Camera crop factor (1 Viewer)

TBMike said:

ALL OTHER FACTORS BEING EQUAL.

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But it never, ever will be: there will always be more pixels under an image that is 1.6x bigger because of optics or physical proximity to the subject than there will ever be by cropping into an image by 1.6 times - either in camera or in PP.

Whether this matters to the end result you're trying to achieve is a different issue, and it doesn't change the fundemental truth that a crop cannot be the same as being optically or physically closer to the subject.

You can take this point to a very silly - but surprisingly illuminating - extreme...

Imagine a "crop" sensor one pixel in size.

To follow the crop = magnification argument to its logical conclusion, the magnification effect here will be nearly infinite (after all, the smaller the sensor, the bigger the crop effect), but you aren't going to get a whole lot of detail in your pictures..!

Keith Reeder said:

But it never, ever will be: there will always be more pixels under an image that is 1.6x bigger because of optics or physical proximity to the subject than there will ever be by cropping into an image by 1.6 times - either in camera or in PP.

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Errm...thats only true if the sensor's pixels are the same size Keith.

Taking the example I used back near the start of this thread...400mm + 20D and 500mm + 1D2N shooting the same subject side by side. Both images appear pretty much the same, with about the same number of pixels covering the whole frame and the subject.

On screen and on paper the images look the same, with the same levels of detail...

mw_aurora said:

Errm...thats only true if the sensor's pixels are the same size Keith.

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The same size as what, Mark?

I'm not talking about one camera compared to another.

I'm just saying that - for any given camera - you don't get the same result from a 1.6x crop that you get from being 1.6x closer to the subject, either physically or optically.

This was in response to Mike when he said:

Mathmatically a APS sensor gives your a 1.6 crop factor which would equate to a 1.6 effective magnification factor ALL OTHER FACTORS BEING EQUAL

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Keith I agree with what you say. I think what I wanted to say was a 1.6 crop factor of the aps sensor relative to a FF sensor. You are a right a 1.6 crop is not the same.

A FF 400 mm lens put the same size image and amount of light on a aps sensor as a full frame sensor. Since the APS is an effective crop of the FF sensor image there is a "effective" magnification factor. (much like digital zoom). In theory with more pixel density it should be sharper. But the advantage of larger pixels in sensor has an effect.

Cool, Mike - I see what you're getting at there.

Tannin

Not sure I would agree that larger pixels are better. If that were really the case we would be seeing pixel sizes of 50-100 microns or bigger?? In fact ,all things being equal, then smaller pixels are better offering high pixel density and resolution. The disadvantage of smaller pixels is predominantly increased noise. So there is a trade off. Camera manufacturers over time, manage to reduce the noise characteristics for each chip allowing them to reduce the pixel size. This offers what is thougt to be an acceptable noise level with increased camera resolution.

If I could have a camera with 4u pixels with the same noise level of current camera's, I would jump at it!
Adrian

So how many angels exactly was that on the head of the pin?

Sorry, couldn't resist. Don't get me wrong, I'm enjoying this thread ( and learning something from it as well ) but really, I mean, we are are talking about taking photographs of birds here and to say that hairs are being split is putting it mildly, particularly when you put this debate up against fieldcraft , that is getting a bit closer to the bird! So OK, I guess some or all of you may already be pretty good in the fieldcraft stakes but what about composition? What are we looking for here, a technically 100% perfect ( or as close as theoretically posible) picture of the bird or birds in question or a pleasing image, that is an image that is aethetically pleasing and/or containing information about the birds behavior or biology? Crop factor, pixel density, chroma/luminance noise ratio is always good fun to debate and long may it continue but at the end of the day, what bearing does it have on taking a good, well composed, photograph?
Apologies once again.

Chris

The equipment you use has a definite effect on the pictures you can take. Say you are the world's best bird stalker and can get within a foot of small skittish birds. Well, if the only lens you have on your 2MP camera is a 21mm fish-eye, you're not going to get a good picture. So, regardless of your level of expertise, for yourself, the more your equipment helps you, the better your pictures are likely to be.

Couldn't agree more, but we are talking about technology/equipment that is pretty similar here, X0D vs IDX etc, my point is at this level, skill and 'eye' takes over as a determining factor.

ChrisSearle said:

Couldn't agree more, but we are talking about technology/equipment that is pretty similar here, X0D vs IDX etc, my point is at this level, skill and 'eye' takes over as a determining factor.

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Chris

There is no doubt that someone with a 10D camera and good fieldcraft skills and getting their metering, focusing and composition right, will get a better picture than an uninitiated person with a 1Ds MkIII. So you have put this thread into perspective.


However, field craft and other camera settings have been discussed elswhere, dont you think its fun to understand what goes on at the pixel level? There are some important concepts to understand, such as why a 1.6x crop camera does not give 1.6x magnification, which is how I started this thread.

Adrian

What Adrian said.

(Though I did enjoy Chris' well-meant curmudgeonliness!)

Agreed and again apologies for hijacking this thread. Indeed I do think its fun to discuss these issues -and interesting and informative as well. As I said earlier I just couldn't resist bring a little perspective. Please continue and I will watch and read with interest.

Chris

No problems here, Chris.

I agree unreservedly that composition is as important as the more technical aspects of photography - indeed, probably more important - but equally, it can be useful (and fun!) to discuss the more "nuts and bolts" issues, and it all adds to the overall body of worthwhile information out there.

Which is pretty much what you said..!

Keith Reeder said:

The same size as what, Mark?

I'm not talking about one camera compared to another.

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OK, but what has that to do with camera crop factor? You can't discuss camera crop factor if there is no crop caused by using a different, smaller recording device...thats just cropping which changes the resolution of the image!

Photovisions said:

There are some important concepts to understand, such as why a 1.6x crop camera does not give 1.6x magnification, which is how I started this thread.

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I agree that 1.6x crop factor doesn't increase the focal length but what is magnification in the context of camera generated images if it is not recording a narrower field of view?

"Magnification is the process of enlarging something only in appearance, not in physical size. Magnification is also a number describing by which factor an object was magnified." Wikipedia.


For those who only joined this photography game recently, camera cropping is nothing new - different film sizes have always changed the recorded field of view and it works in both directions from 35mm, when you consider larger formats. For example, the Hasselblad H series cameras typically use film/sensors that grab a field of view (very) approximately 1.5x wider than 35mm SLRs.

Digital image resolution is the number of pixels in the image, so the same as the number of pixels recorded by the sensor - I don't see what is misleading in that description Adrian (post #26)?

Image quality, resolution and the ability to crop has nothing to do with with the camera crop factor directly. It has a lot to do with pixel density and quality at the sensor.

Whilst we are on the subject, camera crop factor can have another advantage - as well as giving you bigger subjects in your images, they only use the (theoretical) best bit of the lens...so those cheaper TCs and lenses may work much better than on full frame sensors or film cameras that use more of the lens' image...

mw_aurora said:

OK, but what has that to do with camera crop factor? You can't discuss camera crop factor if there is no crop caused by using a different, smaller recording device...thats just cropping which changes the resolution of the image!

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Yes the resolution of the total image is different, but the resolution of the bird in the image is not.
Adrian

Mike

I agree that 1.6x crop factor doesn't increase the focal length but what is magnification in the context of camera generated images if it is not recording a narrower field of view?

Look at it the other way, lets ridiculously crop the image to just 10x10 pixels, does that improve resolution?
There are two concepts to understand here:
1) camera chip resolution which is proportionate to the number of pixels in the camera
2) Object resolution which relates to the pixel density covering the object (ie bird) of interest

Obviously, it is the latter that we are interested in


"Magnification is the process of enlarging something only in appearance, not in physical size. Magnification is also a number describing by which factor an object was magnified." Wikipedia.


and notice that this refers to the object, not the whole chip



Digital image resolution is the number of pixels in the image, so the same as the number of pixels recorded by the sensor - I don't see what is misleading in that description Adrian (post #26)?


Thats okay and refers to the resolution of the chip, but not of objects


Image quality, resolution and the ability to crop has nothing to do with with the camera crop factor directly. It has a lot to do with pixel density and quality at the sensor.

Lets break that down a little:
Image quality, which I will define as less noise, good metering, good focus is due to many factors such as noise characteristics, tonal range, A/D conversion, QE of the chip etc
Resoluton is related to pixel density, There are other factors above that can influence this


Whilst we are on the subject, camera crop factor can have another advantage - as well as giving you bigger subjects in your images,

It will only give you a bigger subject in your viewfinder, NOT in the downloaded image


they only use the (theoretical) best bit of the lens...so those cheaper TCs and lenses may work much better than on full frame sensors or film cameras that use more of the lens' image

I agree with that, although the Canon L series lenses handle 35mm very well

Adrian

Photovisions said:

Yes the resolution of the total image is different, but the resolution of the bird in the image is not.
Adrian

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I can only assume you are joking...

To start, if you are going to quote someone, probably best for credibility to get their name correct...

Look at it the other way, lets ridiculously crop the image to just 10x10 pixels, does that improve resolution?
There are two concepts to understand here:
1) camera chip resolution which is proportionate to the number of pixels in the camera
2) Object resolution which relates to the pixel density covering the object (ie bird) of interest

Obviously, it is the latter that we are interested in

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But that is cropping the resolution of the image - I am talking about magnification...

and notice that this refers to the object, not the whole chip

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OK, now you are really picking at semantics!?!? This was a definition of the word magnification, the word that you used and I quoted...which was not quantified with object, subject or anything else.

Digital image resolution is the number of pixels in the image, so the same as the number of pixels recorded by the sensor - I don't see what is misleading in that description Adrian (post #26)?


Thats okay and refers to the resolution of the chip, but not of objects

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In the context of your original post (#26) this is exactly what you had a problem with - the description of the resolution of image and chip!?!

Whilst we are on the subject, camera crop factor can have another advantage - as well as giving you bigger subjects in your images,

It will only give you a bigger subject in your viewfinder, NOT in the downloaded image

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I do not agre with this at all...the image is recorded larger in the final image if the device is smaller - that is what is viewed by the user (see my first point). See all the text you chose not to quote about film size etc.

they only use the (theoretical) best bit of the lens...so those cheaper TCs and lenses may work much better than on full frame sensors or film cameras that use more of the lens' image

I agree with that, although the Canon L series lenses handle 35mm very well

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I didn't say different - I am talking about the Tamron/Tokina/Sigma/etc kit.

Cheers

Mark (the clue was in my signature)

Mark


To start, if you are going to quote someone, probably best for credibility to get their name correct...

Apologies for getting your name wrong



I do not agre with this at all...the image is recorded larger in the final image if the device is smaller - that is what is viewed by the user (see my first point). See all the text you chose not to quote about film size etc.


I presume you meant the object is recorded larger in the final image? What you are referring to here is that the object is proportionally larger with respect to the whole chip. That really doesnt mean anything, otherwise I would like a camera with a 10x crop factor and the bird will fill the frame. Does that mean we have better resolution or magnification of the bird?

Lets take a practical example:

Two camera's with the same pixel size of 10 microns. In reality this doesnt happen and camera's like the 400D and 40D have smaller pixels than the full frame 5D and 1Ds MkII. This will offset the 1.6x crop factor to some extent, but for this example, I want to keep things simple to illustrate my point.

The full frame camera has 3000 pixels horizontally and the smaller chip camera has 1875 pixels (1.6x crop) Both camera's are used with the same 500mm lens to take a picture of a bird 30M away and the resultant object (bird) covers 400 pixels in the length dimension. As the pixel sizes and therefore pixel density are the same for both camera's, the bird will cover the same number of pixels.

We would both agree that the bird would look proportionately larger in the view finder of the smaller camera

Now download the two images and display them at 100% side by side on a computer monitor (lets assume we have a 50 inch screen!). The whole image will be larger for the 3000 pixel camera than for the 1875 pixel camera, but the bird will be exactly the same size of 400 pixels. This means that the resolution if the bird will be the same for both camera's, i.e. even though the resolution of the camera chip is larger for the larger camera, the object resolution is the same. This is an important concept to understand and explains the effects of a 1.6x crop, yet you referred to this as "semantics"

So you are not getting any resolution or magnification effect with a 1.6x crop.
As I explained earlier, the 40D and 400D have smaller pixels which offsets the 1.6x crop effect. If we take the 40D and 5D with pixel sizes of 5.7u and 8.2u, the sampling rate of the 40D will be better by a factor of 1.44. Therefor the object resolution (pixel sampling) of a 40D is better by a factor of 1.44 compared with a 5D. So if we compared these two camera's after taking the bird image, the 5D which has a greater chip resolution, has a bigger total image, yet the 40D will have a smaller total image and the bird will be larger by a factor of 1.44.

I dont think I can explain this any easier, unless I showed two photos side by side.
Adrian