Drift Alignment Frustration

[Crowmium]

Hey guys, following on from my last thread regarding drift alignment issues, I finally (after a year and a half of trying) managed to get what seemed to be precise polar alignment using the drift method. The goal of this is to get long(ish) unguided subs. My setup is a Skywatcher NEQ6, SW 80ED Refractor, Canon 100D DSLR and i'm using BackyardEOS to control the camera. I don't yet have a focal reducer or any form of autoguiding.

Here is an image of my altitude alignment (using the D.A.R.V method), using a star at around ±10° dec from the celestial equator, as near to the east horizon as possible.

(Apologies for the poor image quality - I had to use my phone camera since print screen didn't seem to want to work on the laptop).

And here is my alignment for the azimuth (taken near the meridian at ~0° dec).

I spent hours trying to get both as precise as possible - I think more precise alignment would have been next to impossible for me to do. Regardless, after finally feeling like i'd got good alignment, I went to take an image and I was pretty disheartened. A 30 second exposure left me with significant star trails. The longest subs I could get without trails were ~15 seconds. After nearly a year and a half of just trying to get good polar alignment, it feels like a bit of an insult, especially given that people often talk about getting 30-60 second unguided subs. But, i'm determined to eventually get there.

So my question is, why is this happening? Could it be that my mount is flawed or damaged from the time I dropped it on my head? Do I just not have enough practice making the small adjustments to the mount required for unguided subs? Could balancing play into this? I've tried to balance my mount as best I can, but the dec axis is still heavily skewed towards the back/camera end of the scope and i'm unable to move the scope any further forward on the dovetail to counter this.

Or could this be that i've simply hit the limit of my setup? I was always intending on buying an autoguider once I was familiar with my equipment and able to get good polar alignment, but would it be worth it? I'm a bit worried that if I can't get better alignment, an autoguider really isn't going to make much difference (and at best give me bad field rotation).

Alternatively, are there any other methods of polar alignment I could use? I don't really want to use the polar scope method, and would prefer drift alignment if possible. I'm aware that pHd has a drift alignment procedure, and i'm tempted to try it if I do end up getting an auto guider. 

Any help or discussion is much appreciated!

 

Cheers,

Crowmium.

 

[wxsatuser]

How long were your DARV exposures?....they look quite short.
The further away you are from the optimal points in the sky the longer the exposures need to be.

Try longer exposures, even if they run off the screen it will not matter.

[Thalestris24]

Hi Crowmium

You need to sort out your balance issues first. You can counterbalance with a small ankle weight wrapped around and taped in place (what I use on my 80mm  ). A little 'east heavy' is recommended for imaging. Good PA is only part of the equation. Also, you are trying to image at 600mm - not a huge fl but longer than it would be with a reducer, and at f7.5 rather than f6.4. Plus without a flattener means your images will have a lot of distortion... Of course, a reducer + guiding will make your life much easier!

Best wishes

Louise

[Adam J]

Huum, that does not sound correct I can easily get 2 min subs with a HEQ5pro when doing an normal alignment with my 130PDS before getting a guide camera...I even have a friend who managed 5 min subs. Its could be that you are too well balanced, perfect balance is actually a bad thing as the gears are kinda floating with respect to each other instead of meshing leading to backlash and jerky progression. 

Make sure you are exposing for a sufficient time during the drift.

If all that does not help it could be that you need to tune up the spacing on your gears, there are tutorials about describing the process, but a belt mod is probably the best idea. 

[Crowmium]

My exposures were 125s total (5 seconds for burning the initial star position in, 1 minute slewing left and then 1 minute slewing back right). I'll certainly try longer exposure times when I next can!

Thanks for the balance advice guys, i'll give that a try too. Sadly, it looks like i'm not going to have time (or good enough weather!) to go out imaging for quite some time.

Adam, thanks for the advice regarding the gears. If the sorting out the balancing hasn't much effect then i'll look at adjusting the gears or getting a belt mod.

Would you recommend getting an autoguider and using something like pHd2 polar alignment instead, or should I wait until I have this sorted first?

 

 

[Adam J]

1 hour ago, Crowmium said:

My exposures were 125s total (5 seconds for burning the initial star position in, 1 minute slewing left and then 1 minute slewing back right). I'll certainly try longer exposure times when I next can!

Thanks for the balance advice guys, i'll give that a try too. Sadly, it looks like i'm not going to have time (or good enough weather!) to go out imaging for quite some time.

Adam, thanks for the advice regarding the gears. If the sorting out the balancing hasn't much effect then i'll look at adjusting the gears or getting a belt mod.

Would you recommend getting an autoguider and using something like pHd2 polar alignment instead, or should I wait until I have this sorted first?

 

 

Its an interesting question, I have both the belt mod and a guide camera and get 20min+ subs. The guide camera will make the most difference but you will still get occasional errors creeping in from periodic error in longer exposures (i beleve the EQ6 suffers more in this regard than the HEQ5). The belt mod might be more affordable but wont 100% give the results you are looking for on its own either.

If you can afford it go for both, if not that then just guiding, if your really struggling then go with just the belt mod.  

[Crowmium]

Thanks for the reply Adam, the only thing that worries me is field rotation. I've heard it can get quite bad if you don't properly polar align and just use an autoguider instead. Hopefully the polar alignment i'm getting will be sufficient - if not i'll look into using something like Alignmaster or pHd2 alignment.

[wxsatuser]

My setup is on a permanent pier but all I do is use the polarscope and get Polaris bang in the centre of the circle.
I find Polaris postion with a Polarfinder app but make sure that you have calibrated your polarscope.

I can get 5minutes and stars just start to get dodgy, I have the belt mod btw.

I balance my setup so it's near perfect then drop the counterweight a tad so the mount just slides back down.
This is east heavy and makes a better worm mesh, this is ok imaging east of meridian.

[rigradio]

Forget the DARV, instead use Drift Align feature in BYEOS.

Rotate the reticle so that the star moves parallel to the crosshairs in Dec and RA when using the slow motion controls.
IGNORE RA drift! You only need to watch DEC drift and make adjustment accordingly.

Adjust with this simple mantra -> "UP RIGHT"
Here is an example -> http://www.astrosurf.com/re/polar.html
You can defocus the star as in the article above.

Here is another good article explaining about the "UP RIGHT" mantra -> http://astrophotographyonabudget.blogspot.co.id/p/drift-alignment.html
Try to contact Doug German the author, and ask him if he could send you the Drift Alignment Simulator and another SWF files which seems all dead in his article.

An example of good PA I achieved within 45min (AVX, 60D, AT65EDQ):

180sec unguided



300sec unguided, see the RA drift  (this is the point where you need to guide)

 

HTH!
Ketut

 

 

 

[Crowmium]

6 hours ago, wxsatuser said:

I balance my setup so it's near perfect then drop the counterweight a tad so the mount just slides back down.
This is east heavy and makes a better worm mesh, this is ok imaging east of meridian.

Thanks for the advice, does that mean I should make the setup west-heavy when imaging west of the meridian?

2 hours ago, rigradio said:

Forget the DARV, instead use Drift Align feature in BYEOS.

All this time i've been using BYEOS and never once have I noticed the huge 'Drift Align' button; i'm feeling rather silly now. Many thanks for the guide, i'll be sure to give that a try instead of DARV. Managing to get 180s unguided subs from under 45mins of drift alignment would be amazing!

[wxsatuser]

1 hour ago, Crowmium said:

Thanks for the advice, does that mean I should make the setup west-heavy when imaging west of the meridian?

Yes, move weights up so camera end is heavy, worth marking bar for future reference.

[Crowmium]

Thanks everyone for all your advice - it's revealed things I hadn't even thought about (balancing the scope properly, BYEOS drift alignment, belt mods etc). However, I managed to get out with the gear again tonight and I came to the realisation that i'm a complete idiot.

All this time (a year and a half), i've had the RA and Dec axis mixed around - i've been mistaking Dec drift for RA drift and ignoring it. For example, when using the DARV method, i've been slewing Up and Down on the keypad rather than left and Right. Tonight I rotated the camera and drift aligned with the axes the *correct* way around, and I managed to get over 60s subs by spending roughly an hour on alignment. I really can't believe I didn't realise I was doing this all this time, especially as an astronomy student who did well in his observational classes.....

I'm super happy that I finally managed to get this sorted, although after about an hour of properly imaging for the first time, my power tank died. I hadn't gotten round to charging it from my last session since I didn't think tonight would be clear - I really have no idea how i've managed to get as far as I have in astronomy

Here's an example of an unprocessed 60s image I took tonight.

Anyway, I think my polar alignment issue is sorted and i'll look into getting a autoguider some time later in the year. Thank you all again for your replies, they're much appriciated!

[wxsatuser]

Certainly looks ok and not bad for 60secs.

[Crowmium]

I'm super pleased with it, especially given that I could certainly improve the alignment by using a longer DARV exposure (or the BYEOS method rigradio suggested above). Now I just need to practice getting super precise alignment