Here are 16 200x200 pixel 100% crops centered on a dust bunny.
The apertures for each swatch are:

5	5.6	6.3	7.1
8	9	10	11
13	14	16	18
20	22	25	29

As you can see the dust bunny isn't really obvious until you reach f/20.

The next set of swatches are the same crops after desaturation, auto levels, and then a manual adjustment to make them the same brightness.

Now, of course, the dust bunny is more obvious.
It is interesting to see direct evidence that something on the surface of the IR filter is far enough away from the CCD sensor site so the angle of light, which is affected by the aperture, matters.

Bill

Visit me, info and galleries at: http://home.comcast.net/~NikonD70

That's a very interesting and informative test. I've often wondered how small an aperture you have to go before dust becomes most visible. I took a dust test shot yesterday at f/22 and found that I've definitely accumulated a few more spots that weren't there several months ago... but I've never noticed them in any recent photos I've taken.

Of course now that I'm shooting more wide angle shots (just got the 10.5 fisheye and I'm waiting on a Tokina 12-24), I will have more photos with lots of sky...which is where you really seem to notice the dust.

It's pretty easy to fix the spots in Photoshop, but that gets old after a few photos. The dust reference thing is kind of annoying as well since you have to keep updating it. I guess it's time for my D70's first cleaning.

Sean

D70
18-70mm AF-S
50mm 1.8D
Nikon 80-200mm f/2.8D ED AF
10.5mm f/2.8 DX fisheye
Tokina 12-24mm f/4 DX
SB-800

FFN
Continuous Learning

This is by far your best work yet...keep up the good work:)

Fred
http://www.butterflydesigns.net/
Photoshop is one big party waiting to happen...