To crop or to use an extender with the 5DII?

[wickerprints]

A 24x36mm "full frame" sensor is 1.6 times larger in linear dimension than a 22.3x14.9mm APS-C sensor. In terms of sensor area, the full frame has 1.6 * 1.6 = 2.56 times the area of the APS-C sensor.


Since pixel count is based on the area of a sensor and not its linear width/height, the appropriate math is


21 MP / 2.56 = 8.2 MP,


so Daniel quoted the correct value.

[Feanor]

A 24x36mm "full frame" sensor is 1.6 times larger in linear dimension than a 22.3x14.9mm APS-C sensor. In terms of sensor area, the full frame has 1.6 * 1.6 = 2.56 times the area of the APS-C sensor.


Since pixel count is based on the area of a sensor and not its linear width/height, the appropriate math is


21 MP / 2.56 = 8.2 MP,


so Daniel quoted the correct value.
<div style="clear: both;"]</div>

Ah OK that makes sense, thanks . Also I checked the specs of the 30D and of course both you and Daniel are right about the pixel density being the same. Which surprises me - why didn't we have a 21MP full-frame sensor in the days of the 30D if the technology was there?? [:S] I guess it's not all about pixel density but also about processing large images quickly as well as storing them. It's an interesting point though - it means there is more to the idea of crop sensors giving greater reach than some people claim.


Daniel - thanks for your explanations too, I see what you're getting at. But if we then take the 7D as an example, with its considerably higher pixel density, then I take it that the gap between cropping and extenders is at least narrowed?

[Daniel Browning]

why didn't we have a 21MP full-frame sensor in the days of the 30D if the technology was there??

Frame rate. The more pixels you have, the slower the readout (for a given cost and technology). On top of that, the DIGIC processing would slow way down too. So they could have made the 5D Classic with 21 MP, but it would have been like 0.5 FPS instead of 3 FPS. That's too slow for most of the market, and it would have sold even worse than it did.

But if we then take the 7D as an example, with its considerably
higher pixel density, then I take it that the gap between cropping and
extenders is at least narrowed?

Yes. The 7D has 49% higher linear resolution than the 30D, so there are some lenses that no longer benefit from a 1.4X TC, particularly the lowest quality zooms. (Good zooms, like the 70-200, still benefit from TC on the 7D.)

[Feanor]

Yes. The 7D has 49% higher linear resolution than the 30D, so there are some lenses that no longer benefit from a 1.4X TC, particularly the lowest quality zooms. (Good zooms, like the 70-200, still benefit from TC on the 7D.)
<div style="clear: both;"]</div>

Hmm. You've got me wondering again whether the 5DII is the right camera for my interests - after the mass bemusement in a thread suggesting I swap a while ago I shelved the idea but I'm really not that interested in landscape photography. The AF points and extra reach would really be a big boon. But then again shots that I do manage to take on the 5DII with the 400mm - assuming I can get close enough and assuming the AF points don't let me down - promise to be stunning.