How to test for dust?
I remember reading about shooting at a small aperture such as f/22 and shoot at a white wall? Is this what you guys do to test to see if dust can cause IQ problems?..

Comments (8)

That works, but a wall might have a very small, almost invisible texture. Better try a clear blue sky (@ small apertures, like f22)

Comment #1

I stop down to f/22, focus set to infinity and shoot fairly close to a smooth light coloured surface like a cupboard door, using flash set for a lot of positive exposure compensation so as to overexpose, which increases contrast between dark dust spots and the light surface. The distance is enough for the flash to illuminate ht efield of view with the camera pointed down a bit to avoid flash reflection. This defocusing means you see the dust spots and not any detail of the light coloured surface..

Cheers from John from Adelaide, South AustraliaJohn Harvey Photography 40D, Canon 20D & Fuji F10..

Comment #2

Very small aperture, infinity focus and a clear blue sky..

The greatest of mankind's criminals are those who delude themselves into thinking they have done 'the right thing.'- Rayna Butler..

Comment #3

GodSpeaks wrote:.

Very small aperture, infinity focus and a clear blue sky..

The greatest of mankind's criminals are those who delude themselvesinto thinking they have done 'the right thing.'- Rayna Butler.

This is probably a stupid question, but how do you set focus to infinity? Just aim the camera to the sky and hold the shutter halfway? If so, I don't see those AF points lighting up...

Comment #4

1. Set aperture to the smallest, if you have f/22 use f/22, if you have f/32 use f/32.2. If it is a zoom lens, set it to max telephoto.3. Set the camera/lens to manual focus. Turn the focus ring to infinite..

4. In Aperture Priority mode, shoot at a piece of white A4 paper (ideally) at no more than 6" away from it. Make sure no shadow is being cast on the paper..

5. Make sure it is in raw, and no sharpening, you may increase the exposure compensation, I increase it by 1ev. Too bright is not a good idea either..

That is for Nikon's dust off reference picture. It shows every little bit of dust on the low pass filter..

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Tasik Biru - 'Blue Lake'..

Comment #5

This is a picture I used in my blog where I test out some sensor cleaning product. You'll get something like this if you follow the settings I just mentioned. Don't mind the red circle and arrow, I'm just explaining that only those two bigger dust specks will cast a visible shadow on normal shots at large aperture. All the smaller ones are usually not visible..

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Tasik Biru - 'Blue Lake'..

Comment #6

To avoid any problems with the wall ( or anything ) you also should switch to manual focus, defocus (!) so the wall is blurred and move the camera to point at different parts of the wall during the exposure..

I usually do this is a darkened room to get a reasonably long exposure..

If you do auto levels on the resulting image ( in post processing ) LOADS of speckles and dust will turn up, but only the very largest would affect your shot and even then only at smaller apertures in normal conditions..


Pentax K100DFuji S5200Fuji E900PCLinuxOS..

Comment #7

Change the lens setting from AF to MF, turn the lens focus ring to infinity..

Best regards,Doug

Http://thescambaiter.comFighting scammers WW for fun & justice..

Comment #8

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This question was taken from a support group/message board and re-posted here so others can learn from it.


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