Posts Made By: Joel Elliott

Fellas,

Alrighty, here's a good 'un. I was browsing the D&G website earlier this year and saw something that keeps me wondering. They've gotten up a line of long-focus refractor doublets, no news there, but now they can render them in rather long focal ratios. Even f/30!
So - let's imagine you had a way to mount up two 10 inch f/30 tubes in a giant binocular system. The spread would be about 550 inches or so, under the way I'd do it in my obviously deranged mind. This crazy idea has been dogging me all year. Math Guys: Is this wide enough to render a 3D image of the moon, parallax-wise?
I know that binoviewer owners report 3D like images all the time, but clearly this is an illusion. Good for them, and I mean that nicely. But seriously though, how wide a spread would it take to get a parallax rendered, genuine 3D image of something about 300,000 miles away?
Does anyone know the math involved in such a computation?

Nuts in NC,
J. Elliott

Especially the one of the Eagle nebula. Wowweee! Boys, where will we be ten years from now? Man, these pictures are unbelievable.

http://sbig.com/sbwhtmls/gallery.htm

Fellas,

Been quite a while since I posted at Astromart. I used to get into the scrums back on the old site, before the redesign. Six years ago or so.

I've been dreaming about a long focus refractor for a long time, and might build one next year. D & G has had long ratio doublets listed for several years now, at not unreasonable prices. I'm not ready to buy and haven't wasted their time asking about availability yet.

I have in mind a sloooowwww doublet. Depth of field for holding focus and natural magnification for planets. I've dreamt up a folded mount to hang onto a 6", but would love to go wild with an 8".

Of course, more length than necessary is only more headaches in the mounting.

What might I expect to find, image-wise, with these four choices, please:

1) 6" f/25
2) 6" f/30
3) 8" f/25
4) 8" f/30

And since we're dreaming, a 10" f/30. Too much residual color? Not in the budget but curiosity beckons.

By the way, do slow ratio lenses tend to be figured better? It seems to me there'd be more wiggle room for getting the shape and possibly smoothness worked out.

I thank you all for your time.

Regards,
Joel Elliott

Fellas,

Howdy again, after such a long break I seriously doubt anyone remembers me. I was an Astromart junky way back on the original site, before the current design. I went cold turkey after spending waaayyy too much time online.

Nice to stop by again.

I'm dreaming about a long focus refractor in another thread, but would really like to build a set of binoculars from the 102 mm f/6.95 ED doublets being featured in several scopes right now. I'm talking about Stellarvue, AstroTech, etc. You've seen them.

I've been to Markus' site and don't see them. Tried Gary Hand and none there either. Does anybody have access to these objectives alone, not as OTA's?

Thank you,
Joel Elliott

Dear Jim,

I've caught about half of this contentious thread, having read the bulk of the replies about two weeks ago. I'm bowing out of completing the saga, but I do have a thought or two. Curiously, I'd considered sending you an email similar to what I'll say below. You've been thrown a tarbaby, fer sure.
One, I think your aggravation will wear off in time. I got dragged into a heated set of volleys on a machinist board last year. It stank, and regardless of what I said and how much effort I put into 'getting things straight' it didn't work out too well. Internet dialog has some serious weaknesses, inherent in the medium, once folks verge away from simple and happy statements. You can't win at this game, it's in the format itself.
Secondly, I think you were dead-on right when you challenged the claims of 1/4 wave optics at F/4 in largish mirrors. As any regular reader of astronomy literature knows, there has been a long-running effort to debunk the flourishing claims of mirror sellers and makers. You are hardly the first fellow to throw down a gauntlet and have the folks making the claims back it all up with proof that the rest of us can understand. Hopefully, you won't be the last.
This all presents a marvelous opportunity for someone who actually IS making large, fast mirrors holding an excellent figure to get up and wave his arms around. Show us the proof! You'll be verified as expert at mirror-making if you can reliably produce 16" plus primaries that cut the mustard. And without any trepidation regarding published testing procedures.
Jimbo, good luck to you. Come on back around sometime. There hasn't been anything new here. It'll pass, and soon you'll be able to sleep again.