How bg is a pixel?

[R.Morrison]

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I recently had a proffessional photographer tell me that he did not want a full-frame sensor in his camera because the APS-size sensor in his camera would have 'more compact' pixels and therefore provide a sharper image. Another way of putting it would be: If a 10 mega pixel camera had a larger sensor than a smaller pixel camera its pixels would be 'spread out' and therefore not provide as sharp an image on a print cropped to the same size as one taken with a small-sensor camera also rated at 10 mega pixels.

What's the thinking here?

 

Yours,

R. Morrison

[stuny]

I'll leave that argument to the engineering members of the Forum, but there is at least one advantage to larger pixels: they can gather more light than smaller pixels and are therefore more sensitive, allowing higher ISO settings before there is objectionable noise.

[mjh]

A pixel, i.e. a picture element, doesn’t have a specific size. Or it can assume any size you want.

 

A sensor pixel, on the other hand, does have a specific size, but it doesn’t directly relate to the sharpness of the image captured.

 

Your professional photographer doesn’t know what he’s talking about. (He may still be a fine photographer of course.)

[R.Morrison]

Thank you gentlemen for your prompt replies.

The photographer to whom I allude is far from the first I have met who does not know the technicalities of his craft. Yes, he is a fine photographer.

Yours,

R. Morrison

[adan]

Your friend is correct in that, for a FIXED number of megapixels, a smaller sensor has "finer" or smaller pixels.

 

I.E. a Canon 7D with 18 Mpixels has pixels about 4.3 microns across (more compact), and a FF M9, also 18 Mpixels, has pixels 6.8 microns across (larger). The M9's pixels aren't "spread out" with gaps between them, though. They are just bigger.

 

HOWEVER - to get pictures with the same content and framing, all the details in the scene ALSO have to be projected smaller on the 7D sensor than they do on the M9 sensor - negating any real advantage of "smaller" pixels. The full picture will be about 5200 pixels across in either case.

 

The analogy would be - shooting Kodachrome on a Minox vs. Ektachrome 400 on a Hasselblad. Yes, Kodachrome is finer grained, but using a smaller piece of film (smaller sensor) negates the advantages of the finer grain.

 

On sensors, pixels usually fall in a range from around 9 microns wide in some medium-format backs down to 0.3 microns wide in some pocket P&S cameras.

[hteasley]

The photographer may be thinking that, with an APS-C sensor of N megapixels vs a full-frame image sensor of N megapixels, that more pixel sensors subtend a visible arc of length P with the same lens. All other things being equal, that might matter. But all other things are not equal, and the problems of the smaller sensor very much outweigh this possible benefit. Fewer photons per pixel is the biggest problem, I believe.

[R.Morrison]

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Thank you again folk!

 

Yours,

R. Morrison

[farnz]

Pixies are smaller than fairies but larger than sprites.

 

Pete.

[mjh]

How many pixels can dance on the head of a pin?

[farnz]

How many pixels can dance on the head of a pin?

As many as camels that can fit through the eye of a needle.

 

Pete.

[janki]

What about the "digital noise "?

 

Will it generally be less visible on an image from a big sensor with large pixels versus the same sized image from a smaller sensor with the same number of small pixels?

 

In other words; even if you do not want to make very large images, will a large sensor with large pixels provide a more beautiful picture than a small sensor with the same number of small pixels?

 

Can any of you say anything about it?

 

Thanks!

[ho_co]

The larger sensor has larger pixels, which accommodate more photons than the smaller pixels of the smaller sensor.

 

All else being equal, the larger number of photons will tend to overwhelm the amount of noise generated at any pixel site.

 

That is--oversimplified--the larger sensor with larger photosites will have a higher signal-to-noise ratio than the smaller sensor.

 

That, plus the fact that the image won't be enlarged as much as from a smaller sensor to get to the same size output, means that the larger sensor will give a better image with less noise at any given size.

[janki]

Thanks Howard!

 

This was a very educational good presentation and elucidation of the topic, very easy to understand.

 

Thanks again!