dawson Posted August 5, 2013 Author Share Posted August 5, 2013 Nah, it's not even in the FOV with a low mag EP. It's defo lots off. JD Link to comment Share on other sites More sharing options...
Perkil8r Posted August 5, 2013 Share Posted August 5, 2013 If it's off by that far then your scope isn't aligned with your mount, or you've got the settings wrong in the handset, or your PA is a mile out. Periodic Error isn't going to make the goto point that far off target, PE only really becomes apparent in long exposure shots. Link to comment Share on other sites More sharing options...
dawson Posted August 5, 2013 Author Share Posted August 5, 2013 Mike, I agree, the periodic error discussion was totally unrelated to my GOTO issues, I tried to make that clear somewhere in this thread, but the thread got side tracked. Again, I've already identified i've got a load of cone error, and I'm taking measures to reduce that (rings). I'm pretty sure my handset settings are good, but going to check the Alt-Az vs EQ question sometime. JD Link to comment Share on other sites More sharing options...
Perkil8r Posted August 5, 2013 Share Posted August 5, 2013 Are you remembering to centre the object and then tell the handset that it's now looking at it? Thereby teaching it as you go along? In theory it should only be a long way out on the very first object you look at that night, the rest (on the same side of the meridian) should be pretty close as long as you are updating it. Link to comment Share on other sites More sharing options...
dawson Posted August 5, 2013 Author Share Posted August 5, 2013 Mike, have a read of the whole thread, I think I've already had this discussion JD Link to comment Share on other sites More sharing options...
Guest Ryuno Posted October 6, 2013 Share Posted October 6, 2013 James, what was the solution of your problem? I read through the whole thread like through a thriller, just to find that everything stops in the middle of nowhere. Very frustrating!! Link to comment Share on other sites More sharing options...
Brantuk Posted October 9, 2013 Share Posted October 9, 2013 Yup - what happened next would be nice to know - any news James? Did you fix it in the end? Link to comment Share on other sites More sharing options...
dawson Posted October 11, 2013 Author Share Posted October 11, 2013 Sorry for the suspense. Not a particularly exciting story though. Well the GOTO works like a dream The solution? I'm not 100% sure, but I think it is mostly the encoders in the mount. - Cone error. I now have my 180 Mak in rings and the cone error is vastly reduced. You guys with scopes in the f/5 range have no idea how narrow the f/15 field of view is The rings are also making the whole scope just so much more stable, so there is even less wobble when focusing, changing eye pieces etc. I've also got a flip mirror which makes life a bit easier framing things in the camera too. - Encoders. These seem to do something chaotic when setting up. The S@N review highlighted this for which I am grateful. They recommend once the polar alignment is done, to turn the mount off and then back on again. I've done this and if I leave the scope in the home position the first star in the alignment is usually bang on pretty close. Turning off the encoders at the time of polar alignment works too. - Encoders. These also seem to, independently from the point above, reduce the accuracy of GOTO, so I have them disabled. Again, the difference between an f/5 and an f/15 field of view is quite different which I'd never really appreciated. Turning them on/off is a doddle in the handset. It can be frustrating to disengage the cluthes and manually slew to something to then remembers the encoders are turned off and the GOTO has then GONE, lol - Backlash. There was a reasonable about of play in both axes of the mount; maybe this only became more apparent after a good bit of use and it loosened the mechanisms up. Graham has very kindly had the mount and made everything nice and snug. I still want to do that test of backlash which I read about on SGL (essentially turn tracking off, point at a distant stationary object, and note the coordinates on the handset, then at the very slowest slew rate, press a slew button until you just see the object in the fov move, then note down the new coordinates and the difference between the two coordinates is the backlash in that axis; repeat for the other axis. I do just wonder how much this amount of backlash will vary though as the gears take the load or not depending on where the scope is at any particular time, but I'm interested to see for the sake of interest anyway. The handset does allow backlash compensation too). - Corrector plate. There was a very subtle clunking noise in my 180 Mak when it slewed from one side of the meridian to the other. It made a small change in the fov and focus. I thought I'd got mirror flop (I'm like an astronomical hypochondriac!) but luckily when I showed this to AstroLeigh the other day over a cuppa, he identified there is a ring which screws on the front of the scope, in front of the corrector plate, and under it is a big washer (the washer is the size of the scopes aperture). Anyway, this ring was lose and allowing the glass in the corrector plate to flop from one side to the other...Oops. So we've tightened that ring up and now there is no flop, all rock solid. - Polar Alignment. I think I'm not bad at this. But again f/15 is different from f/5; very different. I'm never going to get 5 minute unguided subs on my 180 Mak because at f/15 trailing will be too obvious early on. So, the other night I managed some 120 second subs without trailing. I have had a play at drift aligning too, which is fun. I've gone for the method of taking an exposure on the DSLR whilst slewing the scope one way, then back and then looking at the resultant image to see how far away the star ends from its starting point. Again, this is largely an exercise for fun at present to see what I can achieve. - F5. Back in the spring I purchased an f/5, blue skywatcher 10" newt for £100; thought it could be something to have a play with at some stage. Anyway, I had a go a few weeks ago and loved it. Just waiting to flock it and fit a focuser which will allow me to do some DSLR imaging on it, then I'm going to see how long I can get unguided subs for on that bad boy So, another learning point for me is about the f/ratio. Yes, there are many DSOs which physically won't fit into the fov of my f/15 Mak, but that isn't really the hindrance for me doing any DSO imaging with the Mak, the issue I have largely come to realise is that I can only probably achieve 120-180 second exposures with it before the very magnified fov shows up star trailing and ruins the background/data. If I could achieve 5 minute subs with the Mak, there are plenty of DSO targets I could image (I looked at the Saturn nebula the other night and did a 60 second exposure to see what it looks like on film and it's a crackingly interesting nebula which would be great at f/15 if I could capture 20 hours worth of data, lol) but individual exposure times are limiting, and I'm just not keen on going for a laptop-driven guide camera at the moment (and the stand alone autoguiders don't have many followers). So, it's taken me some time to realise, if I want to do planetary or lunar, use the Mak, and if I want to do DSO imaging, use the newt. But as I've said, I do enjoy the research and tinkering and learning. Whilst the drift alignment stuff could be boring, holding one button on the handset for four minutes and then slewing the other way for four minutes, it's actually really nice to just sit there or stand and look at the sky a bit more. So, I think that's where I am at. Now, just waiting for another builder to give me a quote for a door to be knocked through from my garage into my garden shed so improve access to the back garden, and then I'm away. I also want to think about putting three permenant tiles in the middle of the lawn for the tripod, below the lawn mower height, but that can wait. I've rubbished the idea of an obsy, this really isn't the garden for one, and I'm not keen on a stand alone pier (as yet). James Link to comment Share on other sites More sharing options...
Brantuk Posted October 11, 2013 Share Posted October 11, 2013 "You guys with scopes in the f/5 range have no idea how narrow the f/15 field of view is" I think we do know James - that's why we told you not to use a Mak for dso imaging months ago lol In any event your subs would take far too long to gather light so a fast newt with coma corrector is a much better idea. Alternatively, a nice little f-5 doublet wouldn't break the bank - but even with perfect pa you'll still need to guide eventually - I know you ain't gonna be happy unless your pics are perfect (if your mount tinkering is anything to go by lol). Read up Noels 3-part tutorial on setting up guiding - it's a lot easier than you think and once you've done it a few times it barley takes 30mins from start to finish. Link to comment Share on other sites More sharing options...
dawson Posted October 11, 2013 Author Share Posted October 11, 2013 I think off axis autoguiding is worth a go! Lol. If an autoguider wasn't £300 i'd just get one and see what sort of subs i could get with the mak on M57 and the like. I might see if anyone on sgl has tried this combination. It's only money after all.... James Link to comment Share on other sites More sharing options...
Brantuk Posted October 11, 2013 Share Posted October 11, 2013 Ahh... autoguiding - good idea. Yeah the Synguiders ain't cheap - I guess that's astronomy for you lol: http://www.firstlightoptics.com/guide-cameras/skywatcher-synguider-autoguider.html Link to comment Share on other sites More sharing options...
+RonC Posted October 11, 2013 Share Posted October 11, 2013 I've had a SynGuider for months and have not used it as yet! I want to test it on the Meg 72 and EQ5 and learn that way, the problem I've found with it is the screen is tiny and a PITA !! Glad your getting sorted James, it looks as though we both might try guiding at the same time, interesting?? Cheers Ron Link to comment Share on other sites More sharing options...
dawson Posted October 11, 2013 Author Share Posted October 11, 2013 Ron, I'm not going to trying guiding just yet. The autoguiding option has most appeal, but has least supporters. And I'd need to see if it would work off-axis as I don't have the set up (yet) for a guide scope. You'll be doing guiding long before me Ron. James Link to comment Share on other sites More sharing options...
philjay Posted October 11, 2013 Share Posted October 11, 2013 Your determined to make life difficult for yourself aren't you James? imaging at F15 on DSO will not be easy and unless you use a decent F ration guide scope and correspondingly sensitive guide cam then you may as well stick to doing short exposure subs unguided and stacking them, it'll be cheaper and lighter on the wallet. I regularly image at F7.5 and that's difficult enough using an ST80, forget finder guiders at that F ratio as well. I also sometimes guide with an F15 guide scope if I want to go right in on a subject at F7.5 and I sometimes have problems with that. As discussed elsewhere, from my experience and that of many others, I would think hard about using a synguider and forget about using one to guide for imaging at F15. Link to comment Share on other sites More sharing options...
+RonC Posted October 11, 2013 Share Posted October 11, 2013 P1000867 by [email protected], on Flickr Synguider and OAG +DSLR! Link to comment Share on other sites More sharing options...
dawson Posted October 11, 2013 Author Share Posted October 11, 2013 Oh nice ron What's the focal ratio of that scope? I'll be interested to hear how you get on with the synguider. It sounds more and more like even thats a bad idea for me at f/15. James Link to comment Share on other sites More sharing options...
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