Can anyone Identify these weird Star shapes?

[obrads (Alex obradovic)]

hello everyone, i need some advice,
i will first state my issue,
then equipment
then what i think

I had my first imaging night a few days ago with my new ASI1600mm and filter wheel plus OAG and i was impressed with the camera! how ever i am getting some odd star shapes that do not look like guiding issues too me. it is the same scope i have always used and didnt see this happen when imaging with my DSLR. I was wondering if some more experienced images could take a look and point me towards what could possibly be the problem and how to fix it.
i am using a belt driven and tuned HEQ6 mount, ED100 skywatcher refactor with 0.85 reducer. guiding with the qhy11 5L mono on an orion off axis guider. i have the 8 position filter wheel and the ASI1600mm.

here are some pictures of my stars. it appears to me that in the 2-10 second subs the stars appear to be smeared, and in the longer subs and brighter stars it looks like the stars have a dint in them. if you have seen anything like this i would love to know what could cause this and how to fix it because its really annoying me haha
Regards, alex

[alpal]

Hi Alex,
are you using PHD2 guiding?
can you post a guide graph?

cheers
Allan

[obrads (Alex obradovic)]

yes i am, i dont have the log or a picture but my guiding was consistent at 0.8-1 arsseconds , no large jumps or dips, i did have a bit of cable drag but i expect that to show up differently?

[alpal]

Originally Posted by obrads

yes i am, i dont have the log or a picture but my guiding was consistent at 0.8-1 arsseconds , no large jumps or dips, i did have a bit of cable drag but i expect that to show up differently?

It could be so many things -
it looks like your OAG is loose or the guide star was too dim -
some of the pics look like your camera is too heavy for the focuser
& it's causing mis-collimation & distortion.

My PHD2 guide graph is normally reading below 0.25 pixels rms.
What was yours saying?

It can take a while to iron out bugs with any system.

cheers
Allan

[obrads (Alex obradovic)]

Hey Allen,
the focuser thing crossed my mind as well since its a pretty bad one, if i want to see if it is that would can i do to test that?
mine is always below 0.25 as well

[alpal]

Originally Posted by obrads

Hey Allen,
the focuser thing crossed my mind as well since its a pretty bad one, if i want to see if it is that would can i do to test that?
mine is always below 0.25 as well

I have no experience with refractors.
I use Newts.
Maybe someone here could help you who has specific knowledge of your model -
ED100 skywatcher refactor with 0.85 reducer.

Maybe your thread should be here:
http://www.iceinspace.com.au/forum/f...splay.php?f=35

[bojan]

Looks like extended sensitivity of the camera for IR... I have similar problem with my Canon 400mm f/2.8 and modified DSLR, before I used UVIR block filter.

[gregbradley]

UV/IR bloat is one possibility, what filters are you using?
More likely some tilt causing elongations. As to those dents in the sides of the stars that's a bit harder to fathom.

Best to eliminate one possibility at a time. Check for tilt by rotating the camera and see if it changes the way the stars look.

Greg.

[obrads (Alex obradovic)]

Originally Posted by bojan

Looks like extended sensitivity of the camera for IR... I have similar problem with my Canon 400mm f/2.8 and modified DSLR, before I used UVIR block filter.

is that an issue for CCDs?

[obrads (Alex obradovic)]

Originally Posted by gregbradley

UV/IR bloat is one possibility, what filters are you using?
More likely some tilt causing elongations. As to those dents in the sides of the stars that's a bit harder to fathom.

Best to eliminate one possibility at a time. Check for tilt by rotating the camera and see if it changes the way the stars look.

Greg.

i agree might be tilt the focuser was extended far, is there a way to fix the tilt?
with the bloating, this was a lum sub at a dark sky site, they are the stock standard ones that come from the asi supplier

[bojan]

Originally Posted by obrads

is that an issue for CCDs?

Yes it could be the issue for refractor, CCD is much more sensitive to IR than standard (and modified) DSLR, and refractors in general are not corrected well enough for wide spectrum.. when doing narrow band, you need to refocus for each filter.

[obrads (Alex obradovic)]

Originally Posted by bojan

Yes it could be the issue for refractor, CCD is much more sensitive to IR than standard (and modified) DSLR, and refractors in general are not corrected well enough for wide spectrum.. when doing narrow band, you need to refocus for each filter.

ah i didnt realize, thank you ill do that next time

[obrads (Alex obradovic)]

i have 100% figured out the the star shapes are due to tilt in the focuser tube since it is extended lots, i am trying to figure out how to deal with this and am considering buying a 2" M- F tube to attach to the focuser tube before my reducer and imaging set up, my thought process is that with will mean the tube doesn't have to be extended as far and will reduce tilt? will this work? if anyone knows. thanks