Deep Sky Stacker

[ultramol]

Had my first go at wide field last night and encountered this problem. After going through the "compute No of stars " in dss it said 35 stars detected and this was at %3. But after stacking it just said there was only one frame to be stacked go and adjust the percentage slider to get more stars. Hope this makes sense to anyone ! When I compute the stars there is 35 when I stack them there is none, anyone any ideas as to what I am doing wrong. By the way I took 15 subs at 20 seconds each and 10 darks..

regards Geoff

[nicks90]

i had the same issue, so i just adjusted the slider to 10% and re-ran the stacking and it worked.

no idea what it does... but it did something and made the magic happen.

[ultramol]

I will try that but when I increased the % it said no stars were found after computing the subs. I will keep on trying. Do you think 20 second exposures are enough to register anything on the camera ?

[nicks90]

absolutely!

this is my take on Lyra - cant remember exact details, but I think they were 15sec explosures x 20, with a few darks (all at same iso and exposure) and about 20 dark bias frames (same iso, just fastest shutter speed).

bear in mind I did these as Jpegs as I forgot to set my camera to RAW. N00b mistake!!!

all i did was load them all in and leave everything on default and up the star count bar a bit and also told it to stack best 90% of the frames and away it went. Saved the file and opened it in GIMP and moved some sliders around in a completely random haphazard way until i had a black background and white(ish) stars. I am sure there is loads more detail in there, but i dont have the foggiest how to do it and i didnt even RGB align in DSStacker, as i dont know what it does......

plus next time I'll use RAW mode...

and read a tutorial or two before I 'process'...

and spend more than 5 minutes doing it... but I'm not that patient...

[ultramol]

Thank you guy's. I will take it onboard and try again, when the sky clears that is !! I am sure with your help something will pop out of the darkness....

[Atreta]

Did you uncheck the median filter option before computing?

it helps a lot

[dph1nm]

After you have run the star detection, check each image out with the star editor in DSS (icon down the right hand side when you display an image). This shows you what stars  have been detected (and lets you delete, and sometimes add extra ones). Check it has found real stars (e.g. not hot pixels) and that it has found much the same stars in each image (no good if it finds 35 different ones in each!).

My other advise is to run each step separately.  So "Register checked images" first (which does the star detection) then "Compute offsets" (which find the offsets & rotation between the images). You will then get a list against each image telling you how many stars it found and whether the alignment worked (if it did, dx dy and angle will be set - if they are not set, the image will not be added to the stack).

NigelM

[ultramol]

Thank you for that . I am sorry I took so long to reply but I have had no internet for a few days and only just got it back on. I will take your advice and see what I can do.

[Astrosurf]

Have you had a chance to try again? I had the same problem and reduced the detection to 3%! I don't understand it, but it works for me.

Alexxx

[ultramol]

Right, here is what I did. I retook the images at an extra 5 seconds (20 instead of 15) and then left the detection rate at 10%, from finding no stars it found 156 or so. I left all settings at the green recommended and run it . The images where then run through photoshop on a curves layer where lo and behold, stars appeared in abundance, albeit slightly wonky but that was because I only roughly aligned that night. I took images of cannes venatici because being a novice I could not find the whirlpool galaxy through my scope but readily Identified where it was with my picture. I now have to learn how to read the sky upside down and back to front...I have been up all hours running and rerunning images through DSS and have come to the conclusion that only practise ( and the invaluable help on here ) will make me a better astrophotographer, there is no easy fix !! I ended up quite pleased with my deep sky image and would show you it but I cannot find were I saved it to...Doh.. If I find it I will upload it. I think I will need a coma corrector though as the stars at the edges are a bit elongated but I think that is because my tracking was off.

Many thanks to you all for helping me and I have no doubt I will be asking for your help againsooner rather than later.

Regards....Geoff

Found one.Out of focus, bloated stars but my first attempt...

[Astrosurf]

Congrats on getting it sorted! If the stars are more elongated/distorted at the edge of the field, that's coma. (Could it also be field rotation guys??)

Onward and upward with AP. Now prepare to empty your bank account!

[ultramol]

I am in the process of buying astroeq, then EQMOD and away I go, well, I need a laptop also but I have a couple of months before the dark season gets here so I can Practise with my pc before attempting it in the dark,  by the way is field rotation caused by bad alignment ?

[Astrosurf]

Yep, it is. See here (there's a good image at the bottom): http://calgary.rasc.ca/field_rotation.htm

Good luck!

[ultramol]

Cheers for that astrosurf, will have a good peruse.....Regards Geoff

[Atreta]

Guys, borrowing the topic about DSS,

i'm stacking some pictures and it gets somewhat blurry around the corners.

is there anything  that can be done to prevent this?

thanks