hey doubles observers (rod)

[ving]

what would this be like?

http://cgi.ebay.com.au/micrometric-KELLNER-31-SOLAR-OBSERVING-EYEPIECE-by-LOMO_W0QQitemZ7583803989QQcategoryZ 3636QQssPageNameZWDVWQQrdZ1QQcmdZVi ewItem

[Rodstar]

Ving, doesn't look much good for doubles observing....more a solar observing EP.

I had a chat recently with Ausastronomer about filar micrometres and reticle EP's. If you are thinking of investing in one, he is a good sounding board.

New, filar micrometers are as much as $1,000 plus. Celestron's reticle is better than Meade's apparently. They each cost around the $200 mark (AUD). I think I might bide my time, given the cost. :P

[ving]

got a link so i know what they look like?

[Merlin66]

You can use a small crystal of iceland spar mounted in an eyepiece to get measures of distance and direction of close doubles .. there was a site in France?
I have some materials and a prototype set-up, can supply details.
Much easier than a filar and very cheap!

[ving]

cool... got details/pics?

[Merlin66]

Just google on iceland spar micrometer and you'll see a reference to Brayebrook Observatory.... worth reading. I have construction details at home, won't get to them until early Feb. So read up in the meantime. I can supply ( free!) a sample of iceland spar to get you started.

Brief summary:
The crystal produces a double image of the double star(!!??) the images are produced a fixed distance apart (depending on the thickness of the crystal, say 3 to 5 sec arc) so you can "estimate" distance by comparison. By rotating the eyepiece you can line up the two sets of images, this then gives the position angele.!!

[ving]

thanks sir! :D

[ving]

had a read.... interesting. i have no idea how i'd go about making one, but interesting :)

[Merlin66]

The attached extract is also of interest. Mybe some of the "smarter" memebers of the forum can validate the theory.

[ausastronomer]

Hi David,

The links and info Merlin gave you may be very helpfull.

I would be happy to chat with you at Lostock (ru going ?) or the next time we meet at Kulnurra about this. Also happy to chat on the phone if you wish.

What I can tell you in advance however is that to undertake astrometric measurements of double stars, the moon, planets etc you need an accurate "tracking" mount. To do the job in textbook fashion it should really be an accurately polar aligned equatorial mount. A dob is no use here unfortunately. I know you are considering another scope and maybe this new found observing pursuit should be factored into your pending scope purchase ?

CS-John B

[ving]

yes and no john.... the new scope is just something to take when i go away with the family... cant pack my dob and family, not enough room...

that said, i have an EQ mount for my dob (an EQ dob?) which tracks in RA only. I may inthe future look into Dce tracking too for it.

[ving]

what sort of file iis it? :(

[Merlin66]

I've re-saved as a doc file.

[ausastronomer]

David,

I didn't realise you had purchased an EQ mount for the dob, what mount have you got ? RA tracking is all you need. A Dec drive would make life easier, but is not essential.

CS-John B