Ever disassemble a Super-Angulon?

[Steve Goldstein]

I picked up a 75mm with a few internal dust specks. There's not a lot, but one of the little buggers appears to be dead-center inside the front element, and is unwilling to budge even with repeated rapping of the lens cell on my hand. I can't see it in the images, but it bothers me. If it's as simple as unscrewing the front retaining ring to pop out the front element I'll give it a whirl, but if all sorts of glass and spacers are going to fall out I'll just have to overcome my inner OCD-ness and learn to live with it.

[Bjorn Nilsson]

Live with it until it's time to have the shutter (and in this case, the lens) CLA'd. Then the tech. will take care of it with the proper tools and caution.
These dust specs will probably not affect sharpness/contrast in any way, but I can understand your concern. (The only thing affected by these pesky dust specs is the value of the lens, so I hope that you made a good deal on your SA 75.)

//Björn

[Arne Croell]

Leave it alone, it won't affect your pictures at all. Even a deep scratch doesn't. The effect of your dust specks is roughly proportional to the area they occupy divided by the whole area of the affected lens surface, which should be a really small number. The only reason to go in, apart from maybe resale value, is removing a haze, since that affects all of the lens surface.

[ic-racer]

Ok how about this. Transfer your OCD to a close examination of the two grooves in the front retaining ring. If there are any signs of it being removed, if the grooves are worn, if there is brassing, or if there are scratches then be: worried, upset, concerned, worry if the elements are all correctly positioned, worry that you have a "tampered" lens, etc.
Contrast that to your OCD about the little dust spec and see which is stronger :)

[eddie]

try compressed air ( i used a machine not a can of air...i have them at work. i am an auto body tech) . i did this on a lens once. i was able to get the spec to move.....

[bglick]

Arne nailed this one, and described it very well....

Also keep in mind..... lenses have mechanical tolerances. These tolerances are required for the lens to perform as the advertised MTF suggests. Dis assembling a lens will surely alter some mechanical tolerance... effecting performance. AT the factory these tolerances are often checked with specialized tooling for that lens... also laser checks confirm tolerances are met. When you try to do this yourself, you leave yourself vulnerable to altering the lenses performance, as you have no way to confirm the re-assembled lens is within acceptable tolerances. Often the tolerances are measured in the .0x mm range.... very very small....

With digitar lenses, to change a shutter, even Copal 0 to Copal 0, the lens must be re aligned with shims at the factory to assure proper performance. Shims are in the micro millimeter sizes...

Below shows the complexity of a tolerance criteria, for mechanical tolerancing ONLY... its remarkable how perfect the elements must be aligned on many axis, to achieve the design performance. This is a very low tolerance simple 4 element eyepiece... see the tolerance ranges at the top...

Tolerancing is a science all to itself these days...

http://www.pbase.com/bglick/image/100722583.jpg

[Arne Croell]

Here is a somewhat extreme, but instructive example of the performance of a damaged lens - a few dust particles are nothing in comparison:

http://www.lensrentals.com/news/2008.10.30/front-element-scratches

[mandoman7]

I picked up a 75mm with a few internal dust specks. There's not a lot, but one of the little buggers appears to be dead-center inside the front element, and is unwilling to budge even with repeated rapping of the lens cell on my hand. I can't see it in the images, but it bothers me. If it's as simple as unscrewing the front retaining ring to pop out the front element I'll give it a whirl, but if all sorts of glass and spacers are going to fall out I'll just have to overcome my inner OCD-ness and learn to live with it.

Our inherently lazy minds will conjur tasks to enable us to divert our attention from the daunting task of making relevent imagery.

[bglick]

Arne, that example is amazing....even I would have not suspected that result !

That lens looks thrashed to me.... we all should not be so anal about dust with our lenses.... this demo shows why!