24mp FF vs 24mp DX

[vipgraphx]

24mp FF and 24mp DX image size the same? I always thought that FF images where bigger thank DX images given MP the same.

I am wrong?? Looking at an image in Photoshop straight from camera RAW a 24mp FF measures 20 x 13.333 which is the same size of a 24mp DX

I have been under the impression that was one of the perks by having a full frame vs DX/crop frame. Where do you really start to see advantages, I thought that low light focusing would be an advantage with a FF, I thought that Bokeh /DOF would be better with FF, Less noise in FF vs DX, I thought that FX would have higher resolution as well over a DX but those same images are both 300dpi FF and DX.

where do you really start to see these advantages only at super high ISO?

If this is the case I have been looking at things all wrong..... if you don't really get higher resolution at same focal distance, ISO, F stop and exposure being all the same then whats really the point FF/DX?

 

[SCraig]

24mp is always going to be 24mp, it doesn't matter whether it's on a full-frame or crop-sensor body. Assuming that the aspect ratio is the same (the ratio of the width to the height of the image) then they will have the same pixel dimensions. That's not where the differences arise.

The difference is in the pitch of the pixels (or more precisely the "Photosites") on the sensor. While both FF and DX will have the same number of pixels (horizontally and vertically) the full-frame sensor will have a slightly greater distance between each pixel (the pixel "Pitch") simply because the sensor is physically bigger. That greater distance between the photosites is what allows the full-frame sensor to have a slightly higher signal to noise ratio which, in turn, allows it to reject noise better. The spacing between the pixels, I think, acts as insulation between adjacent pixels allowing the FF sensor to reject noise better.

These days the differences are far less prevalent than they were only 3 or 4 years ago. Back when bodies such as the Nikon D700 were the king of clarity the difference between FX and DX was dramatic. These days the differences are much more subtle because of the ability to manufacture much better DX sensors that are less prone to interference. Still, if you look at the low-light performance of camera bodies on DxO Mark you'll see that the top performing bodies are still full-frame.

On the other hand the densely-packed DX sensor provides a narrower field-of-view which is good for those who regularly find themselves cropping their images heavily since the resolution in the cropped area is higher providing more detail. As always, it's a trade-off that the photographer needs to be aware of and choose the tool that works best given the situation.

 

[Garbz]

Resolution? What resolution?

As said above 24mpxl is 24mpxl regardless if you're using a phone or a sensor in a space telescope. The difference is spatial resolution. A 24mpxl DX camera will have a higher spatial resolution than a 24mpxl FX camera. The pixels are smaller, spaced closer together, i.e. more resolution. To get the same resolution in an FX you'd need a 54mpxl camera. At that point the FX and DX sensor have pixels which are the same physical size.

Speaking of physical size, that's what FX is about much of the time. A 24mpxl FX camera has bigger pixels than a 24mpxl DX camera and by being bigger they capture more photons which means a higher signal to noise ratio -> better picture quality.

And all this without mentioning the effectit has on lenses such as depth of field.