Refractors- how tough are the lenses?

[jetstream]

I'm curious what others experiences with refractor glass are. Has anyone actually damaged one or had something happen from use? I'm not really counting a crash off the mount but these experiences are welcome too.

[Saganite]

Hi ,

You may have seen this before as I posted it some months ago to canvas opinion on what caused it.  The consensus was that it was damage caused by the shock from  a blow.  It is the inner element of an ED100 Skywatcher doublet, and the outer lens is pristine.  The chap from whom I bought the scope , for parts really, did not say what had happened. Curiously, in spite of the damage it still worked very well.  The lens looks awful but there is not the slightest external damage, all internal, and the glass is perfectly smooth.  The rest of that telescope has been utilized into a new hybrid scope, and the lens is a rather good magnifying glass/paper weight.

Edited August 21, 2021 by Saganite

[jetstream]

4 minutes ago, Saganite said:

The rest of that telescope has been utilized into a new hybrid scope, and the lens is a rather good magnifying glass/paper weight

How big was this chip? pretty small? Years ago I saw images of horrendous damage that didnt really affect the views. Did you get a new lens or whats happened with the scope?

[Saganite]

There is no chip in the glass at all, in fact if you handled this lens with your eyes closed, you could not tell that it is so damaged.

I replaced the doublet with a TAL doublet to make an f10 lens in an f9 tube thereby making it ready for native focus binoviewing.  There are pictures and write up in this very forum, 9 threads below entitled " I have a bino friendly TALwatcher".

 

cheers

Steve

Edited August 21, 2021 by Saganite

[jetstream]

Well it seems the 100ED did very well, giving vg views despite this "flaw" or whatever we call it. I'll check out the thread.

Edited August 21, 2021 by jetstream

[johnturley]

Sometimes the coatings can be quite delicate, I managed to damage the coating on an early (pre Starfire) Astro Physics Refractor than I used to own, probably through not being as careful as I should have been when it came to cleaning, although I think that the coating was a lot more delicate than that on a Vixen Refractor that I used to own at the same time. 

Nowadays I think the coatings on most lenses are a lot tougher than they used to be. 

John 

Edited August 21, 2021 by johnturley

[jetstream]

16 minutes ago, johnturley said:

Nowadays I think the coatings on most lenses are a lot tougher than they used to be. 

I think but dont know that magnesium based coatings could be softer than others.If so I would presume caution would be in order for eyepieces that use it as well.

[vlaiv]

I had ST102 fall from about 1m onto a floor (hard surface / tiled with ceramic tiles). Scope partially hit the floor and partially my foot as I intentionally put my foot under it trying to soften the fall. One of scope rings broke into pieces - very strange the way it shattered - it revealed low quality of material used to cast it (probably leftovers from some industrial process).

Tube suffered a minor dent and scratch.

Lens was perfectly fine and scope performed the same as before the incident - collimation was perfectly fine after that.

[John]

I had my Vixen ED102SS fall off the mount onto a stone patio a few years ago. It made a horrible noise as it hit the floor but the damage was limited to the end of the dew shield and the focuser pinion, which got bent. No damage to the glass thank goodness and no effect on collimation either. Quite a tough scope !

Other than that, I've been fortunate not too experience damage to the optics in any of the refractors I've owned.

 

 

 

[jetstream]

I had my SW120ED "spin" around and hit a tripod leg hard ( my fault, mount wasnt up to it) from some wind. Zero affect on the scopes performance. I also use this scope down to -40c and while this scopes cell will distort sometimes (not most of the time) I have no issues- including bringing it out from the house into this. I keep the scopes near ambient in a sea can now and they regularly experience cold temps (and hot 34c yesterday here).

So far no lenses have blown up.

Edited August 21, 2021 by jetstream

[John]

I'm expecting the lens elements of my Tak to melt, explode or disintegrate any day now, according to comments made in another thread on another forum

Clearly I've taken a big risk unpacking the scope when it arrived and then using it regularly since then

[jetstream]

3 minutes ago, John said:

I'm expecting the lens elements of my Tak to melt, explode or disintegrate any day now, according to comments made in another thread on another forum

Clearly I've taken a big risk unpacking the scope when it arrived and then using it regularly since then

🤣

yeah and then are there those that mention battery acid in relation to lenses... dont know about you John but my skin sure wont take the acid lol! Ridiculous IMHO.

Edited August 21, 2021 by jetstream

[jetstream]

8 minutes ago, John said:

I'm expecting the lens elements of my Tak to melt, explode or disintegrate any day now, according to comments made in another thread on another forum

Thats ok, I only have bubble filled FLP glass and I'm just shocked that the lenses havent blown right up from thermal shock in my temp extremes.

[ScouseSpaceCadet]

I've only had one mishap, with my favourite telescope though... A dew soaked 102ED was gently placed on a partially full accessories bag that was in turn sitting on top of the telescope flight case. I turned around to walk back out and clunk... and an immediate sickening feeling as a I turned back to see the scope on the conservatory floor. On inspection not the slightest mark and next use collimation was still the same. Soft parquet flooring, a full 2L diet lemonade bottle sitting next the case and solid engineering saved the day. 👍

I feel for people who have worse mishaps, that feeling in your guts when that expensive scope goes clunk is horrible!

 

[John]

10 minutes ago, jetstream said:

🤣

yeah and then are there those that mention battery acid in relation to lenses... dont know about you John but my skin sure wont take the acid lol! Ridiculous IMHO.

The manufacturers really ought to put some warning stickers on the scope:

"Warning: do not immerse the optics of this scope in battery acid, roll over them with a road roller, or allow high velocity rifle bullets to be fired at them. If such treatment occurs we cannot guarantee that the performance of the objective will remain fully up to the original specification"

Edited August 21, 2021 by John

[jetstream]

5 minutes ago, John said:

The manufacturers really ought to put some warning stickers on the scope:

"Warning: do not immerse the optics of this scope in battery acid, roll over them with a road roller, or allow high velocity rifle bullets to be fired at them. If such treatment occurs we cannot guarantee that the performance of the objective will remain fully up to the original specification"

One smiley aint enough! 😃

[jetstream]

 @John I'll share something that I now consider ridiculous on my part. I read that the TSA120's non adjustable lens cell could easily knocked out of whack- on you know where. I went into a frither of activity searching out the truth lol!

Tak and scope expert, Matt @Rainmaker (on here) from Aus straightened me out on this, thankfully. Zero issues with my TSA120, or his (many). He also taught me how to adjust the "junk" Tak focuser... that can hold a 2" Zeiss prism and hvy binoviewers at zenith, in the cold and is smooth as silk.

Now its bubbles in the glass or melting fluorite...

I'll relate what I do and dont do with my fracs in a bit- just the dew/frost thing.

[badhex]

Whilst I was still in the UK I picked up a Bresser AR-152S cheap that had been knocked about... I say that, by the time I took delivery it turned out it had a lot more damage than I thought - looked like it had been chucked down the stairs 😱

In the end though I managed to repair most of the damage and the only thing not easily repaired was the clamshell chip to one half of the objective, which didn't seem to cause any issues in my limited testing after repairing the lens cell.

Sadly, I never really got chance to properly test and adjust any further, as I "temporarily" moved to Berlin (now been here 6 years 😂) 

[Andrew_B]

2 hours ago, johnturley said:

Sometimes the coatings can be quite delicate, I managed to damage the coating on an early (pre Starfire) Astro Physics Refractor than I used to own, probably through not being as careful as I should have been when it came to cleaning, although I think that the coating was a lot more delicate than that on a Vixen Refractor that I used to own at the same time. 

Nowadays I think the coatings on most lenses are a lot tougher than they used to be. 

John 

Anti-reflection coatings made of magnesium fluoride are very soft so perhaps that's what you experienced. I think these days it's usual to add a hard coating of something else like silica to provide extra protection and scratch resistance which might have been what your Vixen had.

[Andrew_B]

1 hour ago, John said:

I'm expecting the lens elements of my Tak to melt, explode or disintegrate any day now, according to comments made in another thread on another forum

Clearly I've taken a big risk unpacking the scope when it arrived and then using it regularly since then

The hilarious thing is that people genuinely believe that the companies which have been making and using these lenses for decades would risk using materials that apparently break at the slightest touch, dissolve in normal atmospheric moisture, or shatter if you so much as look at them funny.

[jetstream]

1 hour ago, Andrew_B said:

The hilarious thing is that people genuinely believe that the companies which have been making and using these lenses for decades would risk using materials that apparently break at the slightest touch, dissolve in normal atmospheric moisture, or shatter if you so much as look at them funny.

Its bizarre, these ideas IMHO.

[Andrew_B]

2 hours ago, jetstream said:

Its bizarre, these ideas IMHO.

I think what happens is that there's often a nugget of truth somewhere but people take an idea and run with it until it becomes nonsense.

Fluorite is quite a bit softer than normal window glass or pyrex and needs more care when handling, but that's mainly an issue when making lenses rather than using them. I just looked up some figures and fluorite is harder than limestone and similar hardness to some types of marble, which are not materials people think of as being very soft.

It's also true that it's soluble in water, apparently you can get 15 milligrams of the stuff to dissolve in a litre of water at room temperature. I wonder how many litres of water there are in a film of dew on a lens?

[jetstream]

43 minutes ago, Andrew_B said:

I think what happens is that there's often a nugget of truth somewhere but people take an idea and run with it until it becomes nonsense.

Fluorite is quite a bit softer than normal window glass or pyrex and needs more care when handling, but that's mainly an issue when making lenses rather than using them. I just looked up some figures and fluorite is harder than limestone and similar hardness to some types of marble, which are not materials people think of as being very soft.

It's also true that it's soluble in water, apparently you can get 15 milligrams of the stuff to dissolve in a litre of water at room temperature. I wonder how many litres of water there are in a film of dew on a lens?

I gave it a smiley but I "like" the answer too.  👍

One thing I'm careful of is condensation or frost from taking the scope into a warm building. My 90mm APO triplet went on so many dark site adventures I lost count, most in the winter. From a warm truck to -30c then back again- it would frost up then melt -on the inside lens too. This SV is a tough little scope lol!

I asked the wife to make me an insulated scope coat- she did out of an old quilt and this slows everything down, preventing the issue.  Now I store in a sea can at or near ambient all the time- the fracs are fine but the big mirrors lag and will have small issues- solved by a small light bulb in each mirror box.

Yes a "nugget of truth" just like a small inclusion in FLP glass! both are pretty small

[Andrew_B]

21 minutes ago, jetstream said:

I gave it a smiley but I "like" the answer too.  👍

One thing I'm careful of is condensation or frost from taking the scope into a warm building. My 90mm APO triplet went on so many dark site adventures I lost count, most in the winter. From a warm truck to -30c then back again- it would frost up then melt -on the inside lens too. This SV is a tough little scope lol!

I asked the wife to make me an insulated scope coat- she did out of an old quilt and this slows everything down, preventing the issue.  Now I store in a sea can at or near ambient all the time- the fracs are fine but the big mirrors lag and will have small issues- solved by a small light bulb in each mirror box.

Yes a "nugget of truth" just like a small inclusion in FLP glass! both are pretty small

I think that's just being sensible with the extreme temperatures you're observing in.

Thermal shock can be an issue and while I don't know what you'd have to do to break a lens that way, why even take the risk of finding out when it should be simple to avoid? Maybe in winter you should just get a big freezer to keep it in!

[jetstream]

48 minutes ago, Andrew_B said:

I think that's just being sensible with the extreme temperatures you're observing in.

Thermal shock can be an issue and while I don't know what you'd have to do to break a lens that way, why even take the risk of finding out when it should be simple to avoid? Maybe in winter you should just get a big freezer to keep it in!

I'm more concerned about water stains inside the lens assy. I never bought an oil spaced frac because the shock can cause oil leaks- maybe. And I just use bubbled filled FLP- maybe all those bubbles give a bit of structural strength in there?

The only issue for the fracs is the lens cell twisting up a bit and causing astig- the SW120ED is most susceptible - so far the TSA120 has had perfect extreme cold cool downs, every time.

I can see that if a cell was tight to begin with, and then moved a lot in the cold that it could conceivably crack a lens. The lens wont crack on its own I dont think but a twisted up lens cell could do it. Never heard of it myself though.

My sea can is the freezer lol!