Re: #EXOS2 My RA on my mount is wiggling, Causing Star Trailing!!! #EXOS2

Walter Vinci

Hi Joseph,

I am totally new to the hobby too (hi everyone :)! ), actually just a couple of nights out with autoguiding, but my ES PMC-8 EXOS2 has a similar (even wider I would say) play on RA and I have no such problem (doing about 2” RMS but with round stars). 

On Jan 7, 2021, at 2:56 PM, Robert Hoskin <devonshire@...> wrote:


This hobby is an endless source of problem-solving opportunities  :-)

Just tossing some things out as grist for your mill...

If you tell me that your mount axes wiggle, well, you may need some mechanical adjustment (see link below).  
BUT... some play in the ring/worm gear connection is entirely normal, so while it's good to keep a mount well-adjusted, there are limits to the mechanical perfection we can achieve. 

Having said that... if you tell me that your guiding looks good, but your stars trail anyway, then I'd wonder about the dreaded "differential flexure". 
Basically, guiding well requires that the two optical trains (guiding and imaging) be absolutely rigid relative to each other. 
Relative movement of scopes in rings, focuser rotators, cameras in focusers, etc... all bad.   
I would guess that if guiding looks good, there may be motion in your imaging train.  On my scope, it was a focuser rotator.  Very convenient for visual use, but its inherent play was a bad idea for my imaging.  I locked its little grub screws down with extreme prejudice and saved the day!  


Mounts: ES PMC-8 EXOS2
Scopes: SV 102EDT, ZWO 60/280 Guide
Cameras:  Nikon D5300, Altair GPCAM2 290M
Software: ASCOM, CdC, AstroTortilla, BYN Pro, Sharpcap, PHD2
Computer:  Thinkpad x230, Win7Pro/64

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