Lens cleaning disaster and a re-purposing of scope.

[LaurenceT]

I bought a used Evoguide 50ED some time ago with a view to using it as a lightweight imaging scope but almost immediately had the good fortune to acquire a WO ZS61 so the 50ED was never used for imaging, I have used it a few times for guiding. My recent back problems have led me to experimenting with ultra light setups again and I decided to sell on the the 50ED in favour of a mini guidescope I already had. 

Yesterday I decided to give the 50ED a bit of a spruce up before advertising it so I started by cleaning the lens. What a disaster, no matter what method I used the smears just kept piling up. I've been cleaning camera lenses most of my life so I thought I knew what I was doing, I should have read first that telescope lenses are quite different, so I have deemed this 50ED as not saleable. But what to do with it? I had a look at Andre Minoia's reviews of the 50ED and he had suggested it's possible use for observing and apart from one other fleeting mention elsewhere that was it!

So I set about putting some gear together. From the ground up: my somewhat ancient but superb and incredibly light Gitzo G1227 reporter mountaineer carbon fibre tripod, topped with a small Manfrotto video head from my vast and embarrassing collection of unused photo accessories together with an Arca Swiss clamp. I had a WO dovetail bar lying around which has an Arca Swiss connection on the reverse side so I mounted the 50ED in it's 3d printed bracket onto the dovetail bar which then neatly seated on the video head. For eyepiece I selected my Svbony zoom.

About 10pm yesterday I noticed the sky was extremely clear with some clouds threatening so I set up the new gear and quickly located M42. Not expecting very much at all from this I was amazed at how clear the viewing was. At the highest magnification I had a brilliant view of M42 with the nebulosity clearly visible. The clouds rolled in so I packed up and can't wait for the moon to show up. The whole thing is as light as a feather and I'd have no compunction in packing this (not including the tripod) in my standard photo back pack with room for still cameras etc.

 

[Franklin]

OMG, what did you use on it Laurence? Jiff😁.

Edited February 19, 2023 by Franklin

[markse68]

12 minutes ago, LaurenceT said:

I should have read first that telescope lenses are quite different,

Really? what were you using to clean it? Maybe it was dissolving paint from inside the dew shield and making a mess. I think the coatings are basically the same. Should be cleanable- use rolled up cleaning tissue, damped with acetone wipe from centre out and trim the end off each wipe until you clean off the residue. I’m using one as a finder- it’s a lovely finder  

Mark

[LaurenceT]

What did I use? What didn't I use!!

I started with standard photo lens cleaner which left a smear so I followed that with camera sensor cleaning fluid which left more of a smear so I then tried isopropyl alcohol which left a smear so I breathed on it which made the smearing worse😢.

The last two attempts were following information I got on the web which as we know is never wrong. Luckily for me someone I know locally who knows infinitely more than I do about all things astro has kindly offered to clean it for me. 

@Franklin I will try Jif, what could possibly go wrong......

Edited February 19, 2023 by LaurenceT

[Elbasso]

I would be very happy if you could share if the professional was able to clean the lens and how this happened in the first place. 

Cheers, 

[Franklin]

1 hour ago, LaurenceT said:

@Franklin I will try Jif, what could possibly go wrong......

Only joking Laurence, I'm sure it will be fine once cleaned up, modern lens coatings are quite durable.

Nice little ED scope btw, what's it like for getting focus? Can you use a diagonal?

Edited February 19, 2023 by Franklin

[AstroKeith]

47 minutes ago, Elbasso said:

I would be very happy if you could share if the professional was able to clean the lens and how this happened in the first place. 

Cheers, 

That would be me! We discovered we lived a short walk away by chance a few months ago.

IPA can be problematic. If the lens is real dirty, then it needs either a) a really good soak and rinse, or b) multiple goes, each time reducing the contaminant.

But a) cant be done in situ. The fluid will seep round the lens and get into the intra lens space and/or the back surface.

So b) is the usual method. One keeps going until it looks 'good enough'. However multiple cleanings is to be avoided if possible as each can cause a scratch etc. Each 'go' if not done expertly may only remove say 50% of the dirt, and so after clean 1 it is 50% dirty, after clean 2 - 25% dirty, after clean 3 - 12.5% dirty, etc. 

Then there is the choice of cleaning solvent. This depends on the dirt! Pure IPA for instance won't lift some non-organic smears. Often a water/IPA mix is used. Each technician has their own favourite ratio. I usually use 90% IPA, 10% water and one drop of pure soap per 100ml. IPA is slow to evaporate and so a wet drag with a lens tissue is needed to finish. Drag the tissue slow enough so that the fluid line evaporates as you go. Should leave no smears! However with a lens in a cell, down a dew shield this is almost impossible.

Sometimes Acetone is needed for stubborn first/stains. Again a wet wipe works, and the acetone evaporates really quickly leaving usually no smear. Acetone can be excellent for spot cleaning an otherwise clean lens.

With a lens in a cell like in this case, one can often be chasing out dirt or grease from the very edge. Often the lens clamp ring is plastic, the edge of the lens has been blackened with paint, or the paint on the inside of the dew shield is soluble in the cleaning fluid (especially with acetone)

I will give Laurence's lens a quick first attempt to judge progress, but I suspect the lens may best be removed for a proper clean. Rubber gloves or finger tips and a proper removal tool are essential. Plus mark the orientation of the lens and any spacers used.

I used to be Technical Director of an optical manufacturing company and learnt from the shop floor technicians who were aces. I must have done 100's of eyepieces and scope since and am 'proficient' but still learning. My most challenging clean was a 150mm AstroPhysics objective that a friend bought to a star party having never ever been cleaned and looking like frosted glass. He was trying to resolve the 'Pup' and getting no where of course. I cleaned it perfectly for him while being watched by a crowd of anxious onlookers. The real challenge - we were at the Texas Star Party in the middle of a mountain desert!

For me smears are just fun, its grit that scares me!

[LaurenceT]

11 minutes ago, Franklin said:

Only joking Laurence, I'm sure it will be fine once cleaned up, modern lens coatings are quite durable.

Nice little ED scope btw, what's it like for getting focus? Can you use a diagonal?

I knew you were joking😀. Focussing is a bit of a pain as the helical focuser has a massive travel but you get there in the end. A diagonal can't be used so it's a straight through job, not ideal although I didn't find it a problem the first time I tried it.

[Elbasso]

4 hours ago, AstroKeith said:

That would be me! We discovered we lived a short walk away by chance a few months ago.

IPA can be problematic. If the lens is real dirty, then it needs either a) a really good soak and rinse, or b) multiple goes, each time reducing the contaminant.

But a) cant be done in situ. The fluid will seep round the lens and get into the intra lens space and/or the back surface.

So b) is the usual method. One keeps going until it looks 'good enough'. However multiple cleanings is to be avoided if possible as each can cause a scratch etc. Each 'go' if not done expertly may only remove say 50% of the dirt, and so after clean 1 it is 50% dirty, after clean 2 - 25% dirty, after clean 3 - 12.5% dirty, etc. 

Then there is the choice of cleaning solvent. This depends on the dirt! Pure IPA for instance won't lift some non-organic smears. Often a water/IPA mix is used. Each technician has their own favourite ratio. I usually use 90% IPA, 10% water and one drop of pure soap per 100ml. IPA is slow to evaporate and so a wet drag with a lens tissue is needed to finish. Drag the tissue slow enough so that the fluid line evaporates as you go. Should leave no smears! However with a lens in a cell, down a dew shield this is almost impossible.

Sometimes Acetone is needed for stubborn first/stains. Again a wet wipe works, and the acetone evaporates really quickly leaving usually no smear. Acetone can be excellent for spot cleaning an otherwise clean lens.

With a lens in a cell like in this case, one can often be chasing out dirt or grease from the very edge. Often the lens clamp ring is plastic, the edge of the lens has been blackened with paint, or the paint on the inside of the dew shield is soluble in the cleaning fluid (especially with acetone)

I will give Laurence's lens a quick first attempt to judge progress, but I suspect the lens may best be removed for a proper clean. Rubber gloves or finger tips and a proper removal tool are essential. Plus mark the orientation of the lens and any spacers used.

I used to be Technical Director of an optical manufacturing company and learnt from the shop floor technicians who were aces. I must have done 100's of eyepieces and scope since and am 'proficient' but still learning. My most challenging clean was a 150mm AstroPhysics objective that a friend bought to a star party having never ever been cleaned and looking like frosted glass. He was trying to resolve the 'Pup' and getting no where of course. I cleaned it perfectly for him while being watched by a crowd of anxious onlookers. The real challenge - we were at the Texas Star Party in the middle of a mountain desert!

For me smears are just fun, its grit that scares me!

Thank you so much for that outstanding description. It's highly appreciated! 

[Carbon Brush]

@AstroKeith Another thank you for your detailed description.
I use Baader fluid on lenses. On the basis that I don't use it by the litre and a 100mL bottle costs a lot less than the lens.
When away from home the little spray bottle is convenient.
For the future, I will definitely try the IPA/water/soap mix. Perhaps refilling my empty Baader bottles.

[AstroKeith]

Here's an update on how the cleaning went!

It wasnt nearly as bad as the photo looked, but bad enough. First attempts didnt go well. There was clearly some reside on the lens that was just being smeared around with each clean.

I had to disassemble the objective. The lens locking ring was locked in with some glue, but acetone shifted that.

Once I had the two lenses it should then have been easy. But again each clean picked up smears. Grrr!

On closer inspection, the rubber o-ring used between the locking ring and lens had been attacked and left a residue on the lens. Plus, the lens edges had been blackened with perhaps a felt pen, and the ink was soluble in IPA.

So now I knew what I was dealing with it got easier. I got the surfaces to about 95% satisfaction, reassembled and then used a cotton bud and acetone to clean up. I would say I got I to within 98% of perfection and Laurence was happy with that. 

So the moral is - be prepared for the worst! Even an 'easy' job can be a challenge.

[westmarch]

Someone tell me, what’s IPA, presumably not India Pale Ale. 🤔

John 

[AstroKeith]

Iso Propyl Alcohol

[Carbon Brush]

Iso-propanol. Or the older name is isopropyl alcohol.

The 70% ingredient in the hand gels we have been using in the past couple of years.

Also used in some electronics cleaning. Pinted circuit boards and components.
Beware. electrical 'Switch cleaners' often contain other things.

However @westmarch if you would like to send me a crate of beer🤣

[Knighty2112]

8 minutes ago, westmarch said:

Someone tell me, what’s IPA, presumably not India Pale Ale. 🤔

John 

IPA - Isopropyl Alcohol

[Knighty2112]

Sorry, that should say IPA = Isopropyl alcohol.