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[Chicago Astronomer - Astro Joe]

Building a Solar Screen for the Venus Transit and other Sun fun

May 2012

I have been playing with the idea of building one of these "Solar Funnel" gizmos, for the Venus Transit and general Solar observation. But, after reading Chicago Astronomer Rich's recent build - it was the encouragement to get moving.

I, like others, chose to use the "Da-lite" material for this project...but wasn't too sure which to get. Light, dark...?

Dunno.

The pics are a general guideline, but it's the description that had more value for me. So, I got four 1 square foot samples, of different characteristics....



They arrived soon after I placed the order and rolled secured in a cardboard tube.

This sample is very thin and translucent.

Might be good for bright solar disk rear projections...maybe even lunar...?

This is a thicker fabric with a solid black backing. Probably reserved for larger aperture scopes and just may bring out deep penumbra detail.

This is a solid Grey on both sides. Uncertain on how it will perform.

I like this one.

It has a bright pearl sheen to it - almost satin-like. On the other side, it's a flat white. I have high hopes for this one.

There will be solar tests on each one of these within the week.

Updates soon.

[Chicago Astronomer - Astro Joe]

First raw tests on the DeLiite Screen materials...

This day brought sunny skies and the time to test out the four new "Delite" projection sheets and what they can do. I set-up the 90mm refractor and slipped in a 25mm 1.25 eyepiece - and set it aside. Other's have used the Funnel method for mounting thier material - and I though I might try it as well.

Using a funnel that is about 8 inches wide, I cut off the short tube and slipped it on the eyepiece itself....but being so close to the eyepiece, of course my solar disk was small and I feared some smoking. Using a cardboard tube, I extended the funnel away, but now I was getting some vignetting and I tossed it all aside - electing for some workaround.

This was just a preliminary test of the performance of the material anyway. I used an adjustable easel stand and crudely duct taped the sheets on to the stand itself and used my light pollution blocking mini umbrella to provide much needed shading...

I began the tests at 3 feet, delivering a nice big solar disk...

But I finally settled on a 16" distance from the eyepiece - a balance between size and brightness for the rest of the loose test.


Starting out with the #41470 - "Pearl"...

It displayed a decent front projection , but I felt the granulation of the fabric "softened" up the image and solar features. This is also a very bright reflective material, but I find that the details were softened by the fabric. The primary side of the sheet is highly reflective, but I preferred the "Backside" for projection, as the surface particles were smaller and providing a sharper image.


Next was the #36225 "DMBB"- Black side sheet...

This is usable only for front projection, as no light passes through the other side - which is good for this purpose. This is adequate, and the surface is very bright...but I have an issue with the surface granulation of the reflective particles softening the solar features. The surface is more "rough" textured than any of the others.


Next #79664 "Pearl"[/color]...

This material is slightly grey on both sides. It provided a moderate front projection image, displaying faculae, and deepened the sunspots nicely. But, poor for a rear projection attempt and not acceptable.


Finally the #81324 "DV"...

The "DV" material is very bright and good for Front Projection, but the "Good" side imparts a slight cultured-pearl like tan hue. The backside, still with reflective properties, is much preferred. The Faculae strand next to the smaller Sunspots grouping was easily visible. In rear projection, the disk remained very bright and displayed solar features very well.

- This was the winner of the test.

But, it wasn't a easy test, as each sheet had it's pros and cons. I layered the four together to get an idea of the direct comparisons of the sheets to each other....

Black backed #36225 at the top,
Pearl white/tan #41470
Dual View #81324
Pearl Grey #79664


Some sheets reflected a sheen, which interfered with the image somewhat and not a desirable artifact.

I had the pics filed with the numbers...but somewhere/somehow....the associated data to the pics got lost...I'm thinkinbg blown away before the end of the test...but here are the shots anyway...

Front Projection




Rear Projection




Front Projection on the Black Back sided sheet




Rear Projection




Rear Projection




Front Projection




Rear Projection




Front Projection




Rear Projection

These next two are Rear Projection shots with the "Dual View" sheet, which I feel wins out....




During my loose test, people stopped by and asked what I was doing, as they always do...

And I take time out to show them the solar surface, with aperture filter and projection. Some asked intelligent questions, after hearing about this massive sunspot grouping on the news.... while others...clueless...

Considering I had the Seymore Solar filter on, I thought I would grab some pics, but solar focusing was difficult...

Near the end of this test, which lasted about an hour, the aircraft activity kicked up...

...with a student pilot making banking passes over the area.

A more controlled test is in order for these Delite material sheets, especially for the rear projection set-ups. I also have an idea on a focusing aid for my solar pics.

But so far...the Dual View sheet is the best for Front & Rear projection methods.

[magic612]

Hey Joe,

Got any extra material I can buy off of you? I plan on joining you at Adler this evening. Let me know - if not, that's cool too.

Thanks!

[Chicago Astronomer - Astro Joe]

Dave,

Sorry man...alls I got is what you see here - four 1 square foot sample sheets still in the experimental stage.

[magic612]

Ah... bummer. Thanks for the heads up Joe! See you tonight.

[magic612]

Joe, I just got my screen samples today. I only tried the "DV" tonight, but it was amazingly simple, and worked far better than I expected. I literally went to the hardware store, found a long funnel about 16" - 18" long, but it was too narrow at the tip. So I cut it where it looked like my 20mm Huygens eyepiece would still fit inside, using a hacksaw.

Dropped the eyepiece in, pushed it snug. Took the DV film, wrapped it around the end and kept it tight/taut with a rubber band, and placed the eyepiece in the scope. After a bit of fiddling to get the image right, BAM! 6 sunspots, easily visible on the film - the same 6 large ones that SOHO shows right now.

Amazing. Too easy. I'm actually looking forward to trying some of the "non-see through" films, and find out how well the light will project onto the screen as a "front" projection set up. But that's for another day. My "Sun gun" works great! And if you only count the DV film and funnel, it was ~$10 to make it.

[-=CROMAN=-]

Excellent news Dave! I think every astronomer needs one or two of these on hand at all times! I was outside looking at those spots this afternoon myself.

[Chicago Astronomer - Astro Joe]

Dave...

Sweet!

Which samples did you get, other than the "DV"?

The "DV" is the champ of all screens I feel - where you can both practice front and rear imaging.

Got pics of your tests?

[magic612]

Rich, I have you to thank too! I had seen the "Sun Gun" years ago, but never went forward with anything. I'm glad both you and Joe worked on these; now I have extra "solar viewer" method in my arsenal.

Joe, I just got to work so I don't have the samples in front of me. I know that two of them were the same as yours, and I picked up two different ones just to try out something else that you hadn't, to see if there was something else that might work well. I didn't take any pictures (yet), but I certainly plan to and will post about it on my blog. I'll be sure to let you know when I do.

[Chicago Astronomer - Astro Joe]

Raw and Dirty testing of the Sun Funnel...and other Solar related testings...

The idea here is to use what I had laying around and try to build a Sun Funnel with the Delite fabric. My first prototype testing wasn't satisfactory with the red funnel and I set it aside. Using PVC piping, the "DV" screen sheet and a dirty long spout funnel. The funnel's long spout was too small to fit over the 1.25mm eyepiece, (25mm), so a lengthy piece was sawed off. The banged up PVC coupler piece, (from my old homemade 50mm binocular finder scope project), fits tightly and securly onto the eyepiece nicely - and I fit the funnel "over" the length of PVC pipe....instead of "into" the pipe - which encouraged "rocking" of the funnel and gross mis-alignment.

I experimented with the focal lengths needed to fill the wide mouth funnel opening, (about 6 inches), with as much of the solar disk that I could without the image dimming from extra length, vignetting of the tube or the disk swimming in excess fabric and too bright. Holding it all together temporarily with duct tape, (God's gift to mankind), I finally got the proper length down, after a couple of hours of cutting, trimming, adjusting and cutting again. Maria worked with me on this project and now ready for permanent assembly.

The screen will either be held on with an embroidery ring or most likely, a pipe clamp...(which are in abundance here at the estate.) The entire set-up will be sheathed in reflective mylar, both inside and out - to keep the image bright and the surfaces cool.

I think it will work well.

I also accomplished an experiment for solar focusing, which is very difficult during projection session - as the image is just too bright and the solar disk difficult to focus on...

From my old film DSLR days, I still had my focus test sheet that I used to test zoom lenses from a distance. Here, using a sheet of well worked on over spray backboard, I attached the focus test sheet and the Black backed Delite fabric and see if the idea had any merit.

Works nicely...

Sharply focusing the Sun's disk on the sheet with the 90mm refractor, I focused the camera sharply on the focus test sheet, which also brought the solar disk in focus...and with just a quick snap of a handheld camera, the disk came into detailed view. One side of the disk had already gone out of the FOV by the time I took the shot, but the test was good. It was much easier to focus on the focus sheet and get it spot on.

And...

I thought I would try out the C11's Full aperture solar filter...

First in tungsten white balance, then in daylight. Good detail and ready for solar events.

The Funnel project will continue over this weekend and updates as they occur.

[Paulie pchris00]

Joe, I took your advice and ordered the Dual Vision. It arrived today. Whew.