(Viewed 6,154 times)

[-=CROMAN=-]

I decided to put together a sun funnel today since I was at home sick. I had all the pieces here so I had a go at it.

Parts List:

1 - 17.75-inch ×5-inch ×5-inch (round top) Funnel

2 - Large hose clamp, 2.5-inch ×5.5-inch

3 - Small hose clamp, 13/16-inch ×1.5-inch

4 - Da-Lite High contrast rear projection screen

5 - Black electrical tape

6 - Small Hacksaw

7 - Sand paper ( med - corse grit ) which I did not have



STRIKE 1.....What I noticed was after I cut the funnel half of it was fatter on the inside than the other. This was not good! A nice piece of sandpaper would have been helpful here but I chose not to use it as this is a test run.

STRIKE 2.....The Da-Lite material I had in my garage had a bunch of rustlike spots embedded in it. This will not work as it will not provide a clear image to the viewer. I will order some fresh material from Da-Lite for the next run

STRIKE 3.....The hose clamps I had were about 1/2" to big so I had to compensate by making the tube under it a bit fatter with tape!

3 Strikes and your out right? Nah.... Test run so I forged ahead.

Here's a few pics for your amusement ;D






















Unfortunately the sun is hidden behind the rain this afternoon so the test will need to wait. Although the build quality is not the best I have a good feeling about it. I think I'll be able to work the bugs out of it and have a decent product after my new da-lite material is delivered.

The scope being used is a 60mm sears refractor with a FL of 900mm. The has a 20mm El Cheapo Huygens EP in place with any color filter. I do have an Orange filter on the way so the next iteration with have that installed.

This setup should give a sun about 3 - 3 1/2 inches in diameter to view.

[Chicago Astronomer - Astro Joe]

Rich...

This is good....and about the same thing I was going to do.

I think it will perform well when you get the kinks out and streamlined.

I was thinking about a larger set-up, something along the lines of a 5 gallon bucket thingy...

[-=CROMAN=-]

Joe...

I was considering the 5 gallon bucket as well. I think that would be a show stopper!

[Paulie pchris00]

Cool. The final version should be awesome, but a couple of cautions for anybody thinking about building their own Sun Funnel.

Skip the colored filter. You're going to be running concentrated sunlight through it. I see potential for melting here. Even if the filter holds up, el Cheapo eyepiece might not. I've melted the edges of the eyepiece I use for solar projection (now the only EP I use for solar projection). Even during the Venus transit, give the Sun funnel some time to cool off, and be careful not to track the Sun too long at one time. It would suck to have a ToV observation end just before second contact because of an EP meltdown.

I'm ordering my Da-lite screen Friday, so my project is coming soon.

store.cousinsvideo.com/95774.html

[Chicago Astronomer - Astro Joe]

Paulie,

I have perused "Cousins" site prior...and I feel it's the place to get this type of material.

But, are you sure the grey shade is the preferred select of your choices? I think, (just by viewing the sample colors on their site), that it may be too dark...?

It may increase contrast, but at the cost of brightness?

I dunno.

I was leaning toward this one first...

I like the "Brilliance" aspect of this hunk of material. If magnifying a section of the solar disk, it will dim - but this lighter surface may limit it.

And this one second...

I like the dual usage of rear & forward projection flexiblities. When I do direct projection on a serious solar public session, I have found that glossy faced photo paper is best for detail and brightness. I don't know how the grain on these materials are, but I hope they would reflect the details projected on them from either direction. My projection screen experiment earlier this month was a limited success, as the granular reflective surface scattered the projected light too much - softening the image.

I could even get both as a comparison.

But Rich.......which one did you get?

[-=CROMAN=-]

Joe,

I have a full blown da-lite rear projection screen, it almost covers the entire 2 car garage door in the summer. I project movies onto it for the kids in the summer. I also have a da-lite standard glossy. I used a piece of the rear projection screen for mine. I dont think you can use the glossy for the sun funnel though.

[Chicago Astronomer - Astro Joe]

Rich...

Which shade?

I'm anxious for you to test out the screen, then we can get an idea of the image of the screen performance.

[-=CROMAN=-]

Joe its a lighter gray than what is pictured on other sites. If the sun ever decides to make an appearance I'll be the first to let you know!

[Paulie pchris00]

May 2, 2012 1:19:50 GMT -6 Chicago Astronomer - Astro Joe said:

Paulie,

I have perused "Cousins" site prior...and I feel it's the place to get this type of material.

But, are you sure the grey shade is the preferred select of your choices? I think, (just by viewing the sample colors on their site), that it may be too dark...?

A fair question. My only answer is that it was the specific shade referenced in the first article I saw on building a Sun Funnel.

transitofvenus.nl/wp/observing/build-a-sun-funnel/


At one time I had looked through other shades, also wondering if this was too dark. My biggest concern with a lighter shade was eye safety. For all of my future public solar sessions, I would like to stay away from direct eyepiece viewing as much as possible, and especially when anticipating big crowds like for the Venus transit. I worried that too light of a screen might be letting too much sunlight through, and perhaps isn't as safe. I figured a darker screen would help to absorb sunlight, and be somewhat safer. Even if the image suffers slightly, I think the trade-off in safety is worth it.

Maybe sometime down the road I can experiment with different materials, but for the transit, I'm going with the screen I linked to above.

[-=CROMAN=-]

im only going to use 2 of three. You are welcomed to the other 20mm if you want it?

[-=CROMAN=-]

I've ordered a square foot of cousins to compare with the stuff I had on hand. If mine burns up then we'll know!

[RobbW]

I, too, plan on building a sun funnel for the Venus transit. I'll be working with the U46 Planetarium here in Elgin. I will be using my C8 SCT during the transit, of course. I was planning to stop down the aperture of my scope using the DIY Baader solar filter mask I made a year or so ago. I'm wondering how much dimmer the projected image will appear on the Da-Lite material using my solar filter than if I didn't stop it down? My reason for using the solar filter is I've heard of bad things happening to people who do full-aperture solar with an SCT. I want to avoid any potential damage to my scope.

[Chicago Astronomer - Astro Joe]

Robb....

The combo of the stopped down aperture and the rear projection method...might really dim the solar disk some - but this is speculation without actually having used a Da-Lite sheet. Rich's upcoming funnel experiment will provide us with a guideline.

But....

I recommend a full aperture solar filter for unmatched sharp detail on the solar disk, but understand the desire for a wider-public friendly viewing experience.

[-=CROMAN=-]

The da-tex performs flawlessly. Highly recommended

[RobbW]

I just placed an order for 4sq.ft. of Da-Tex. Can't wait to build my own sun funnel. Where did you get the "official" funnel from? Just any auto parts store? Where have you seen instructions on building a 5-gallon bucket version? Wouldn't that make your scope fall down and go boom?!?!

[-=CROMAN=-]

Robb.. Walmart on randall road. 2.69

[erikruud]

May 8, 2012 22:56:31 GMT -6 RobbW said:

Where have you seen instructions on building a 5-gallon bucket version? Wouldn't that make your scope fall down and go boom?!?!

I guess that all depends on how you mount it.

There is this idea: Sun-In-A-Box

Or this: Son-Of-A-Gun

It's not a bucket, but I really like this one: Top Gun

[erikruud]

Joe, do you know anything about this?
www.sunguntelescope.com/ADLER.html

[Chicago Astronomer - Astro Joe]

Erik...

Negative.


I have not seen seen anything resembling the "Sungun" in our inventory of scopes.... but I have not been in the Doane Observatory in quite awhile...so maybe, it's in there.

I'll check.

But, the link is quite mysterious and no data.

[erikruud]

If you click the "Return" link it will take you to the main page.

It looks like he has donated them to 4 other institutions as well.

[-=CROMAN=-]

Here is a link to my public dropbox page. I have some images utilizing Build #2 of the sun funnel. This funnel has an 18mm meade plossl.

www.dropbox.com/sh/rr4j0urftwu1lgc/nZBl9AK2nY

[Chicago Astronomer - Astro Joe]

Erik,

I inquired about the "Sungun" at the Adler....and we do indeed have one.

It arrived last week, but has yet to be tested out.

I think that I will put it through it's paces and evaluate it for the C.A.

[erikruud]

Cool!

[-=CROMAN=-]

Awesome! When do you think testing will begin?

[Chicago Astronomer - Astro Joe]

Dunno.

Early next week perhaps?

[RobbW]

Rich, have you tried the sun funnel on your C8 at all? I'm just wondering about the size of the Sun's disk when using a larger-aperture scope. In your pics, you're using a 60mm refractor. The full disk of the Sun is visible on the projection plane of the funnel. I'm trying to figure out how cropped the image will be on my C8. I know it depends on what FL eyepiece I use. However, the calculation I have seen to match the best size EP with the scope and sun funnel gives a 42mm EP size for my scope. I do not have a 42mm 1.25" EP. I have a 42mm 2" EP that I rarely use, but not a 1.25". I'm wondering if I would be better off trying to build a bigger sun funnel than trying to find a 42mm 1.25" EP. I have 5mm, 16mm, 26mm, and 32mm EPs that I can use. How large would I have to make the sun funnel in order to fit the full disk of the sun using one of those EPs?

[erikruud]

I thought that solar projection of this type was a bad idea for SCT's and MCT's due to the heat build up.

[RobbW]

It can be, Erik. That's why I will be using an aperture mask on my C8. Basically, I have the dust cover for my C8 with a 2.5" off-center hole cut into it . Additionally, I have Baader solar film applied over that 2.5" off-center hole. I have no worries about overheating my SCT. On the contrary, I'm kind of concerned that I may be stopping-down my C8 too much and making the image too dim.

[RobbW]

I just remembered that I also have a Celestron f/6.3 focal reducer I can use on my C8. This should shorten my scope's focal length enough to make the full disk of the Sun visible on the funnel using the 32mm EP.

[erikruud]

May 15, 2012 20:48:43 GMT -6 RobbW said:

... On the contrary, I'm kind of concerned that I may be stopping-down my C8 too much and making the image too dim.

I would agree, especially with stopping down and filtering both. I don't think I have seen anyone use an objective filter with projection at all.