Re: [ATM] My scope

["Nils Olof Carlin" <nilsolof.carlin@telia.com>]

Jerry, Ken
>
> Years ago I had a Barlow that my father made to be a light friction slip 
> fit
> to the draw-tube. It had no shoulder to prevent it being inserted to
> different depths in the draw-tube and then the eyepiece went into the
> draw-tube as usual. Want more power?. shove  the Barlow further down.

What you need to do is vary the distance Barlow lens assembly to eyepiece 
(the Barlow "gain" varies directly with distance), then you have to move the 
Barlow lens towards the secondary in order to reach focus.

You will have the details you need for experimenting here:
http://www.atmsite.org/contrib/Carlin/barlow/ - it is no doubt the cheapest 
way to get a full range of magnifications (given enough in-focus).

Nils Olof

>
> What you failed to mention, and what most ATM's don't know is that there 
> is
> almost an infinite choice of Barlow powers from the same device. The
> Barlow's power is derived from the ratio of the incoming light cone angle
> compared to the outgoing light cone angle. If you move the eyepiece closer
> to or farther away from the Barlow's optical element, the power changes.
> There's no need to purchase different Barlow's to get different powers. 
> Just
> slide the eyepiece out, refocus, and the power changeses.
>
>
>
> At one time a Barlow was sold where the optical element was manufactured 
> to
> slide in and out inside the Barlow's tube. It came with a calibrated 
> plastic
> insert that was used to set the power of the device. I guess the
> manufacturer figured he could make more money by sellong different devices
> and they quit making the "Adjustable Power Barlow" as far as I know.
>
>
>
> I took the element from a 2X photo attachment and made a similar device
> years ago and it worked great! It's still somewhere in a box. Haven't seen
> it for years.
>
>
>
> Ken Hunter
>
> (KB7H)
>
>
>
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> 


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