Another newbie with 2 star alignment issues!

[Geo]

Hey Guys, first post and apologies but it's gonna be long.

I've just bought myself some gear in the hopes of eventually doing some astrophotography. I'll give a run down of my purchase before asking the questions.

OTA = D200mm F1000mm Saxon/SkyWatcher
Mount = HEQ5 Pro
Eye Pieces = 28mm, 10mm & 5mm
Accessories = Variable Projection Camera Adapter
Camera = Nikon D7100 & T ring

I've spent the past few nights and days working on this and have yet been able to get a working alignment. Watched videos read the stickies on here and past threads but just couldn't quite get it to work.

Q.1. Two star alignment isn't working for me. Definitely something Im doing but can't figure out what it is. Can anyone give some advice?

Background to the question and what I've tried:

I'm a Surveyor by day, when it comes to reducing error, levelling gear etc. I'm incredibly pedantic. I spent alot of time initially levelling the tripod and adjusting the legs to get a well rounded level setup. Rotating the spirit level on 90 degrees around the tripod until the error was very close to the same or within a minute or two of level. The level of the tripod was fine from what I've seen.

I setup the N leg pointed towards True South, not magnetic south, to within from what I could see a degree or two using a Compass app on my android phone. I then placed the mount and OTA on the tripod. screwing everything into place. I checked to make sure the mount was set at 27 degrees on the dial. I proceeded to balance the weights and OTA following the examples shown on here in the tutorials and from what I've learnt from the person I bought the gear off. I then pointed the weights on the down position and the OTA in line with the N leg which was pointed to true south.

Turned on the mount and ran the setup procedure. Entered the date, time, +10 (Brisbane) and the almost exact coordinates in Lat & Long (Survey grade GPS!). I started the two star alignment and initially turned to Sirius which was almost directly overhead. It was to the right of the finderscope so I aligned it in the finderscope then finished the alignment in the OTA. Accepted it but then struggled to find a second star which was visible where I was. I tried approx. 4 stars as a second star but none of which were that easy to see. The one that appeared to look the brightest I centered over that one and accepted it. The error it gave me for True South (I believe thats the error it spits out, but please correct me) was within minutes, not degrees.

I then proceeded to Slew to the moon which was over the horizon to the east and it was off by 10's of degrees. Everytime. Only one of the four setups I've done I was able to slew back to Sirius accurately. The first star I aligned with. Each time it was even off from Sirius!

So I decided to take everything down and start again, re-levelling the tripod etc. and still couldn't get the alignment right.

I've a feeling the second star I'm using isn't the right star. I know Sirius and Canopus are incredibly easy to see but apart from that I'm struggling to distinguish stars when I've slewed to them. However it's still accepting the alignment and returning to home position.

I'm using stellarium to search for a star the controller wants to use first, before slewing to it to ensure it's viewable from my position and not obstructed.

Anyone any ideas?

Q.2. Gaining focus with the Variable projection camera adapter. Does anyone have one of these and able to help? I can get focus easily with the 28mm and then with the 5mm it took me a while but I was able to see Jupiter quite clearly with it (no tracking, oh how I long for tracking!). I've got a cheap 10mm eyepiece inside the Variable adapter and the D7100 hooked up to it but no matter what I've tried I can't get it to focus. However, I was getting a bit annoyed with myself over the two star alignment so that might be why. I gave up on that relatively quickly.

I guess I'd really want to be locking in the 2 star alignment first and worrying about getting focus after that.

If you've managed to read my entire post thanks!

Any help would be appreciated.

Cheers,

Geo

[The Mekon]

Are you sure you are identifying stars correctly? For example Sirius is not overhead until around midnight from where you are, so I assume you are not starting just after dusk. Your methods seem correct, I assume that you are only slewing to the second star when you think you know which and where that star is. If you are finding this aspect difficult - (the synscan does have some obscure stars in the alignment program), then get some charts and binoculars and start to recognise where these stars are. I have found that entering the correct time (to within a few seconds) helps alignment greatly. Aside from that ensure date is entered as month first, and use the 10mm eyepiece and get as close to the centre of field as you can before accepting the star. Also hit "rate" then 5 or 6 to make slewing to the star faster.
Good luck - you appear to be on the right track. Polar alignment is not that critical for goto ops to be successful.

[Geo]

Hey thanks for the quick reply.

Yeh I'm almost certain Sirius was right as I first checked on Stellarium with my laptop on location. We were bringing in the new year with the telescope last night so my setup was between 11pm and 1am. I'm certain I've entered everything right, even when doing a new setup after the rollover to January 1st it was still slewing the same way.

I mean I was pretty close to the moon each time I slewed. Just couldn't get it slewed to the centre.

Thinking back it must be the second alignment star as I wasn't as confident with it. I centred it on the brightest star in my scope as I made the assumption the alignment should be alot closer to the second star than it was to Sirius. Maybe this is where I'm falling short.

Is there any star you might recommend using? Bearing in mind I'm in Brisbane. I was by the waterfront last night with some obscurities I could only see about 3/5ths of the sky. Anything west and close to the horizon was not achievable. I cycled through stellarium with the stars my controller offered to see a rough location and whether it was worth slewing to.

In regards the rate I had just read that this morning and was thinking to myself how silly to have not done that myself. It was taking me forever to move the scope because it must have been set on a low rate. Great tip.

[barx1963]

Hi Geo and well done getting some gear and having a go.
I have recently purchased the same mount and have been enjoying the "challenge" of alignment. I at least have nearly 7 years of observing behind me so I at least know most of the bright stars!!
Couple of things. Time spent getting things perfect is time that can be spent observing or imaging so try to do what is necessary. Levelling the tripod is OK but really only needs to be done in the east west direction. Polar aligning will take care of the other direction. I check it to make sure it is not grossly out but never spend more that 30 seconds adjusting it. (just to clarify, I use a simple spirit level to level the tripod. When I say east west direction, I mean the level is lying with one end pointing east)
Alignment cannot take care of all the errors that can occur. Cone error is one. That is misalignment of the optical with the RA axis of the mount. A three star alignment will take care of some of the cone error. There is a procedure in the manual that came with my mount to checking for cone error but the procedure for rectifying it is Northern Hemisphere based. I have just done the check and it would appear that most of my pointing errors are due to it.
I have found with these mounts they are not perfect, but once you have it reasonably setup tehy do a pretty good job.

Cheers

Malcolm

[jenchris]

I'd suggest Canopus and Rigel as setup stars. They're both visible and the only stars in that part of the sky with that magnitude.
Sirius is ok early evening, but if it is directly overhead, it may be allowing your backlash into the equation.
Check your power cable is anchored - if it moved in it's awful little socket, it may be giving you false movement signals.
I still haven't soldered a lead on mine, but I do clip it into a position where it can't move in the hole.
Getting the star to the centre is quite critical too.
Errors are compounded by being a little off on both stars.
I put the camera in and focus it on a bright star (Sirius) then go back to zero (vertical pointing at SCP) and start up my capture programme (APT - free download but they'd like you to purchase eventually - it works for me) there's a cross hair on that and at x10 you can get it very close. Then I can centre both stars with the camera already on the rig.
This means I can go straight to imaging once the system is aligned.
I also use PHD for guiding once all is running.

[Geo]

Thanks for the welcome Malcolm. Well the main reason I mentioned being pedantic with levelling was for this very reason, to see if I'm going overboard. Clearly I am so duly noted thanks!

Ive read about Cone error but never thought it might be an issue. I will definitely perform a test on this tonight to confirm how far its out and make adjustments accordingly. Didn't occur that this may be some of my problem.



Canopus and Rigel, got it. Will try these out tonight. With my surveying background you'd think it would have clicked that an obs like Sirius directly overhead would be bad, but no.. I think it was because I knew that star and felt vest to stick to something I know! Noted to not use stars directly overhead. Thanks.

Hmm doing an alignment with the camera sounds very appealing. It means there's no chance of bumping anything. Once I manage to get the alignment working I think l switch to that method. I'm guessing its a good idea to balance with the camera on too?

Checking the cable is another great tip. Would never have thought movement of the cable could cause error.

Thanks guys, from the sounds of it I'm not too far off. Just need a little more patience.

[The Mekon]

Geo,
a couple of other matters. Once you have aligned the first star, do not assume when it slews to your second star it will be any closer - the opposite can happen, and this is OK.
Also I have been told that time spent slewing the star to the centre of the field is time lost in tracking. Hence a slow and cumbersome centring can really add up some errors. (anyone feel free to contradict this if you know otherwise) If this is the case, then it is most essential you have the rate on 5 or higher for each star (it resets once to standard rate once you accept a star) and centre as efficiently as possible - only time actually pressing the slew buttons is "lost" so you can take your time to do the centring, just not too much time pressing buttons.
And others have suggested Rigel & Canopus is a good pair, Betelguese and Canopus better, the problem is that the stupid program often will not allow the combinations that appear "best".

[barx1963]

I have found that the star selection in the handset is extremely frustrating. It will offer a nice star like Canopus then next star is Alpha Cent, then Mimosa then Alpha Crucis. All are low in the sky ATM and behind bushes. And given I reject 1 of them, why would it offer them when they are all close together?
I am used to Argo Navis which allows me to select my alignment stars.

Rant over

Malcolm

[Allan]

Some good rules that apply to 2 star alignment with dobs, that I see no reason wouldn't apply to GEM's.

Pick stars between 30 degrees and 70 degrees above the horizon.

The 2 stars you pick should be at least 10 degrees different in altitude.

The 2 stars should be separated by at least 90 degrees. I try to find something in the south and something in the north.

I've tried everything to improve the GOTO accuracy, and found the choice of alignment stars was what affected the accuracy the most.

[Dealy]

G'day Geo, and welcome.

Yet another point to be aware of is backlash. When centering on your alignment stars the final movement should be with the right arrow and up arrow buttons. This removes backlash error.

So when centering, overshoot the mark with the left and down arrows then centre using the right and up.

Also, setting to 27deg using the dial may not be accurate enough. Get yourself a digital inclinometer (https://www.carbatec.com.au/machinery-and-accessories/machinery-accessories/digital-angle-finder-box).

There are cheaper ones around. This will be a much more accurate way of adjusting latitude.

Cheers, Kev

[Geo]

Hi Guys,

Think I'm cursed. Nothing but cloud cover here in brisbane the past few nights. I got about 45 mins of clear skies Saturday night. I actually think I had almost got it. I slewed to a couple of bright objects which weren't in my alignment and I was just off centre before the cloud set in for the evening. Was getting excited until then!

Weather permitting will be going to a meet up on Saturday. Might grab some more tips and lock the process in soon enough.

Thanks.

[MattT]

Hi Geo,
After you set the scope up, choose and slew to the first alignment star, how do you centre the star? I always moved the mount in az and alt with the mount bolts not the motors. When it was close to the centre then I'd use the motors but only when the star was very close to centre. The second alignment star was always pretty close to centre. I used the motors only on the second star. Star choice does matter. Canopus and Formhult (sp?) worked well for me.

Matt

[Geo]

I always used the motors. Will use the Alt and Az adjustment screws next time there's good weather. Which is hopefully in the next couple of days...

I'm guessing you mean Fomalhaut right?

[Howard]

Hey Geo. Send me a pm if you like. I am Bayside Brissie with HEQ5 PRO and happy to run through alignment stuff. I studied quite a bit of surveying stuff in my Mining Eng degree and worked for years in Earthworks at minesites so understand your background. Cheers,
Howie

[Geo]

Great stuff man. I'm going to a meet tomorrow night at Wyaralong dam. I'll see how I go with that. I'll PM you anyway.

[OwenS]

I've also had a lot of issues trying to align me GEM scope...

[jenchris]

Ha - I was at Wyaralong on Thursday night!.
Could have given you a run through then!
Best of luck with the weather.
By the way it gets very dewy after about 11pm

I used PHD2 last night when I reset the observatory pier - to do a drift align - boy was that good - very quick and accurate