Law of Diminishing Returns and the Canon 50d

Last week, I had the pleasure of attending an art auction fundraiser for Art City Toronto, a store-front art drop-in centre for under-privileged kids in Toronto. I donated a couple of works to the silent auction and I'm delighted to report that an 18x12 framed print of my Phonehenge image sold for nearly $400. Here's the image:


It was fascinating to watch people in the silent auction as they looked at the artwork. For this particular image, a lot of people did a double-take when they noticed the old English phone booths (the photo was taken on a farm in southern Ontario in Canada). Many people walked up close to the photo to look at the details and, I'm happy to say, at 18x12, the details hold up just fine. The photo is quite sharp at that size.

Nowadays, I take most of my photos with a full-frame 12.8 megapixel camera, a Canon 5d, but the Phonehenge image was taken with an 8 megapixel APS-C camera, the Canon 20d. With the recent advent of the 50d and the 5d mk II, I've been starting to think about upgrading the 20d. In fact, I've placed the 20d on permanent loan to my son while I cogitate about an upgrade.

You can imagine my interest level when DPreview published an in-depth review of the Canon 50d. After reading the review and looking at the resolution stats and the RAW noise levels of the new camera, I must admit that I now have misgivings. With the current state of the art in sensor silicon, it looks like the sweet spot for APS-C sensors is around 10-12 megapixels. Any larger and noise levels start to increase. Not only that, but system (i.e. camera and lens) resolution becomes a matter of diminishing returns. Look at the following tables extracted from DPReview:

Camera	Measurement	Absolute resolution	Extinction resolution
Canon EOS 50D	Horizontal LPH	2250	2700
	Vertical LPH	2200	2700
Nikon D300	Horizontal LPH	2200	2600
	Vertical LPH	2100	2600
Pentax K20D	Horizontal LPH	2250	* 2300
	Vertical LPH	2250	* 2500
Sony DSLR-A700	Horizontal LPH	* 2200	2900
	Vertical LPH	2100	2800
Canon EOS 40D	Horizontal LPH	2100	2300
	Vertical LPH	1800	2300

Camera	Measurement	Absolute resolution	Extinction resolution
Canon EOS 30D	Horizontal LPH	1850	2100
	Vertical LPH	1650	2100
Nikon D200	Horizontal LPH	2100	2250
	Vertical LPH	1700	2200
Canon EOS 5D	Horizontal LPH	2300	2500
	Vertical LPH	2000	2500
Canon EOS 20D	Horizontal LPH	1850	2100
	Vertical LPH	1650	2100

Looking at the absolute resolution, moving from 8 MP (20d) to 10 MP (40d) to 15 MP (50d) results in a gain in horizontal resolution from 1850 to 2100 to 2250. If this was correlated to the number of megapixels, you would expect 1850 to 2336 to 3608. Clearly, there is something (e.g. lens resolution) hitting the wall that is preventing these new sensors from delivering on their promise. Not only that, but noise seems to go up beyond 10-12 megapixels, so the extra resolution may be getting obliterated by extra noise.

All other things (i.e. automatic sensor cleaning, larger LCD, LiveView) aside, is it worth paying $1,500 to get an uplift of 22% in resolution at the expense of more noise? Consider this in the context mentioned above, where an 18x12 image produced at a resolution of 1850 lines holds up to a room full of people examining the image up close.

I'm thinking that I might wait for the 40d to come down in price and buy a good used model instead.