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LBN 576 - The Garlic Nebula

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Posts Made By: Alan French

March 29, 2006 04:38 PM Forum: Telescope Making

Inspirational Bi-Newt

Posted By Alan French
A lovely design and wonderful workmanship. I would, however, give some thought to where the observer is when using the scope. Body heat can be a big issue with some designs.

Clear skies, Alan

March 30, 2006 05:41 PM Forum: Telescope Making

Thoughts on spider veins

Posted By Alan French
About 20 years ago I made a piano wire spider for my 10" f/9.5. I was surprised at how obvious the spikes were. Out of curiosity I mounted my old vanilla Novak spider at 45 degrees to the piano wire version. The spikes from the Novak were less obvious than those from the piano wire spider.

Clear skies, Alan

April 2, 2006 01:08 PM Forum: Equipment Talk

Feedback on turrets?

Posted By Alan French
Darlene Fung said:

Can anyone give feedback regarding the optical performance of the TEC I-Turret or the Van Slyke HEX Turret? With a 130 mm f/6 AP and a Maxbright, what do you loose visually by substituting the turret for the diagonal? Any other issues?

Thanks for your comments and clear skies!

DFung


I would love to own a turret, and seriously considered buying the TEC version. Then I thought about conditions here. We get a lot of dew, and I could just imagine all the eyepieces in the turret dewing over. I suppose you could keep caps on them when not in use, but that seems to negate part of the advantage of the turret. They are also still hanging out where they are going to get nice and cold, making dewing more likely when uncapped.

Probably a better investment for me would be a heated eyepiece box. A friend made a nice one from a small cooler.

Clear skies, Alan

April 2, 2006 05:27 PM Forum: Deep Sky Observing

If M42 is green, is this with a filter?

Posted By Alan French
Floyd Blue said:

I once again ask this question. Is the color seen with or without a filter?

One night, many years ago, I was up at our club's observing site in Sanders Preserve, which is about 7 miles outside Schenectady, NY. Even then Schenectady had a pretty good light dome. I was observing Saturn with my 10" f/9.5. We noticed the fog had rolled in down in the Mohawk Valley, greatly reducing the effect of the city lights and darkening the sky.

I turned my scope toward M42, and it was amazing how vividly green it looked.

Clear skies, Alan

April 9, 2006 11:30 PM Forum: Equipment Talk

Meade Starfinder Dobs

Posted By Alan French
carol anderson said:

Anyone ever hear of, or had experience with The Meade starfinder Dobs? Especially the 12"?

Our club has an 8" and a club member has a 10" Starfinder Dob. Both of these scopes are completely closed at the bottom, and have a heavy steel weight inside the back of the tube. With dropping temperatures, they never cool down properly. (The gentleman with the 10" opened up the back and moved the weight.)

I'd check and see if the 12" has a closed back.

Clear skies, Alan

April 15, 2006 12:22 PM Forum: Refractors

Antique Glass

Posted By Alan French
Herbert,

Thanks! I have Baker's book, and this never caught my eye, or, if it did, it didn't take. I spent some time looking for my values for the indices for BSC2 and DF2 and had no luck. (I hope they were not tucked away in the copy of Taylor's book that went missing.) At least I have values for one wavelength now.

Clear skies, Alan

April 15, 2006 01:19 PM Forum: Refractors

Antique Glass

Posted By Alan French
I found my crib sheet with the indices for BSC2 and DF2, so I'll try to sit down with ATMOS later this weekend.

BSC2 Crown
V = 64.55
n(d) = 1.51707
n(c) = 1.51461
n(f) = 1.52262

DF2 Flint
V = 36.60
n(d) = 1.61715
n(c) = 1.61218
n(f) = 1.62904

Clear skies, Alan

April 16, 2006 12:51 AM Forum: Solar System Observing

Silly question

Posted By Alan French
I suspect you can't. A 10" f/4 has a lunar image 0.35" in diameter in the focal plane. If you double the aperture, you quadruple the light grasp, but you also double the size of the lunar image to 0.70", so it is spread out over four times the area. The brightness of the image per unit area is unchanged. You could concentrate the image more by using a faster system, but I don't think it will come close to getting you there.

The Sun is magnitude -26.75 and the Moon is -12.7, so the Sun is 14.05 magnitudes or about 417,000 times brighter than the Moon.

There may be issues with the energy outside the visible spectrum too. Does some we get directly from the Sun get lost when light is reflected off the Moon?

I think you'll still need matches.

Clear skies, Alan

April 21, 2006 02:19 PM Forum: Solar System Observing

Comet in Corona Borealis

Posted By Alan French
john boyce said:

Can anyone tell me the name of the comet in Corona Borealis? The one that is presently near a ? Im sory to ask such a simple question,I am very new to astronomy, can anyone direct me to a good place to check on such information?

Thank You,

John Boyce

John,

It is fragment C of Comet Schwassmann-Wachmann 3. The comet has broken into several parts, and C is the brightest.

Clear skies, Alan

April 23, 2006 08:14 PM Forum: CCD Imaging and Processing/Deep Sky

Heaviest G11 payload?

Posted By Alan French
Andre Moutinho said:

Hi,
What is the heaviest setup I could use on a G11 mount for astrophotography purpose?

Thanks,
Andre

Keep in mind that a long, lighter tube may be less stable on a mount than a shorter, heavier one. It isn't just about weight.

Clear skies, Alan

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