From: Alan Friedman <alan@greatarrow.com>

Date: January 21, 2010 11:08:04 AM MST

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] New Images

HI Milton,

Thanks for sharing your new images. I especially like your capture of M46 - have always enjoyed this object visually with the ghostly planetary nebula haunting the field. 

There was a thread in the Astro-Physics Yahoo group about a problem with reflection around bright stars - I think the cause was being associated with certain RGB filter brands, but I didn't follow the discussion very closely... might be worth a look. I seem to recollect that some deep sky folks have been switching to Baader's RGB filter set for this reason.

best wishes,

Alan

On Jan 20, 2010, at 4:03 PM, milton_aupperle wrote:

Hi Folks;

I've posted some first draft DSO images that I captured on the Nights of January 16 and 18, the only clear nights I've had in nearly a month. It was a balmy -4 to -8°C those nights, so I only needed to wear a heavy sweater when outside and didn't need to use heating pads to keep the scope or laptop from freezing up. I used the C8 @ 1150 mm, LRGB Astrodon filters, a Hutech IDAS LPR, the Grasshopper PGR camera (cooled to -20°) and a monochrome PGR Camera with the Celestron OAG for guiding. I shot Lumas at 1x1 and then binned all the RGB shots 2x2 when capturing. That reduces my RGB exposure times by a factor of 4 times, so instead of needing 24 minutes per Red image, I can shoot 6 minutes. I can go after 3 or 4 targets in a single night now as it's dark here at 6:30 pm and doesn't start getting light until 6:00 am.

Turbulence was low (+/-3 arc seconds) on Jan 16 and moderate (+/-8 arc seconds) on Jan 18.

I've discovered that I have a really bad reflections happening when I have bright (i.e. Mag 4 stars) stars in the FOV for long (15 minute) exposures, as shown in the Running Man "NGC1973" or the IC417 images. It's most pronounced with the Green filter, but happens for all LRGB images. I'm not sure what is causing it, but it looks like the light is bouncing off one or more of the glass surfaces multiple times and then becomes out of focus, which is why we have the collimation rings. It could be off the glass plate over the CCD on the camera, the LRGB filter, the LPR or maybe even the Focal reducer.

In any case here are the images..

Auriga reflection nebula (need a lot more exposure time under less light polluted skies):
http://groups.yahoo.com/group/Astro_IIDC/files/DSO/IC417_LRGB_20100116.jpg

Running Man nebula in Orion (haloed stars):
http://groups.yahoo.com/group/Astro_IIDC/files/DSO/NGC1973_LRGB_20100116.jpg

Messier 38 open cluster in Auriga:
http://groups.yahoo.com/group/Astro_IIDC/files/DSO/M38_20100118.jpg

IC 434 the Horse Head nebula in Orion
http://groups.yahoo.com/group/Astro_IIDC/files/DSO/HorseHead_20100118.jpg

M46 an Open Cluster and NGC 2438 a ring planetary nebula that only gets 20° above the horizon up here:
http://groups.yahoo.com/group/Astro_IIDC/files/DSO/M46_20100119.jpg

TTYL..

Milton Aupperle