A few dust particles will not affect the photos. The only issue is the resale value of the lens will be lower should you sell it in the future..
If it is only one or two dust particles in a used lens and if it appears they are actually embedded in the glass, this should make NO difference to the image quality at all. So, provided everything else about the lens is okay, you should have no problems..
Another way of thinking about anything opaque in a lens is that all it does is obscure a negligible amount of light from hitting the sensor. Think how big a piece of "dust" your sensor sees the lens diaphragm as at, say f8, and yet you get a sharper image with greater depth of field because of it. This is not of course an EXACT analogy, but puts any dust particles that might be in a lens in perspective...
I and the shop people tested some sample photos against awhite background, etc. and we did not see any specks come out on thephotos..
You will never see dust in the lens on the picture, it simply can't be in focus. Testing this way at all is a waste of time and not to the point. Seems they only did so to reassure you, very unprofessional. But indeed, as others said the theoretical degradation of the image is not a problem really.Boyd..
Thanks for the replies. I am now better educated about "dust" in the lens and glad to hear that when embedded it shouldn't have any material effect on the photos. The particles are not in direct line of the apeture anyway, so that was also reassuring (I guess).
I am not 100% convinced that the lens in question is the right one to to fit my lense roadmap, but it is a top contender and at least the dust particles won't be an issue..
Thanks again for the replies...
I used to see people do that in the past..
Nowadays, everyone just talks about dust on sensor...