Mould Inside an MCT

[Mariner]

Hi All,
I was wondering if mould on the inside of the meniscus lense/corrector plate of a MakCas is a death sentance for the scope? Is there no comeback short of a new lense without compromising optical integrety? Can they be cleaned or restored or recoated? How does an MCT get mould in it anyway?

There is an ETX on ebay for sale with some mould in it should i steer clear of buying such a scope in the first place?

Thanks, F.

[asimov]

I've been battling fungus & mold as well. I'm assuming it's all to do with the humidty. I had to clean the inside of my corrector on the C11 & it came up ok..I suspect some breeds of moulds etc. eat anti reflective coatings, but I'm not certain. Can't imagine you'd have to gone down the road of replacement though.

[UniPol]

Mould and fungus usually forms in situations where moisture condenses on optical glass due to temperature changes i.e. bringing your scope in from the cold and into a warmer relatively humid room and packing it away in a box or case. Mould and fungus like this kind of treatment and it is worse in tropcal countries. Generally speaking it is best to let the scope "air" so to speak before packing it away.

Coatings can be eaten away by the action of fungus however I think earlier coatings from the 1940's - 1960's were more susceptible as they are relatively soft by today's standards. The amount of area eaten away is very small in comparison to the overall surface area of the lens and you wouldn't really notice any difference in optical performance. In the old days when lenses and mirror had defects such as bubbles or chips, the optician would simply black out the affected area.

Having said all that, just take the corrector lens/plate out making sure it is marked on the periphery for correct replacement, dust it off and clean with the usual solutions. To kill fungus and mould in its tracks so it won't come back, use chemical (pure) grade acetone on the affected spot. Acetone is used on the coatings on mirrors as well.

Unsightly as it may look, coatings that have been attacked by mould and fungus have little or no effect on optical performance but for many reasons the value of optical equipment drops in value, most likely for cosmetic reasons.

[casstony]

I make sure my gear gets completely dried before the end of the next day to avoid mould. Air conditioning in the summer helps as does gas heating in the winter, both of which reduce humidity.

I have read that exposing the objective to direct sunlight is good for killing fungus spores so I've started giving the scopes an occasional sun-bathe, being careful to keep the scope on an angle to avoid focused light.

[[1ponders]]

Definitely keep the lenses at an angle and watch the sun moving. I had to turf a pair of 20x80 binos cos the focused light melted plastic and rubber elements around the eyepieces and apart from melting the plastic and rubber the smoke created coated the optics and ruined them

[casstony]

It's easy with a schmidt cassegrain because the corrector doesn't focus light but extra care is needed with a refractor - I think of a magnifiying glass when I position a refractor.

I imagine mould is a much bigger problem for you guys up north.