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[Chicago Astronomer Joe]

Telescope Aperture Solar Filters

I have been looking into solar filtering for awhile now, and Chicago Astronomers are gearing up for the June 2012 Venus Transit with projection and filter ideas and equipment.

Film or glass, blue, neutral white or orange, off-axis or full aperture....it's all about preference. I'm going to do my best, (as as much as I can afford), to test out various types of filtering. I got six months and the material/equipment will be cheaper now, then when the Venus transit hype takes off.

Primarily, the search will be for a suitable filter agent for the C11 beast. Full aperture I think - as limiting the aperture for off-axis viewing, (is good), but steals the magnification and resolution power of any given scope - I don't care what anybody says... Atmospheric & OTA turbulence and secondary obstruction is often quoted against full aperture filtering - but if so, I'll have the option to cut down the usable surface with suitable blocking as the need arises with a full aperture set-up.

No film or filter will be wasted, as there are finders, smaller scopes and binoculars to protect for solar observation.

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My first selection is the "Seymour" Solar filter sheet...

At 9"x10", it's large enough to make several test caps for my optics. It's a black material, providing a Yellowish-Orange tint to the disk. Pleasing to the eye, but I understand that this skew to the red part of the spectrum cuts out other wavelengths - primarily the blue...where the sharp definition lays. Granulation and faculae may not be as sharp, but with free shipping...the price is right.

If suitable then I'll order a full 12x12 ($18.00) for the C11 and make a suitable cell holder.

They do have both Off-axis and full aperture rings already made...

If I like this film, I'm seriously thinking about the $179.00 full aperture filter...

Details when it arrives, but the search continues for affordable solar filtering...

[Paulie pchris00]

Dec 20, 2011 3:38:00 GMT -6 Chicago Astronomer Joe said:

I got six months and the material/equipment will be cheaper now, then when the Venus transit hype takes off.

You have 168 days, 2 hours, 5 minutes.

But I'm not counting or anything...

[Paulie pchris00]

Good luck with the search, btw. Full aperture on the C11 is probably overkill, but would be totally freaking awesome overkill. The benefit of full aperture would be much improved resolution at high magnification. I'm not so sure that high mag would be the best way to observe the transit, but with solar max coming up, I could see that it could be useful to tease out fine detail in sunspot groups. You would be compromising by magnifying the imperfections in seeing conditions, but that's always the case. As you said, it is all about preference, and I know you're well aware of the trade-offs involved (there's always a damn trade-off when it comes to astronomy).

[Chicago Astronomer Joe]

Agreed on the trade-offs.

On overkill...the Solar Telescope mirror in Arizona is 5.25 feet. They like it and I figure that 11 inches is cool.

With full aperture, I could highly magnify sunspot clusters, pick out individual granulation cells and with the Venus transit - perhaps view the tear drop affect closely.

I can devise some sort of adjustable shutter-like window to adjust the aperture and control light.

It's an enjoyable experiment.

[Paulie pchris00]

5.25 ft. solar telescope. Why? Not to collect more light, but for higher resolution.

Full 11" aperture filter for the C11. Why? Higher resolution.

I think I might be coming around to your way of thinking. I only used about 2"x2" for the 4.5" Newtonian solar filter. I haven't touched the material since. Now I'm starting to think it would be good to do full aperture for the 6" Dob. Or if I need to conserve material, maybe mask off the inside half inch, and make it a 5" filter. My secondary mirror obstruction isn't very big, and even 5" will give me much better resolving power than the offset filter for my 4.5". I want to try the full 6" if I can. I've seen the dark cores and lighter penumbras of big sunspots, but don't have the resolving power to really pull in greater detail than that. I'm hoping that with a bigger filter I'll be able to get in tight on sunspot groups, and maybe even pull in the faculae surrounding them. And, of course, there is the black teardrop for the Venus transit, and just before that, maybe even see the crescent of Venus's atmosphere during ingress. A full aperture solar filter might not be such a bad idea.

[Chicago Astronomer Joe]

I say do it!

You can always aperture down, but I think the added opening will enable you to kick up magnification without dimming.

We have a few months to experiment with. I got an email stating that my filter was on the way...but still not here.

Dang!

[Chicago Astronomer Joe]

My Filter came in...

Took longer than I expected, but with C.A. Paulie counting down to the Venus Transit, I felt comfortable with the delay.

It arrived in a sturdy flat and stiff envelope...

Carefully using a razor knife, I cut the clear tape bond and flipped open the two flaps and slipped the film and instructions out...

One side is glossy and the other rather flat - and looks like a X-Ray plate. It is not stiff like a film negative, but as floppy as a page from a magazine - (.002" thick).

No pin holes that I could make out, but again, I'm writing this pre-view at 3:00 am. Taking that into consideration, I examined the closest thing I had to the Sun here at the Chicago Astronomer desk - a 100 watt incandescent light bulb...

I could easily make out the glowing filament without strain or uncomfortable glare. The sheet did get warm, absorbing the radiation from the bulb. I assume it will get rather warm out in the full Sun.

I tried to scratch off the coating/material with my fingernail, but it rebuffed my attack. I used the razor blade to scratch a minute area near a corner - and it did show the scratch marks...but no material flaked off.

The instructions are pretty basic and lead you to a website to make a filter cell. They recommend to make an off-set axis for anything larger than a 8" scope, but do not explain why. More than half of the instruction sheet is dedicated for user safety and usage.

But...I'm going for full aperture gusto...

I will do some preliminary solar viewing on the next sun filled day.

Updates soon.

[Paulie pchris00]

Dec 30, 2011 3:20:02 GMT -6 Chicago Astronomer Joe said:

Took longer than I expected, but with C.A. Paulie counting down to the Venus Transit, I felt comfortable with the delay.

I will try to make my countdowns sound much more urgent. 158 days, 7 hours, 44 minutes, 30 seconds will be here before you know it.

Dec 30, 2011 3:20:02 GMT -6 Chicago Astronomer Joe said:

Carefully using a razor knife, I cut the clear tape bond and flipped open the two flaps and slipped the film and instructions out...

You are brave, sir.

When I made my first filter, I pulled the film out of the sleeve just far enough to cut. The leftover material hasn't even come close to seeing light of day, nor will it until I am ready to cut again.

Looking forward to the report.

[patrickm]

Joe,
Are you not worried about heat build up?

Paulie,
didn't you melt something in a smaller scope?
p

[Paulie pchris00]

With no filter, I had a cheap eyepiece start melting within seconds trying to use my Dob for projection. A full aperture filter should be just fine.

[Chicago Astronomer Joe]

Patrick,

At first, long ago when C.A. Robb brought this up about a solar filter for his C8, I did not like the idea of solar light bouncing around in there in a sealed tube. Projection ok for refractors, but reflectors can build up too much heat.

But, I have that dual reading temp gauge installed on the C11 already - and during it's first dry run, will monitor the internal heat with the filter secured on. I suspect there will be just a bump in the temp.

I think it'll be ok.

[patrickm]

Joe, I forgot about your thermostat! Brilliant!

Paulie...not so brilliant.

[erikruud]

I following in your footsteps on this one Joe. My sheet of Seymour Solar Film just shipped.

[Chicago Astronomer Joe]

Erik...

Today...I'm going to do some preliminary solar shots with filter and camera alone.

Should be good.

Pics soon.

[Chicago Astronomer Joe]

Erik encouraged me to take a quick and dirty shot of the Sun through the Seymour Solar filter just now...

Peering with both eyes through the filter, I could clearly see the Solar Disk through my trees. Grabbing the Canon, I held up the filter to the lens, set it at infinity, clicked to manual and shot a couple of frames at ISO 800/f3.5/12x optical zoom...

Processing them now, I think I can detect a Sunspot?

Checking Spaceweather.com...

....there she is...1389.

For a sloppy hand held shot...not bad.

Perhaps later, a scope test, but for now...I dig the filter... #Thumbsup#

Thanks for the nudge Erik!

[Paulie pchris00]

The solar filter gives an orange tint?

[Paulie pchris00]

I have had no luck so far imaging the Sun with my solar filter.

I have 154 days, 5 hours, 32 minutes to figure it out.

[Paulie pchris00]

Nothing like the first sunny day of the year for a little solar testing. Did not go well. Something is wrong with the SD card in my digital camera, and I've wanted to test some redundancy measures, so I tried getting solar images with a webcam. The results were even worse than I've been able to get so far with my point and shoot digital camera.

First, the webcam was overwhelmed by all the sunshine, not to mention the glare from yesterday's dusting of snow.







Second, just as I posted the other day, using my laptop outside in the daytime really requires some sort of shade. I could barely see the screen. It was just about impossible to focus the webcam in those conditions.


Third, when I tested webcam imaging of the Moon last summer, it did not go well. Whether held to the eyepiece, or trying to find prime focus without an eyepiece, nothing turned out as recognizable lunar features. Today's imaging of the Sun was even worse. I'll have to go back and look at the threads on webcam imaging later.

Here's how bad it was.




The only thing discernible is the yellow tint from my #12 filter.




Without a colored eyepiece filter, my solar film gives a bit of a purplish-blue tint, which doesn't look nearly as noticeable in the eyepiece as it does here.




Struggling to see my laptop screen.


Oh well. It was fun to have my first light of 2012, and I still have 154 days, 3 hours, and 20 minutes to figure out my solar imaging problems.

[Chicago Astronomer Joe]

Paulie,

Yes...the Seymour filter displays the disk in a orange-yellowish hue.

At the Adler, we use the glass Baader full aperture filters that show the disk in a white hue, but I always throw in a yellow filter on the eyepiece for contrast and more importantly...interest. The public is quite bored with a white disk and granulation is difficult to discern. A lot of "Oh..is that all?" is often heard at the plain white disk...especially during the long sunspot minimum we all experienced.

The yellow color brings some visual interest and brings to life the "Yellow Sun" of Superman.

But...both type of filters provide different aspects in viewing, as each is dominant in the different section of the spectrum. The orange play in the longer wavelengths - (570/590 nanometers) and the white in the bluish shorter wavelengths - (475 nanometers). Each focusing at different parts of the solar playfield.

Personally...I dig the orange hue of this filter...and I feel that the general public will too.

[-=CROMAN=-]

From today. My webcam had some bad artifacting. I think the sensor is shot



www.youtube.com/watch?v=k24jhZEZyoI&feature=youtube_gdata_player

[Chicago Astronomer Joe]

Rich,

I dig that vid...just a nudge in focus.

There are also six UFOs in formation.

Look to the skies.

[-=CROMAN=-]

Joe... I had taken off the corrector plate to adjust the protostar flocking and may not have put it back exactly. The ufos are due to the "brand new" webcam sensor going bad! such is life.

[Chicago Astronomer Joe]

Rich,

On the edge of the corrector plate, there should be some I.D. Markings.

They should correspond to to those on the mirror - which are at approx. at 2 O'clock...for proper orientation.

[-=CROMAN=-]

Joe, I looked for thise the first time I took it off. No marks! I went by the cork placement.

[Paulie pchris00]

Joe, it's definitely nice to have a yellowish or orange hue to the solar image. My solar filter delivers n image that is very white. Even for my own use I use a #12 yellow filter. I could live without it if I had to, but it does lend a pleasantness to the observation.

Rich, even with the sensor going bad and focus problems, that's not a bad effort. I can easily recognize those as sunspots. How did you have the webcam attached? I have to be doing something wrong, or using an unsuitable webcam. If all goes well, I will have a true astronomical camera soon, and the webcam will be unnecessary. It's good to have redundant capability though.

[Chicago Astronomer Joe]

Preliminary Seymour Filter pics....

It's such a bright sunny day this January afternoon...and quite warm - in the low 50's!

(End times I say.... )

I figured to take advantage of the semi-clear day and do some test shots with the new Seymour filter. I keep everything, 'cause you know...it'll come in handy someday. Layin' around are these plastic holders I took off a bulky projection television that a friend was throwing out. They originally held the colored filters, (R,G,B), merging the three guns and projecting the image onto the screen.

They looked like something I could use and just kept them in a bag...

With a little filing, this one holder fit nicely into the dew shield of my 90mm refractor finder scope. I cut off a square piece of filter and temporarily taped it to the inside of the holder, popped it in with a friction fit...and I was ready.

My trees were in the way, so I had move about 25' to my neighbor's garage and set-up the scope. My neighbors came out to see what I was doing and I shared their first view of the Sun, talking astronomy and how Pluto got the shaft...

This last one was the best of the lot, as visually - it's rather easy to focus, but through the camera, it's mighty difficult...

But I did manage a couple of decent close-up shots...

Nice Penumbra and smaller sunspots. 1391 at the upper left - 1388 & 1389 at the lower right.

I did not notice any faculae or granulation, but again I was only using the 90mm and a 25mm/17mm 1.25" eyepiece.

Perhaps with a Crayford focuser I can achieve prime focus, but I can't see definition in the LCD screen. But, the filter works fine and some more experimentation is called for.

I shall order a large sheet for a full aperture filter on the C11 for better resolutuion and focus...see what happens. But I would l; like a Baader white-light filter as a comparison, which I think are somewhat cleaner and sharper.

And the holder?

With some adaptation, they will work just fine... ;D

[jeremy]

I really am enjoying this thread and pictures. So inspired I ordered a filter for my Dobs which is arriving on Wed! Plus Orion has them on sale right now which helped. I figure they might be in shorter supply the closer to the transit we get, so better get it now. Now if we can hold these warm and clear days until it arrives...

[Chicago Astronomer Joe]

I was looking at the Orions as well for a full aperture solar filter and leaning that way as well.

They are glass, which I like - but they also impart a yellowish tint to the image too. I like C.A.Paulie's white light filter, bringing in the full spectrum, and then filtering with a yellow or orange filter at the eyepiece.

But either way, get them now...as I see many types are now "Backordered".

[Chicago Astronomer Joe]

Here is what I boiled it down to.....

The key is economical/affordability and these are ok within the Chicago Astronomer's budget -

Thousand Oaks Full Aperture Glass Solar Filter


Long before the solar observing revolution began, there was Thousand Oaks Optical. Founded more than 30 years ago, Thousand Oaks Optical products now fly above the Earth in NASA's Space Shuttle and serve on the ground for users such as ABC, BBC, CBS, NBC, NOVA, The Discovery Channel, National Geographic and most major universities and observatories throughout the world. Originally located in Thousand Oaks, California and open for business in 1979, this small staff of dedicated professionals have produced literally tens of thousands of solar filters over the years. No wonder millions of solar observers world wide know the Thousand Oaks Optical name!

Thousand Oaks Solar Filters are an observing standard. The Thousand Oaks Type 2+ Glass solar filter was created from high quality hand selected glass which is in turn coated with the exclusive metallic Solar II Plus - simply the most durable on today's market. Thin layers of vacuum-deposited nickel and chrome are applied on the inside surface of the glass substrate, keeping the coating shielded from damage during use. Thousand Oaks Solar II Plus coatings reject 99.999% of the solar energy spectrum - from ultra-violet to infrared. This ensures complete safety for both your eyesight and your telescopes optics! The glass filter elements are then placed into a polished friction-fit spun aluminum cell which is custom tailored to your telescope's outer aperture diameter specifications. A wide exterior cell band is then lined with supplied self-adhesive felt strips for a secure fit. This design helps to prevent heat from building up inside the telescope tube, protecting its exterior and interior components. No danger of a cracked mirror or eye damage... If handled with care, your Thousand Oaks Solar Filter should last a lifetime! Providing a aesthetically pleasing yellow-orange solar image against a black background sky, your Thousand Oaks Type 2+ Filter will show dark umbra and dispersing penumbra sunspot regions, as well as convection-cell granulation on the Sun's surface.

Thousand Oaks Solar Filters Features...

Wide exterior cell band.
Custom self adhesive felt liners for a perfect fit.
Most durable coating available on today's market.
The safety of this product is guaranteed by ensuring the coating has a transmission of 0.001% or less.
All solar filters are covered by a limited liability warranty from defects in material and workmanship.

Here, although glass....I would assume is the same type of black film materialappearance that the Seymour film is made from. At $109.00 and free shipping - looks good....but....

It briefly mentions a 4" Off-axis...and leaves it at that. The images of the filter show full aperture filtering. Needs a call to verify.

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Description

Kendrick "Baader" Astro Solar Filters are full aperture filters (some are "Off Axis" type, if indicated) for all the most commonly used telescopes in amateur astronomy.

The cells are aluminum and all have three nylon thumb screws to facilitate a secure fit on the front of your telescope. The filter material itself is the famous BAADER AstroSolar Film.

This film has set a new standard for white light filters and gives a very pleasing and high resolution image. The image color is a bluish white.

Optical quality: This highest precision film consistently produces strehl ratios of 94 to 96 percent at interferometric tests - thus it performs optically like a Fluorite Triplet Lens by Carl Zeiss or Astro Physics (Interferometric test results).

With Baader AstroSolar filters the Sun appears in it's real color - Neutral White. Other films and most glass filters produce a blurry Bluish or Reddish Solar image, thereby cutting part of the spectrum. Especially with an Orange Sun, it is very hard to see faculae regions which are visible predominantly in the Blue wing of the spectrum.

Eye safety: AstroSolar is essentially free from pinholes, since - other than with even the most expensive glass filters - it is coated on both sides, so that the chance of two pinholes overlapping each other is extremely faint. Baader AstroSolar safety film has been approved for eye safety by the National Bureau of Standards in Germany, the PTB. Unlike any other Solar Filter on the market, AstroSolar is CE-tested according to EG-Norm 89/686 and EN 169/92 ( notified body 0196). All processes connected to this product have been thoroughly tested. Coatings are inspected constantly for consistency to ensure your eye safety!

With a Baader Astro Solarfilter you are set to see the Sun's hidden grandeur at a fraction of the cost for comparable equipment. Real professional solar work was always restricted to a few dedicated amateurs who would put up the $1000 or more for a real precision 1/20 wave glass filter or 2" Herschel wedge.

The development of AstroSolar was only possible due to the incredible demand during the 1999 eclipse. Dozens of miles of film were destroyed during tests to produce the tooling and process techniques to receive an absolutely uniform molecular structure for the substrate. Not to speak of the related treatments, annealing and dual side coating that the film undergoes until it has attained the desired properties.

Here, at $79.00 and free shipping, it's a deal. It is the near-full spectrum white light filter that I desire, and it's a Baader - but it is not glass. Just a preference over functionality. And again, it mentions a Off-axis configuration and leaves it at that - with the image showing a full aperture filter.

A call here is required as well.


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A must-have filter for safely observing the Sun through an 11" Schmidt-Cassegrain telescope without damaging your eyes

Solar filter with a 12.31" inside diameter fits snugly over your telescope's front aperture to block 99.999% of incoming sunlight
Glass elements are machine-polished and triple-coated with nickel-chromium stainless steel

Each Orion telescope solar filter is mounted in a foam-lined aluminum cell featuring three equidistant securing thumbscrews, 4x 1/16" thick adhesive foam tabs, and 4x 1/8" thick adhesive foam tabs for customized friction fit to your telescope

Note: All Orion solar filters are designed for use with an adequate friction fit attachment. Thumbscrews should ONLY be used to keep filter securely in place once a friction fit has been achieved


Who said you have to be in the dark to do astronomy! Turning your telescope to the Sun is fun and educational. Watch the march of giant sunspots, the clouds of glowing vapor in the photosphere, and solar "granulation" detail. But be sure to protect your precious vision with a safe Orion solar filter! Looking at the Sun without one, even for an instant, can permanently damage your eyes.

Superior to Mylar
These full-aperture optical glass filters deliver superb views of the Sun, without risk to your eyes. While more expensive than Mylar filters, Orion solar filters provide better contrast, a more natural yellow-orange—color rather than blue—and are more durable. They’re ideal for photographing the Sun too.

The glass elements are machine-polished and triple-coated with an advanced nickel-chromium stainless steel alloy for a scratch-resistant surface. The filter passes only a fraction of the incoming light, rejecting harmful ultraviolet and infrared radiation.

Each Orion filter is mounted in an aluminum cell that slide-fits over the front of your telescope. Size shown in the chart below is the ideal diameter of front of telescope; filter will fit diameters up to 1/4" smaller with foam tape liner supplied.

At $119.00 + shipping, it's one of the most expensive filters, but it is glass and I like the heft it has. We use these at the Adler Planetarium and I like them. But if dropped...they shatter quite easily...as we discovered when one of the temp goofs dropped a 6" aperture one.

A decision will be held of until I can get some more concrete data if the two here are indeed full aperture or off-axis types.

[Chicago Astronomer Joe]

While deciding on what full aperture filter to get, I was thinking about the possible consequences of having an expensive piece of equipment unprotected in the broiling sun.

Safe enough I'm sure, but I do plan to conduct solar sessions in the coming year and that heat beating down is insidious - and hot metal not great to touch, (as is cold metal.... ).

So, like C.A. Paulie, our Solar Czar, I'm planning ahead. I have seen instruments protected by aluminiumized Mylar...and ordered this...

I'm thinking about wrapping the OTA and mount in this Mylar while it's set-up during the daytime sessions. It will certainly keep things cool and might even look cool too! And it will keep the heat transfer from the outside migrating to the interior- helping to keep the build-up low - knocking down the equilibrium time to stabilize temps for the evening's star parties.

It would even make for a good Exterior Dew Shield wrap, slowing down the heat loss around the Corrector Plate and fending off the dew longer.

(I do intend to use the mighty Astrobrella for some much needed shade for Chicago Astronomers working daytime sessions. I don't do open session in the Sun for extended periods of time... )

Cheap insurance for positive gains.