones, and I think it's clear that the difference in resolution between two 20cm X 30cm prints generated with the same FF lens on an FF camera and on an m43 camera (with a sensor having the same resolution as the FF camera) using a good speedbooster will be much smaller than the difference suggested by the 69 and 267 times required enlargement factors you mentioned, or do you disagree?

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

In my first thought example, I used a single lens , two cameras and an ideal speedbooster.

Now, let's talk about two different lenses - one designed to project an FF image circle, the other a smaller m43 image circle. Earlier, you said:

Regardless, there is a limit how good a lens can be, thus a larger format in principle has a higher ceiling for image quality in this regard as well.

You have not explained here what physical principle connects the first half of your sentence with the second half, especially taking into account two lenses designed to project different sized image circles?

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.

While this is true, the thought experiment is a simple illustration of the fact that we must not forget to take into account the differences in image circle size each lens is designed to project.

A question: What is the mathematical relationship between sensor size and how much more visible the imperfections of a lens become? There must be a mathematical relationship, after all, if enlargement is the actual cause of the differences in lens performance w/r/t different formats that we're discussing.

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

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