WO Megrez 80 II Objective

[Carbon Brush]

I have seen the start of some small 'icicle' like patterns at the edge of the objective. This is on an inner surface. There is also a small 'dandelion seed' type of growth on an inner surface.

Neither are large enough to affect views - yet. However, sorting now will hopefully prevent serious problems later.

Removing the objective cell complete is easy enough. However, does anyone have experience of dismantling these cells? It looks like it should come apart with a standard lens spanner on the inner surface. Losing collimation on reassembly is my worry.

My glass cleaning has always been restricted to the outside surfaces of a cell. I have never taken an objective cell apart. But given a 'heads up' on anything to watch out for, I m happy to do this.

Alternatively, does anyone have experience of anyone competent who does this sort of repair? I'm not really interested in going to a shop who 'send it away'. It would rather deal with the repair man direct.

Thanks, David.

[Carbon Brush]

Here is an attempt to photograph the icicles. They look worse on the picture than to the eye.

[laser_jock99]

Fungus between the lenses? It's only bad news if the optical elements are cemented together. Otherwise it should be straight forward to dismantle the lens cell and clean each optical surface. Just make a good note of the way each lens sits in relation to the others. It's very easy to build them up again incorrectly!

[ronin]

It doesn't look as if it should be there, that being a pretty obvious statement.

If you are OK with dismantling and cleaning then I would suggest you do so. If it is a fungus it will spread and what you see will remain damaged, the fungus will have "eaten" something, most probably the coating. It may be cleaning liquid that has gotten inside and seeped.

Used to have the name of an optical company in Kent think it was something like kvoptical. Try a search on them, they were helpful about a lens I had, just in case you do not want to strip it.

Have a read: http://www.truetex.com/lens_fungus.htm

[Carbon Brush]

Thanks both for your comments.

I will take the lens apart in the next few days when I have the time to do everything in one go. As growth is in the early stages, there is not yet enough damage to affect the view. The truetex link is interesting. No well defined mechanism, or known prevention measures.

Under normal circumstances my lens cleaner is Baader wonder fluid. I'm wondering though about something a little stronger in this case. Perhaps neat isopropanol? The problem is that not knowing what chemicals are used in the lens coating, I don't know what will damage them. Apart from the obvious sandpaper or fungus! Anyway I will start with the tried and trusted Baader and go from there.

The scope has been stored in the dark during my ownership. That is capped and in a storage case. Also mostly in the observatory so on average the temperature is lower than in a house.

So for the future, and for my other kit. Is there a case here for storing scopes in the freezer until used? Also keeping bags of silica gel in there? Is there a case for occasionally subjecting them to short wavelength UV to kill fungus? Not thinking of the suntan lamps. But those that used to be used for erasing memory chips 20/30 years back.

However, in this case the growth definitely inside the objective. Between the elements. Does this suggest poor housekeeping at manufacture? Or is it because the outer faces of the objective might have been cleaned occasionally?

It is odd that I have heard of lens fungus, but this is the first time I have suffered it. Among my 'glassware' collection are numerous old camera lenses and binoculars. Some 30+ years old that have had a chequered history. None shw fungus on casual inspection. But maybe under a magnifier?

[Peter Drew]

If you are happy to do so it's probably better to remove the objective for cleaning as the problem is likely to get worse than better. Be carefull that the two optical components don't come apart unexpectedly, at best juggling with them can lose the orientation, at worst a breakage. It pays to make a pencil cross on the edge of the glass with its centre on the join, this will allow you to match the orientation and retain the correct way round of the components, an arrow also marked will indicate the front of the objective. The foil spacers, if present, usually stick to one of the surfaces, be carefull not to lose or damage any of them. Good luck.

[Carbon Brush]

Thanks Peter. Some very sound advice.

I have been reading a bit more about this problem on camera lenses. Not exactly cauldrons and eye of newt. But very little science in the explanations.

Short UV light is thought by different people to aid growth, stop growth and pass (or not) through the lens.

Cleaning fluids range from soap, to hydrogen peroxide, to ammonia to meths. Even hydrogen perxide mixed with ammonia. Definite mould killers there! Don't fancy standard dyed meths leaving stains though.

It is also seen as more of a problem in warm humid parts of the world. In some countries lens strip and clean is seen as a routine service.

There were also reports of lenses becoming slightly fogged due to volatiles in lubricants and seals evaporating over the years. I have some old binoculars that may have suffered this. I also have newer binoculars that just have poor coatings.

In my case the growth is between the lenses, not in the tube and not on the outside. This suggests that past cleaning has dealt with accessible mould. Or maybe someone at WO used spit containing bits of sandwich to clean the lenses on assembly! Urgh.

The prevention measures are avoiding leather lens cases and keeping some silica gel in the storage boxes. The obvious don't put the wet lens away in an airtight bag came up.

My plan is to carefully split the lenses, then clean with distilled water and isopropanol. Where I go from there depends on the results of cleaning.

For the future, I am thinking about precautions on scope and eyepiece storage. But more on that later. The immediate task is to keep this (excellent) scope in good order.

I will keep you posted on progress.

[Carbon Brush]

Last night the cloud came and went and nothing drew me to the telly.

I started out with the plan to just remove the lens cell and take it apart another night. But I got carried away and did the whole job.

I marked the exposed face of each lens with a small black dot from a marker pen. This was to make sure I kept correct rotation on re-assembly. Didn't know if might be semi-permanent. But a 0.5mm dot at the edge of the lens - who cares? As it happens, while cleaing the outer faces after reassembly, the marks went completely.

The internal mould came off very easily with Baader wonder fluid (my favourite glass cleaner) and gentle rubbing from a new lens cloth. There was no sign of any etching or other damage. So 'stitch in time saves nine' applies here.

I suspect the entry path was from the outside. The outer lens butts against the holder without a seal or packing. So rubbing dirt into the corners and washing it in with lens cleaner or dew, or rain, seems the probable cause.

The lenses are spaced by small self adhesive pads about 0.1mm thick. They remained stuck to one lens. So no worries about losing them.

As a precaution against adding food (from me) for any spores, I wore surgical gloves. Powder free latex variety. The ordinary DIY store gloves are often dusted with corn starch so would be much worse than a few skin flakes. Yummy said the fungus.

A quick look through the odd gaps in the cloud indicated I had put everything back correctly. With an eyepiece for x100, Jupiter showed moons and cloud bands correctly and the trapezium in M42 was discernible.

Thanks everyone for your pointers.

Comparing my easy fungus removal with the reports of wrecked lenses, confirms the advice to look with with a magnifier and sort it out early.

[Peter Drew]

Good result, well done!

[E621Keith]

Good work. Baader fluid is great on fungus, even better than pure IPA.

In the future, you should keep the OTA in an air tight container loaded with desiccant.

I use these. They turn pink when the silica gel is saturated, so I know when to recharge them (by microwave).

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[Carbon Brush]

Hi Keith.

Thanks for the pointers. At present the scope is in the WO rucksack, along with the accessories. I'm certainly thinking about storage options not just for scopes, but eyepieces as well.

Like most people, I get lots of these little silica gel sachets that I must not eat. They come in shoes, cameras, etc. But I disregard the instruction to throw them away. I have historically hung onto them for use in dive camera housings. Larger bags are sometimes found in computer monitor packing, etc. The only problem will all this free silica gel is that is does not have an indicator.

I was thinking about putting silica gel, with a bit of copper sulphate as indicator in the 'right places'. Not yet worked out all the right places. But a start would be 35mm film canisters, perforated and shoved into the 1.25 eyepiece. Or a perforated bolt bottle in an eyepiece case. I think you get the idea.

The idea is that my home made dessicant capsules are made to fit in with the scope kit. Rather than having to accept 'non astro' standard packaging.

I don't know (yet) enough about the chemistry of silica gel to decide the best way to bond it with an indicator. Or what inidcator is used by manufacturers. But I'm going to find out. I have already speculatively ordered some copper sulphate. If the idea idea of a dessicant indicator fails, then I will have to look for another use for the copper sulphate. Look out for my copper plated scope kit!

David.