Fungal growth on optical surfaces

[Nerf_Caching]

Hey all, I opened up my scopes today to find fungal growth on both my refractor and SCT lens and corrector respectively. I live in a humid climate but I’ve never paid much attention to mold until now. Does anyone know how, if even possible to get rid of it? I heard that they ruin coatings, so I’m erring in the side of caution here. Thanks!

[Alien 13]

Plenty of daylight will normally stop the growth but in bad cases its worth stripping down and cleaning with a "lens cleaning" solution as the fungus will etch the glass if it takes hold.

Alan

[DaveL59]

ideally you need to keep some silica gel sachets in with the optics to reduce the moisture levels, and keep them recharged (dried out in a low heat oven) regularly, which may help slow things down. As to killing off the fungus, exposure to UV would work, either exposed to sunlight for a few hours or using UV light source and do that periodically. Other than that you're looking at dismantling the optics and treating with hydrogen peroxide, ammonia, these articles may give some useful guidance:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3864060/

https://richardhaw.com/2016/03/27/repair-fungus-cleaning/

I guess the problem with astro gear is its rarely getting to see any sunlight/UV and moisture can build as they're moved from cold night environs into warmer after use. Makes having dessicant sachets even more important. Not found a source here in the UK for the sachets shown in the second article, they look very useful to have for optics in longer term storage, was thinking of those for the bino collection but they all have silica gel packs and I try to give each a cycle under UV every couple months just in case.

[alacant]

Hi. We once did an old refractor. Best to dismatle it, swab in 1% copper sulphate solution -sold as swimming pool fungicide- and rinse well with distilled water. Use one of these to shine through it over night every few months. HTH.

Edited May 26, 2019 by alacant

[Nerf_Caching]

9 minutes ago, alacant said:

Hi. We once did an old refractor. Best to dismatle it, swab in 1% copper sulphate solution -sold as swimming pool fungicide- and rinse well with distilled water. Use one of these to shine through it over night every few months. HTH.

Hmmm, not feeling that brave to take apart my optics right now🤨. As with gel sachets, I do have some, although it might need some replacing. I normally store my scopes in the closet with a gel sachet in the closet. If I expose my SCT to sunlight, I have to be careful not to cause internal heat buildup due to the folded light path. Could give it a try, if I even get any clear days.

[Ricochet]

5 minutes ago, Nerf_Caching said:

If I expose my SCT to sunlight, I have to be careful not to cause internal heat buildup due to the folded light path

You don't need to point the telescope directly at the sun. Pointing at the sky, somewhere east of where the sun is when you set up, will do. 

[Alien 13]

As above just general fresh air and daylight will do the job even if its cloudy, make sure the path of the Sun doesn't go down the tube...

Alan

[Gabby76]

A 35mm film canister with holes in it filled with desiccant will fit in a 1.25" adapter or a tea ball filled with desiccant for a 2" and larger focuser will help take care of humidity inside the tube while in storage. 

[cotterless45]

Needs sorting pdq. By products of fungal growth are acidic and can eat into the lens coating . Used to get this in doublet objectives in the air gap.

One productive remedy is to gently supply heat so that temperature change year round does not produce humidity. Easiest way is a 6W reptile heater pad, under the ota at the covered objective end and Make sure that the ota is dry when put away. Always check and keep an eye on anything invading gear ,

Nick.

[John]

I would probably deal with that rather than leave it. At least a corrector lens is a singlet so the issues will be either on one side of it or the other. When they get between the lenses in an air spaced optic the cleaning exercise gets quite a bit more complex.

I've cleaned an SCT correct in a similar state to that by removing it from the scope (taking note of the alignment marks on it's edge) and using Baader Optical Wonder Fluid and the micro fibre cloth. It came up pretty much pristene.

 

[Nerf_Caching]

Update: So I finally decided to have a go at cleaning the corrector plate today using pec pads and some lens cleaning liquid coupled with a micro fiber cloth to mop up  any remaining lens cleaning fluid on the surface. I have to say that the corrector looks remarkably cleaner without a single scratch in the process it seems. What do you think?

[Nerf_Caching]

On 27/05/2019 at 19:30, John said:

When they get between the lenses in an air spaced optic the cleaning exercise gets quite a bit more complex.

 

 

I think there could be fungal growth in my achromatic doublet as well. Don’t think it warrants a clean yet I think.

[Gabby76]

Better to clean fungus sooner than later, you can also blacken those screw tips while you have it open :)

[cotak]

You need to store them in a dry box in Hong Kong. Almost everyone with camera kit in HK use dry boxes. For scope a dry box that big would be kind of expensive but you can make do with any sealable box and some silica gel packs. Or you'll get the fungus again.

[Ags]

What does this fungus eat?

[chiltonstar]

1 hour ago, Ags said:

What does this fungus eat?

In older lenses, it used to be the Canada Balsam which cemented the components together. In an air-spaced achromat, I suspect it is the organic residues (bloom) which gradually form on any glass surface (pollen, tars and compounds from plants etc). My 102mm f13 had this problem a year or so ago. I dismantled the doublet, cleaned it with solvent and then a lens cleaning compound and reassembled the crown and flint components with new spacers which bizarrely improved the resolution cpd with when it was new (thinner spacers I think).

To avoid the problem with my 180 Mak, I store it outside in a sealed B&Q storage box with three or four silica gel sachets.

Chris

[Macavity]

I did wonder too... (what it eats)! But the above sounds plausible...
Random "dust" (from cleaning even!) is cited in the following:
http://www.truetex.com/lens_fungus.htm

Intrigue by the idea that "UV light" might kill it... Thinking of crazy
ideas like giving lenses a quick burst of "black light" every so often?
Maybe a (lower powered) UV Diode stuck inside the lens caps... 😛

Edited May 30, 2019 by Macavity

[Ags]

It probably eats UV too.

[chiltonstar]

13 minutes ago, Macavity said:

I did wonder too... (what it eats)! But the above sounds plausible...
Random "dust" (from cleaning even!) is cited in the following:
http://www.truetex.com/lens_fungus.htm

Intrigue by the idea that "UV light" might kill it... Thinking of crazy
ideas like giving lenses a quick burst of "black light" every so often?
Maybe a (lower powered) UV Diode stuck inside the lens caps... 😛

Might be the ozone generated by the uv of course? I UV irradiated my lens after assembly with a mercury vapour lamp I have. 

Chris

[Carbon Brush]

This thread may be of interest.

Given the recent threads about filter damage on solar scopes, I wonder about the wisdom of intense UV for long periods.

In all the solar scope damage, the offending glassware has been replaced, often at no cost by the scope manufacturer. But no definitive cause or explanation provided.

David.

[Zakalwe]

1 hour ago, Carbon Brush said:

This thread may be of interest.

Given the recent threads about filter damage on solar scopes, I wonder about the wisdom of intense UV for long periods.

In all the solar scope damage, the offending glassware has been replaced, often at no cost by the scope manufacturer. But no definitive cause or explanation provided.

David.

The BG failure on Lunt's isn't caused by fungus though, is it? And the "rusting" failure on PSTs is also caused by another agent.

[Carbon Brush]

At risk of diverting away from the OP question.

Ref Zakalwe. Correct - The Lunt & PST issues are not fungus.

But the failures were (to the best of my knowledge) never explained by the manufacturers.
The approach was simply to provide a replacement that should be OK.
Reports from numerous users do not identify cleaning fluid, damp storage, etc as being to blame.

The most obvious usage difference between astro and solar scopes is the amount of light they receive.
It is far more than 'day use' optics like spotting scopes.

Degradation of various plastics and rubbers from UV is well known. As is paint fade and the like.
The Lunt experience suggests optical filter coating can be damaged.

For these reasons I wonder if excessive UV into an astro scope might do harm.

Obviously a few minutes of unfocussed sun does no harm to the scope.
But a scope left all day?
What about taking the scope into the suntan lounge with you to kill fungus? 5 minutes here browns your skin more than most UK days.

I await an informed comment. Preferably from a manufacturer of optical equipment.

As a precautionary step, I have made a lens cap for my Lunt scope. A simple push on cap instead of the fine pitch screw on cap.
If I walk away from the scope, the cap goes on. That way the scope optics are only subjected to the sun only when in use, rather than all day.
My preferred use of the scope is to set up in the garden early morning and leave it on a tracking mount all day.
When (if?) there is a 5 minutes gap in the clouds, or I get a chance to take a look, it is immediately accessible.

David.

 

[Macavity]

Argh... I realise, in retrospect, that the article I quoted showed the FUNGUS
developing on a "Heat Filter" for Mercury Arc light! So maybe not "UV"? 😛
(Basically, I wouldn't want "bad stuff" to happen from my suggestions! lol) 

Ah, Solar Astronomy... a minefield of "Mythos versus Genius"! [teasing] 😸
Ozone would "oxidise anything" organic! But back to Oven Cleaning...

P.S. I am leaving a "sacrificial" ST120 in my observatory. All other scopes 
inveigle themselves back into  my Lounge... As "Fireside ornaments"? 🤔

Edited May 30, 2019 by Macavity

[Zakalwe]

56 minutes ago, Carbon Brush said:

At risk of diverting away from the OP question.

Ref Zakalwe. Correct - The Lunt & PST issues are not fungus.

But the failures were (to the best of my knowledge) never explained by the manufacturers.
The approach was simply to provide a replacement that should be OK.
Reports from numerous users do not identify cleaning fluid, damp storage, etc as being to blame.

The most obvious usage difference between astro and solar scopes is the amount of light they receive.
It is far more than 'day use' optics like spotting scopes.

Degradation of various plastics and rubbers from UV is well known. As is paint fade and the like.
The Lunt experience suggests optical filter coating can be damaged.

For these reasons I wonder if excessive UV into an astro scope might do harm.

Obviously a few minutes of unfocussed sun does no harm to the scope.
But a scope left all day?
What about taking the scope into the suntan lounge with you to kill fungus? 5 minutes here browns your skin more than most UK days.

I await an informed comment. Preferably from a manufacturer of optical equipment.

As a precautionary step, I have made a lens cap for my Lunt scope. A simple push on cap instead of the fine pitch screw on cap.
If I walk away from the scope, the cap goes on. That way the scope optics are only subjected to the sun only when in use, rather than all day.
My preferred use of the scope is to set up in the garden early morning and leave it on a tracking mount all day.
When (if?) there is a 5 minutes gap in the clouds, or I get a chance to take a look, it is immediately accessible.

David.

 

 

To be fair to Lunt they replace the BG filter with no quibbles, regardless of the age of the diagonal.

The PST is a different kettle of fish.

I wonder would a blast of UV from a UV bulb down an OTA every now and then help or hinder?

[DaveL59]

UV supposedly kills the growth, assuming the lens and coatings don't absorb it all of course, so periodic exposure can retard or eliminate fungal growth. Needs more than a quick blast though. Expose to daylight for a few hours, or use a UV light for say 30-60 mins as it'll be more a intense closer located source. Storage-wise, several silica gel sachets is always better than one in a larger space, very available to purchase cheaply in different sachet sizes to suit.