Sensor size and cropping (2 Viewers)

[MalR]

Does sensor size, as opposed to resolution, have any relevance when it comes to cropping? I know that with sensors of the same size, one with a higher resolution will give greater scope for cropping, but what about different-sized sensors that have the same resolution?

For example, if you took a 20mp APSC sensor, a 20mp micro four thirds sensor and a 20mp 1-inch sensor, would the ability to crop diminish with the decrese in sensor size?

Malcolm

 

[Mono]

A general rule of thumb is that the bigger the sensor the better quality the image (all other things being equal). The physically bigger each pixel sensor is the greater the signal to noise ratio.

Most of the time you are not looking at the image on a pixel to pixel level (100%). Even viewed on a 4K monitor your 20MP image is only showing 40% of its pixels, most computer screens are showing far less. The image is being resized and averaged out, on the fly by whatever software. When you crop each individual pixel is contributing more to the overall image until you get to the "100% crop" when you are viewing each pixel. It is only down at this level you get to see the quality of the sensor.

The multi-megapixel sensors allow cameras, especially phone cameras, to cover up the atrocious quality of such tightly packed tiny sensor pixels. The final image is a resized smush of the millions of pixels. As you smush together less and less pixels you get to see the quality of the individual pixels and bigger the sensor pixels the more likely they represent a true capture of the light falling on them and not the electronic noise of the camera.

 

[Chosun Juan]

Malcolm, to compare the different sensor sizes, multiply or divide by the square of the crop factor relative to full frame (called 35mm).

ie. 20MP 1" = 146MP FF = 65MP APS-C = 36MP M43

20MP M43 = 80MP FF = 45MP APS-C = 11MP 1"

and 61MP FF = 27MP APS-C = 15MP M43 = 8MP 1"

There is debate about pixel pitch and light gathering ability, ISO or dynamic range performance, and IQ, so the relationship is not linear - ie. less than what I have put above. For that to be the case, the focal length (equivalent, x crop factor, so for example a FF 400mm lens on an APS-C camera is 600mm eq) also needs to be the same.

In practice other things are also going to play a part, lens resolution, sensor performance, atmospheric conditions, etc, etc






Chosun :gh:

 

[MalR]

Thank you both for taking the trouble to reply.:t: It's clearly a bit more complicated than I thought, as in having to factor in the variables that Chosun has mentioned.

Malcolm

 

[njlarsen]

I believe in great light you will find very little difference. In poor light, the problems with smaller sensors should kick in.
I myself use the m4/3 format and feel comfortable cropping quite a bit, especially in good light.

Niels

 

[opisska]

The problem with the question is that it's not clear, what is the purpose of the "cropping". Because that's never the end goal, the end goal is to take an image of something.

So imagine you take a lens and pair it with an 20Mpix FF sensor and crop it to the size of the 1-inch sensor and call it image A. Then you take the same lens, but pair it with a 20Mpix 1-inch sensor and call it image B. Now you have the same scene on both images, but image B has much more resolution. Sure, if you cropped image B by the same amount as you cropped image A with respect to its original, then the result will be by all likelihood worse - not only because of the higher noise of the small pixels, but because you are now trying to see smaller things with the same lens, inevitably showing more optical aberrations. But you don't need to do it, the image is already showing the scene.

I think there is a weird situation where people are overly fixated on the size of the sensor in situations where it is not relevant. Yes, a bigger sensor gives you a lot of gain for wide-field photography, because, well, the field is bigger. But once the scene you want does not fill out the entire chip, the presence of its outer parts no longer matters. This used to not be true in the old times where chips had such a small resolution that you wanted to avoid cropping at all cost and a lot of this thinking carries over - hell even in some big wildlife photo competition, cropping is explicitly prohibited by rules, which is utterly absurd, because buying cameras with smaller chips isn't against the rules

If you want to look at cropping from the flexibility standpoint - you want to have a fixed focal-length lens, but be able to get a wide range of fields of view on shots - then a large chip is an advantage, because of the aforementioned reasons: signal/noise ratio and optical aberrations. If you want to crop in order to get the most reach out of your lens, to see the smallest possible objects, a small chip may be an advantage - unless you can get a large chip with the same pixel density. That is against the rules of this specific question, where all the different chips have the same amount of pixels - but in general, if you care about reach, don't look at pixel count or sensor size in isolation, but look at pixel size in microns.

 

[MalR]

Thanks, Niels and Jan, for your input. Much appreciated.:t:

Malcolm

 

[LittleGreyCat]

New to the site and searching through.
I confess to being confused about cropping, and also sensor size.

I think:
Full Frame means the sensor is the size of a 35mm film negative.
That is, 36 x 24 mm.
I was well confused, then realised that back in the day, negative formats were full plate, half plate, and 35mm.
Professionals used full/half plate cameras and amateurs used 35mm.
Times have changed and now 35mm is the professional option.
[Just checked and my Nikon D40X has a 23.6 x 15.8 mm DX-sized Sony CCD.
Hmmm...that looks roughly 2/3 of 35mm.]

Back in the days of film, to crop was to mask off part of the image when enlarging onto photographic paper, so you were only printing part of the image.
In small cameras and mobile phones I think cropping is the equivalent to digital zoom - that is, only recording part of the full image.
This does not always give good results.
I have always been told to ignore digital zoom figures, and go for an optical zoom where you get the image across the full sensor and therefore more pixels recorded for the same size/resolution sensor.

Beyond that, I am getting lost with cropping lenses and cropping adaptors (if I am understanding the terminology).

 

[Mono]

The digital camera world is stuck in the world of 35mm wet film for its measurements. The magnification of lenses is often quoted as the 35mm full frame equivalent. Few cameras have a sensor that is full 35mm frame size, most are smaller often much, much smaller. Cropping an image is just taking a subset of the pixels to get a new image, modern cameras have so many pixels that taking only the middle 10% will still produce a usable image particularly if you are just going to use it on the web. The resulting cropped image has a much bigger percentage of the pixels on the bird rather than the background, (it still has exactly the same number of pixels of bird, you are just throwing away the background pixels). The larger bird in the picture looks like it was taken with a bigger lens, hence some people equate cropping with zooming.

Digital zoom is usually the camera cropping out the middle of the picture and then interpolating (inventing!) extra pixels to keep the pixel count the same. These images are often terrible! Some more modern, high pixel count cameras will do digital zoom by taking the middle of the picture and not interpolating the resulting image is has a smaller pixel count but is often still more than adequately sized. Digital zoom of both types is nothing that can't be done by editing the image after the fact on a computer. The result is often much better on a computer as you have more processing power on hand and an undo button.

 

[njlarsen]

I shoot raw so do not use any of the in camera options. I have read enough statements that I believe - at least in some models - that the shooting only the center of the image in camera can in some circumstances lead to improved focusing. If you are shooting a D40 I do not believe this applies to you. I agree with the rest of what Mono wrote.
Niels