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Great magnifying glass !


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A few years ago I bought a damaged ED100 for a project. It cost me practically nothing and actually worked surprisingly well, but I replaced the doublet with a TAL doublet.  It has always intrigued me how the damage was caused.

If you handle this lens with eyes closed you would never guess that there was a problem, all the fractures being inside, and I wonder if this has been caused by exposure to the Sun. The outer lens of the doublet is perfect and I cannot bring myself to use it but this lens makes an amazingly good magnifying glass for star charts.

Can anyone venture an opinion ?

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That's a cemented doublet ? Temperature driven strain might do that but I haven't seen it happen to any of the objectives I've used on the sun. Then I think the majority , by way of sampling the ones I've used, are air-spaced. 

 

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Is that a single element Steve ?

The ED100 has an air spaced doublet objective doesn't it ?

 

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5 hours ago, Saganite said:

A few years ago I bought a damaged ED100 for a project. It cost me practically nothing and actually worked surprisingly well, but I replaced the doublet with a TAL doublet.  It has always intrigued me how the damage was caused.

If you handle this lens with eyes closed you would never guess that there was a problem, all the fractures being inside, and I wonder if this has been caused by exposure to the Sun. The outer lens of the doublet is perfect and I cannot bring myself to use it but this lens makes an amazingly good magnifying glass for star charts.

Can anyone venture an opinion ?

 

 

 

I'm going to suggest an impact with something hard, but blunt. The shockwave has been transferred through the lens to cause the fracture inside. Think Newton's cradle.

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8 minutes ago, Shimrod said:

I'm going to suggest an impact with something hard, but blunt. The shockwave has been transferred through the lens to cause the fracture inside. Think Newton's cradle.

Could it be a dropped scope that landed dew shield first?

Lens would be still in lens cell so impact would be evenly distributed along the edge of the lens with retaining ring being sort of "soft" - but stress would cause internal fracture as you suggest.

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54 minutes ago, John said:

Is that a single element Steve ?

The ED100 has an air spaced doublet objective doesn't it ?

 

The one shown John is the rear or inner element, the outer element I have tucked away and it is pristine. I bought the whole scope for a ' song '.   The doublet in the ED100  is air spaced. Before I took it apart I tried it out and was astonished at how well it still worked.

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Posted (edited)
1 hour ago, Shimrod said:

I'm going to suggest an impact with something hard, but blunt. The shockwave has been transferred through the lens to cause the fracture inside. Think Newton's cradle.

That is interesting. I had discounted that as there is not a single tiny shard missing, totally smooth all round but what you say makes sense and is confirmed I think by Vlaiv.

Thanks for that

Edited by Saganite
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1 hour ago, skybadger said:

That's a cemented doublet ? Temperature driven strain might do that but I haven't seen it happen to any of the objectives I've used on the sun. Then I think the majority , by way of sampling the ones I've used, are air-spaced. 

 

Thanks for your input, but as you say, from experience, which I can confirm, the ED100 is air spaced.

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A geologist would describe those as conchoidal fractures .

I'm reminded of prehistoric flint tools I've handled , the best person to assess exactly what sort of impact caused this pattern would be an experimental archaeologist with practical experience in flint knapping . Fascinating stuff to watch being done , I bet there are plenty of vid.s online .

Heather

 

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28 minutes ago, Tiny Clanger said:

A geologist would describe those as conchoidal fractures .

I'm reminded of prehistoric flint tools I've handled , the best person to assess exactly what sort of impact caused this pattern would be an experimental archaeologist with practical experience in flint knapping . Fascinating stuff to watch being done , I bet there are plenty of vid.s online .

Heather

 

Thank you. I will have to look that one up later when the clouds arrive and I am forced to come in....:smiley:

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11 hours ago, Tiny Clanger said:

A geologist would describe those as conchoidal fractures .

I'm reminded of prehistoric flint tools I've handled , the best person to assess exactly what sort of impact caused this pattern would be an experimental archaeologist with practical experience in flint knapping . Fascinating stuff to watch being done , I bet there are plenty of vid.s online .

Heather

 

I met someone who did this 'semi-professionally' on a geological survey I volunteered for a few years ago. He identified something I found as being a stone age tool. It was the only thing found during that survey.

Back to the subject though. Is the ED element the inner lens? And would it be softer than the outer? If so, then an over-tightened retainer ring might also do that kind of damage. Perhaps the ring was cross-threaded (might explain the gap in damage) and the previous owner kept on trying to tighten? Knapping of stone doesn't always require sharp impacts, so the pressure caused by over-tightening the ring, plus a relatively soft impact might do this too, although the fracture near the middle is a bit puzzling. It's similar to what I do at work, except we deal with metal fractures.

Edited by Roy Challen
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On 24/03/2021 at 18:52, Tiny Clanger said:

A geologist would describe those as conchoidal fractures .

I'm reminded of prehistoric flint tools I've handled , the best person to assess exactly what sort of impact caused this pattern would be an experimental archaeologist with practical experience in flint knapping . Fascinating stuff to watch being done , I bet there are plenty of vid.s online .

Heather

 

I have had a look at your suggestion of Conchoidal fracture Heather and it is clear from this and the corroboration from Shimrod and Vlaiv that a blow of some kind, but certainly a force is the cause and not solar heat as I suspected, so thank you all......👍

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14 hours ago, Roy Challen said:

I met someone who did this 'semi-professionally' on a geological survey I volunteered for a few years ago. He identified something I found as being a stone age tool. It was the only thing found during that survey.

Back to the subject though. Is the ED element the inner lens? And would it be softer than the outer? If so, then an over-tightened retainer ring might also do that kind of damage. Perhaps the ring was cross-threaded (might explain the gap in damage) and the previous owner kept on trying to tighten? Knapping of stone doesn't always require sharp impacts, so the pressure caused by over-tightening the ring, plus a relatively soft impact might do this too, although the fracture near the middle is a bit puzzling. It's similar to what I do at work, except we deal with metal fractures.

Hello Roy, I hope you are well.

I am happy now that it is force whether by a blow or by pressure as you suggest that has caused the damage, not by Solar heat.

Thanks for your input. 

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Solar heat tends to shatter or melt things at the EP end, i.e. near the point of focus, not at the objective, which isn't exposed to any unusual concentration of sunlight. So indeed, this is more a case of "blunt-force trauma" ;)

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47 minutes ago, michael.h.f.wilkinson said:

Solar heat tends to shatter or melt things at the EP end, i.e. near the point of focus, not at the objective, which isn't exposed to any unusual concentration of sunlight. So indeed, this is more a case of "blunt-force trauma" ;)

CSI SGL ! 🙂

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On 24/03/2021 at 19:52, Tiny Clanger said:

A geologist would describe those as conchoidal fractures .

I'm reminded of prehistoric flint tools I've handled , the best person to assess exactly what sort of impact caused this pattern would be an experimental archaeologist with practical experience in flint knapping . Fascinating stuff to watch being done , I bet there are plenty of vid.s online .

Heather

 

Interesting. My sometime neighbour is an amateur experimental archaeologist, though at a level which includes teaching PhD students from Marseille University. He makes exquisite flint tools and says, as you suggest, that pressure is the key. (Recently he came up with a widely approved explanation for the use of notched stone age mussel shells, a puzzle which had not met with a satisfying explanation prior to his.)

Olly

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6 hours ago, ollypenrice said:

Interesting. My sometime neighbour is an amateur experimental archaeologist, though at a level which includes teaching PhD students from Marseille University. He makes exquisite flint tools and says, as you suggest, that pressure is the key. (Recently he came up with a widely approved explanation for the use of notched stone age mussel shells, a puzzle which had not met with a satisfying explanation prior to his.)

Olly

Yes, I've not looked it up, but have a vague recollection that once the major shaping is done with a rock used as a hammer, the more delicate edge forming is done with a pointed tool, possibly a bit of antler, using carefully targeted pressure rather than blows. I have a rather basic book covering the Palaeolithic tools (Flint implements of the Old Stone Age, by Peter Timms ) which I'm going to have to re-read now 🙂  I was lucky enough to be able to handle some museum specimens a while ago, including a strikingly beautiful , made from one piece of flint, Neolithic sickle . I think it had been found in Norfolk . Astonishing to think it was used at the dawn of settled agriculture in Europe.

Heather

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