Quote:
Originally Posted by ausastronomer
Hi,
Some suggested mods which will improve the contrast of your dob by up to 40% :-
1) Baffle the tube. Flock the entire tube or as a minimum flock a large section opposite the focuser. In addition you can add a tube extension which helps a lot.
2) Blacken the edges of your secondary mirror with a black texta pen.
3) Baffle the inside of the focuser. You can do this by using some 1/4" self adhesive foam weather stripping.
4) You can go a step further and install annular baffles (ring knife edge baffles) into the tube at the top on either side of the focuser and at the bottom just above the primary mirror to prevent stray light entering the tube.
I have some photographs on my work computer which I will post tomorrow from work, showing exactly the modifications I have done. If you go to the Pony Club on Saturday night I will be happy to explain them all to you at the scope. I can't bring the scope because that would mean leaving the 18" behind.
Cheers,
John B
|
Attached are the photographs.
In the first photograph you should observe the following
1) tube is completely flocked and
PROPERLY BAFFLED
2) annular knife edge baffles (plywood rings) inside the tube on either side of the focuser drawtube.
3) baffles inside the focuser. you can see the first baffle right at the edge and the second baffle deeper in the focuser drawtube.
In addition, although you cannot see it from the photograph, the edge of the secondary mirror is blackened with a texta.
In the second photograph you will notice a row of screw heads about 4 inches above the machine screws holding the primary mirror cell. These screws hold a plywood ring baffle identical to the two at the top end of the scope, just above the primary mirror stopping stray light entering from the bottom end of the scope. Believe me if you observe in a light polluted environoment and observe the moon, planets and double stars, a lot of light gets up the bottom of the tube. Later design mirror cells may have rectified this problem, but in my scope it was a major source of stray light.
Cheers,
John B