A and E numbers that are high on the first couple of aligns are not unusual, because this Gemini is on portable mount, I would, and do myself on my portable mount, a quick Drift Align, that gets you close to the mark.
As you guide with the RS 232 port and not the Autoguder Port, out of curiosity, what is your Guide Speed. I have a gut feeling that you might find that is where your guide errors are coming from.
Jase, as John has picked up on my Losmandy is my portable setup, the LX is permenantly mounted (works like a dream). So considering I don't use a compas (the only one I have is a dodgy no good thing) and I simply rely on knowing roughly where sigma Oct is, it would not surprise me if my initial alignment is considerably off - perhaps 10 degrees in azmith, who knows.
I will be interested to take more note of the A & E numbers now, and look that info, I've never explored the "Show Information" menu option.
John, having to do any drift alignment is exactly one of the things I'm trying to avoid, simply because I figure "there has to be a quicker way", I always used to do drift alignment with my previous portable mount. To be honest I think I'd instead (assuming PAC doesn't work for me straight off) use 2 stars and hop between them using TheSky adjusting just the alt and the az as appropriate, I have had some success with this in the past ... but need more trialing and experience with it.
The guide rate for autoguiding - I am still not sure what's best here, considering I'm working through the RS232. Last time I was trying it out with the Gemini set to 2x sidereal, but to be honest I'm unclear as to exactly how this affects autoguiding. My current understanding is that using it how I am, GuideDog won't actually change the rate of movement but will change the amount of movement, it will do that depending on what figure I put in it's setup and in it's N/S/E/W text area that defaults to "500". My understanding is that because GuideDog doesn't alter the speed of the slews, only the time of them, if I set the Gemini to 8x instead of 2x it'd move a lot more for each correction. Which means if I'm not seeing much change resulting from autoguiding I'm guessing I should increase the rate up from 2x ... but 2x is pretty big for autoguiding I figure.
For suggestions and tips on using the RS232 port on a Gemini for autoguiding, I have found the Barkosoftware support pages valuable. These guy produce Guidedog software that does the autoguiding.
I appreciate what you are trying to do but, in my opinion, nothing beats a reasonable Drift Align, at the most it takes me about 15 minutes and is done during twilight, that will get you well under a degree from the pole and, in which case, improve your tracking.
I feel you are way to high with your Guide Speed, in my opinion, what is happening is that you are getting an ocillation. Guide Speed with the Autoguider Port is 0.8 as default. I personally would drop your guidespeed vide the Hand Controller to 0.5 - 0.8 and see what happens.
My understanding of GuideDog is that those numbers you mentioned are for the amount of time the guide mode is operated, not the actual speed. On my non-gemini GM-8, I still have to set the guide speed to 0.5 using GuideDog.
There was one other thing I found during extensive testing some 12 months ago, even though the Gemini Manual say's it can be done, I found that I had to uncheck the simultaneous guide signals. I know that if you have the DIN motor plugs you can do simultaneous corrections to both axis, I found that using an LPI you had to uncheck this option and only have sequential corrections.
Hi Roger,
Been following the thread to see how it goes as I will set up autoguiding in the future.
With the polar aligning I usually just drift align for a hour to get real close.
But what I found with my last mount was that when I had the mount very well aligned I would have a finderscope that sat on a little dovetail plate and I had alignment marks on both sides the dec axis, then I adjusted the finder to put the crosshairs on the closest star in Octans Sigma (I think). So next time I set up I just line up the marks on the dec and put the little finder on the mount and adjust the mount till the crosshair was on sigma oct again. Worked very well.
Might sound lame but might be good if you are travelling a bit.
Cheers Gary
As much as getting a polar alignment I'm now trying to understand what the Gemini is telling me.
I am out here for the first night since all this info was posted in this thread and I've done an alignment via a particular method. After that my pointing accuracy was close in DEC but far off in RA. I then did several additional alignments to build a pointing model and have these numbers shown when doing "Show Information" which don't match the acrynms in the manual:
Meanings:
dH=?
dD=?
A=Azimuth misalignment
E=Elevation misalignment
NE=non-perpendicularity at the equator
NP=non-perpendicularity at the pole
IH=Hour Angle index error
ID=Declination index error
I see no values for CF, FR, FD mentioned in the manual, presumably 2 of them are dH and dD.
Can anyone explain these numbers in simple terms to help me understand from these numbers how my alignment is off, or, if I'm seeing huge numbers because of an L4 bug?
I'm about to commence a drift alignment to see how that changes things.
Thankyou for all the help provided, I'm learning lots from this.
Another question (I hope you guy's don't mind me being such a pain asking so many questions, but there are so many...)
More a Losmandy question than a Gemini question probably: It seems when I make small corrections (at say 2x siderial) in RA and DEC, there's some drift that occurs after the movement. That is, the movement isn't precise, it moves as I tell it to, then keeps moving somewhat. It's not a "short sharp burst" like I get on my LX200.
Any ideas what that could be?
(and yes, the system is balanced in all directions)
Roger - I set up the other night, did a 6 star model, and was told I was A=-180 E=-60..... so I drift aligned using your website instructions, then cold started and built another similar model ---- A=-1 E=-2..... your name was gold around here then....
Sheesh though - drift aligning at the western horizon..... the only star I found was only really visible with averted vision, trying to watch it whilst standing on a ladder looking into the EP..... we need a bunch of Dec=0 supernovae I think! hehe
To be quite honest, I personally don't take any notice of all those numbers, the only one's that I do take notice of is the A and E numbers, mine are 0 and -1. My honest opinion is that after a lot of years of using a Gemini, they are the only numbers that mean anything. All these numbers are taken into account when Gemini builds it's Pointing Model, that is why I don't bother with them.
I, like Lee, am a firm believer of doing a proper Drift Align first off, I still believe this is the most accurate way of getting the scope and mount close to the poles.
Not sure what those abbreviations mean, will have to look them up but, I would say one has to do with counterweight flexure.
The overshoot sounds a bit like a backlash problem, your worm MAY be a little too loose. Before mucking around with the worm, I would try to unbalance the mount slightly, have the weight pushing against the worm, you may have it balanced too well.
Well after my last post last night I then did a drift alignment, the good 'ol way. That worked a treat. Interestingly my elevation was out by about 4 degrees! The rotation was pretty much correct, only small change there.
Lee - good to hear the page is useful I always used to do a drift alignment before I got my Losmandy, since then I've been trying other methods to try and speed up the process (even though a drift alignment only takes 30 odd minutes..) .. I will now regress back to drift alignment and save myself the hassles. Seems to save time in the long run.
I am still interested in understanding what's going wrong with my other attempts "the gemini way", but not sure I'll get that understanding until I discuss it in person with someone who's been through it all before.
I didn't get to trying autoguiding last night, so that one is still up in the air - not sure the results of the new ASCOM version yet, have only been using TheSky last night.
Tonight I'm going to have another crack at it, at a semi-dark location so will see how that goes. I'll be doing the drift alignment.
I'm doing drift alignment only now, back to my old trusty drifty alignment instructions. Last night I spent about 45min doing that but was talking to people etc during that time. Reached reasonable alignment but still could have been improved. When doing a few additiona alignments I found the Gemini reported A: 12 and E: 26, which are far smaller numbers than I was getting using other methods.
While doing the drift alignment I was careful to tighten the mount before slewing, as I've noticed that in particular the azmith of the GM-8 has quite a bit of wobble/flex in it if you do'nt have both the knobs tensioned. Remembering to tighten it all up once aligned helped too (easily forget that sometimes).
With the polar alignment working OK, it seems GuideDog instantly became more happy. Last time I simply couldn't get it workiing yet last night I couldn't seem to break it. It does appear that changing the slew speed on the Gemini hand controller does affect the behaviour of GuideDog (as expected). I sended up setting it to Photo Mode and it worked well there. It took a little while to centre the star each time because of the slow movements, but it got there in a minute or 2. I think I still need to adjust the speed a little, it was hopping around a reasonable amount sometimes, I think because the guide speed needed to go down a little. Haven't tested that theory yet. Viewing conditions were horrific.
Guiding at 1400mm instead of 700mm made a nice difference to the resulting DSLR shots, quite a dramatic decrease in trails. The DSLR was shooting through the Megrez @ 480mm (abouts).
The 6 point scope rings for the guide scope are a must, as is the extension bar I had my back neighbour machine up for me to extend the distance between the rings. I'm not entirely happy with the solution here, as the guide scope can slide down the rings, but haven't pursued the solution for that yet.
The Orion Accufocus meant I easily achieved focus with the 350D when I otherwise would have taken a while longer, and was able to tweek it later very easily. Without it, I was having to walk back and forth from computer to scope, make manual adjustments I hoped was right, lock the focuser between each adjustment (heavy camera) which introduced some semi-random movements every adjustment, etc. Again my back neighbour and his wonderful workshop came into use with him constructing an alluminium bracket and brass bush to attach the Accufocus to the Megrez.
A fellow amateur astronomer was kind enough to give me his broken Telrad. I've mounted that on my Megrez using cable ties (not quite sure what to do there in the long term).. and I fixed it by replacing the broken glass with a piece of a CD cover.
On the software front, I installed the new ASCOM 4.1 release that includes the new communication for the Gemini Level 4. I'm not sure how much difference that is made, it did successfully connect and move the telescope with the old (2.something) version. I'm yet to work out this new version, it seems to reset the Gemini's settings when it connects, destroying the pointing model and other parameters like screen brightness, slew speed, etc.
So, to summarise I have:
- Reverted to drift alignment
- Bought scope rings for the guide scope
- Bought an Orion Accufocus for the Megrez
- Using a doubler on the guide scope for longer focal length guiding.
- Installed new ASCOM runtime so it's compatible with the Gemini L4 software.
A few pic's attached.
The saga continues....
A few things from last night that I need to work on:
My DEC worm gear is "sticky" again, after several attempts at being told to move it will suddenly jump/skip a significant amount, infact outside the search area for the guide star which messes everything up. I've adjusted the worm before, not sure if adjusting it again will solve the issue or if balance was slightly out, or if I need to re-grease it or something.
I still have some drag/delay in RA and DEC movements, in that after telling it to move it will take a while to stop moving. Doesn't seem to happen when GuideDog is moving it in Photo Mode but does happy at 2x Sidereal.
It'd be nice to fit the Telrad somewhere else where I can view through it at a closer distance. But the whole setup is quite crammed as it is.
I still have limited understanding of why the Gemini Polar Alignment Correction and Polar Alignment Assist are resulting in an incorrect alignment, and what all the Gemini parameters (in Show Information) mean.
Hi Roger,
What you are doing is the "Gemini Way" by using the drift method. The Gemini Polar Align Assist is simply an automated drift method process. Once you get close, you can optionally use the Polar Axis Correction (PAC) feature to get you a little closer. Don't expect to be able to use PAC straight away when you've just set up.
Predominately you should focus on the A and E figures. The other measurements can be used to optimise your set up further. However considering you are setting up and tearing down every night, there are a lot of changing variables. It's different for a permanent set up. I've spent some time manipulating these figures like "CF" by moving the counterweights further up the shaft while still maintaining good balance. Moving the worm block for FR and FD. There are many resources available on the net to optimise losmandy mounts.
I assume that every time you run PAC and make an elevation or azimuth adjustment you know that you must redo the pointing model. Straight after you made the changes, just do a cold start and start a new pointing model. Once you have a new pointing model, you can run PAC again to get closer if desired. I've ran PAC three times to average out seeing, rebuilding an accurate pointing model each time. PAC is only as accurate as your pointing model, which brings me to an early post you made. You mentioned that when you slew and center a start for alignment, the mount appears to over shoot the mark when pushing the controller button. It kind of drifts and looks like there is a lot of play in the system. I experienced this too, but only when in visual mode. I would highly recommend you change to photo mode when building the point model. This should resolve what you are experiencing. Alternatively use "all speeds mode". Though I've only used this mode in v3.x, not 4.x.
I had a look at the photo you posted. Is this raw, i.e. no post processing other the dark frame substracted? The stars look reasonably round to me, even when magnified.
Roger are you aware that if you are using the hand controller to move the scope if you push the opposite button after pressing the first Gemini will jump up to the next slew rate. ie Photo>center or centering >slew. This might help to make your centering quicker.
Roger are you aware that if you are using the hand controller to move the scope if you push the opposite button after pressing the first Gemini will jump up to the next slew rate. ie Photo>center or centering >slew. This might help to make your centering quicker.
Ahhh. Now that you mention it, I remember reading that a long time ago. I had the same understanding as Lee, that it just sets it to slew. I will be experimenting with this!
I guess this is how I could set it to Photo Mode, and do my alignment using that .... I was wondering how I could use Photo Mode for alignments when it moves at 0.8 siderial!
Hopefully I'll report back with success in a couple of days.
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