From: "Dwight K. Elvey" 
To: atm{at}shore.net
Reply-To: "Dwight K. Elvey" 


>From: Peter 
>
>Hi,
>
>Just have a question regarding the correct secondary baffling of my
16" folded
Newt. If I have a well placed baffle inside the focuser tube (i.e.. nicely
matches the light cone), do I still need a large light shield behind the
secondary?
>
>I found this link for a similar design and they do not appear to have any
secondary baffle. Please select 36" folded Newt on the following site:
http://www.stabilite.com/mainnew.html  I'd like to know how they get away
without the shield???

Hi
 Yes, I'm afraid so. You also need to account for the largest
field angle you expect to use on the baffle in your focuser tube. Depending
on the size of the secondary, this baffle may be smaller than what is
required for the maximum filed angle because the secondary vignettes it
anyway.
 I recommend that you draw the entire thing out on a piece of butcher
paper ( 1/2 or 1/3 scale ). This will allow you to see where the various
angles are important. You can draw the field stops of your eyepieces and
their effective lens( at the eyepiece focal length from the field stop ).
This will allow you to ray trace the light paths into your eyepiece that
can be important. Dwight

>
>Thanks for the feedback.
>
>
>Peter

--- BBBS/NT v4.00 MP