erandolph Loc: La Pine, Oregon USA

Can someone help me out here. I have a cropped sensor camera with a 24.3 MP Sensor. (Sony A77). The Sony A99 a full frame camera also has a 24.3 MP sensor. So the sensor is larger and the MP's are the same.
Does this mean less pixel density on the full frame camera? How about image quality? Why is the full frame better in this respect?

Thanks for any clarification you can provide.

FredB Loc: A little below the Mason-Dixon line.

It could mean a density difference, and/or a pixel size difference. Generally, given the same number of pixels, a larger surface affords better image quality through a reduction in electronic 'noise' between pixels. Also, the larger surface area means more light gathering ability. Look at it like this - the original Canon 5D full-frame sensor had 'only' 12MP worth of sensor yet its' images can be stunning.

More pixels doesn't necessarily mean better quality, but it can. A lot also depends on the digital processor (CPU) that massages those little bits of 1s and 0s.

stevenswild Loc: sin city

well said Fred! :thumbup:

mikemilton

Well, there are surely fewer photosites in any given area. Given that they are from the same manufacturer, they are likely similarly engineered so, yes the full frame version is likely a more capable sensor.

That said, a photosite has a few things involved. There is the actual light sensitive bit which is *smaller* than the overall photosite. How much smaller varies from design to design. There are the electronics associated with that site. There is some space for the circuitry carrying the signals to where they are read out. Above all this are a filter and a lens which can also have a big impact (for example, the manufacturer may have elected to 'use up' the added sensitivity to apply a better, but denser filter or they may have used gapless lenses on the smaller sensor but not the larger one to deal with costs. As mentioned above there are also readout and DSP techniques that make a huge difference to noise.

My only point is that bigger is better is simplistic and does not account for design trade offs or issues of cost management.

GrahamS Loc: Hertfordshire, U.K

Does this help?

http://www.robsphotography.co.nz/Sony-SLT-A77-A99.html

Willy Loc: Alaska

The number of Megapixels is simply how large a print you'll be able to produce.
If you're not printing anything larger than a 8"x10" then 4 Megapixels is sufficient. For a 16"x20" print you'll need at least 8 Megapixels.

( This info comes from Scott Kelbys book "The Digital Photography Book" Volume 1)