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Internal Heat Using Solar Mask

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#1 patindaytona

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Posted 17 September 2019 - 02:12 PM

I made a off axis solar filter of about 3.5" aperture. I found the sun was pretty bright. I reduced the aperture to about 1.5" instead and it's much better, but still pretty bright.

Is their any kind of concern about making an aperture "too" small? 

What about the heat generated inside my telescope with that mask covering the open end? I can barely touch my telescope it's so hot! Could it damage my primary?



#2 beggarly

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Posted 17 September 2019 - 03:02 PM

Did you use any kind of solar filter material ( https://www.baader-p...140x155-mm.html ) to cover the aperture? Or did you cut a hole in some material and leave it open?

https://www.telescop...rd=solar filter


Edited by beggarly, 17 September 2019 - 03:10 PM.


#3 photoracer18

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Posted 17 September 2019 - 03:19 PM

If you are just using a hole, depending on your type of telescope, you may have already done some damage or you are lucky you have not. Easy to damage a catadioptric type scope (SCT and MCT) or a Newtonian because all the light and heat hits the smaller secondary mirror. However an off-axis mask (what you made) can work if you use a Herschel diagonal so that the heat is taken out of the tube, although I don't recommend doing that even though I have been using those type of diagonals for close to 50 years. Otherwise you need some kind of solar material on the front to eliminate the heat before it gets into the tube. Refractors can work with any decent kind of solar device because no secondary mirror.

Cheap refractors used to come with an internal sun filter that went on the end of the diagonal or eyepiece. The lens cap had a reduction hole cap that was the only part you were supposed to take off to use this. I would consider that method potentially dangerous as it did not really reduce the heat until the limited light cone got to that little filter. Anything like that could burn the eye if something went wrong like the filter cracking from the heat.



#4 patindaytona

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Posted 17 September 2019 - 03:28 PM

Did you use any kind of solar filter material ( https://www.baader-p...140x155-mm.html ) to cover the aperture? Or did you cut a hole in some material and leave it open?

https://www.telescop...rd=solar filter

I used the Baader Film over an off axis aperture.  I wouldn't look at the sun through an open aperture!



#5 patindaytona

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Posted 17 September 2019 - 03:31 PM

If you are just using a hole, depending on your type of telescope, you may have already done some damage or you are lucky you have not. Easy to damage a catadioptric type scope (SCT and MCT) or a Newtonian because all the light and heat hits the smaller secondary mirror. However an off-axis mask (what you made) can work if you use a Herschel diagonal so that the heat is taken out of the tube, although I don't recommend doing that even though I have been using those type of diagonals for close to 50 years. Otherwise you need some kind of solar material on the front to eliminate the heat before it gets into the tube. Refractors can work with any decent kind of solar device because no secondary mirror.

Cheap refractors used to come with an internal sun filter that went on the end of the diagonal or eyepiece. The lens cap had a reduction hole cap that was the only part you were supposed to take off to use this. I would consider that method potentially dangerous as it did not really reduce the heat until the limited light cone got to that little filter. Anything like that could burn the eye if something went wrong like the filter cracking from the heat.

I can see how using the Baader Film over my off axis aperture is NOT causing heat to build up inside my telescope. Good.

But when i touch the outside of my metalic (xt10i) telescope it's pretty %$# hot! Maybe that is not a reflection on the temperature "inside" though.

Since reducing the off axis aperture, does that cause a lesser field of view to any particular eye piece?


Edited by patindaytona, 17 September 2019 - 03:33 PM.


#6 TimK

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Posted 17 September 2019 - 03:54 PM

I used a factory Off-axis solar filter built into a lens cover on a C-14.

With the flat black paint the lens cover got very hot.  The tube is usually in the shade but it does warm up considerably.

Since the filter blocks out 99.X% of the light I doubt the optical train is getting overheated.

Some folks use that Reflectix insulation to wrap the tube but I think a decent piece of white cardboard that extends over the edge of the front lens/cap by at least a few inches should solve the problem.

If it is a little larger it will even keep the observer in the shade!



#7 patindaytona

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Posted 17 September 2019 - 04:23 PM

I used a factory Off-axis solar filter built into a lens cover on a C-14.

With the flat black paint the lens cover got very hot.  The tube is usually in the shade but it does warm up considerably.

Since the filter blocks out 99.X% of the light I doubt the optical train is getting overheated.

Some folks use that Reflectix insulation to wrap the tube but I think a decent piece of white cardboard that extends over the edge of the front lens/cap by at least a few inches should solve the problem.

If it is a little larger it will even keep the observer in the shade!

I think about cars here in Florida. With the windows closed, it gets extremely hot inside because the infra red radiation is trapped.

I'm afraid it might be the same situation with the mask over the telescope end.

Maybe it might be a good idea to take off the 1.25" eye piece adapter quite frequently, but that would be a hassle at the same time.



#8 George9

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Posted 17 September 2019 - 04:52 PM

I am surprised that it is that bright at just 3.5" aperture. Are you sure you are using the Baader visual film and not the Baader photographic ND3.5 film? That would be dangerously bright.

 

But yes you are losing resolution by cutting to 1.5". Assuming everything is safe, better to use a Moon filter or a green filter or other ND filter to lower the brightness without cutting the aperture.

 

George



#9 Napp

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Posted 17 September 2019 - 05:18 PM

If you are using Baader film for visual it may well appear quite bright to you.  Baader film is known for a bright image.  But it is not bright enough to hurt your eyes.  I have one and it does appear brighter than the other orange filters I have looked through.  I have heard of someone adding a light neutral density filter to decrease brightness just for personal comfort.  I personally add a Baader Solar Continuum Filter not to diminish brightness but to enhance contrast.  However, it does turn the image green.


Edited by Napp, 17 September 2019 - 05:23 PM.

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#10 patindaytona

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Posted 17 September 2019 - 05:44 PM

I am surprised that it is that bright at just 3.5" aperture. Are you sure you are using the Baader visual film and not the Baader photographic ND3.5 film? That would be dangerously bright.

 

But yes you are losing resolution by cutting to 1.5". Assuming everything is safe, better to use a Moon filter or a green filter or other ND filter to lower the brightness without cutting the aperture.

 

George

Yes, quite sure it's the correct Baader Solar Film...i doubled checked and it is.

At this point, since i already constructed alot, I put a almost 3" aperture on it again.

Yes, i am considering the use of a Polarizing filter sometime in the future.



#11 patindaytona

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Posted 17 September 2019 - 06:07 PM

2.jpg 1.jpg

Got the ring from Michael's.  The tape i wrapped around it caused abrasion and started taking off black paint from the end piece of my telescope. I taped some softer material i found. Has one side aluminum foil, other side like baking paper. Works good now.



#12 NorthernlatAK

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Posted 17 September 2019 - 07:44 PM

Here's my full aperture filter made of posterboard, glue, and double-sided sticky tape. I wrapped about 4 layers of posterboard strips around the end of the ota with the tape and then glued the ring to the sandwiched filter cell. Works like a charm. The cellphone shot doesn't show the granulation visible though.

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#13 NorthernlatAK

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Posted 17 September 2019 - 07:45 PM

.

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#14 patindaytona

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Posted 17 September 2019 - 07:52 PM

.

Wow, that's great! I know what I can expect now.  When was this taken?

Another thing that seems hard to see is limb darkening.


Edited by patindaytona, 17 September 2019 - 07:53 PM.


#15 NorthernlatAK

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Posted 17 September 2019 - 08:02 PM

That was taken May 8th, the last time we had any significant activity. Visually I see the center of the disc as brighter than the edge. Handheld cellphone shots don't seem to do justice to what is seen.

#16 NorthernlatAK

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Posted 17 September 2019 - 08:12 PM

During brief periods of good seeing decent detail can be seen within the spots. These 2 drawings are a day apart and both show lightbridges crossing the spot and how they evolved in 24 hrs.

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#17 George9

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Posted 17 September 2019 - 08:15 PM

On my 10” DOB I use a full-aperture Baader film filter. At low power it is pretty bright so I would need an ND filter. But I am usually looking at high power and so the extra light is appreciated. I also have a 4” off-axis filter that I never use any more.

One rule of thumb is to keep the view no brighter than sunlit grass.

George

#18 NorthernlatAK

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Posted 18 September 2019 - 10:23 PM

There shouldn't be any significant heat going through the baader solar film. When the scope is pointed at the sun the tube shouldn't be exposed to sunlight due to the shadow of the edge of your filter. Perhaps before you set up, your scope was sitting in the sun? The XTi dark tube would heat up rapidly exposed to the sun... I setup quickly doing solar so my tube doesn't heat up. Seeing is better in the morning anyway before it gets hot out so try that maybe. As for brightness, try a ND or polarizing filter.

Edited by NorthernlatAK, 18 September 2019 - 10:24 PM.


#19 patindaytona

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Posted 19 September 2019 - 06:26 AM

There shouldn't be any significant heat going through the baader solar film. When the scope is pointed at the sun the tube shouldn't be exposed to sunlight due to the shadow of the edge of your filter. Perhaps before you set up, your scope was sitting in the sun? The XTi dark tube would heat up rapidly exposed to the sun... I setup quickly doing solar so my tube doesn't heat up. Seeing is better in the morning anyway before it gets hot out so try that maybe. As for brightness, try a ND or polarizing filter.

Perhaps it was in the sun a while beforehand....even so, until i check it again, seems that the filter mask alone isn't going to protect the entire telescope from being "sunbathed".

I know what you're saying though about the cast shadow if it's pointing straight at the sun.

It's just that the telescope is "enclosed" and that traps heat no matter what.

I'll do some more checking again later.

By the way, thought about using a small funnel (plastic you use for oil etc) just to be able to know the telescope is pointing at the sun (when it's light comes out of the funnel onto my hand)


Edited by patindaytona, 19 September 2019 - 06:27 AM.



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