Quote:
Originally Posted by Merlin66
Craig,
""I complete my PA routine and attempt to slew to a target, invariably it won't accurately slew to that target as where the mount thinks it is pointing is not exactly where it is pointing."
OK
EQMOD (I don't know about the other programs you mention) doesn't require a plate solve at SCP.
It is reliant on the scope being set to the "home position" (ie pointing towards the SCP. This doesn't have to be 110% accurate.
The "encoders" used by EQMOD then use the "home position" as a starting point for the subsequent slew. When you reach the first target position ( according to EQMOD) there may be a error ( the home position wasn't 100%, flexure/ movement of the scope etc etc). By then moving the scope to the actual target (handcontroller/ plate solving) and syncing on that point you are providing corrections to the EQMOD alignment model which is then applied to subsequent slews.
For accurate slews you really should have a series of syncs which surround your target area(s).
Once you have a good set of sync points they can be re-used on subsequent nights....
All this is well covered in the EQMOD manual (in the EQMOD download folder)
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Thanks for the additional info. To address the points you've raised -
The "encoders" used by EQMOD then use the "home position" as a starting point for the subsequent slew. When you reach the first target position ( according to EQMOD) there may be a error ( the home position wasn't 100%, flexure/ movement of the scope etc etc). By then moving the scope to the actual target (handcontroller/ plate solving) and syncing on that point you are providing corrections to the EQMOD alignment model which is then applied to subsequent slews.
Yep, this bit I do understand. I think my problem is that sometimes the home position is clearly out by enough that where I end up slewing to is far enough away from my desired target that getting it into my frame, and then syncing to it, is impossible. For example, let's say I am at the home position and wish to slew to Jupiter to focus on (I find it makes a good focus target.) I execute the slew and unless Jupiter happens to be at least partially in my frame (which it often would not be), I am "lost" - I know I am
somewhere near by but I end up blindly slewing around trying to find it, wasting time. If I can accurately sync my coordinates before getting started, it ultimately means that when I want to land on a specific target I can with accuracy.
For accurate slews you really should have a series of syncs which surround your target area(s).
Indeed, but it comes back to my problem is that if Platesolving fails, I am blind, so to speak, unable to sync on a target I cannot find.
All this is well covered in the EQMOD manual (in the EQMOD download folder)
I did read through this when starting out but I should probably dive back in and read it again, thanks.
Quote:
Originally Posted by jahnpahwa
Craig, my routine is exactly the same as yours except I use my main scope images for PS.
One thing that might be mucking you around here is the focal length setting in APT in "tools" tab, down the bottom. Do you have this set to the focal length of your imaging scope or guider? When i swap between OTAs for imaging, I need to change the FL here, or else my PS will not work (455 to 1000). I assume you are getting the feed from your imaging camera into APT? I'd definitely be using my imaging OTA for APT feed, and therefore platesolving. I use mine for sharpcap too.
So, my advice would be to find a way to approximate your focus point before setting up (maybe take a pic of the focuser draw tube during a session once you've focussed it?). It only needs to be close enough so that you can live view and dial it in with APT or sharpcap once you've turned it on. Once you're focused this will all be no problem at all. Maybe changing exposure times in either software will help with the solving/focussing intel too.
The other thing I'd mention is that, like you I slew back to home in APT after PA in sharpcap, then solve and sync there, then go straight to a nearby bright star (Rigel Kent), solve and sync and GOTO again, and it should be bang on. I focus properly there. If I go straight from a sync at the SCP to M8 or similar, I am sometimes a way off... I think you need to give the map a bit of space from the pole so it can chew on where it is, but if you go half way across the sky straight away, it can be miles off.
I hope that helps?
If not, I'd be happy to PM or chat!
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Thanks for the reply!
To answer your points:
One thing that might be mucking you around here is the focal length setting in APT in "tools" tab, down the bottom. Do you have this set to the focal length of your imaging scope or guider?
An excellent question, and this has mucked me up before. But, on recent evenings I've been sure to check this and it hasn't been the source of my woes!
I assume you are getting the feed from your imaging camera into APT? I'd definitely be using my imaging OTA for APT feed, and therefore platesolving. I use mine for sharpcap too.
I run PA in Sharpcap off my guide scope, and my initial Platesolving in APT is also off the guide scope. I find the imaging OTA near impossible to focus without a bright enough star, and I find it near impossible to accurately slew to a bright enough star without platesolve and sync. Classic chicken and egg
My guidescope on the other hand is a cinch to focus on any star.
So, my advice would be to find a way to approximate your focus point before setting up (maybe take a pic of the focuser draw tube during a session once you've focussed it?). It only needs to be close enough so that you can live view and dial it in with APT or sharpcap once you've turned it on.
Yeah, I do do this, I will always set the focus on the imaging OTA to "roughly" where it should be (helps with balancing too) but I find the focuser on the Esprit 80 super touchy, and even being fractionally out from the proper focus spot can leave you wildly out of focus. Even matching up the focuser position exactly to a photo from a previous session usually leaves me a long way off
The other thing I'd mention is that, like you I slew back to home in APT after PA in sharpcap, then solve and sync there,
I'd like to drill in on this actually. You go back to home position in APT after PA, platesolve and sync on the home position? How are you able to sync the PS results in the home position? I consistently, without fail, get an error when I try and sync coordinates platesolved in the home position, which is supposedly an EQMOD limitation (can't remember where I read this though.) As soon as I slew away from home/SCP, assuming a successful platesolve of course I have no issues syncing. So my issue comes down to: 100% success rate platesolving at the pole, 0% success rate syncing at the pole. 30% (maybe?) success rate platesolving away from the pole; 100% success rate syncing away from the pole.
What's your trick to sync at home/SCP??
I hope that helps?
If not, I'd be happy to PM or chat! Very helpful thanks, and I may well take you up on that offer! Much appreciated.