Newt Dew/Light Shield Length

[asloan (Adam)]

Hi Everyone,

I am in the process of making a dew/light shield for my dob mounted reflector. I have noted that the general rule of thumb is to make the shield as long as 1.5x the primary diameter. I have also noted that this length should be taken from the focuser. My query is, should the length be taken from the centre of the focuser or from the top of the focuser? For a 2" focuser the difference would only be up to 1", however I might as well be as precise as I can. Any thoughts would be greatly appreciated! Thanks.

[gbeal]

Can't help you with the maths, didn't stay long enough at school, but one way I could suggest is to look through the focuser, without an eyepiece, and with the focuser in as close to the tube as you can. If you can see the end of the tube, or past it, then you could use more.
Gary

[Space Dog (Ric)]

Hi Adam, I recently made a dew / light shield for a 200mm Orion reflector telescope and measured from the upper edge of the focuser using the 1.5 x rule and have not had any problems with the shield obstructing the field of view.
I hope that information is some help to you.

Cheers, Ric.

[Starkler (Geoff)]

The 1.5x is a suggested minimum, so if you can and wish to err on the conservative side, there's no problem with that.

[asloan (Adam)]

Thank you all for your very useful replies!

[chrisp9au (Chris)]

G'day Adam,

Finished mine a few days ago, pretty much follows the 1.5 rule, cost only a few dollars, flocked on the inside just like the tube, secures with velcro tabs. Plastic sheet is a 'Jasart' folio from Office Works, flocking is felt sheet from Spotlight, velcro from Bunnings, artwork from IIS

Cheers
Chris

[pmrid (Peter)]

Originally Posted by chrisp9au

Plastic sheet is a 'Jasart' folio from Office Works, flocking is felt sheet from Spotlight, velcro from Bunnings, artwork from IIS
Chris

And the snappy 4-on-the-floor gear shift knob by MG perhaps. very sporty look.
Peter.