FF vs APS ( 5D vs 20D sensor) article

[nycandre]

Thanks for this  informative article (*). I am still not certain on how it would apply to the following real life situation:

The article seems to indicate that the 5D sensor will do better in general.

In this situation, though, shooting 5D vs 20D using a long lens, say 100-400L to shoot a specific flower at 400mm, as an end result filling the same frame, plenty of light.

This calculation tells me that whatever I shoot, *if I am at the extreme end* of the long lens, say 400mm, and the flower fully fills the APS-C sensor, so I would have to crop the 5D shot, the end result would be sharper with the 20D than with the 5D. Because the 20D sensor packs 8.5 Megapixels vs 5 Megapixels for the 5D ( 5 equals 12.8 divided by 2.56 the surface ratio FF /APS, ie  (24x36)/(15x22.5) ) 

The situation would be different, *IF* I had an 800 mm lens - in that case the 5D would be best.

Just wanting confirmation. And now thinking I'd better get an 1.4X extender ;-)


(*) http://www.bobatkins.com/photography/digital/full_frame_vs_aps-c.html

[Bob Atkins]

That's pretty much correct, though if you fill the frame at 400mm on an APS-C camera like the 20D, you'd "only" need a 640mm lens on a full frame camera (400 x 1.6) to fill the frame, assuming you were shooting from the same distance.

[nycandre]

Allright - thanks for the confirmation - and the added complication re shooting distance ;-)