Dust in Lens: When does it matter?

This is a follow up to a question I asked earlier regarding my new VC

28mm Ultron. It arrived with one particularly troublesome bit of

dirt that looks like a paint fleck nearly dead center in the lens.

 

I did a test to see if the dirt would affect in the image. I shot a

piece of plain white matte board, focused at 3 ft., at every

aperture from f2.0 to f16, figuring that any darkening of the image

would show up plainly against the white background. The result: I

could see no effect at all at any aperture. (I expected that I would

see it stopped down, if at all.)

 

As I got a good deal on the lens, I plan to keep it. But I wonder,

at what point would dirt and dust inside the lens degrade the image?

I would expect that dirt on the front lens element of a macro lens

focused close would show up first. Does anyone have any experience

or answers? Was my test valid?

Your test was valid. All lenses have dust in them unless they are

assembled on the space station!! You would need alot of dust to

cause optical deterioration so relax and enjoy your new lens and

the great deal.

Kevin. Dust inside a lens hardly ever mades a difference in image quality. Lenses are not vacuum sealed, so over the years, the act of turning the focussing ring draws in dust and dirt, to varying degrees. It has got to be pretty bad (which means obvious when you shine a light through the lens) to have any effect on the image.

 

I don't worry about particles of dust. Haze or fog is another matter.

Dust is almost never an optical problem...as mentioned above. It is more of a ersonal annoyance than anything else.

 

I totally despise it when I sell a lens, the buyer shines an arc light through the lens. Any flash light shine directly through the lens will show flaws...even the most exotic of new optics...such is a trick to bring down the price!

 

Nothing is totally pure...not even me! ;>)

 

I remember when an air bubble in a fine lens was a sign of quality!

 

Ignore the dust!

Hmn, well I've looked through a Noct or 2 and on some elements the coating has really fine little bubble-like items on them. So dust would seem to do even less to the final image, ie: probably nothing.

I have a Nikon zoom lens that could be named a "dustar" it has so much dust in it. Those push pull manual focus lenses suck it in like a vacuum. It is still tack sharp even with all that crud in there.

My feeling would be that to the extent that dust degrades the image in any way, it might be by way of reducing contrast, were the dust particles to reflect or scatter any of the light. Unless there should be a great deal of dust present, I think it might be a very difficult thing to detect any difference in the print or transparency. It might require a side-by-side comparison of the dusty lens with a perfectly clean one. I don't think the dust could ever be visible in the print, since it is so far out of the plane of focus.

If you wear eyeglasses, just take them off and look closely at the lenses...You will probably see lots of dust and scratches, yet when placed directly in front of your eyes the view is clear. Same with camera lenses when attached to cameras. All of this obsession with dust and teeny tiny scratches is just so much anal retentive paranoia, really. Silly me, I just snap a new lens onto the camera and take pictures with it rather than examining it through a microscope, and guess what -- most of 'em work just fine.

Now that is silly! :D

When I'm afraid there's dust in the lens, I just take my glasses off and look really closely at it. That always relieves me because I end up not seeing anything.

A little dust shouldn't affect image quality but sometimes it bugs you.Had an

old 50mm Sonnar on Contax 2A with a couple of bubbles ... image quality

wasn't affected.

Michael Kastner: just like I do. Peter

<i>All lenses have dust in them unless they are assembled on the space station!</i><br>Uh, Albert, I'm afraid even a factory there will be dusty. Perhaps if you assemble them in total vacuum somewhere in outer space... then, when you bring them to earth, they will "suck [dust] in like a vacuum", as Andrew Schank wrote.<p>Btw you wouldn't believe what my contact lenses look like when I remove in the evening, and yet I see perfectly well all day!

My Summarit has obvious cleaning marks and my Canon 50 f1.2 has a 1cm scratch on the rear element. Both have dust inside. No effect on photos. IMHO avoid sending a lens for cleaning unless it's absolutely necessary.

To my experience dust nor small scratches on the front lens affect picture quality. I did more or less the same test as Kevin did against a white background with a new lens that had virtually no dust inside and a heavily used lens with dust specs and some minor front lens scratches: I couldn't tell any difference. Even with the sun almost shining in the lens I saw no difference.

Small particles of debris in or on the lens are too close to the lens surface to record on the image. The cleaning of a lens surface usually does more harm than a little dust. If the lens is new send it back for replacement as further flecks may occur from a problem in the final finish. Too many flecks could be a problem...

Given the very high price for a new Leica lens, wouldn't you think that Leica (or other major camera/lens manufacturers) would assemble them in a "Class 10" clean room environment, with HEPA filters and all? I'm surprised if that's not the case. Does anybody know for sure?

 

Kevin, the dust won't how up at all, so enjoy the lens you found.

"Given the very high price for a new Leica lens, wouldn't you think that Leica (or other major camera/lens manufacturers) would assemble them in a "Class 10" clean room environment, with HEPA filters and all?"

 

Steve, they probably do manufacture them under controlled air flow situation but it doesn't matter. The lenses are not hermetically sealed. :-) Every time you focus, you can potentially draw paricles of dust into the lens. Every lens will accumulate dust over time. I guess the air sucked in is where fungus comes from, unless it is there from the beginning.

I was talking to a Leica rep and it was stated that in a factory tour there are windows that are hermetically sealed to prevent contamination. Also, it was stated that the collimation occurs on a granite bench. I haven't really seen much for foreign particles in Leica lenses.

So would you guys say the huge load of dust in my lens has nothing to do with this photo? shot at f20 with a very dirty zoom? thanks for sharing your knowledge everyone!

 

Couldn't a find focal length lens be sealed? Focussing the lens would only draw dust into the camera body behind the lens, not into the lens itself,

Reminds me, I have a Panasonic camcorder with the usual wide zoom range.

 

I once had it zoomed out, and then wondered about the strange view on the LCD display.

 

I finally figured out that the AF had managed to almost focus on dust on the UV filter.

With enough depth of field, it can do that.

For years we were told that specs and bubbles were common in optical glass, which was often produced in small, platinum pots for casting. These defects largely disappeared in the 70's due to improved processing. Dust in assembly has largely been eliminated by filtration and laminar flow hoods, developed for semiconductor and pharmaceutical operations. What happens in the real world is another matter.

 

Dust in the lens is visible because the intervening elements act like a magnifying glass, and you see the particles illuminated against a dark background. The closer they are to one of the nodes, the less their effect on the image. Dust on the outer objective or filter may be seen if the lens focuses close enough (common with big zooms on sub-inch video cameras). At worst, dust inside the lens might contribute to flare, but it would need to be pretty gross.

 

Lenses what focus and zoom internally are unlikely to suck in dust. That can't be said for lenses which shrink or expand significantly in these operations.

 

For what it's worth, lenses, semiconductors and digital sensors are produced in the same type of lab gear used to make space modules, for the same reasons.

And for usual depth of field reasons, dust or bubbles will be more visible when stopped down.

 

Other effects are visible with a bright light source, like the sun, within the field of view.