[ATM] Make A Barlowed Laser Collimator?

[RodShea]

That is a great idea! 

Thanks,

Rod

----- Original Message ----- 
From: "Scott Ewart" <scotte at frontiernet.net>
To: <atm at atmlist.net>
Sent: Saturday, March 31, 2007 8:08 PM
Subject: Re: [ATM] Make A Barlowed Laser Collimator?


> Rod,
>    I built my own collimator similar to an EZ-Collimator.  In the 
> angled viewing surface with the hole in it, I inserted a very small 
> sleeve made of aluminum.  I did this to make the beam smaller and 
> rounder (the beams from cheap lasers are a bit elongated).  This 
> causes significant scatter off the inside of the hole.  At first I 
> didn't like the idea of this, until I started using it.
>    The scattered light makes the primary's central mark more visible 
> in difficult lighting conditions while collimating the secondary. 
> Then when I go to align the primary, the reflected scatter shows the 
> silhouette of the central marking ring on the angled viewing surface, 
> just like a barlow would, except that you still have the central point 
> of light.  No need to remove the laser to screw on or add a barlow.
>    This has the further added feature of being able to show very 
> clearly the source of any collimation change due to changing altitude. 
> Does the point of light move within the shadow of the ring?  It's the 
> secondary moving.  Do the ring shadow and point move together?  It's 
> the primary moving.  Simple and elegant.
> 
> Scott
> 
> 
> ----- Original Message ----- 
> From: "RodShea" <RodShea at comcast.net>
> To: <atm at atmlist.net>
> Sent: Saturday, March 31, 2007 7:38 PM
> Subject: [ATM] Make A Barlowed Laser Collimator?
> 
> 
> |I have a red 635 nm laser collimator with a hologram that screws into 
> its "business end" with the same thread that is used in a 1 1/4" 
> filter.  That is, if I unscrew the hologram holder, I can screw in an 
> 1 1/4" filter.  I'm thinking that a small plano-concave lens or 
> negative achromatic doublet mounted (somehow!) in a filter "barrel" or 
> "ring" would produce a diverging beam.  I also figure I could machine 
> an angled surface plug, similar to a BLUG, that could fit, 
> permanently, into the filter ring, perhaps sandwiching the lens in 
> place.
> |
> | This would allow me to unscrew the hologram ,then screw on the 
> diverging lens assembly and use the laser for Barlowed laser 
> collimation, using the angled surface to see what I'm doing while 
> collimating.  This would be a lot more compact than an 1 1/4" Barlow, 
> and probably lighter, since a full diameter lens, and ? the doublet, 
> would not be needed.
> |
> | Am I right on this, and can anyone tell me approximately what focal 
> length lens I want, or point me to a site that would help me calculate 
> it?  The scopes I would use it on are Newtonian, with focal lengths of 
> between 60" and 100".
> |
> | Thanks,
> |
> | Rod
> | _______________________________________________
> | ATM mailing list http://www.atmlist.net/
> | 
> 
> _______________________________________________
> ATM mailing list http://www.atmlist.net/
>