Can Live Stacking Negate Auto-guiding?

[Desbarry]

Recently bought a new Altair 26C super low read noise 16 bit APSC sensor. My guiding worked a while back but I cannot get it to calibrate in PHD2 "star didn't move enough" etc Until this is sorted here is my question. If I use the brain function to get my ballpark exposures for my given imaging time lets say 3 hours. If I start Live stacking with these settings of lets say 45 sec subs and save individual raw frames as 16 bit fits, will these be aligned by the stacking software so that I dont get any drift by not auto guiding? I then could then take some darks and put the saved raw files into Pixinsight to create a fully master light of all the stacked individual frames. Will I notice egg shaped stars even although I haven't been auto-guiding?

Is this a way around my PHd2 not working? Is Live Stacking as good as doing individual guided subs but without the need for PHD2? I wont be saving as seen but saving the clean raw frames for the weighted batch pre processing script in Pixinsight and adding my dark frames etc.

Hope someone can help just in case I cant get PHD2 to work again. Thanks
Derek

[oopfan]

Derek,

If the star moves during a 45 sec sub, then you will have egg-shaped stars. Fortunately you can instruct LiveStack to reject that sub from the stack due to its low quality. That is my understanding.

Brian

[admin]

Hi Derek,

yes, it depends on how well your mount tracks - take a few 45 second subs without guiding and have a good look at the stars. If they look round then you should be fine (if the subs are good then the stack should be good - the software will correct for the small offset from one sub to the next). If you are seeing elongated stars in a 45 second sub, then you need to either go shorter or get PHD to work!

On the PHD from, the two things that come to mind are...

1) PHD was tracking a hot pixel, not a real star, so it didn't move
2) The mount is not moving as expected (guiding settings, or perhaps backlash, or if you are using an ST4 cable, maybe a bad connection

cheers,

Robin

[Desbarry]

Hi Robin, its almost certailly the guiding settings as it did work months ago, the mount is a fairly new EQ6R and Im using an EQDIR cable NOT the ST4 and only downloading subframes on a USB2 cable to limit the bandwidth on the usb controller, Im using a HP laptop not a full PC desktop. Heres a 247 sub stack of 45 sec subs with the 115 APO Altair 26C and this mount so getting ok unguided but was just wondering if Live Stacking could further tighten the stars.

M42 sharpcap view.jpg (993.72 KiB) Viewed 1315 times

[admin]

Hi,

it's difficult to see in that image whether there is much trailing in the stars - if it is consistent across the image then it is probably down to tracking, most likely within each individual frame. If it varies from one part of the image to another then potentially optical issues (although polar alignment that is a fair way off can lead to a small amount of field rotation).

cheers,

Robin