New lease of life for a Meade 18mm UWA

[badhex]

Hello all,

I've had a Meade 18mm UWA for quite a few years, and some time ago it developed a bit of a weird coating issue which meant it wasn't completely unusable but did cause some softness of the image. I retired it, and replaced it with a (much better) 17.5mm Morpheus. 

More recently I discovered the wonders of tiny widefield scopes via a Celestron travelscope 70 and now a WO Zenithstar 73 which makes a really excellent - albeit expensive - portable/travel kit. 

I was always a bit sad about my first expensive EP being put out to pasture, and now I also had a cheap, lightweight and pretty capable scope which performs best at widefield views also not being used... I'm thinking I can pair the two, and give a second life to the Meade as an *even more* portable travel kit. Chuck in a Celestron 25mm Plössl and 5mm BST, throw everything in hold luggage and not worry about breakage or weight.

I set about denuding the Meade which makes it huge amounts smaller, albeit only a touch lighter. On the third picture I tried to capture the weird coating issue in the reflection - it covers about 25% of the fields lens and is slightly tactile. As I say still usable, at least for this application! 

[Don Pensack]

That looks like a smudged fingerprint on the outside.

Did you try removing the lower lens and cleaning both sides?

[badhex]

14 minutes ago, Don Pensack said:

That looks like a smudged fingerprint on the outside.

Did you try removing the lower lens and cleaning both sides?

I was always very careful to very gently clean any fingerprints or other debris with Baader wonder fluid when it was regularly in use, and then it went into storage for about 6-12 months (dry cellar, inside an EP case with silica packs.). When I got it out it looked like that, all other EPs were completely fine. 

It's hard to capture a good photo but my best guess is that some sort of residue must have been on it and caused a reaction with the coating. I'd be surprised if it was mould as from my reseaech it did not bear the typical hallmarks.

Whatever it is, you can feel that the coating is no longer smooth. A few years ago thinking it to be a lost cause, I did try some slightly more vigorous cleaning which I think improved the view through the eyepiece, but possibly at the cost of removing some of the coating where it had reacted.

See my original photos and post below - a few people suggested it might be moisture on the inside as the photos seem to suggest, but it was definitely something external. 

 

 

[Mr Spock]

Looking at how bad it is it may be worth risking some invasive cleaning.

[badhex]

58 minutes ago, Mr Spock said:

Looking at how bad it is it may be worth risking some invasive cleaning.

The most recent photo I posted is actually of it when I first had the problem some years ago. The photo I posted at the beginning of this thread is how it looks now - it's significantly better, and mostly appears to affect the outer 10-15%, and only on some edges. This gif will give you an idea:

Also, I'm not sure what I could do, to be honest. Perhaps someone more skilled than me could do more, but the problem is only on the field lens and only on the outside - not sure if taking it apart would do any good. 

[Don Pensack]

You could try a stronger solvent.

A step up from the normal lens cleaning fluids is pure acetone.  It's also safe for lenses, but don't let it drip inside as it could dissolve some of the paint on the edge of the lens.

The next step up from that is paint thinner, but if acetone doesn't touch it (use cotton Q-Tips), then your supposition that something got on the lens and harmed the coatings could be correct.

If it's organic, though, acetone will take it off completely.

Note for some viewers: some case foams outgas when a case is kept closed for a long period of time.  This stuff can coat the lenses in an eyepiece with hard-to-remove exudate.

So ALWAYS store the eyepieces in the case with caps tightly on.

[badhex]

Thanks Don. I'll have a look at acetone. The biggest challenge is that it's a convex lens, so will need to make sure the cotton bud is only just wet so it doesn't run off and into the edge of the lens. 

[TheLookingGlass]

I had one of those eyepieces sent to me a few years ago and on the bottom was fungus. I returned it to the seller.

[badhex]

On 07/10/2021 at 21:55, TheLookingGlass said:

I had one of those eyepieces sent to me a few years ago and on the bottom was fungus. I returned it to the seller.

Funnily enough was talking to another member on here who had a 2" 20mm version which had a similar problem. I wonder if these EPs are susceptible for whatever reason? Formulation of the coatings or something.

There was no obvious fungal growth on mine but whatever caused it is on the outside of the field lens and the coating has degraded.

[TheLookingGlass]

On 10/10/2021 at 05:29, badhex said:

Funnily enough was talking to another member on here who had a 2" 20mm version which had a similar problem. I wonder if these EPs are susceptible for whatever reason? Formulation of the coatings or something.

There was no obvious fungal growth on mine but whatever caused it is on the outside of the field lens and the coating has degraded.

Seems like an ongoing problem with these. 🤨

[Louis D]

1 hour ago, TheLookingGlass said:

Seems like an ongoing problem with these. 🤨

I'm picturing the coatings were made from agar (think Petri dish lining).

[badhex]

This weekend I had a brief session with the above mentioned setup - Travelscope 70, the 18mm Meade UWA and for comparison, a 17.5mm Morpheus and 25mm Celestron Plossl. I put everything on a TS AZT6 and TS carbon fibre tripod, and everything packs up into two small bags - the tripod bag plus another, almost identical to the tripod bag but around 10cm shorter. Setup is very quick. Maybe ten minutes to get everything in place. Can easily be picked up and moved around with one hand. Despite being such a small scope I think it still needed ~30 mins to cool before it settled out.

First I had a sweep around with the Celestron plossl. It's not a bad EP all told, something I can't put my finger on that I quite like about it - maybe that it's so compact and does have a rather larger eyelens for its size. That said, having been primarily observing with my ZS73 and often either 2" or widefield EPs like the Morpheus, it did feel a little restrictive. Still, ~3.1deg. TFOV is not bad for a comparatively tiny 25mm Plossl.

UWA next. Since deshrouding, the first thing I noticed is that eye positioning is a bit tricky with no eyecup, and stray local LP not really helping the experience. Once I'd managed to get settled, and cupped the EP with my hands, the ~3.7deg view is not bad, much more immersive than the 25mm Plossl and more sky to boot. I believe that this is pretty much the largest TFOV I can get out of this scope without vignetting, and I spent most of the time with the double cluster as a comparison piece. At first* I could only really notice the field lens 'fogging' round the edges of the view which presents as lower contrast. Not the best vies ever, but certainly copeable and perhaps would be much less noticeable under darker skies than my usual Bortle 7/8.

Last I switched in the Morpheus and it's immediately clear it is a far superior eyepiece. 3.3deg TFOV but all the nicer for the much larger eyelens, sharper, contrasty views and comfortable eye position. Of course I knew all this already, but on direct side-by-side comparison you really see the difference - for example the eye lens on the UWA feels reaaalllly small. I switched back and forth a few times and unfortunately as well as the aforementioned differences, the fogging/contrast is noticeably worse in the UWA.

 

Overall, I do think it could work as a cheap and cheerful, very compact and lightweight kit and I like the idea of the UWA having another lease of life as per the post title - but I worry that I when I'm at the eyepiece I would just be wishing that brought the Morpheus with me instead!

Edited October 18, 2021 by badhex