Blocking filters and wintertime
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Blocking filters and wintertime
All,
Does temperature affect the performance of blocking filters? I know Lunt makes a heater for theirs. I read somewhere that the filters work poorly below 60 degrees. Is that true? I observe the sun daily and it would suck not to be able to use the Coronado in the wintertime. Would the Lunt heater fit the blocking filter of the Coronado? I could also use a dew strip or maybe wrap something around the blocking filter diagonal to insulate it. Or maybe use a blow dryer to keep it warm??
James
Does temperature affect the performance of blocking filters? I know Lunt makes a heater for theirs. I read somewhere that the filters work poorly below 60 degrees. Is that true? I observe the sun daily and it would suck not to be able to use the Coronado in the wintertime. Would the Lunt heater fit the blocking filter of the Coronado? I could also use a dew strip or maybe wrap something around the blocking filter diagonal to insulate it. Or maybe use a blow dryer to keep it warm??
James
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Re: Blocking filters and wintertime
You'll clearly see whether the temperature is having a detrimental effect on you blocker, if it is use a dew strip if you have one, alternatively go for the Lunt heater, both will do the same thing.
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Re: Blocking filters and wintertime
Interesting subject....
What documented evidence for the temperature effect on blocking filters????
Ken
What documented evidence for the temperature effect on blocking filters????
Ken
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Re: Blocking filters and wintertime
Hi all...
In my experience, the cold hasn't made an effect on the blockers (Ha or CaK) in the cold. I've posted images taken during the winter in airtemps down to -26C with no heat applied. This is the extreme, but -5 to -15C is typical in the winter.
I think the bigger concern is taking the cold filter into a warm storage after use and getting condensation on (inside?) the elements. Since I have my equipment in an observatory, I leave it out year round as close to the ambient temp as I can. Of course, this may not work for everyone. I will have to look at Lunt's website to see the heaters referred to.
Brian
In my experience, the cold hasn't made an effect on the blockers (Ha or CaK) in the cold. I've posted images taken during the winter in airtemps down to -26C with no heat applied. This is the extreme, but -5 to -15C is typical in the winter.
I think the bigger concern is taking the cold filter into a warm storage after use and getting condensation on (inside?) the elements. Since I have my equipment in an observatory, I leave it out year round as close to the ambient temp as I can. Of course, this may not work for everyone. I will have to look at Lunt's website to see the heaters referred to.
Brian
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Re: Blocking filters and wintertime
I wonder how the Lunt heater attaches to the blocking filter, and since my scope is a Coronado will it work?
I have wondered about condensation too, since I have read reports of rust on Coronado blocking filters. Does Lunt have that issue?
And does the cold have an effect on the etalons?
James
I have wondered about condensation too, since I have read reports of rust on Coronado blocking filters. Does Lunt have that issue?
And does the cold have an effect on the etalons?
James
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Re: Blocking filters and wintertime
Re Blocking filter failures....
It's the built in ITF ( the front element) which fails.
Both the Coronado and Lunt ITF fail....due to temperature variation affecting the bonding/ seal and moisture ingress.
It's recommended that the blocking filters be stored in a seal container with silica gel when not in use......
It's the built in ITF ( the front element) which fails.
Both the Coronado and Lunt ITF fail....due to temperature variation affecting the bonding/ seal and moisture ingress.
It's recommended that the blocking filters be stored in a seal container with silica gel when not in use......
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Re: Blocking filters and wintertime
I have a small foam lined case just big enough to fit the blocking diagonal. Now to find some silica gel.
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Re: Blocking filters and wintertime
Hmmm
Some Lunt(?)(don't know about Coronado) users are mentioning on CN that the blocking filter seems to loose it's CWL at low temperatures...
Hence, I suppose Lunt marketing a $179 heater....
This is something I've never heard before...there will be some residual heat coming through the scope to warm the blocker (?) and what exactly causes the mentioned CWL shift?
See:https://www.cloudynights.com/topic/6747 ... ng-module/
Some Lunt(?)(don't know about Coronado) users are mentioning on CN that the blocking filter seems to loose it's CWL at low temperatures...
Hence, I suppose Lunt marketing a $179 heater....
This is something I've never heard before...there will be some residual heat coming through the scope to warm the blocker (?) and what exactly causes the mentioned CWL shift?
See:https://www.cloudynights.com/topic/6747 ... ng-module/
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Re: Blocking filters and wintertime
Hmmm
Found this reference:
""Change due to temperature
Temperature changes affect a filter's performance due to thermal expansion and contraction of the materials used to construct them. Most filters are designed and specified for operating at 23°C, and deviations from this value will produce peak wavelength shifts approximately linear with temperature. The exact shift coefficient will depend on the particular design wavelength of the filter, and, typically, ranges between 0.15Å and 0.20Å per °C at 4000Å and 8000Å respectively. Bandwidth and peak transmission changes observed are relatively minor, of the order of 0.01Å per °C and 0.013Å per °C respectively.""
See:http://www.ing.iac.es/astronomy/filters/shift.html
Found this reference:
""Change due to temperature
Temperature changes affect a filter's performance due to thermal expansion and contraction of the materials used to construct them. Most filters are designed and specified for operating at 23°C, and deviations from this value will produce peak wavelength shifts approximately linear with temperature. The exact shift coefficient will depend on the particular design wavelength of the filter, and, typically, ranges between 0.15Å and 0.20Å per °C at 4000Å and 8000Å respectively. Bandwidth and peak transmission changes observed are relatively minor, of the order of 0.01Å per °C and 0.013Å per °C respectively.""
See:http://www.ing.iac.es/astronomy/filters/shift.html
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Re: Blocking filters and wintertime
It was, I think, on the Cloudy Nights forum where I too read about blocking filters having issues with cold temperatures. Winter is coming so I will have to address this.
What does CWL stand for?
What does CWL stand for?
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Re: Blocking filters and wintertime
CWL = Central wavelength
This is important to register/ align the filter elements at the same wavelength.
This is important to register/ align the filter elements at the same wavelength.
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Re: Blocking filters and wintertime
That was my guess. Thanks Merlin
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Re: Blocking filters and wintertime
My Lunt LS80’s B1800 blocking filter begins to show effects at 45F, is noticeably worse at 35F, is not very good at 25F. A 3” dew heater solved the problem.
I have not measured whether it is a CWL shift or other induced aberration. The effect is loss of contrast and dimming.
I have a new B1800 so I am curious if it will also be affected by the cold.
George
I have not measured whether it is a CWL shift or other induced aberration. The effect is loss of contrast and dimming.
I have a new B1800 so I am curious if it will also be affected by the cold.
George
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Re: Blocking filters and wintertime
Thank you George. I need to know what to expect. And need to find a way to counter it. Fortunately winter days are not as cold as winter nights. In January where I live in the mountains of North Carolina we average a high of about 45 degrees in January. But still, below freezing days do happen. I gotta prepare for winter solar observing. In all ways!
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Re: Blocking filters and wintertime
The temperature of the blocker is important. You need to match it up with the etalon so that it will block the next peaks.
Air spaced etalons use an blocker that is 6-8Ang at the HW. If they are at 6563Ang at 23C for the CW. Then when it is 43C the CW has moved to 6566.3Ang into the red. So Now you maybe using the edge of the bandpass. The same works if it is cold. Instead it will be on the blue side by 3.6Ang. This can drop the transmission of the overall filter system. It is the same with solid etalons. You needs to match the blocker to the operating temperature of the etalon. At Ha the blocker moves almost twice as much in wavelength than a solid etalon does with the same temperature change. These numbers are for standard blockers.
Mark W.
Air spaced etalons use an blocker that is 6-8Ang at the HW. If they are at 6563Ang at 23C for the CW. Then when it is 43C the CW has moved to 6566.3Ang into the red. So Now you maybe using the edge of the bandpass. The same works if it is cold. Instead it will be on the blue side by 3.6Ang. This can drop the transmission of the overall filter system. It is the same with solid etalons. You needs to match the blocker to the operating temperature of the etalon. At Ha the blocker moves almost twice as much in wavelength than a solid etalon does with the same temperature change. These numbers are for standard blockers.
Mark W.
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Re: Blocking filters and wintertime
Mark,
Thanks for that.
I’d be interested to know what the operating temperature of the blocker is v’s ambient temperature during a normal observing session??
Ken
Thanks for that.
I’d be interested to know what the operating temperature of the blocker is v’s ambient temperature during a normal observing session??
Ken
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Re: Blocking filters and wintertime
This is very interesting as I always have a problem getting my Solarscope on band in February when it is usually around zero degrees, all through the summer it works very well but the frustration in February maybe that it is too cold. Interesting.
Alexandra
Alexandra
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Re: Blocking filters and wintertime
Alexandra, All,
I am curious how my Coronado SMII 60 is gonna do at freezing temperatures. It's coming. It would be nice to find an easy way to alleviate it.
All of what I have read is the cold temperature affecting the blocking filter. Does it have any affect on the etalons themselves?
James
I am curious how my Coronado SMII 60 is gonna do at freezing temperatures. It's coming. It would be nice to find an easy way to alleviate it.
All of what I have read is the cold temperature affecting the blocking filter. Does it have any affect on the etalons themselves?
James
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Re: Blocking filters and wintertime
Update,
So far winter temperatures have not been an issue with my Coronado BF 15 blocking filter. I have observed down to about freezing with it with what appears to be only a slight loss of detail. I have no trouble getting the scope on band above 42 degrees or so but still am able to when it is colder but with a little more difficulty. But still it seems to work. Not to see what happens when cold weather really hits. Hopefully it is not a big issue after all.
James
So far winter temperatures have not been an issue with my Coronado BF 15 blocking filter. I have observed down to about freezing with it with what appears to be only a slight loss of detail. I have no trouble getting the scope on band above 42 degrees or so but still am able to when it is colder but with a little more difficulty. But still it seems to work. Not to see what happens when cold weather really hits. Hopefully it is not a big issue after all.
James
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Lunt, Coronado, TeleVue, Orion and Meade eyepieces
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" Way more fun to see it! "
Orion 70mm Solar Telescope
Celestron AstroMaster Alt/Az Mount
Meade Coronado SolarMax II 60 DS
Meade Coronado SolarMax II 90 DS
Meade Coronado AZS Alt/Az Mount
Astro-Tech AT72EDII with Altair solar wedge
Celestron NexStar 102GT with Altair solar wedge
Losmandy AZ8 Alt/Az Mount
Sky-Watcher AZGTI Alt-Az GoTo mount
Cameras: ZWO ASI178MM, PGR Grasshopper, PGR Flea
Lunt, Coronado, TeleVue, Orion and Meade eyepieces
Visual Observer
" Way more fun to see it! "
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Re: Blocking filters and wintertime
As an additional info, the CWL drift with temperature also depends on the substrate (e.g. BK7 versus fused silica) and on the technology (soft coating versus hard coating).
Hard coating and BK 7 have a lower drift with temperature.
For example, 0.004 nm/°C for fused silica and hardcoating in near UV, versus 0.002 nm/°C for BK7 and hardcoating.
Hard coating and BK 7 have a lower drift with temperature.
For example, 0.004 nm/°C for fused silica and hardcoating in near UV, versus 0.002 nm/°C for BK7 and hardcoating.
Christian Viladrich
Co-author of "Planetary Astronomy"
http://planetary-astronomy.com/
Editor of "Solar Astronomy"
http://www.astronomiesolaire.com/
Co-author of "Planetary Astronomy"
http://planetary-astronomy.com/
Editor of "Solar Astronomy"
http://www.astronomiesolaire.com/
- Bob Yoesle
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Re: Blocking filters and wintertime
My gut is telling me that the original Coronado blocking filters may have been a bit more temperature stable. Then again I'm a lightweight and don't really enjoy cold weather observing in the middle of deep solar minimums, so my experience level may not be valid.
The OEM's face a tough niche competitive market, and cutting supply costs and reducing prices might have necessitated lower cost materials. Perhaps this is what has now led to the need to keep Lunt blocking filter elements warmer...
The OEM's face a tough niche competitive market, and cutting supply costs and reducing prices might have necessitated lower cost materials. Perhaps this is what has now led to the need to keep Lunt blocking filter elements warmer...
Diagonally parked in a parallel universe.
Curiosity is the father of knowledge; uncertainty is the mother of wisdom.
Dark-Sky Defenders
Goldendale Observatory
Curiosity is the father of knowledge; uncertainty is the mother of wisdom.
Dark-Sky Defenders
Goldendale Observatory