See I'm confused - you seem to understand the science well enough to know that a 40D wouldn't be able to magic up a huge amount of extra performance out of the same lens, yet you started this thread by musing about spending $1500 on one in a heartbeat. Something does not compute.

And I'm not sure what's confusing about "the extra (frames per second) speed and reach." Those are still true and still advantages of a cropped sensor camera.

But Erik, it's the denser pixels, and only the denser pixels, that allow the 1.6x crop without the reduction in pixel count you mentioned upthread.

Yes, I know… but smaller pixels (denser pixels) is rarely a good thing. I'm not sure what your point is. The added "reach" is due to cropping. The fact that they maintain 8 or 10 megapixels or more is due to the denser pixels. They're two related - but different - things.

Graham said on February 27, 2008:

So yes, your original assertion that a crop sensor camera would give you "extra speed and reach" is not entirely thought through, to say the least.

Yes, it does. The "reach" still holds because even the Canon 1Ds Mark III is only 21.1 MP (to the 40D's 10.1 MP). And the "speed" still holds because even the 40D does 6.5 FPS while the 1Ds Mark III does 5 (and the 1D Mark III does 11). I wasn't using the term "speed" to mean amount of light. I tend to limit my use of "speed" in that definition to the lenses themselves. I was talking about the more literal speed - frames per second. Crop cameras tend to be faster in that regard.

So while there's a real compositional advantage to a crop sensor camera, the technical advantage you tout is purely about the 40D's pixel density, nothing to do with cropping. And as you say, there's a real trade-off in noise.

Similarly, the DoF calculations demonstrate that a 200mm lens pretending to be a 320mm is much darker that the real thing. Your 200mm f/2.8 only gets as much light to the sensor as a 320mm f/4.5, because it doesn't have the big iris of a real 320mm f/2.8 lens.

So yes, your original assertion that a crop sensor camera would give you "extra speed and reach" is not entirely thought through, to say the least.

The question do you prefer a full frame versus a "cropped" sensor is moot.

I don't think so. There are tradeoffs in going with either of the two forms. And yes, I define "full frame" the same way everyone else in the industry does. The lenses we have still produce an image circle that covers (barely) a "full frame" sensor.

Heinrich said on February 26, 2008:

Do you really want to pay $1500 for larger sensor, so you can shrink it down and post it on the web?

Let's not assume most of my photographs end up on the web. I still print more than I put on the web. And it's obviously not just the "larger sensor" that accounts for any differences in price. I get what you're saying… but tone it down just a little there Heinrich.

Graham said on February 26, 2008:

What you're actually after is the denser pixels on the 40D's sensor (5.7um vs 8.2um), which allows it to resolve a bit more detail from the same lens. Nothing to do with the cropping.

No, that's not what I'm after. The 40D has a resolution of 10.1 MP. My 5D does 12.8. The 40D's pixels are much, much denser which really leads to increased noise - definitely something I wouldn't "be after."

Graham said on February 26, 2008:

What do you mean by "your depth of field changes", btw?

I mean a 200mm lens, f/8, subject distance of 20 feet gives you 0.9 feet of DoF with a 40D but 1.42 feet with a 5D. Bump the 5D to 320mm (200 x 1.6), the "equivalent" focal length of the 40D, and you're down to 0.54 feet. Calculations done by the always handy DoF Calculator. So that's what I mean.

What do you mean by "your depth of field changes", btw?

If you define "Full Frame" as a sensor the size of 35 mm film, any manufacturer can make a sensor that size...and result in a three megapixel image.

Just as digital photography is DIFFERENT from film photography with regard to image capture physics, some of the physical characteristics (sensor size = film size) are not true comparisons.

Of course, with the marketing of "bigger megapixels equal better image" is not really true.

Do you really want to pay $1500 for larger sensor, so you can shrink it down and post it on the web?

I have blown up images taken with 2 megapixel Coolpix 2100 to 8.5 x 11, and the noise fields and the pixelation were visible if you got close up. But at normal viewing, the image looked fine.

I guess what I am trying to say is the secret isn't in the sensor, it's in the equiptment that best suits what you trying to do at the time of the shot and in the photographer's skill (of which, I have none).

P.S. I am super happy with my D300 and will be for YEARS to come. I have no desire for a D3.

Don't take it personally: I hate everyone with a 5D, not just you.

That's fine, but c'mon now, that's not what you said (or implied)…

ramanan said on February 26, 2008:

If the feature you are after is the 1.6 crop, then why not get an older used body? You can probably get a 20D or 30D for far less than $1500. You can get old Rebels for a couple hundred bucks.

I had an old rebel (two, actually) and sold them. The 350 and the 400. I'd definitely want the next step up for the second wheel if anything. An older model (20D/30D) isn't a bad idea, but at this point, even the $1000 is better spent elsewhere. Like on the MacBook Pro I ordered today.

If the feature you are after is the 1.6 crop, then why not get an older used body? You can probably get a 20D or 30D for far less than $1500. You can get old Rebels for a couple hundred bucks.