Dust on sensor ?

[Hyena]

Hey guys.

I'm still new to the DSLR world so I'm not sure if this is dust on my sensor or not. Learning the ropes and swapping different lenses back and forth and playing with reversing rings I guess it's more than likely I've got a spec or 2 of rubbish in there.

Anyway, just wanted to check before venturing onto the next step.
I took 3 shots, the 18-70mm, 50mm and the 3rd with no lens on.
When the sensor has dust on it is it normal that you don't see the dust with no lens on (as in this case) ??

Thanks

18-70mm

50mm

no lens

[DaveB]

Of course you'll see no dust with no lens on: the dust is sharpest at very small apertures. For advice on taking test shots have a look at this page.

Yes that does look like crud on your sensor, but a proper test shot will show you the full extent of the problem.

[Laurie]

thats interesting.
im going to say something very stupid, but if the camera has no lens on it it can not focus the light on the sensor properly, so the dust will not show up.
im probably very wrong and have probably given a couple of the pros here a laugh, my job is done
_Laurie

[DaveB]

Think of it this way:

With a large diffuse light source (e.g. a wide-open lens mount) the shadow cast by the dust onto the sensor will be very diffuse.

With a point source of light (well, something like f/22 is small even if not a point) the shadow cast by the dust will be fairly well-defined.

[Yi-P]

You cannot form an image without any sort of lens.

You can see because your eyes are the lenses.

Without a lens, the sensor will only pickup the scattered lights in the ambient, and no light is converged/concentrated into particular areas which can form an image. So without a lens, you cannot define the actual shape of lights that lands on the sensor and so as the dust will not show up.

[Gordon]

You cannot form an image without any sort of lens.
...

Not quite true- a pinhole or small aperture will form an image with no lens!
Look under a tree during a partial solar eclipse and you will see hundreds of small crescent images of the Sun. There are small round images of the sun normally with no eclipse, but the effect is not so obvious then. A hole the size of a 50c piece in a heavy curtain will form an image of the sunlit outside world on the opposite side of a darkened room too.
I'm sure placing a pinhole over your camera body with no lens will show any dust spots... but I'd recommend using a lens and f/22

Gordon

[Yi-P]

Not quite true- a pinhole or small aperture will form an image with no lens!

Gordon

Ah yes, this is another way to converge light into a point.

[Laurie]

i was right. *gasp* shocking

[Link]

Because of its shape, it certainly looks like dust to me. A careful blow should take care of the long oneat the top, and then you'd be sure it was only dust.

Link.