Cleaning WO lens

[Rob_Jn]

I’ve come to use my WO72FD after some months stored in my observing shed in a case and found a deposit on the inner surface of the lens. I’ve tried blowing warm air down the tube thinking it was just condensation but no luck. I can get the dew cap back to reveal the lens housing which has a grub screw in. I removed the grub screw thinking the lens housing might screw off but no luck. Anyone know if it should screw off or will I have to clean the inner surface down the tube? 
thanks,

Rob

 

[wulfrun]

Ouch, hard to be sure but that looks suspiciously like fungus. Needs dealing with ASAP. Can't help with how it comes apart, or the advisability of DIY I'm afraid.

[Rob_Jn]

Yeah I thought it looked a bit more suspicious, worried that it might be between the lens elements 😒

[Jonk]

If it’s fungus, giving it a good dose of UV (sunlight) should help stop more growth?

[mikemarotta]

Obviously, you want to clean it without damaging the coatings. I cannot help. However, I do want to thank you for mentioning the Williams Optic brand. I had no idea that they exist. I went to their website. I am impressed. In our local club, if someone in the public community turns to us for our outreach people just echo the most common brand names. I am not sure that we are doing a service. I am going to recommend to the executive committee that we think about a standard reply with a broader range of vetted details. Be that as it may, thanks again, and good luck. You have an outstanding instrument that deserves the best care.

Mike M.

 

[Rob_Jn]

I’m glad something good has come out of my troubles Mike, William Optics are well known over here, I’ve had the 72FD for 10 years or so and it’s always performed very well.

I’ll probably expose to some UV as Jonk has suggested (we have a uv exposure frame where I work in the absence of sunlight at the moment!) but very carefully, I don’t want to degrade the paintwork.

Rob

[John]

I have cleaned a couple of objectives which were in a similar state. It is a delicate business though. Doublets are not too awkward although a lot of care is still required to keep the rotation of the lens elements correctly positioned and, if they are used, the foil spacers correctly spaced. I would be very hesitant to do a triplet lens though. The optical centering of the elements is even more critical with those. A job for a specialist really.

The only William Optics scope that I've owned was a Megrez 90 doublet (bigger brother to yours really) which was quite a nice scope. I bought that new though so the objective was pristine when it arrived. And when I sold it for that matter.

I hope yours gets sorted in due course. It does look as if it needs a clean as well as the UV treatment.

 

[wulfrun]

Exposing it to UV will help kill the fungus, it shouldn't harm the paintwork. White paint is more likely to be de-yellowed by UV and the black parts should resist it too. You won't be leaving it exposed for long enough to do damage.

Wherever you were keeping it is too damp so you'll need a new, dry, storage location. I'd be very wary of cleaning as  DIY unless you're experienced, there are many things to go wrong. If the fungus is not just on the front surface of the front element, I'd say it's a job for a pro. I've removed fungus from camera lenses but you need the right tools, patience, care and knowledge. In one case, the fungus had etched the coating on one element but it suffered no ill effects optically that I could tell (potentially it was more prone to flare).

[Rob_Jn]

Phew, I have succeeded in cleaning it without removing the lens but took a soft lens cloth on a rod and gently tried rubbing a small area and it seemed to clean up, carried on very carefully and although it’s not perfect it’s nearly back to normal ( most of the dust you can see is on the outside now 😊) I suspect I’ve been very lucky in that it has started to develop recently with the onset of damp and cold weather. Lesson learned though I’ll be keeping it indoors from now on. 

thanks for all the advice guys,

Rob

[wulfrun]

Glad there was a good outcome. I'd still try and get some UV on it to kill any spores that may still be present but definitely keep a careful eye on things to make sure it doesn't return. Weak hydrogen peroxide is also good, just be sure not to flood it on, use a cloth-dampened application and wipe dry gently.