From: Milton Aupperle <milton@outcastsoft.com>

Date: February 1, 2009 12:20:07 AM MST

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] Re: M37 Image


Hi Mark;


On 31-Jan-09, at 11:26 PM, Mark Gaffney wrote:

Hi Milton something I found here about the Meade OAG mentions a 90 degree tilt; " a small part of the light at the edge of the telescopic field is diverted at a 90° angle to the unit, where it is observed on the crosslines of an illuminated reticle eyepiece to detect any change of position."


The Meade is a fixed prism at 90 degrees.


What is the range of prism tilt in your Celestron Radial Guider?


About 30 degrees. I can twist it so I'm seeing nothing but barrel, either the inner edge above the prims or the lower edge opposite it.


It means I have a vertical field of view that the centre extends from about 20 arc minutes to 35 Arc Minutes.


At 90° you have no latitude, the star is either in or out of the FOV of the camera and you can't change it.


All I can find about the Orion Deluxe OAG is; "Features prism tilt adjustment and more than 100 degrees of radial adjustment for easy guide star location"


Right, it's basically a modified / probably improved version of the original Celestron design. It has the helical focuser which is certainly a good improvement, but the radial rotation is more limited.


I`ll see how I go with the Meade for a start! It has 360 degree rotation at least; "The slip ring allows 360-degree rotation of the guider body for guide star selection."


All Guiders can do that. You unscrew the SCT end, rotate the guider, then tighten it back up. That rotates the camera and everything else attached behind the OAG, which is not a good thing because you flat images have now been rotated too, which mucks them up.


However the Orion and Celestron can rotate around the axis without unscrewing the SCT attachment, and therefore don't change the Camera position. The Celestron does 135 degrees, where as the Orion does only 100.


If you look at the Meade unit


http://www.astronomics.com/main/images/OffAxis/close_ups/777cu.jpg


the guider arm is a fixed piece. To move the radial guider arm means rotating the entire unit and everything behind it.


If you look at the Celestron unit 


http://www.astronomics.com/main/images/Filters/close_ups/ceoagcu.jpg


that silver knob you see locks/ unlocks the radial guider arm into position. Unlock it and you can swivel the guide camera around for 135 degrees, without unscrewing the SCT end.


HTH..


Milton Aupperle