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Sunday, October 26, 2008

NGC 2024, Flame Nebula

Unguided, 272 x 15 sec JPEG frames, 1600 ASA, and noise reduction enabled. Had a little trouble getting this one, but in the end it didn't turn out too bad. I appear to be having battery amp glow issues as of late. Not too sure what that's all about. Nights have been getting cooler, too. Strange. It has been more prominent lately. Thinking about charging ahead of time and letting the batteries refrigerate for a bit.

Friday, October 24, 2008

Eric, "supersize" has been restored

The friendly folks at Google recently made a change to Picasa regarding the embedded picture hotlinks. Currently, the embedded references constrain you to a few fixed viewing sizes and does not directly provide a link to the full-size JPEG that is stored I used to be able to get.

I figured out how to bypass this. If you happen to notice the new links Picasa uses now, you'll find a size code inserted in the URL pathname. For example, the 288 pixel-wide view includes .../s288/... in the pathname. If you instead use .../s0/... for size zero, then apparently it defaults it to the full-size image stored there!

Programmers are so predictable.

So, all the 9 embedded links since that change in the Messier and NGC collections sidebar have been supersized, and I'll do so for all new pics.

Cheers, Eric. Thanks for letting me know you liked that feature.

Messier 1, Crab Nebula

Unguided 251 x 15 sec JPEG frames, 1600 ASA, noise reduction enabled. Always wanted to get a snapshot of this. Could stand to be taken at higher magnification.

Messier 15

Unguided, 212 x 15 sec JPEG frames, 1600 ASA, noise reduction enabled. This globular cluster and the stars around it bare a close resemblance to the view of M13 in Hercules.

Tuesday, October 21, 2008

My next telescope...

This hybrid Cassegrain design from Vixen is awesome. The VC200L uses a sixth order aspherical primary mirror and a convex secondary mirror, replacing the meniscus corrector plate with a triplet corrector lens near the end of the optical chain. Focusing is performed using a 2" Crayford focuser at the end of the optical chain, rather than moving the primary mirror and suffering mirror shifts during focus. The optical tube is baffled and the secondary is oversized. At f/9.5 it is somewhat faster than traditional Cassegrains.

For $1700, it is certainly more pricey than my $380 Newtonian. Yet, the step in optical precision is significant, and comparatively well-priced against competing and mainstream high-end designs.

Of all the optical systems I've researched, Vixen's VISAC design is the only one that addresses spherical aberration, coma aberration, and field curvature. Even chromatic aberration is far less than the exceptional (and more exceptionally expensive) flourite lens refractors. Considering that field curvature is eliminated, suggests better optical correction than even a Ritchey-Chretien...and new manufacturing methods for RC scopes are producing some much less expensive designs

From what I've read and observed from vendors and blogs, I think the VISAC design hasn't caught on simply due to technical arrogance in much of the user base and limited marketing visibility. It just isn't sexy enough and there simply are not any additional distractions or operational steps to get in your way. But, as of today, you can buy them from Orion Telescopes online!

Eliminating the corrector plate and complex mirror focusing mechanism clearly helps reduce the manufacturing costs. Baffling and Crayford mechanisms are cheap. So, the cost is likely rolled up into the improved mirror coatings and the corrector lens. A fair trade, I'd say.

All my deep sky photography relies on the reflectivity of my 6" primary mirror and oversized secondary without any loss in light transmission due to an intermediate lens configuration, though my reflectivity is somewhere in the mid 90% range (it's less than $400 bucks what do you expect). So in my view, the VC200L decrease in transmissivity by adding a triplet lens is offset by the 1.8" larger aperture and higher reflectivity from the superior Japanese mirror coatings.

Don't just take my word for it, read this article by Astronomy Technology Today. Note, the article is taken from Vixen's web site as access online requires subscriber login. I just need to save my pennies.

Messier 34

Unguided, 208 x 15 sec JPEG frames, 1600 ASA, noise reduction enabled.

Messier 52

Unguided, 223 x 15 sec JPEG frames, 1600 ASA, noise reduction enabled. Nice clear and dark night. Open cluster in Cassiopeia, discovered by Charles Messier in 1774. Even caught a glimpse of the Bubble Nebula near the upper left.

Monday, October 6, 2008

Baader Coma Corrector and the Sculptor Galaxy

Unguided, 247 x 15 second JPEG frames, 1600 ASA, with noise reduction. The camera was also fitted with a Multi-Purpose Coma Corrector (MPCC) from Baader Planetarium, Germany.

The MPCC attaches to the T-ring right in front of the camera, and comprises what appears to be 2 lenses complete with 7 layer coatings to provide a completely flat field and eliminate coma from the fringes of the field of view.

Well, I've definitely observed an elimination of coma around the edges of the larger master photograph (all my images are cropped to scale to a widescreen display). But, any time a lens is introduced less light makes it through, and two or three elements (lenses) has some impact. You can see in the image that the diffraction lines are barely visible and the stars less point-like.

Another unexpected downside due to the proximity of the MPCC lens surface to the CMOS sensor, is the radiated energy from the active CMOS sensor electronics in the camera being reflected right back onto the sensor! Arrrgh, this adds more noise the point it interferes with getting a cleaner image. I've taken several other photos so far with and without the MPCC, and the additional reflected noise is consistent. Never occurred to me before I bought the thing.

Its my opinion at this point, dealing with coma means spending more for a higher quality instrument such as a Mak-Newt, SCT, or of course an RC telescope. There is a hybrid made by Vixen, the VC200L, where the front plate is removed and a 3 element corrector optic is placed at the end of the focuser assembly. Comparable light loss might be mitigated by the fact it has an 8" aperture rather than 6" in my scope. Its possible the VC200L lens surface is far enough from the camera's CMOS sensor (at least 3 or 4 inches) that it might reflect very little back.