Does sensor dirt shows up at smaller apertures only?

I have been doing the blue sky check about once a week as I change my lenses pretty often...everything was good until today...definite goobers on the sensor.

I just checked a few days back and was really surprised to have as many as I did. One thing I noticed is that when I did the test, I was stopped at f22...then boom! They popped right out at me. Looked at a few other photos with f10 and below, and could find them only cause I knew they were there.

Is this typical?

Yes. It has to do with the angles that light comes in at with different F-stops.

http://www.pbase.com/c​opperhill/ccd_cleaning

Hmmm...no wonder I thought everything was fine...thanks...just ordered the copperhill kit.

Love that Adams' quote, by the way...totally true.

On one day of shooting at a consistent wildlife subject, I was using mostly f/8 to f/11, and I never saw any sensor spots in the images. Then, to change the depth of field, I changed up to f/16 or so. All of a sudden the dust was visible. Of course, the dust was there all along, but I never saw it until f/16.

---Bob Gross---

You realize, of course, that if you don't see it on your pictures, it doesn't matter.

Very typical.....my first 20D even had bad dust at f8 right out of the box....but the further up you go, the worse it'll get.....mine looked like someone had dumped a handful of sand in it when I got it to f22...

Nice enough of my local shop, they replaced it for me with a new one.....

You gotta wonder if all this out-of-box sensor dust is a clever ploy by Canon to induce owners to upgrade when a future model comes out with a anti-dust mechanism.

Oh, you know Canon will get us somehow...whether it is megapixels or speed or an anti-dust feature...they will get us, oh yes.

That is why I will always replace with the lowest price body...all those features trickle down at some point! Put my money into the lenses.

Yes, right...only reason I noticed is I've got my new Tokina and am looking for the landscape shots at higher f-stops. I am usually in the 8-11 range.

By the way, Bob, you're a great resource...I read you all over the forum a voice of reason.

Not so sure I agree. If the dust is there it's affecting the image in some way, reduced contrast, resolution etc.

The two reasons for contemplating f/22 are
1) to make dust visible so you know when to clean, and how successful you have been and
2) where you *absolutely* have to have the depth of field to get two critical objects , near and far, equally in "focus"

Otherwise f/22 will soften the whole image noticeably due to diffraction.

I know this because I once shot some (what I thought were going to be) very nice shots after cleaning my sensor and it was still at f/22 - d'oh Didn't want it to happen to others...

AJSJones wrote:
The two reasons for contemplating f/22 are
1) to make dust visible so you know when to clean, and how successful you have been and
2) where you *absolutely* have to have the depth of field to get two critical objects , near and far, equally in "focus"

Otherwise f/22 will soften the whole image noticeably due to diffraction.

I know this because I once shot some (what I thought were going to be) very nice shots after cleaning my sensor and it was still at f/22 - d'oh Didn't want it to happen to others...

I'll add another:
3) Very bright scenes where the fastest shutter speed still leaves your photo overexposed.

f/22 may be not quite as sharp, but should be very useable.

(Repeat note to self - get a 5 or 6 stop ND to go with the 2 and 3 stop grads)
Yup, you're right of course - so ISO 50 would also be an option in some cases.
I was surprised by how big an effect it had compared to say f/11 or even f/16. WIth good sharpening to recover it and modest print size, it's "useable" but I'd use it only in extreme cases...

I found that out the hard way. I went to the beach for a shoot, which involved clients, and well found out my photos had all these spots against the beach background of blue sky and water. It was very disheartening and a bad impression made upon my new bosses.