Join Date: Oct 2012
Location: Sydney, Australia
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 2 Post(s)
Three words: DON'T DO IT.
You'll never get it back together properly.
The ONLY way to clean lenses thoroughly is to completely remove them from their mounting so that deposits on the mount are not brought onto the glass surface. This needs to be done in a jig that holds the lens element only by the barest edges. Trying to clean a lens in its original mount is a mug's game.
The Isco lens would be hermetically sealed. Any quality lens is hermetically sealed. Our lenses have 5 greased O-ring seals, with all screw holes to the outside filled with industrial thread sealer, for example.
Dust and moisture accumulate if there is no seal. Moisture will inevitably cause a fungal buildup. You'll never get fungus off, as it eats into the coating. Dust is not so much of a problem unless it gets very dense. Although regarding dust, some lenses are (amazingly) open to the air. Some even come with cleaning instructions for internal elements. I shudder whenever I see this.
Cleaning lenses is an art as well as a science. It involves the right combination of solvents, proper techniques, cleanroom-specified cleaning swabs (we use an average 30 per lens, as they can only be used once) and luck. There will always be one annoying speck of dust that seems to come from nowhere. So regular inspection throughout the clean and assembly process is mandatory.
It's not only the lenses that need to be clean. The housings need to be perfectly dust free too. We water-blast ours - every part - then triple rinse in de-ionized water, finishing off with a double rinse in distilled water, with a final rinse under clean room conditions in filtered, de-hydrated methanol to remove water and aid in drying.
Our lens sealing and cleaning process is performed in a an ISO Class 2 clean room environment under flowing, de-ionized air. This typically takes 2 hours.
Once assembled and sealed against dust (but not moisture, as yet), the lens is transported to a non clean room environment for calibration with a video microscope, laser calibrated stand, projector and screen. This rotational calibration has to be performed to within a cumulative 1/50th of a degree of rotation across all three groups of elements.
Rotation is absolutely a key factor with cylindrical anamorphic lenses, as they have no vertical power, only horizontal power.
The slightest error in alignment of rotation will first cause a skewed image (i.e. it will be slightly out of rectangular alignment). After a 1/10th of a degree of cumulative error 4K performance suffers. At 1/15th of a degree nominal "4K" performance becomes "2K". At 1/8th a degree error nominal "4K" becomes 720p (plus, of course a centimeter of skew on a 120" screen). Our lenses are set up using an 8K test pattern, guaranteed to deliver better than 4K performance.
The end target result is guaranteed 4K performance, with a skew factor of less than 1mm in 3000mm (0.03%).
When the calibration is completed the O-ring seals are tightened, thus sealing not only against dust but also against moisture. Our lenses are moisture sealed to 15 metres equivalent depth of water.
Having said that, a simple two-lens-group device like the Isco requires only one lens to be rotated against the other (which can remain fixed as the "datum" lens). Our lenses require TWO groups to be rotated against the third to achieve the same consistency and clarity of image. That is why our specifications and procedures are so strict.
Trying to do this yourself, without any fixed guides like laser levels, calibrated stands and projectors, NOT in a clean room - apart from all the fiddly mechanical aspects like trying to engage a multi-start focusing thread accurately - is a horrifying prospect. If you DIY it, the lens will almost undoubtedly be out of alignment and filthier than it was when you started, probably with solvent smudges and dust everywhere from the cleaning swabs. If you do try it, DON't use water-based cleaning solutions as they inevitably leave tiny droplets that evaporate and turn into micro-rings of mineral deposits all over the glass surfaces. These will eat into the coatings permanently and you'll never get them off.
Better to get it done by the professionals at Schneider. If they have to remove fungus, that "$300" figure mentioned above will skyrocket, as the lens(es) will need to be stripped of their coatings (both sides) and re-coated.