23 replies to this topic

[MazzifLOL]

I was looking at doing a solar filter.  Id like a 2" threaded that I can use in my filter drawer or filter wheel.  Im not seeing one.  Am I missing something here or do they just not make one?

Thanks in advance,

[Notdarkenough]

Solar is very different than celestial observing. The heat from the sun will cook unprotected gear and eyes. So, no guessing. Specifically, what optics are you looking to incorporate? Binocular? SCT? Dob/Newt?

[gstrumol]

The reason you can't find any is because they are incredibly unsafe to use and should have been banned many years ago. The heat from the sun's nearly focused rays will potentially crack the filter letting the concentrated light directly into your eyes. That will cause blindness (in the worst case) or at a minimum real damage to your retina.

 

I speak from experience. When I was a child I got a telescope that had one of these. I took the scope out in the winter and at one point I screwed it onto an eyepiece and tried to view the sun. While I was trying to locate it (by the minimum shadow method) I heard a sharp 'crack' and could see the top of the EP glowing. The filter had cracked from being cold and the heat of the sun's rays. If my eye was there before the crack .... You get the picture.

 

Stop looking for one. Don't do it. Period.

 

If you want to look at the sun in white light use either a Herschel wedge at the end of a refractor of less than 5" aperture, or place a solar film filter over the front of the scope (any type).

 

Gary

[maroubra_boy]

+1 what Gary said.

I bought a new small refractor as a gift for a nephew & opened it before giving over the gift specifically to remove & bin the sun filter that came with it.

A stupid & dangerous device that some retail outlets, such as eBay, ignore the pleads to remove & ban these from being sold.

 

You have a 10" Newt - think about the massive amount of energy that scope would be putting through such a device - you really think a 2" filter would handle this?

 

Now a 2" aperture filter would be enough for safe viewing & photography with a 10" scope - a full aperture filter is not required with the Sun.  These are white light filters showing nothing more than sunspots & some surface granulation.  Be aware though that if the intention is to photograph solar prominences, filaments, etc, a Hydrogen Alpha solar scope is required.  There is also an Hydrogen Alpha filter from Daystar the fits before the eyepiece of an ordinary refractor, their Quark, but these are also specialised bits of gear made expressly for safe viewing and photography.  I have the Prominence model that I use with an ED80 refractor.

Alex.

Edited by maroubra_boy, 05 February 2023 - 03:25 PM.

[MJB87]

Moving to Solar Observing and Imaging for a better fit.

[vincentv]

The closest thing to what you suggest is the herschel wedge. It substitutes a refractor's diagonal.

Here's the kicker: 90%+ of the energy is sent to a heatsink. The rest is dealt with using an ND3 filter, like a moon filter but darker.

Point is that absorbing 99.999% of the suns energy in a delicate glass is calling for trouble, as others have noted.

[MazzifLOL]

+1 what Gary said.

I bought a new small refractor as a gift for a nephew & opened it before giving over the gift specifically to remove & bin the sun filter that came with it.

A stupid & dangerous device that some retail outlets, such as eBay, ignore the pleads to remove & ban these from being sold.

 

You have a 10" Newt - think about the massive amount of energy that scope would be putting through such a device - you really think a 2" filter would handle this?

 

Now a 2" aperture filter would be enough for safe viewing & photography with a 10" scope - a full aperture filter is not required with the Sun.  These are white light filters showing nothing more than sunspots & some surface granulation.  Be aware though that if the intention is to photograph solar prominences, filaments, etc, a Hydrogen Alpha solar scope is required.  There is also an Hydrogen Alpha filter from Daystar the fits before the eyepiece of an ordinary refractor, their Quark, but these are also specialised bits of gear made expressly for safe viewing and photography.  I have the Prominence model that I use with an ED80 refractor.

Alex.

I appreciate all the feedback.  My intended purpose is for casual EAA and intro into solar imaging.  A white light filter would be fine to start.  I have tubes in the 50mm, 61mm, 66mm, 81mm, an 8" and 10" newt.  I see the solar film type aperture covers, but all my OTA utilize a filter drawer.  Just seemed more user friendly to find a 2" that could interchange between OTA as with any of my other filters.  I do not own a single eyepiece.  Visual other than through a display isnt for me. 

[Battlestamps]

I appreciate all the feedback.  My intended purpose is for casual EAA and intro into solar imaging.  A white light filter would be fine to start.  I have tubes in the 50mm, 61mm, 66mm, 81mm, an 8" and 10" newt.  I see the solar film type aperture covers, but all my OTA utilize a filter drawer.  Just seemed more user friendly to find a 2" that could interchange between OTA as with any of my other filters.  I do not own a single eyepiece.  Visual other than through a display isnt for me. 

You'll need a solar filter that fits over the front of the OTA of each scope you want to use for solar. What you're asking for - a 2" solar filter for a filter drawer doesn't exist and it doesn't exist for good reasons other folks already went over above. The 1.25" "Sun" filters that do exist are just straight up dangerous to scopes, cameras and eyes alike.

[gstrumol]

I'm not sure we got through folks. It does raise an interesting question, though. Could the focused light from the sun burn out a $1000 camera's imaging chip? And if so, how long an exposure would be needed? 

 

Oh well, that's a silly question as no one would risk that ...

Edited by gstrumol, 05 February 2023 - 07:21 PM.

[MazzifLOL]

Got it, don't ask questions.  Noted for future reference. 

[Zhengyi]

If you want the ability to interchange between scopes, you need to get a Herschel wedge, either 2" or 1.25". However, the wedge can only be used on refractors.

[jwestervelt]

a 12" scope will collect almost exactly 100W of energy from the sun.  that energy has to go somewhere.  ideally, a majority would be reflected back to space via an objective-mounted filter... but a herschel wedge will do the job by reflecting a majority of light into a heatsink, but only on a pure refractor design and never on a reflector/cassegrain/etc.

to elaborate on the preceding comment, the reason you can't use a wedge on a reflector is because the secondary mirror is close enough to the focal plane that it will overheat from the sun's energy.  you have to reject the energy prior to the primary on a reflector, so aperture-mounted is the way to go.  

[EsaT]

I appreciate all the feedback.  My intended purpose is for casual EAA and intro into solar imaging.  A white light filter would be fine to start.  I have tubes in the 50mm, 61mm, 66mm, 81mm, an 8" and 10" newt.  I see the solar film type aperture covers, but all my OTA utilize a filter drawer.  Just seemed more user friendly to find a 2" that could interchange between OTA as with any of my other filters.  I do not own a single eyepiece.  Visual other than through a display isnt for me. 

8cm magnifying glass collects enough sun's energy to make wood start smoking after few seconds and ignites it fast.

10" aperture gathers almost 10 times as much energy.

 

Only filter which could take that would have to be made of some kind "thermal superconductor" (well, diamond is pretty good) and have big heatsink.

[fishonkevin]

Thousand Oaks makes their 48mm Solarite film filter.  And sold by Agena Astro.

 

https://agenaastro.c...ilter-48mm.html

[Notdarkenough]

Got it, don't ask questions.  Noted for future reference. 

The concern isn't  your question, it is your proposal. I am sure you can find "something" to do what you want. We are trying to tell you how dangerous what you want is for your eyes and gear. Look for a post or two about beginning solar observing, or see an Observing Guide on Celestron's site about it. Solar work is wonderful and you can get some excellent pics too. However, anything small will fail and burn up you camera. 

 

If you are really serious about imaging the sun, read up, plan, and understand what types of gear will show which layers of the gas mass that is the sun. White Light filters are the most basic, and belong in front of the OTA. Other filters include an Energy Rejection Filter out front and then something else before the eyepiece. I use my 8" EdgeHD and to do so safely I needed an ERF and the Daystar Quark Chromosphere directly in front of the eyepiece. There are many excellent threads in the Solar Forum. Start there.

[rblackadar]

8cm magnifying glass collects enough sun's energy to make wood start smoking after few seconds and ignites it fast.
10" aperture gathers almost 10 times as much energy.
 
Only filter which could take that would have to be made of some kind "thermal superconductor" (well, diamond is pretty good) and have big heatsink.

Not quite a fair comparison because the focal length is much longer -- image at the focal plane is a disc, not a tiny spot. Still, it's hot enough to melt plastic, as I once unwisely discovered, and likely to fracture glass. (I was an idiot to try the plastic, but luckily wise enough not ever to put my eye to it.)

Also, can we just note, 10" is kind of a ridiculously large size (for a DIY solar scope with neutral filter of any kind) given the practicalities of daytime seeing. Something like an ST80 with full-aperture filter would make more sense.

[jwestervelt]

another point here is that if image quality is a concern, putting that much heat into a glass element is likely to induce optical effects... be it astigmatism from uneven thermal expansion of the glass or turbulent airflow inside your OTA.  So yes, there are people chiming in here about safety, but even if safety were disregarded, there are other matters which call the endeavor into question because there are better and less expensive ways to solve the energy rejection problem.

[eblanken]

Hi All,

 

Sometimes a "simple question" has dangerous implications.

 

Sometimes people on Cloudy Nights read right past the Original Poster's (OP) intentions and genuine curiosity and "flame him or her" instead of being helpful. This seems to be the case for this post. Can we just turn down the volume of the retoric and help this OP ???

 

I am going to try to answer this "innocent" question with my limited knowledge and experience:

 

(1) Controlling the energy that one allows to enter the Optical Tube Assembly (OTA) is important. The sun "illuminates" each square meter of the earth's surface with about (in round numbers, people) with about 1,000 Watts/ Square Meter. This is an average in the middle of the day.

 

(2) One should calculate how much in Watts can enter the scope. The average external filter reduces the energy by 100,000x (ND 5.0), so the amount that is processed by the OTA becomes safe and manageable. This external filter is what I recommend for the OP.

 

(3) There are three basic types of external filters that can work "out front" with a Newtonian Telescope: (A) Glass, (B) Milar Film & © High Quality "thin film" like the Baader film that people who care about preserving the resolution & quality of the image that the OTA provides at night.

 

(4) There are "sub-aperture" filters like one poster (vincentv) has mentioned like the Herschel wedge. These filters are not recommened by me for a person like the OP. These filters offer "the best" Quaity and Resolution when used with a HIGH QUALITY REFRACTOR, but I would not recommend these to the OP. They are for people who want "the very best" and are willing to pay a premium and live with the technical challenges inherent in this "best" approach.

 

(5) If one calculates "how many suns" are present from the front of an OTA to the focal plane, one can see that it is unwise to do what the OP "proposes" inherent in the question asked (the way it is asked). Say I have a 10 inch refractor that is f/10, so the focal length is 100 inches. At the input to this system we have "1 sun" as a reference point. Now halfway down the tube, that becomes like a 5 inch diameter, so the "number of suns" is more than at the input to the OTA (like 4 x more, right ???). so a 10 inch scope can "Swallow" (10/2*10/2* PI) SQUARE INCHES. and at the halfway point there are (2.5 * 2.5 * PI) SQUARE INCHES, right ??? So, to carry this forward, at the 2 inch filter "drawer" we now have 1 * 1 * PI SQUARE INCHES that have to process the same energy that was collected by the 10 inch input to the system. If I didn't make a mistake doing this math in my head, I get 100*PI divided by 1*PI = 100 suns at the 2 inch filter, right ??? This energy density is OK for a Hershel Wedge (maybe just barely, LOL !!!), but would be inappropriate for a secondary mirror of a Newtonian Reflector, in my humble opinion.

 

(6) I would suggest that "easing into solar" for the OP is wise and prudent. Start small with one of your smaller refractors and protect that with an external filters that safely mounts on the front of the OTA. I usually start with a glass filter (from a supplier like Orion or Thousand Oaks). This will get you a pleasing and safe view (usually in yellow/orange light) at the eyepiece of a small refractor. After you have this experience. You can try the Baader film and appreciate the added quality that this gives you, but also experience what I call "the down sides" of the (TRUE COLOR of our closest star) in "white" light (including some UV & IR, that you probably don't want and should address before that light gets into the eyepiece and into your eye.

 

(7) After you get this down, you can buy a "SOLAR CONTINUUM FILTER" and see an even better quality view in "a weird green color", that may or may not please your brain. Once you have all this down, then and only then should you consider the Hershel Wedge. That's my advice. 

 

Edward A. "Ed" (aka eblanken) Blankenship

Edited by eblanken, 07 February 2023 - 12:40 AM.

[eblanken]

Hello again,

 

I appreciate all the feedback.  My intended purpose is for casual EAA and intro into solar imaging.  A white light filter would be fine to start.  I have tubes in the 50mm, 61mm, 66mm, 81mm, an 8" and 10" newt.  I see the solar film type aperture covers, but all my OTA utilize a filter drawer.  Just seemed more user friendly to find a 2" that could interchange between OTA as with any of my other filters.  I do not own a single eyepiece.  Visual other than through a display isnt for me. 

 

Another approach if you don't own an eyepiece and don't want to ever look thru one, is to go stright to the Baader film (ND 5.0). These come in various sizes. I would start with one of your smaller refractors and try the Baader external filter that works with that refractor size.

 

Link for example: https://optcorp.com/...BCABEgJzq_D_BwE

 

and add to your collection of 2 inch filters the following: (1) a UV/IR, (2)  Baader Solar Continuum Green, (3) A good quality 30nm H-Alpha (4) Sodium Yellow, (5) Orange, etc.

 

Ed

 

P.S. Tell us more about your imaging camera (Mono or RGB Color, etc.). Can your filter "drawer" allow you to "stack" filters ??? (for example can you stack a UV/IR and a Green Filter and an Orange filter ???). What filters do you already own ???

 

P.P.S. Don't forget to keep sunlight out of your finder. I recommend something like this: 

 

https://www.telescop...er/p/102778.uts

Edited by eblanken, 07 February 2023 - 01:27 AM.

[jwestervelt]

There is also a concern that someone is going to do a search based upon a desire to do something similar, see milquetoast "nah, don't do that bruh" responses, and then not be discouraged because people didn't put the fear of jesus into the OP, and by that token, anyone who should later stumble across the thread.  

In other forums, sure... but in the solar observation forum, safety is a major concern.  I'm not saying to roast people for the sake of roasting, but don't mistake a firm rebuke as a petty flaming.  Some of us like this forum and would rather avoid seeing it shut down due to legal/safety concerns.

[eblanken]

Hi again to All,

 

There is also a concern that someone is going to do a search based upon a desire to do something similar, see milquetoast "nah, don't do that bruh" responses, and then not be discouraged because people didn't put the fear of jesus into the OP, and by that token, anyone who should later stumble across the thread.  

In other forums, sure... but in the solar observation forum, safety is a major concern.  I'm not saying to roast people for the sake of roasting, but don't mistake a firm rebuke as a petty flaming.  Some of us like this forum and would rather avoid seeing it shut down due to legal/safety concerns.

 

I agree 100%, and I see the need to balance the direct response to the OP with the much more general posting to the wider audience.

 

I am an Engineering Scientist with 45+ years of experience in high technology and three college degrees. I forget that some people just do a Google search and assume that what they find is "good-to-go" for them too. 

 

So, SCARE THEM FIRST and answer their question after is a better approach, I guess ?!?!? I vote for educating them at some point.

 

Best regards,

 

Ed

 

P.S. I see that the moderator moved the post here into the Solar Observing and Imaging Forum from somewhere else.

[jwestervelt]

P.P.S. Don't forget to keep sunlight out of your finder. I recommend something like this: 

This...

I saw someone with a proper filter over their objective, and I caught him just as he was about to absent-mindedly put his eyeball up to the finder... might not have resulted in permanent eye damage since it was only a 20mm finder, but that would be a horrible way to ruin your eyesight.  besides, you also have to worry about onlookers who might not know better and who might try to sneak a peak. 

[gstrumol]

Amateur astronomy is generally a safe hobby. Sure, you might injure your foot if a counterweight slips off from a GEM mount, or strain your back if you attempt to lift too much weight by yourself. You might even sprain an ankle stepping in a hole while moving around under extremely dark skies. These are the risks we sometimes take while pursuing our hobby at night.

 

But viewing the sun is a whole other thing. It's very different from viewing any other object in the sky, and requires very special equipment and considerable knowledge of the steps to make it safe. It is our duty, our responsibility to make sure people understand those dangers because the consequence of not understanding could be permanent blindness. Viewing the sun is not achieved by simply turning a filter wheel.

 

We all encourage questions here. Ask which is better: a wedge or a front filter? What's the difference between a glass filter vs a film filter? How can I see prominences off the sun's disk? We'll give you advice and point you in the direction for more information. But when someone's eyesight is in danger (not necessarily the OP's but anyone else who might have glanced at the idea of adding one to their color wheel and thought 'that sounds convenient') we must put down that idea strongly. We're only looking to protect you from a mistake that could be permanent.

 

Gary

[jwestervelt]

I honestly feel that there should be a giant disclaimer on this particular sub-forum, and maybe even a checkmark that must be read and ticked the first time a person seeks access to it which basically indemnifies the site and encourages the user to seek advice before doing anything they are planning to do which involves uncertainty when viewing the sun.  sometimes relatively small changes which seem logical and harmless can come with disastrous consequences.

there is a reason your telescope and mounts come with warning labels and your Go-To controller will give you a gentle reminder every time you slew to the sun...

On a somewhat related note, I thought at one time that there is room in the market for a device which can be placed in an EP holder that measures total IR, visible, and UV irradiance that is coming through your optical train that can alert on unsafe or uncomfortable levels.  

Edited by jwestervelt, 07 February 2023 - 12:38 PM.