Phd2 question and multiple nights data question

[Rusty2]

Hello !

I firstly just want to say what breath taking pictures you people are capturing , I'm always stunned when I look at them : )

This has been a long and slow journey for me mainly because I don't have a lot of time and the clouds seem to know what I'm up to . I've bought myself a steep learning curve but I've been doing my homework : (

I believe I've now got the basics to start capturing data which I've managed to do on 2 seperate nights recently , with long exposures and nice round stars : )

My first question is , how does one combine data from multiple nights ? Do you just jam all the "Lights" together , all the "Darks" together ? Last night I was experimenting with exposures lengths . 5 minute exposures didn't seem to bring out quite enough detail so I want to do longer exposures on the same target as well . Do I have to process each night seperately ?

My second question is about Phd2 . I've been practising drift aligment for the last 3 months or so , intermittently . I now have my alignment so close that the purple error circle is so small you couldn't physically improve it any further . BUT..........the trend line still shows a small deviation away from a dead flat line . Although there is a deviation , guided long exposures are still producing nice round stars .

In the drift alignment tool , I have my Y setting at Y: +/-4" . This seems to show up inconcistencies much more than Y: +/-8" .

Any thoughts would be greatly appreciated : )
Russell / Rusty / Russ

[Startrek]

Russ,
Deep Sky Stacker is a popular , user friendly, reliable and excellent free open sourced software to stack your raw data images prior to post processing

I’ve written procedures to stack multiple nights data using either OSC/DSLR or Mono data ( see attached )

In regard to PHD2 and polar alignment, you can get away with 10 arc minutes of PA error and still guide successfully ( although some image shift / rotation over time may occur ) You don’t have to be obsessive or compulsive about super tight polar alignment , around a few arc minutes if fine ( refer PHD2 user guide ) but most folk aim for an arc min or below. I’m usually around a few arc minutes and image up to 1250mm focal length with 5 min subs , dithering and tight round stars.

I’ll also attach some of my PHD2 docs as well

Good luck and enjoy
Sounds like your doing that already
Cheers
Martin

[Startrek]

Some PHD2 docs attached
Cheers
Martin

[Rusty2]

I greatly appreciate your advice and information Martin !
I'll start reading .
Thank you :)

[Startrek]

Glad to help where I can Russ
It’s not an easy hobby

Some more PHD2 docs to read (the PHD2 analysis graph doc is an excellent resource)

Hopefully some other folk can chime in too

Cheers
Martin

[Drac0]

Hi Russ,

Great advice & documentation from Martin as always. As he says, don't get too pedantic about "perfect" polar alignment, within a few arc-minutes is good enough. In fact, it's often easier for PHD2 if the PA is that tiny bit off anyway. The only thing with PHD2 is to make sure your graph settings use arc-seconds & not pixels. The pixel setting graph will look nice & flat, but it doesn't really tell you much.

As for your stacking question, there are a number of very good free options. Martin suggests DSS which is a great free program and does well. I used to use it all the time, but now I mainly use ASTAP for stacking. It's quite a powerful program but not as well documented as DSS. And the extra tools it provides come in handy. Additionally it's something that I already have installed as a plate solver with my capture software anyway (APT). So it's doing double duty from the start.

Cheers,
Mark

[Ramius]

Martin
As a beginner I am about to tackle my first stack with different exposure times and while my tracking is OK I am working through options to improve it. Your procedure docs in both these areas are really handy and have gone into my reference folder. Just wanted to say thanks.
Bill

[Rusty2]

Hi Martin , I've been reading through your PDF files , thank you !

I've got most of it wired and already have several documents about PHD2 thanks . The "obsessive or compulsive" comment was probabaly the most helpful , because I do get fussy and want things "perfect" , it's just the way I am : )

Because of my inexperience , I should have mentioned that I was using pixinsight and also bought the book "Inside Pixinsight" to help me . The book has helped me a lot and I've been through the process maybe 4 times . Because of this I now realise I need longer exposures .

I have noticed sawtoothing and dealt with that weeks ago . Tuesday night went well and long exposures were good .

I have seen the odd spikes in the PHD2 graph and quickly raced to check for snaggs but couldn't find any . I think I have flexure (piggy backing) in my rig when facing south but not when facing west . I'll get there , thanks again : )

Hi Mark , yes I have my graph set to arc-seconds & not pixels .
As mentioned above I have pixinsight : ) I'll stop being lazy and check the book to see what it says about stacking multiple nights . Thank you !

[Startrek]

To All,
Glad to help where I can
Get used to the Dec and Ra spikes whilst guiding, some nights in Sydney I’m almost flat lining at 0.45 arc sec total and other nights ( high humidity/ bad seeing ) it’s see sawing at 0.85 + arc sec total. You can’t guide your way out of bad atmospheric conditions. The night sky is a moving target when it comes to atmospheric stability ( unless you live in a desert )
Consistent poor guiding is generally caused by mount mechanical problems or bad atmospheric seeing or a combination of both
Medium to Big periodic spikes generally can be caused by periodic error in mount worm gear , wind gusts , cable drag or snag and atmospheric conditions

I recommend you join the PHD2 forum for future support and help
If and when you have serious issues you can post your guide logs and Bruce and Brian can evaluate your issues with a timely reply and recommendation.

Cheers
Martin

[Startrek]

Mark,
I only use ASTAP to evaluate my subs before loading into DSS, excellent for stretching and viewing raw fits files.
ASTAP stacking apparently does some auto colour balancing on the fly during the process which doesn’t work for me as I use Startools. Startools requires clean stacked linear data to allow optimum signal tracking performance.
Cheers
Martin

[Drac0]

Yes, ASTAP can do auto colour balancing & auto levels but these options can be disabled in the Stack Method tab. But you produce great results doing things your way so it shows that DSS can work very well. I'm just happier with ASTAP, especially for stacking mixed NB data - different filters, exposures, temps, flats, darks etc. ASTAP can handle it all at once. :)

Cheers,
Mark