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Lens condition / coating?

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#1 Trackerthedog

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Posted 25 November 2020 - 09:21 PM

I'm hoping someone can help me identify what it is that I'm seeing on the lens of my large refractor. It has only seen about 10 hours of use so far. When not in use, it sits with a tarp over it and light bulb on all the time under the tarp - all inside an observatory. It also has a desiccant container just inside the (dew shield) lens cap. So, I'm thinking this should not be due to moisture. I contacted Yuri Petrunin (since it's a TEC), but he doesn't know exactly what would be causing it. The images were taken while shining a regular flashlight into the dew shield and onto the lens (it is a triplet with a fluorite middle element). ... Any comments are welcome. Thanks in advance.

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#2 xonefs

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Posted 25 November 2020 - 09:58 PM

This sounds pretty obvious, but have you tried cleaning it? It looks like it's on the outside and just from condensation and dirt/dust mixing in. In use mine can get pretty dirty in just a few hours but it can be kind of humid here. 



#3 Star Shooter

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Posted 25 November 2020 - 10:00 PM

That looks like dried water spots from dew on the lens. 

 

Glen



#4 PKDfan

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Posted 25 November 2020 - 10:01 PM

Sure looks like a condensation cloud. To my mind a dessicant or other mitigation unless heat will only help with the outer lens so moisture could condense to the different humidity inside the tube. But dont have a 10"anything so a grain of salt thing. Really hope you work out the situation the views must be beyond spectacular!😎

Clear skies & Good seeing
Edit clarity

Edited by PKDfan, 25 November 2020 - 10:05 PM.


#5 Star Shooter

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Posted 25 November 2020 - 10:12 PM

I am curious. How do you like your big refractor?

Any pros or cons yet?

Glen



#6 Spikey131

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Posted 25 November 2020 - 10:44 PM

Cap the lens and leave the tarp off.

#7 TOMDEY

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Posted 25 November 2020 - 10:56 PM

Desiccant containers have to be replaced or dried in an oven... otherwise they become the opposite... like a giant wick saturated with water. Some desiccants are color-change indicators. Some can be recharged, some can't. And even the indicator ones eventually the indicator itself stops changing color... even when saturated! Containers can also be too tight. The moisture trapped in there has no way to escape... can become a steam bath inside.     Tom



#8 Trackerthedog

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Posted 25 November 2020 - 11:11 PM

Desiccant containers have to be replaced or dried in an oven... otherwise they become the opposite... like a giant wick saturated with water. Some desiccants are color-change indicators. Some can be recharged, some can't. And even the indicator ones eventually the indicator itself stops changing color... even when saturated! Containers can also be too tight. The moisture trapped in there has no way to escape... can become a steam bath inside.     Tom

Thanks, Tom. I check on the desiccant very frequently and use a high quality desiccant. It is changed when the color indicates it is about half-way to being saturated. ... The desiccant was added to the dew shield after the images of the lens were taken.



#9 Trackerthedog

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Posted 25 November 2020 - 11:12 PM

Cap the lens and leave the tarp off.

Thanks, Spikey131. I will try this. Should I leave the desiccant in the dew shield when I try it.



#10 Trackerthedog

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Posted 25 November 2020 - 11:16 PM

This sounds pretty obvious, but have you tried cleaning it? It looks like it's on the outside and just from condensation and dirt/dust mixing in. In use mine can get pretty dirty in just a few hours but it can be kind of humid here. 

Thanks, xonefs. I am trying not to clean the lens unless absolutely necessary. This is also Yuri Petrunin's advice. He said to clean the lens as little as possible. I guess that's why I was trying to figure out what was causing the effect in the images.



#11 Trackerthedog

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Posted 27 November 2020 - 11:03 AM

Just got this back from Yuri Petrunin after I asked a few more questions. grin.gif

 

"Hi Neil,
the period of cleaning of optics depends not only on the optics condition, but mostly on the nature of the person: happy people look at the lens through the eyepiece and seek help less often. Those who shine a bright light on the lens turn more often.
Performance difference is not easy to notice between cleaned (right part) and actual condition of the APO160 lens sample that was used for a few years at the location near ocean.

You may post above on the CN?
Best regards, Yuri"

 

160 near ocean cleaning.jpg


Edited by Trackerthedog, 27 November 2020 - 11:05 AM.

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#12 Kunama

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Posted 30 November 2020 - 02:59 PM

I'm hoping someone can help me identify what it is that I'm seeing on the lens of my large refractor. It has only seen about 10 hours of use so far. When not in use, it sits with a tarp over it and light bulb on all the time under the tarp - all inside an observatory. It also has a desiccant container just inside the (dew shield) lens cap. So, I'm thinking this should not be due to moisture. I contacted Yuri Petrunin (since it's a TEC), but he doesn't know exactly what would be causing it. The images were taken while shining a regular flashlight into the dew shield and onto the lens (it is a triplet with a fluorite middle element). ... Any comments are welcome. Thanks in advance.

That looks a lot like my TMB-LZOS 152mm lens did when I bought it. The original owner lives within 10 miles of the ocean and I believe the 'haze' is from the salt laden air that is abundant that close to a marine environment.

 

I removed the cell in mine and cleaned it when I bought the scope and the 'haze' was definitely salt from the air. The scope has not been near the ocean since and has remained clear as the day I cleaned it.

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#13 shivaram

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Posted 30 November 2020 - 11:21 PM

By experience.... If it ain't bothering you, don't clean it unless it is fungus....



#14 Kunama

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Posted 30 November 2020 - 11:38 PM

By experience.... If it ain't bothering you, don't clean it unless it is fungus....

I'm still betting that it is salty air that is the culprit.....  Not sure how far the OP is from Comox but unless he is more than 15klms from the salt waters .......

If it is salt then it can affect the cell as well and may make it near impossible to dismantle the cell in future if the salt reacts with the cell material...... (ask me how I know undecided.gif , it took quite a bit of effort to get my LZOS lens cell apart and the threads had a white substance on them)

 

(all clean now as the pic above shows flowerred.gif )


Edited by Kunama, 30 November 2020 - 11:40 PM.



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