plasticman Posted February 10, 2011 Share #1 Posted February 10, 2011 Advertisement (gone after registration) Another member here instructed me today on exactly the best way to check for internal dust in a lens (holding it up at an angle to the bright, even light of a cloudy midday sky, while catching the light on the lens surfaces and looking through to the dark background of the internal barrel). Anyway, I did this with a lens that is almost 30 years old - and the result was that I couldn't see any dust inside, whatsoever. Can this be right? Was I simply doing the test wrongly? Is it realistic to expect that a lens (that has possibly had a filter on for the majority of its life) could be TOTALLY dust-free? I haven't repeated the test on my other lenses yet - I did the test during my lunch, and sitting back in the office now, I'm worried that I did it totally wrongly. Link to post Share on other sites More sharing options...
Advertisement Posted February 10, 2011 Posted February 10, 2011 Hi plasticman, Take a look here Can a 30-year old lens have NO dust in it whatsoever?. I'm sure you'll find what you were looking for!
k-hawinkler Posted February 10, 2011 Share #2 Posted February 10, 2011 You also could use a flashlight at the other end. K-H. Link to post Share on other sites More sharing options...
Xmas Posted February 10, 2011 Share #3 Posted February 10, 2011 Hi If you strip the lens in a clean room, clean and rebuild it it wont have any (much) dust. The problem is it may have been etched by lube or fingus, e.g. Canon in 50 to 60 used high refractive glass which was prone to etching and many lenses are scrap. The etching shows e.g. as a faint mist on the lens surfaces. Dust you can clean if it annoys you the mist is etched on... Optical glass is not like window glass. Noel Link to post Share on other sites More sharing options...
treeplanter Posted February 10, 2011 Share #4 Posted February 10, 2011 Yeah, it can happen. I recently took apart an ancient Canon 100mm "R" lens, which was the lens line Canon made for their first SLRs' (Canonflex). I noticed that the rear lens group was totally sealed (in it's own module that couldn't be opened). Not a spec of dust inside and no way dust could get inside. If that sort of construction is used in a lens, it probably is possible that no dust would be inside. Jim B. Link to post Share on other sites More sharing options...
plasticman Posted February 10, 2011 Author Share #5 Posted February 10, 2011 Okay - thanks guys. I realized I'm a bit naive about these things - I never really inspect a lens so carefully because I always buy from what I believe are reputable and trustworthy sources, and I simply have faith in their judgement. When a lens arrives, I tend to try it on the M8 first, and if it focusses accurately (that is an obsession), and has a nice feel to it and looks externally and internally as described, I'm happy. Only today did I realize that simply looking straight through a lens at a bright light source tells you practically nothing. I'll know better in future. Link to post Share on other sites More sharing options...
k-hawinkler Posted February 10, 2011 Share #6 Posted February 10, 2011 Okay - thanks guys. I realized I'm a bit naive about these things - I never really inspect a lens so carefully because I always buy from what I believe are reputable and trustworthy sources, and I simply have faith in their judgement. When a lens arrives, I tend to try it on the M8 first, and if it focusses accurately (that is an obsession), and has a nice feel to it and looks externally and internally as described, I'm happy. Only today did I realize that simply looking straight through a lens at a bright light source tells you practically nothing. I'll know better in future. Hi plasticman, Not necessarily. What's amazing to me is that some lenses have the potential to make gorgeous images. However, on close inspection with a flashlight one can see all those little blemishes, dust, etc. That doesn't seem to matter. I think that's very encouraging! Only when a lens has deteriorated significantly, then those damages seem to leave their mark in some of the images taken with them. Crud on lenses is much more forgiving compared to being close to the sensor, especially when stopped down. Good luck with your gear. Best, K-H. Link to post Share on other sites More sharing options...
Washington Posted February 11, 2011 Share #7 Posted February 11, 2011 Advertisement (gone after registration) Lenses suck dust through the "piston" action of focussing in and out. I creates a partial vacuum which can draw in air with dust floating about with it. Some lenses are tighter than others and some are not used much. So, yes, a dustless old lens is entirely possible. Link to post Share on other sites More sharing options...
mgreernz Posted February 12, 2011 Share #8 Posted February 12, 2011 No dust at all in an older lens? Well, I guess anything is possible, but I would really think it would be pretty unlikely. If it's a sealed component of elements within a larger set of elements, yes. But I agree with Washington that the "bellows" action of almost all lenses (to a greater or lesser degree depending on the design) is the most likely contributor. But is it the defining problem? For me, no. Rarely, will a "normal" amount of dust on the unsealed elements seriously compromise the quality of a photo. More likely to be of concern is a chip or scratch or over-vigorous cleaning of the front or rear element. Or the inevitable fogging that will occur on internal elements over the years or the beak-down of early coatings. Fortunately, most fogging and coating failure is redeemable (Sherry Krauter worked a miracle on one of mine). The chip and the scratch are more of a worry, but even then, such defects don't necessarily confine a lens to the trash. If there's no obvious refraction off a small mark, there can be life even in a marked lens. Although I've never tried it, there are many references to the use of a minute dab of black matt paint to minimise the refraction off a small chip. So for me, I'm sort of relaxed about dust in the lens. But on a digital sensor? Or drying marks, hair and finger marks on my b&w negatives? Dang! That's another question entirely! Link to post Share on other sites More sharing options...
Washington Posted February 13, 2011 Share #9 Posted February 13, 2011 Sherry is great! But, I have indeed run into many an old lens that was as clean as new. Who knows? Just now I have the opposite problem with a Novoflex f4.5, 240mm lens head (no "piston action" here) but it's loaded with dust…. and I can't get the front element retaining ring off to save my life. Link to post Share on other sites More sharing options...
plasticman Posted February 14, 2011 Author Share #10 Posted February 14, 2011 Dust isn't a problem to me either. I'm always extremely careful from whom I buy, and now I confine myself to two or three specialists in Europe, so i always include a careful specification about what I expect in quality to match the rating that these sellers have given online. For me the quality of the rendering from a lens is far more interesting than whether it contains a few specks of dust. I wonder how much dust a lens would need to contain before it had any influence whatsoever on the image. I think I remember someone had done an online test with a lens that contained a dead fly in the middle of one of the elements, and naturally the effect on the pictures was zero... Link to post Share on other sites More sharing options...
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