S.H.O. Coronagraph test/development jig.

[Astroman]

Well, here it is, such as it is.

I highly recommend against trying this yourself, until you gain experience with this sort of thing, do years of research as I have, have spent as much time as I have viewing the Sun and building instruments to do so.

It's kind of ugly, but works for what it is. The scope on the left will collect and focus the Sun's light at a point between the two scopes. At the focal point, a lens, essentially an EP lens, will change the light path to parallel. It will then encounter the first cone-shaped occulting disk, which will block the intense solar light, leaving just the light from the corona. Another occulting disk, called a Lyot Stop will further reduce light and scattering and pass the coronal light into the second scope which will in turn behave in the usual way with an EP at the focal point. I find the focal point of the coronal light by physically moving the second scope forward and backward, and by moving the occulting disk forward and backward. It's all up in the air at the moment, but we're under development.

[GazOC]

Looks like a great way to burn your eyes out if you don't know what you're doing....

Very interesting AM, I've never seen one of those before. Keep us posted!!

[Astroman]

I highly recommend against trying this yourself, until you gain experience with this sort of thing, do years of research as I have, have spent as much time as I have viewing the Sun and building instruments to do so.

Here's an illustration on the occulting disk setup. Further refinements are being studied, but you get the idea, I hope.

O1 is the first telescope objective.

F1 is the first eyepiece lens.

O2 is the second scope objective.

So far, the sun's image from the first scope is ~5mm across at focus. The occulting disk will therefore be made at least twice that size to begin and adjusted accordingly.

[barkis]

I think your warning is very apt AM. Only an expert with loads of knowhow would attempt work of this nature with an optical bench like that.

I am sure you have more sophisticated plans laid out for the final instrument. I hope you keep Rosie well away from this sinister looking contraption. I hope you have a fail safe device, such as some Semtex that will blow the first objective if any stray light gets past the occulting disc.

I know full well you are a very capable guy, but I hope no one attempts to copy what you do.. It looks more dangerous than your Tesla rigs.

[Kaptain Klevtsov]

So you actually look down this with your eye? I don't like risking more than a webcam in my PST! Take care AM, it looks very dangerous indeed. I am wondering what happens when the dust settles ever so slightly under one of your chairs, or if the rig slides along the chair arms?

Kaptain Klevtsov

Remember kids, don't try this at home.

[Astroman]

Thanks for your concern, guys. This is only the test bench I referred to in another post. (Didn't want to hijack it.) It's ugly, but it'll work until I get the specifics down. Then, I'll do a proper job of engineering to make it safe as a baby's bottom. Uh, no, safe as sitting on your mother's lap. Yeah, that's it.

Ron, Rosie's excited and wants me to finish it ASAP, along with the spectrohelioscope, the HA telescope, buy a PST...She's hopeless. I like it. BTW, isn't Semtex somewhat dangerous too?

KK: Yes, you look through this with your eye. It's designed to simulate a total solar eclipse, and allow views of ONLY the corona. The occulting disk takes the place of the (somewhat spurious) Moon to block the bright solar disk.

[Ryachu]

Does the occulting disc have to dissipate a lot of heat ?

[barkis]

BTW, isn't Semtex somewhat dangerous too?

Only if your blind when it goes off

[Astroman]

Does the occulting disc have to dissipate a lot of heat ?

Not as much as I'd thought, originally. As the Sun's image at focus is ~5mm, (not cm as I posted first), the heat is distributed over that area. The cone shaped occulting disk appears as a circle through the optics, but adds ~3x the surface area for heat sinking. I had in my head an elaborate heat sink scheme at first, but the cone solves the machining problems.

Good question!

[Kaptain Klevtsov]

So would it be best as a shiny cone then? I'm assuming that the "spare" light will get thrown away between the two 'sope like objects in your photo.

Kaptain Klevtsov

[Solar B]

Mmmmmmmmm....Total Eclipse....Anytime....sounds great....when you,ve made and tested it all....will you sell it to me....

When observing the sun i tend not to warn experienced astronomers as the vast majority of people will use their common sense.

Baader used to make a coronagraph http://www.cloudynights.com/item.php?item_id=38 i don,t think it,s still available.

Brian

[Astroman]

Hadn't thought of color or lack thereof for the cone yet, KK. Need more research, but offhand, I'd think something of low reflectivity would be better to prevent stray light. The entire contraption will be enclosed when completed, with maybe a heat sink feature fed through the box where the cone is. (Maybe, that's down the road a bit.)

Brian: No. I won't sell it to you. Maybe a new, improved model, once the kinks are worked out. Price is negotiable. :shock: I put a warning in everywhere because there are a lot of new people through here. Better to keep them safe, but yes, if I'm giving a talk or something to people I know are experienced, I may just give it a quick, "Don't try this at home" and call it good.

[Kaptain Klevtsov]

I was thinking from a heat transfer point of view AM. If the thing is shiny (low emissivity) it won't absorb the heat much, whereas if its black it could get really hot. I suppose you really need something like a Newtonian secondary blasting out of a hole in the side of the instrument? That would be very awkward to get the right shape though I imagine.

I'm guessing that having a hot bit inside the instrument would cause some tube currents which would degrade the image a lot, and it might also cause some differential expansion which would move the disc out of position. Re-aiming would alter the heating effect and move it again.

Obviously I'm only guessing here, but heat transfer is what I do for a job, so I'm interested.

Kaptain Klevtsov

[Astroman]

I understand your points, KK. And very good they are. Early tests have shown there's not that much heat to dissipate. I have considered where the heat will go, as well as the light. I'm thinking something like a brushed aluminum finish so the aluminum will dissipate the heat, but the finish will scatter the light rather than reflect too much. I'm sure there will be a hole for heat dissipation, but haven't considered tube currents much yet.

I'll keep you posted.