Baffle question (re-post) and building an ultra-light-bucket

Maybe I've ended up in too many killfiles, maybe no one has a suitable
answer, but I'm asking this again just in case it fell below the radar.

What's the downside of using baffles that follow the 75% light cone, as
opposed to using baffles of all the same diameter?

Thanks,
Stephen Paul

"Stephen Paul" wrote in message
...
Maybe I've ended up in too many killfiles, maybe no one has a suitable
answer, but I'm asking this again just in case it fell below the radar.

What's the downside of using baffles that follow the 75% light cone, as
opposed to using baffles of all the same diameter?

Stephen,

I'm baffled. What is the 75% light cone?

I think you're kind of stuck with a Newt, since the light goes down the tube
before it hits the primary.

Clear skies, Alan

"Alan French" wrote in message
...
"Stephen Paul" wrote in message
...

What's the downside of using baffles that follow the 75% light cone, as
opposed to using baffles of all the same diameter?

Stephen,

I'm baffled. What is the 75% light cone?


Heck if I know, exactly in context... that's why I'm asking g. The _Newt_
software has a checkbox for "Fixed diameter baffles". I'm contemplating
baffling my 12.5" Starfinder Dob, and want to know what are the downsides to
fixed vs. not fixed. If you deselect the option (and "follow the 75% light
cone"), the baffle openings decrease in diameter as you approach the
primary. If you select the option, they are all the same diameter as the
front baffle.

-Stephen

"Stephen Paul" wrote in message ...
"Alan French" wrote in message
...
"Stephen Paul" wrote in message
...

What's the downside of using baffles that follow the 75% light cone, as
opposed to using baffles of all the same diameter?

Stephen,

I'm baffled. What is the 75% light cone?


Heck if I know, exactly in context... that's why I'm asking g. The _Newt_
software has a checkbox for "Fixed diameter baffles". I'm contemplating
baffling my 12.5" Starfinder Dob, and want to know what are the downsides to
fixed vs. not fixed. If you deselect the option (and "follow the 75% light
cone"), the baffle openings decrease in diameter as you approach the
primary. If you select the option, they are all the same diameter as the
front baffle.

-Stephen

If you choose "75%" baffles (i.e., fixed baffles = off), each will be
tend to be different from the others and therefore it will be more
work to make them. Fixed diameter implies standardization, although
perhaps lower performance.

The 75% light cone represents the distance from the optical axis where
the illumination has dropped to 75% of the max possible. Below this
number the vignetting is said to be more obvious, although YMMV.

"Stephen Paul" wrote in message
...

"Alan French" wrote in message
...

I'm baffled. What is the 75% light cone?

Heck if I know, exactly in context... that's why I'm asking g. The
_Newt_
software has a checkbox for "Fixed diameter baffles". I'm contemplating
baffling my 12.5" Starfinder Dob, and want to know what are the downsides
to
fixed vs. not fixed. If you deselect the option (and "follow the 75% light
cone"), the baffle openings decrease in diameter as you approach the
primary. If you select the option, they are all the same diameter as the
front baffle.

Stephen,

Thanks. I got the general idea from your post, and then W. Snell gave the
full explanation.

Clear skies, Alan

Hi Stephen:

"Stephen Paul" wrote:



Heck if I know, exactly in context... that's why I'm asking g. The _Newt_
software has a checkbox for "Fixed diameter baffles". I'm contemplating
baffling my 12.5" Starfinder Dob, and want to know what are the downsides to
fixed vs. not fixed. \

Newt is a wonderful program, but in my opinion, the whole baffling
function is terribly misguided. It's not that it's wrong exacatly,
it's just that if your scope is otherwise properly built, the baffling
strategy Newt encourages amounts to a lot of work for nothing.

As immodest as this might sound, I'd recommend digging up my article
on the subject, "Newtonian Baffling Made Easy," which appeared in the
April 2001 issue of Sky&Telescope. It's also available through the
S&T archive on the Web site, www.SkyandTelescope.com if you don't have
that issue at hand.

Follow the steps outlined there and you won't need ring baffles.

Regards,

Gary Seronik

(Remove the "z" for my actual e-mail address.)

wrote in message
...

Newt is a wonderful program, but in my opinion, the whole baffling
function is terribly misguided. It's not that it's wrong exacatly,
it's just that if your scope is otherwise properly built, the baffling
strategy Newt encourages amounts to a lot of work for nothing.

As immodest as this might sound, I'd recommend digging up my article
on the subject, "Newtonian Baffling Made Easy," which appeared in the
April 2001 issue of Sky&Telescope. It's also available through the
S&T archive on the Web site, www.SkyandTelescope.com if you don't have
that issue at hand.

Follow the steps outlined there and you won't need ring baffles.

Gary,

I agree. I spent a lot of time thinking about baffles for one of my Newts,
and decided there were too many drawbacks and better ways to approach the
problem. Some folks, though, seem to feel, "if it is good for a refractor,
it must be good for a Newt."

Clear skies, Alan

Thanks Gary.

wrote in message
...

on the subject, "Newtonian Baffling Made Easy," which appeared in the
April 2001 issue of Sky&Telescope.

As immodest as this might sound, I'd recommend digging up my article
on the subject, "Newtonian Baffling Made Easy," which appeared in the
April 2001 issue of Sky&Telescope. It's also available through the
S&T archive on the Web site, www.SkyandTelescope.com if you don't have
that issue at hand.

Follow the steps outlined there and you won't need ring baffles.

Agreed, and it isn't immodest for me to say it. A very clear article showing
only what makes an impact. Baffles running down the length of the tube are
going to contribute very little.

Clear Skies

Chuck Taylor
Do you observe the moon?
Try the Lunar Observing Group
http://groups.yahoo.com/group/lunar-observing/
Lunar Picture of the Day http://www.lpod.org/
************************************


Regards,

Gary Seronik

(Remove the "z" for my actual e-mail address.)

Stephen I assume your talking about newt25 or similar. Fact is this newt
baffling
issue has been discussed here many times with numerous tests by people
reporting
back at saa and privately, and the sad fact is all the baffles newt25 would
have us
use ... is baffling and nonproductive. Even the rear baffle just before the
primary
was eliminated precisely for the obvious reasons - it interfered with air
flow
around the primary and thermal stability. Most people settled on the
foremost
baffle to keep out stray light and left it at that, because: it turns out
the most critical
issue in stray light is dampening (blacking) the area across from the
secondary/focus tube. Keeping stray light away from the secondary and out
of the focus tube are the
most critical newt issues. The next crucial newt issue is air flow across
the surface
of the primary - side fan(s) do help especially on larger newts. I would
stop/baffle
the front of the tube then move to the issue of secondary flocking opposite
the
sight tube, then worry about the fan issue - and if you do all three you
are in good
shape. Thats my opinion.
Jerry


Stephen Paul wrote:

Maybe I've ended up in too many killfiles, maybe no one has a suitable
answer, but I'm asking this again just in case it fell below the radar.

What's the downside of using baffles that follow the 75% light cone, as
opposed to using baffles of all the same diameter?

Thanks,
Stephen Paul