Optimum pixel density?

Started Oct 27, 2008 | Discussions thread
John Sheehy Forum Pro • Posts: 19,124
Re: Optimum pixel density?

GeorgeML wrote:

Basically, the 15mp of the 50D resolve as much detail as 12mp FF
cameras - and that's with prime lenses .

I get aliasing with zooms with the 50D.

With some of the popular zooms, the 50D will actually resolve less
detail - despite its higher pixel count (15mp vs 12).

You seem to be working with a model where the resolution of the lens is modest

There's nothing wrong with increasing the number of megapixels. But
the question is, where are the lenses that will match the high pixel

The immediate need for many people is more MP when it means fairly high pixel-level contrast. However, the benefits do not end there; they just become more costly in terms of storage and speed. If storage and speed were not a problem, I would want a pixel density in which my sharpest lenses at their sweet spots took at least 5 pixels inclusive to go from black to red or black to blue. This would mean no aliasing in the color channels. The red and blue channels can be extremely aliased, even in the 50D. That's one of the reasons that pixel-level detail can look so sick in ambitious RAW conversions. Over-sampling in the spatial domain means that converters do not have to take the input of single pixels very seriously, and could, in fact, treat the highest frequencies as garbage, which they are. With a 6MP DSLR, the high frequency noise exists at the same frequencies as detail which ambitious converters are trying to extract, because the lenses are often undersampled.

Is Canon going to change their entire lens lineup to match the
resolution of a 20mp crop camera, for example? If not, what's the
point of increasing the number of megapixels on the 60/70/80D to 20mp?

I certainly wouldn't want Canon to hold back because of the softest lenses. Yielding to the lowest common denominator does not make sense; there are many lenses DSLR-format lenses, which, when used with good technique, in optimal conditions, could take advantage of pixels down near 2 microns or less.

I just stacked multiple TCs on my Tamron 90mm macro, a $450 lens, and still had near-pixel-level sharpness, with my 50D. At 4x, that means that I could have had that level of pixel-level sharpness with 4.7/4 = 1.175 micron pixels, or about a 242MP APS-C sensor (of course, the corners of the frame may not warrant the resolution, so this is only guaranteed near the center).

So, optimal density is a relative term.
The current Canon lens lineup seems to handle fine 12mp crop and 21mp
FF cameras.
It’s a stretch after that.

Hardly. The best lenses are WAY sharper than the ones that are disappointing, or what technique or stability often allow.

Here's a 100% crop of my Tamron 90mm multiplied 4x on my 50D (there is purple fringing/haloing due to scattered/OOF IR light from all the stacked TCs):

The lens that just keeps on giving ...

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