What is lens dust and should I even worry about it? Maybe. Small amounts of dust and flecks are a very common issue for all lenses. A small amount of dust will have no effect on a lens' performance. Older lenses will always have some dust.
Inspecting Lens For Dust
Looking at the front or objective element of the lens, you can typically see some dust particles in all lenses. To check closer, remove any filters and clean the front element of the objective lens. Looking straight into the lens from the lens' front, and look for dust. Then inspect the lens holding it at a slight angle and you may see more dust behind the front glass element.
Use a LED flashlight and with the camera iris open as far as possible (smallest f number possible), shine it looking again from the front side of the lens. A darkened room will help. While changing the angle, look for more dust. You will most likely see some dust perhaps only on one element.
If you find dust, and you most likely will, there is no cause for alarm. The dust typically does not cause any problems during filming. The reason is the dust is NOT located within any areas where the dust can have any real, noticeable effects.
How Lenses Gather Dust
How does dust get inside a lens? Every time a lens is focused in and out, it “breathes”. The physical length on the lens is slightly changed and the resulting change compresses (pushes air out) or draws (pulls air in) air into the lens.
It is during this lens "breathing" than the lens tends to "inhale dust particles". Dust can enter the lens as most lens to not have tight seals. If lenses were completely sealed to air entry, the lens would compress the air and hinder focusing.
What To Do With Lens Dust
You have notice some dust in your lenses. What should you do? Usually the fix is to "do nothing". Don’t be concerned about it. You can minimize dust problems by storing your lenses properly and doing routine cleaning on a regular basis.
Can I Remove Lens Dust Myself?
Don't try to remove internal dust youself. If the dust shows on finished film you basically, have 2 options: 1) have the dust cleaned by a professional or 2) replace the lens. If you decide to have the lens cleaned by a professional, get an estimate first. The cost to clean the lens may be more than the replacement cost.
Some people think they can "blow the dust out" with compressed air. This does not work. More likely you will drive even more dust in to the lens body. Best bet is to leave it alone unless is presents a problem and then have it either professionally cleaned or replace it.
If it is a Bolex made Switar or Yvar lens, you may be able to find somebody to clean it. Maybe not. There is more to cleaning a lens than just unscrewing a few things and dusting off the elements. Some lenses need to be re-collimated. A fancy word for realigned, and it requires expensive equipment.
Some other lenses such as Elgeet, Wolensak and others, are designed to easily come apart to be cleaned. A warning to those who would take a chance and work on their own lenses:
Be sure if you do this yourself that you note the order of the elements and the direction (in or out) of the curved part(s) of the element. Some lens elements look flat but are actually curved slightly. If you put element in backwards, the lens will not function correctly.
You may leave a fingerprint on the lens element. Be sure to clean it. Fingers have both acid and oil on them and can actually etch the glass rendering the lens useless. Lens parts and screws are very, very tiny easy to loose and very difficult to find. For a lens cleaning solution, the best is made by Pancro. You can mail-order it here:
Minimizing Dust And Fungus
Shooting in relatively clean environments, properly storing your gear in a cool, dry place and take care of it by performing regular cleaning and maintenance is the best way to eliminate fungus and minimize the amount of dust that ends up on and in your gear.
If you are in a high humidity environment, consider using anti-moisture packets. Do a Google search on "moisture absorber packets".
High moisture will contribute to fungus. Fungus typically looks like a light-ish white to dark black, wispy fine hairs in a small spot or as a black "dot". Depends on the type of fungi in the area where the lens used to live. If the fungus is on the inside of the objective lens, it can usually, but not always, be cleaned off.
If the spot is small, and/or located on the outer edge of any lens element, it typically will not show or affect the film's quality.
It depends on the lens involved and location of the elements. Fungus left to its own devices over a long period of time can permanently damage a lens' coating. If fungus is on an element that has been coated, cleaning the fungus may remove some or all of the coating. Any doubt? Don't clean it.
Haze is a grayish appearing coating. It is formed from storage in a high temperature environment and the chemicals of the lubricant are "off-gassed" and reform onto the lens element surfaces. Haze may look smoky or oily. Haze can be cleaned.
If a scratch is big enough to see, chances are it may show as a bright line on finished film. Unless you want the look, the lens is not usable if its on finished film. No fix - replace. Small, fine scratches near the outer edges of the front element can be ignored if they don't show in finished film.
Very fine scratches aka, "cleaning marks" are probably not a concern. If you are buying from eBay, ask about seller's return policy and bid lower on the lens. If it films ok, you got a deal. If not, return it.