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RICHARD COFER

VdB 141 Ghost Nebula

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Posts Made By: Roland Christen

May 29, 2009 08:40 PM Forum: CCD Imaging and Processing/Deep Sky

IR/UV cut filter question

Posted By Roland Christen
When you deep stretch the image, that's when you begin to see the effects on stars. Here's an example where a UV/IR filter would have helped: http://www.danilopivato.com/tabulae_coeli/1300_n30/m3_brc_hires.htm

And here's what it should look like (courtesy of Anthony): http://www.perseus.gr/Astro-DSO-NGC-6205.htm

Rolando

June 1, 2009 06:02 PM Forum: CCD Imaging and Processing/Deep Sky

A shocker in Serpens! Sh2-64

Posted By Roland Christen
Tom "Dusty" Davis does it again.

Rolando

June 1, 2009 06:11 PM Forum: Equipment Talk

Astrographs vs wide field scopes

Posted By Roland Christen
Astrographs are specialty instruments that have been designed to produce a flat field image with no coma and no astigmatism, sometimes also with no distortion (barral or pincushion) and be fully baffled so no off-axis light can reach the focal plane, plus have full or nearly full illumination to the corners of the field. Almost all normal "wide field" scopes have one or more of the above defects. Yes, they can produce nice looking images but when you want edge resolution same as center resolution, then an astrograph (properly designed) is going to be your best bet.

Because of the various requirements listed above, an astrograph will usually not be a good visual instrument. The mirror types will have oversize central obstructions and be generally way too fast for good eyepiece performance. Even the best eyepieces will begin to add significant on-axis spherical and off-axis aberrations to a scope that is faster then F4.

Rolando

June 3, 2009 11:17 PM Forum: CCD Imaging and Processing/Deep Sky

M3--2nd Light with my 152mm

Posted By Roland Christen
very sharp image, but you have clipped the bottom of your histogram, so you have lost all the faint data.

Rolando

June 4, 2009 06:11 PM Forum: CCD Imaging and Processing/Deep Sky

M27

Posted By Roland Christen
Full size crop

June 4, 2009 10:56 PM Forum: Equipment Talk

Now trying the new Astro Tech 8" Ritchey-Chrétien

Posted By Roland Christen
>>quartz mirrors with Dielectric high reflectivity coatings>>

If it's really dielectric, then that's not a good idea. Any mirror over 2" diameter will warp with dielectric. We tried a 5" diagonal and ended up with a pretzel. Dielectric only works on mirrors where the wavefront occupies a tiny fraction of the surface area, and then only for small optics.

Of course, it could be that it's a simple aluminized surface with a 2 or 3 layer overcoat. It may be "marketeer speak" to call it a dielectric. It would not surprise me. I've seen just about everything when it comes to marketeering in this business.

Rolando

June 5, 2009 04:31 PM Forum: Binoviewers

Canon 15X50 "All Weather" Image Stabilized Binocul

Posted By Roland Christen
I had a similar experience with a Sony digital camera. $600 camera, it quit working about 1.5 years after we bought it. Shutter froze up. They said repair costs would be $450 to $500 plus shipping to California. I don't think that any of these major Japanese companies stand behind their products these days.

Rolando

June 6, 2009 05:25 PM Forum: Astro-Physics

Exoplanet XO-1b in CrB

Posted By Roland Christen
Impressive data.

Rolando

June 9, 2009 03:01 PM Forum: Bad to the Bone Autos

Chick Magnet

Posted By Roland Christen
Latest update from the streetfighter Mustango:

Wins:
Subaru GT - spanked big time
Pontiac GTP - haha, not even close
Evo - got embarrassed by the mighty Roush Mustang
Harley Hog - no chance for this bike, not even close

Losses:
Honda CBR - this was a fast little crotch rocket (make note to avoid in future)

2000cc custom chopper with very fat rear tire - now this bike really creamed the Mustango, faster yet than the CBR. His fat tire grabbed right off the line and left me smoking my tires. The bike shot forward with such ferocity that I had a hard time adjusting my eyeball focus. And it was LOUD! Like shotgun blasts going off at 6000 rounds per minute.

June 9, 2009 09:19 PM Forum: CCD Imaging and Processing/Deep Sky

Drift NS - 7479

Posted By Roland Christen
How are you guiding in RA? Seperate guide scope?

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