Having some issues

[Phillyo]

Well, where to begin.

I think I'll start with field rotation. My usual set up routine is the following;

• Setup Tripod and Mount (EQ6) and point roughly where I know polaris will be (don't always ensure I am perfectly level with spirit level, not sure if i need to)
• Connect all cables, power, laptop etc and wait for stars to appear. (Scope is Megrez 72 with FF/FR 6, camera is QSI 583wsg with Ha, OIII and SII filters)
• Using EQMod I do a polar alignment
• I then use Alignmaster 3 or 4 times to accurately align using SGP to centre the star using slew commands with EQmod.
• I then focus on a brightish star (mag 4??) using manual focus methods for now using FWHM in APT (Or HFD in SGPro)
• Once focused I slew to my target and plate solve to accuaretly frame the target (I have to use Astrotortilla with APT for this as I cannot for the life of me get plate solving working in SGP) but I have to take a 5min exposure to sometimes see the faint target to ensure I have the angle correct, not sure how I take a 5min test shot in SGP so I use APT for this too.
• Once framed I start PHD2 and begin the process of guiding. No real issues here, guiding graph is pretty flat. (Guiding use Lodestar X2 via integrated QSI OAG)
• I then begin my imaging sequence using APT as I haven't fully figured out SGP yet.
• Once the first image comes in (30min exposure) I have nice stars right out towards the edges but the corners show field rotation.

Where am I going wrong there? Is it just not accurately polar aligned? Do I need to do a drift alignment? I can't see south due to my house being in the way so not sure how i'll manage that.

Next up is SGPro plate solving. I've tried Elbrus but it doesn't do anything. I slew to target, click centre and solve or whatever it's called, it solves, syncs but doesn't move the mount? Tried using Astrometry.net and that doesn't do anything other than keep on solving. I'm "fairly" sure I have the fov set up correctly but I may be wrong?

Finally I managed to lose about 4 hours of data last night due to the scope touching the mount and stopping. Very annoyed and worried I may have damaged something, time will tell.

However I now need to figure out automated meridian flip, reacquiring my target and continuing imaging without my intervention would be ideal as I normally go to bed and leave it imaging over night.

I have heard EQmod can do it, as can SGP but does anyone know of anything else or use any other software to take care of it? Or if using either of these options is it hard to set up?

Thanks,
Phil.

[Charic]

You........

 

• Setup Tripod and Mount (EQ6) and point roughly where I know polaris will be (don't always ensure I am perfectly level with spirit level, not sure if i need to)

Me..........

• Set down  Dobsonian and point anywhere I like .........Done!

I feel your dilemma, but I'm  just glad I don't have these issues that seem to plague folk now and again. Someone will have your answer shortly.

[ronin]

Is this a case of mixing up polar alignment and what is in effect goto alignment?

For any imaging the polar alignment is vital, the goto alignment is simply so the mount can aim the scope at whatever you ask it to find. In effect if the polar alignment is off then the goto compensates for this, so a target will appear in view but the polar alignment is still off.

Will say I would expect EQMod to perform a polar alignment, simply from the name, but not 100% convinced.

I also have the idea that needing a scope on to get the initial polar alignment is questionable since you do not point the scope at polaris alone, you point the scope at what is basically everywhere in the sky.

I would simply suggest levelling everything you can as reasonable as possible - this will reduce goto errors even if not polar alignment - then spend some time getting good polar alignment with the polar scope. Then see what occurs.

[Phillyo]

Hi Ronin thanks for the reply.

I don't use the scope for the inital polar alignment, for that I use the alignment scope going through the centre of the mount. Slewing the mount round to the correct point using EQmod then manually moving the AZ/Alt bolts so that polaris is centred in the small circle. The scope is just on the mount ready to go when I'm set up.

I did think though that Alignmaster was used to calculate errors on polar alignment not goto alignment? For goto alignment i just use syncs in eqmod using plate solving.

Thanks,

Phil.

[Phillyo]

This is one image from last night, uncal and just stretched to bring it out. I'm fairly certain it's field rotation around the corners of the image...

[Owmuchonomy]

Interested to know why you conclude its field rotation and not one of the many other possibilities? I say this because I am diagnosing problems with my set up and field rotation is easily excluded.  Have you used the test in DSS to check for it?

[Owmuchonomy]

This is one image from last night, uncal and just stretched to bring it out. I'm fairly certain it's field rotation around the corners of the image...

Just seen your photo.  That is also symptomatic of incorrect sensor spacing, the sensor being too far from the required distance.  You can check by doing short vs long exposures.  If it is spacing then it will look the same at all exposure lengths.  I've just been through this myself.

[Phillyo]

Thanks Chris, I'll do some tests after work. The only reason I think rotation is because i'm pretty sure my images from a couple of weeks ago didn't show this but I'll check.

Phil

[Owmuchonomy]

At least you can exclude other issues by testing.  Hope you sort it.  This was posted by Ian Bird.

Too Close.

 

 

Too Far.

 

 

It really does work! Honest. Well - it worked for my Riccardi Reducer/Flattener on my WO98.

[Phillyo]

It seems you are correct! Just had a very quick look at my 5min test shot for framing and it shows the same thing. Looking at the two images you've posted above it looks like I'm too far away. How strange! I thought I had it bang on. Thanks for this Chris, this has saved me a lot of hassle! Just need to look at the spacing now.

Phil

[Owmuchonomy]

It seems you are correct! Just had a very quick look at my 5min test shot for framing and it shows the same thing. Looking at the two images you've posted above it looks like I'm too far away. How strange! I thought I had it bang on. Thanks for this Chris, this has saved me a lot of hassle! Just need to look at the spacing now.

Phil

I can't take credit for this.  It came from the community.  I would try with a shot just a few seconds long to be absolutely sure.  I wish I could sort mine.  I have the opposite effect!

[Phillyo]

I will try next clear night. I'm super confused though because I'm sure this issue wasn't there a few weeks ago and nothing has changed. If it isn't one thing it's another!!

Phil

[Thalestris24]

Hi

Just a thought, are you trying to plate solve via narrowband filters? Can you not dial in a luminance filter? It should only need a matter of seconds of exposure to acquire an image for plate solving but nb filters aren't really practical for doing that. Maybe try doing drift alignment to achieve precise PA? Then setup guiding before plate solving so that you're ready to go straightaway after centering the target.

Louise

[Phillyo]

Hi Louise,

I'm not using any filters at all as I only own Ha, OIII and SII filters (no broadband filters due to poor light pollution). I have no problems at all plate solving using Astrotorilla. Once the images is captured and downloaded it solves within about 10-15 seconds and slews to my target accurately. When using Elbrus or astrometry.net it either doesn't solve or it solves but doesn't move anywhere. Confusing eh?

I've never done a drift alignment, but I was under the impression that to do one I would need to be able to see the south meridian as close to the equator as possible? If that's not the case then correct me and I'll give it a try.

Thanks,

Phil.

[Thalestris24]

Hi Phil

I'm confused by "I then use Alignmaster 3 or 4 times to accurately align using SGP to centre the star using slew commands with EQmod". Shouldn't you be adjusting alt/az bolts to centre the star? (http://www.alignmaster.de/Alignmaster.aspx)

I've only ever used Astrotortilla to do PA so I might be misunderstanding....

Louise

[Phillyo]

Hi Louise,

When using alignmaster you use the hand controller, or in my case eqmod to centre the selected stars so that it can calculate how far off alignment you are. After centering the second star using eqmod it then asks if you want to align az, say yes and it will move the mount a small but precise amount. You then use the az bolts to recentre the star. Repeat using the alt bolts and you should be pretty close to polar alignment. I repeat until I'm happy I'm as close as can be to polar alignment.

Awesome bit of software.

Phil.

[Thalestris24]

Ok, wasn't clear before. Similar to AT then. I take it you do that part with no filter?

Louise

[Phillyo]

I do all of it with no filter until imaging However I think after speaking to Chris above that the fault isn't rotation, it's CCD spacing. Going to look at it hopefully this evening if it clears up. Just need to work on the other issues now like Plate Solving and, more importantly, meridian flip!

Thanks for the help,

Phil.

[Thalestris24]

Ah ok

Spacing is critical! Good luck!

Louise

[Davey-T]

I've never done a drift alignment, but I was under the impression that to do one I would need to be able to see the south meridian as close to the equator as possible? If that's not the case then correct me and I'll give it a try.

Thanks,

Phil.

You can drift align pretty much anywhere, it's just easier low in the East and high in the South as you get faster easier to interpret drift.

Dave

[Phillyo]

Well I removed the 5mm spacer and tried again last night, I think it's looking better than before but I'm not sure it's perfect yet. Still, an improvement is a step in the right direction.

Thanks,

Phil