UTA Baffle Questions

[skyraider]

So I need to make a new UTA external baffle for my scope (25"f4 Obsession). Currently I have a "thumbnail baffle" that extends 14 1/2" above the UTA, that covers 1/3 the circumference of the UTA, placed opposite the focuser. I am contemplating shortening it a tiny bit, but making it go all the way around the UTA. If I put my eye at the very bottom of the focuser and look all the way up, I can see just the tiniest bit above the baffle when it extends 12 1/2" above the UTA, so I'm thinking of making my new one 14" high AND having if goe ALL the way around. So two questions for y'all:
Would I gain any advantage by making it higher?
Do I gain any advantage by making it go all the way around the entire circumference of the UTA?
While I'm interested in any info on the subject, I would love to hear from people who have tried different forms of UTA external baffling.
And yes, the entire UTA is flocked.

Thanks for your help,

Josh Wright.

[lamperti]

Josh,
I assume you are a member of the Obsession Yahoo group. I had posted pictures of the baffle for the UTA of my 22"UC
https://groups.yahoo.com/neo/groups/obsessionusers/photos/albums/637231243

If not, let me know and I can either send you the images or you can see them when we observe at Blue Mountain next time.
Al

[Mark McCarthy]

Hi Josh,

You might avoid the thumbnail altogether by putting the baffle at the focuser. Mel Bartels has a calculator for that:
http://www.bbastrodesigns.com/baffle.html

Myself, I use a "original" style Astrocrumb filter slide which doubles as a focuser baffle. The slide has four holes, three of which are threaded for filters, the fourth is empty and can be positioned to act as a focuser baffle. The assembly might vignette a tiny bit of light from reaching the primary, but so little it's not noticeable. I haven't had any problem with stray light coming from above the UTA. Scroll down on this webpage to see it mounted on an Obsession style UTA.
http://www.astrocrumb.com/

Best,
Mark

[skyraider]

Thanks Al and Mark, I appreciate the help.

Al,
It looks like the amount of baffle you have added on your UC Obsession is similar to the amount of baffle already offered by the UTA on my Classic Obsession, so I'm again wondering about how much difference the external baffle makes. I don't mind overkill, but I don't want to have to deal with the extra weight and wind profile on my UTA unless it is justified.
Currently the distance from the center of my focuser to the top of my UTA is 7 1/2 inches which means I need my external baffle to extend 17 1/2" according to this. http://home.digitalexp.com/~suiterhr/TM/Topten.htm#06 I'm curious as to your thoughts.

Mark,
I'm nervous about putting anything inside my UTA (probably unnecessarily concerned, but a buddy of mine had a bad experience with hardware in his uta meeting his primary mirror), so I have never been filter slide fan . I can't picture exactly how to make/mount a focuser baffle, so any suggestions would be welcome. But again, I feel the less I have mounted in my uta the better.

Thanks,

[Bill Weir]

A focuser baffle is a simple thing. Thin rigid black plastic is all you need. Essentially cut a washer disc of it with the outer diameter being that which will wedge into the bottom of the focuser or parracor and the inside being the diameter you require to be at the clipping point of the light cone coming off the secondary. Then wedge it into the bottom of the focuser/Parracor. I was shown this by Gary Seronik and what one appears like can be sort of seen in this article of his. Zoom in on the bottom of the focuser in this scope conversion article and you will see the baffle. I believe there is also a link in the article to a baffle size calculator. If cut well to be a tight fit it won't come out. Mine hasn't in over a decade of use.

http://www.garyseronik.com/?q=node/189

Bill