Testing the TS OAG with 30min subs

[Catanonia]

I really wanted to push the TS OAG with my QHY9 mono and Skywatcher MN190

So here is 4 x 30min unbinned Ha 8nm subs of the Wizard Nebula NGC 7380.

Wanted more subs, but around 1am tonight, the clouds rolled in and I was completely dewed up even with heaters.

Still, managed to get some observing of Jupiter for a change.

So 2 hours of Ha on the Wizard with 4 subs, the noise isn't too bad and I have applied darks / flats to the image.

Full sized here http://dl.dropbox.com/u/10801850/Astro%20Pictures/Large%20Files/Wizard%20Nebula%20Ha%2030mins.jpg

[johnh]

That is looking good and 30min subs will really kill the noise but you have to have little or no cloud to get this length. The TS OAG is a wonder with its 9mm thickness but takes some fiddling to get it all running but worth it.

John.

[ollypenrice]

You set yourself a challenge there, Cat! Seen at 100% there is a small elongation running 1 o'clock to 7 o'clock. It is pretty minor for 30 minutes, though. Is it on all subs and do you think it's guiding or field rotation?

Olly

[Catanonia]

You set yourself a challenge there, Cat! Seen at 100% there is a small elongation running 1 o'clock to 7 o'clock. It is pretty minor for 30 minutes, though. Is it on all subs and do you think it's guiding or field rotation?

Olly

Definately a challenge Olly to really stress it out. I too noticed the elongation at 100% and am unsure. The guding looked good, however there was mashoosive amounts of dew around last night. The corrector lens was a right mess by 2am.

I was unaware you could get field rotation with a EQ mount, unless of course I am not perfectly Polar Aligned and no amount of perfect guiding would fix this.

John : I was more amazed I got no plane or satellite trails

[Psychobilly]

Looking good...

What did you stack in Cat..?

Something seems to have "removed" the pixels from the center of the stars in the top left of the image (on 100%)...

I have seen DSS do this from time to time usually as a a result of applying the Cosmetic Hot pixel removal option...

Peter...

[Catanonia]

Peter,

I think this may have been due to the due and hence off focus on the edges. Noticed this morning I had a loose connection on the heaters and hence all the problems.

Was stacked and calibrated with PI, but used 20min darks instead of 30min darks as I had no of this length. That also might be the problem for removal of hot pixels.

Just stripped and cleaned the MN190, front corrector, the lot and re colimated, so might get another go tonight. Taking some 30min darks now to see if that was the problem.

[Psychobilly]

It definitely wasn't "consistently" there across the whole frame... If I ever do anything other than Video stuff with the SCT I'll have to dust of my OAG-9...

[ollypenrice]

I think the right darks will make a difference. Doing a stack without any, just to look at the stars, might be interesting. Only polar misalignment will introduce field rotation on an EQ, as you say, but it gets more critical at 30 minutes! I don't think that's the issue here, personally.

I wonder what you'd feel about guiding at or beyond 2 metres on an EQ6? It is under discussion here. http://stargazerslounge.com/equipment-discussions-help-mounts/155007-cgem-vs-neq6pro-2.html

Olly

[Tim]

It's a nice image Steve, but how do you mean is it testing the OAG??

What long exposures really do is test the imaging camera, and the polar alignment of the mount. If the alignment is close to perfect then the only thing that will stand in your way of very long subs is the ability of the camera to stay cool and noise free, and the amount of time you get before a meridian flip.

I have found that in most cases, the extra data you get with 120 minute subs is not worth it compared to say 40 - 45 min subs. The exception so far is the really feint outer rings of things like M57 and M27, the extended exposures do help to give those more structure and form.

What anti-dew measures are you using btw? I have never had a problem with the MN190 and dew, using a dewshield and a heater tape, even on really wet nights.

[Tim]

Oh btw, the collimation is off, probably a rotated secondary. The stars top left are not focused, whereas bottom right they are, indicating that the optics aren't properly aligned.

How do they look individually? The same?

Cheers

Tim

[Catanonia]

Thanks Tim,

I was stress testing my whole setup with 30m subs for Polar Alignment, focus, etc etc.

I have a dew shield and heaters, but seemed to have a malfunction in the heaters last night.

I have removed and cleaned the corrector lens on the MN190 and totally re-colimated so hopefully these issues will go away.

Also about to process with 30min darks I have just finished to see if they make any difference.

[Tim]

You've probably noticed, but the secondary has an etched donut to mark the optical axis. If you mount your laser in the focuser, after having set the secondary to be aligned visually with the focuser, then the laser beam should point dead in the centre of the etched donut. If it doesn't, and the secondary is properly set, then your focuser may need shimming to bring the focuser axis in line with the optical axis.

Cheers

Tim

[Catanonia]

Thanks Tim, Pretty sure my focuser is dead center to the secondary, but will re-check agter my recent strip and colimation.