Too much dust inside the inner lens of an Oly 12-40 f2.8 Pro ?

Started 2 months ago | Discussions thread
cba_melbourne Senior Member • Posts: 3,137
Re: Too much dust inside the inner lens of an Oly 12-40 f2.8 Pro ?
7

martin_sc42 wrote:

cba_melbourne wrote:

The 12-40 is an external zoom. It changes it's length (or trombones) when zooming. This means it breathes in air as you expand it. The 12-40 is fitted with a mesh filter to keep out sand and coarse dust particles. But finest dust (as well as vapor and smoke) will obviously get through the mesh, and deposit on interior surfaces.

12-40 lens. The yellow bit is the filter mesh that goes around the barrel. It is just a very thin fine mesh, not something like a felt or a foam that could trap finest dust particles. I have seen somewhere a picture of that filter, but can't remember where.... sorry.

Thank's for sharing. That is my point. See also
http://digitalphotographylive.com/olympus-m-zuiko-digital-ed-12-40mm-f2-8-pro-lens/

When extending to 40mm and with some light into the front you can clearly see the Oly front chamber. In the diagram this chamber is closed to 12 mm.

If somehow something comes in via the airflow or even via the tube by slipping under the seals it should settle in the front chamber (front lens or back lens). If it somehow comes in from behind it should settle on the back chamber, maybe the moving inner zoom and focus elements. Yet the lens unit holding the aperture control is exactly in the middle. As it also is the smallest in diameter this amount of dust clearly should cost some sharpness.

I am no photo technician yet an tech engineer. Using a lab control LED you can see this when lightning from back to front as some of the lenses are coated on the back and when reflect some light like halo.

a) I see dust on the lens in the aperture control hole.
b) I see no dust on the lens more closer to the front (front chamber)
c) I see no dust on the inside of the front lens
Similar on the back

So weather sealing works. Even if i wanted to destroy a lens I have now idea how to achieve this effect without dismantling it

I would speculate a product defect in the aperture control
https://en.wikipedia.org/wiki/Aperture#/media/File:Aperture_in_Canon_50mm_f1.8_II_lens.jpg

A rational explanation maybe that the aperture blades have some friction and distribute particles or similar.

I did not check this so strictly as i bought it 13 months ago ... grmpf ...

The filter mesh is there to prevent water entering. Water drops stay on the outer surface of the mesh. It is not there to "clean" the air.

Look through your lens as you zoom from 12 to 40mm. The front section moves forward, the middle section with the aperture moves also forward but but not as far, the rear section does not move. At the same time, air is sucked into the lens from outside to fill the voids created both before and behind the middle section. Have not taken the lens apart, but I could well imagine that part of the displaced air will be pushed through the aperture iris opening at high velocity, if so any fine dust will deposit with preference onto the lens surfaces in front and behind the aperture.

If you want a dust resistant lens, you have to go for internal zooms or primes, that do not change their outer length when zooming, and do not breathe air but are often filled with Nitrogen or Argon gas. Internal zooms are always larger though. It is a choice you make when buying a lens, and it comes with advantages and disadvantages.

External zooms are never sealed, no matter what marketing tries to make you believe by deceiving implication. They may be weather protected, but just cannot be sealed. Solids ingress such as sand and dust are excluded from warranty.

Whilst dust can enter the lens and fog the glass, sand can be wedged under the o-ring seals and destroy them, or cause mechanical binding. An external zoom is not a good choice if you want to use it during sand storms in the desert.

***

You are a tech engineer. Look up what the rating "weather sealed to IPX1" means. The suffix "1" is the lowest possible sealing grade against water, and the suffix "X" means there is no protection whatsoever against solids. X and 0 have the same meaning:

The Olymus 12-40 when mounted onto a weather sealed Olympus camera is rated IPX1. If dust or sand or water is found inside, you have abused it and warranty will be declined.

For comparison, the Olympus TG cameras are dust and water sealed, and rated IP68 to 15m water depth. Quite a difference. The TG is a diver camera and is suited for a windy sand beach or a desert storm, without precautions. If water or dust is found inside, you have a warranty claim and will get the camera replaced for free (provided there is no previous accident damage like a cracked housing).

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