Re: Noisy EXOS 2 PMC8?

Wes Mcdonald


If you go to settings there is  button to show the alignment data.  It starts out as all zeros and is updated after the last star is synched.  You can do this inside and watch the result.  Just press sync each time the procedure moves the mount to the next star.  There is also a button to reset alignment data which restore it to all zeros.  These are what I meant by a mount model matrix. Alignment calculates a transformation matrix which converts the desired pointing angle into the proper mount position given there is error in mechanical alignment.   If the mount were perfectly polar aligned and level and the time were perfectly known by explorestars then the only transform needed would be motor count to ra-dec -- a transform that could be hard coded into the software.  No doubt this transform is known and used initially by the explorestars.  But with errors in polar alignment and time one has to apply corrections.  This is what the 3 star computes.  

I agree peeping through the polar scope is next to impossible for me.  That is one reason why I sprang for a polemaster.  Look it up, it is really the way to go .  You get polar aligned in 10 minutes and use your computer screen.  Easy.  The standard CGEM mounting adapter is correct for the EXOS II.

Coarse alignment is OK for visual but without pretty good alignment gotos will not be in the eyepiece.  And dim objects cannot be seen in the finder.  Thus a pretty good coarse align is needed.  If the coarse alignment is fair, and you can find the object in the finder, then after centering in the eyepiece the object will hang out there  pretty good as the rates of tracking are right....but since the PA is not spot on the object will be sliding slowly out and you have to adjust both the DEC and RA  position to keep centered.  

So this is the real problem with doing a 2 or three star alignment. When you start out with a plopped down mount poorly aligned it is easy to have 5 or more degrees of error.  That  of course puts any alignment star out of the main eyepiece FOV. Then you have to use the finder and identify the correct star and use the controls to move it to the center of the eyepiece.   This needs to be pretty danged accurate for the synch to solve for that matrix.  It is best to have a illuminated crosshair eyepiece, though for visual after alignment one can do well enough if you eyeball center with a pretty high power eyepiece.  I like to use something like magnification of 100 which is a 26mm in my lx200.  (You know the magnification = scope focal length / eyepiece focal length.)  So the first challenge is to identify the correct star in the finder field of view and the second is to get it close to the dead center of the eyepiece.  BTW sometimes I go all the way out to very low power (like 40 or 50) at first, center that and change eyepieces to get closer.  In my experience if you want your gotos to place you in the eyepiece FOV you need to take the time to center the star in the main eyepiece and not just in the finder...the finder just has too much error relative to the  main telescope line of sight.  Do this three times with three stars and things should be plenty good for visual.  

Your cell phone can really help with your coarse  alignment.  Use it as a digital level to set your scope at the correct angle = your lattitude.  Don't use only the mount scale it is not accurate.  Use the phone's compass  to point things to true north...make sure that is correct and not magnetic.  When that is all about right Polaris will be in view of a lowish power eyepiece ( mount in home position PMC8 off).  You will know you have polaris by a couple of means.  First it will be the brightest star in the eyepiece and second, if you boost the mag enough you will see it is a binary (Polaris B -- actually it is a ternary system but you can't see the other).  Seems to me the companion is blueish in color and pretty close to Polaris A .  As polaris is close to the NCP you can rotate the scope in RA and polaris should rotate in a circle which stays in the FOV of a low power eyepiece.  When this works you are pretty danged good.  If you can see polaris in the eyepiece but it rotates out you are still pretty good.  So you can fiddle with your ALT and AZ mount adjustments to make it rotate better  or just set the mount at home and turn on the PMC8 and run the 2 or 3 star alignment.

A trick I learned to do recently involves the program Sky Safari.  Version 5 for Android is free.  Load it.  It gives you this incredible virtual reality view of the sky.  With my Meade I can place the phone on the wedge which is normal to the mount orientation and adjust the AZ-EL mount knobs to center polaris in the virtual reality screen.  That only happens when the elevation and azimuth of the wedge are pretty danged close to the NCP.   So that's all well and good if you have such a surface -- it's sort of like using the polar scope but it is all virtual and quite easy to do.  That is all well and good when there is a flat surface normal ot the desired line of sight but with our mount this is not the case.  Perhaps you can find some edge of the telescope tube to align the phone with.  Worst case you can stand behind the scope and just sight along it using the Sky Safari virtual reality display as a guide.  Being behind the scope is a pretty good way to get things toward true north using the cell phone.

Good luck.   This all just takes some practice.

Join to automatically receive all group messages.