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Posts Made By: David Brodeur

September 17, 2003 01:26 PM Forum: Deep Sky Observing

Re: New O-III Filter???

Posted By David Brodeur

An OIII filter is designed to pass the emissions of doubly-ionized oxygen at 496 & 501 nm, which would put its bandpass in the blue-green. So your color impressions seem about right.

As for "everything else" being invisible, what else did you try it on? The filter works by blocking all light except maybe a 10nm band. The OIII emissions are passed virtually unattenuated, making certain objects (planetary nebulae primarily) more obvious. Note that it won't make them any brighter; it just dims the surrounding stars and any hydrogen emissions, so the planetary stands out.

One use for these is to "blink" planetary nebulae. Put the filter in front of your eye while looking at a low-power field containing a small planetary (e.g., the Saturn nebula in Aquarius, NGC 7009). All the "stars" but one will dim; the one being the PN of course.


September 28, 2003 05:33 PM Forum: Refractors

Re: AP 130 vs TV 102--not a sure bet!

Posted By David Brodeur

I think a good 4" will almost keep up with a good 5", which seems like in general what you observed. As far as the double star thing, that's puzzling, but there are a lot of factors that could affect your results:
-Larger aperture results in larger exit pupil at a given power, making any aberration in your eye more troblesome.
-Faster scope challenges the EP more; supposedly not an issue for Naglers, but maybe just a little?
-Telescope cooldown.
-Larger aperture, shorter focal ratio is slghtly more sensitive to seeing and defocus.
-Possible local variation in seeing.
-Differences between your eyepieces - maybe the 22 is just better or cleaner than the others?
-Viewing position. A comfortable viewing position and correct eye position can affect how well you see.
-Familiarity with the instrument; it can take a few sessions to get comfortable with a new scope, so you can find the perfect focus, etc.

In any case, you probably need a few more double star comparisons before you can draw a firm conclusion.

September 28, 2003 09:14 PM Forum: Refractors

Re: AP 130 vs TV 102--not a sure bet!

Posted By David Brodeur

It's the objective lens that provides the resolution to split a double. The eyepiece merely magnifies it enough so that you can see it. Given good seeing and good optics, it also takes slightly better than average eyesight, which Mr. Howe apparently has.

June 23, 2002 04:30 PM Forum: Refractors

Question for the Optical Police: Am I nuts?

Posted By David Brodeur

It could be atmospheric refraction or eyepiece aberration. One thing I noticed when I moved from an achro to an apo is that things like that are much more clearly seen in the apo.

You may also be seeing the residual color in the TV102 itself. Residual color in an apo is only _very_ slightly out of focus, so it can show up as a tiny but bright halo. Secondary color in the achromat is more diffuse, producing an overall veiling haze that may not be as obvious.

David Brodeur

October 7, 2002 01:27 PM Forum: Deep Sky Observing

observing nebula

Posted By David Brodeur

I manage to see the Crab in a 5" refractor from my urban backyard on a good night. "Good" for this site means Milky Way suspected near the zenith, so you should be able to find it in your 8" at your site. Under my observing conditions, it seems more obvious in a wider field of view. Try a 32mm eyepiece and look for that small patch of haze. Avoid the Ultrablock here, it will filter out most of M1's light; not sure whether the Skyglow would help.

As for the North American Nebula, you might be able to see at least "Gulf of Mexico" region with your Ultrablock filter, but you really need a site where the Milky Way is obvious. I have spotted it in binoculars on a good night, 60 miles out of Seattle. The nebula is probably bigger than your widest field of view, so you'll have to pan around to take it all in.

Dave Brodeur

June 10, 2003 01:39 PM Forum: Deep Sky Observing

North American Nebula

Posted By David Brodeur

I have seen the North American Nebula in 8.5x44 binoculars, and in a 5" refractor at 27x. Large faint objects like this are easiest to see in a wide field of view, so use your lowest power eyepiece. The area around the "Gulf of Mexico" is the most obvious, due to the dark cloud that defines the gulf.


October 19, 2003 05:08 PM Forum: Equipment Talk

Overpriced Astro Gear

Posted By David Brodeur

Anytime you have a small specialty market, you will find overpriced merchandise. Some of it is priced that way simply because the manufacturer needs a high margin to make a low-volume business profitable. Sometimes it's just because there isn't enough competition to drive prices down, although the introduction of good-quality Chinese products is changing that for a lot of things.

Also, at the upper end of the market you have things that are luxury goods and priced accordingly.

But there are a lot of crossover products where you can certainly find much less expensive equivalents from non-astronomy sources. The dessicants you mention are a good example. If you don't mind the extra work of making your own packages, you can buy the bulk stuff as you mentioned. Or you can go to or and buy ready-made re-useable dessicant capsules for around $5.

Another example is the aluminum eyepiece cases sold for $50 or more that are essentially identical to the tool case Lowe's sells for $24.

Other hobbies are similarly susceptible to commodity products being re-packaged or re-labeled and sold for ridiculous prices. Caveat emptor as usual.

November 11, 2003 11:45 AM Forum: Equipment Talk

Tak 5mm LE

Posted By David Brodeur

My 5mm Tak LE is my favorite short f-l eyepiece. Its casemates include a 6mm UO ortho, 6mm Vixen LV, and 8mm TV Plossl. To my eye, the Tak is the best of that admittedly small group, in terms of contrast, brightness, and sharpness. (The TV Plossl is a close second.) I also find it a very comfortable eypiece to use in terms of eye relief and sensitivity to eye position.

In my 130mm f/6.2 AP refractor, the 5 gives me about 160x, and I barlow it to 320X in good seeing.

I've had some limited experience with Radians and Naglers, but not enough to tell you how they stack up versus the LE. But many people like them as planetary eyepieces.


November 15, 2003 08:12 PM Forum: Equipment Talk

Which 2 of 3 AP scopes you will choose.

Posted By David Brodeur

I'd get whichever _one_ of the AP's best suits your intended use, and get a 12.5 or 14" Starmaster for the other one.

But if you've already got the large-aperture niche filled, or if you've just got to have _two_ AP's, get the Traveller and the 155. The Traveler gives you a great portable scope and wide-field views, and the 155 gives you as much aperture as you can get in a new Astro-Physics. And two scopes just an inch apart in aperture seems redundant.

(got the 130, saving for the Starmaster).

November 20, 2003 04:20 PM Forum: Equipment Talk

Apo's ???

Posted By David Brodeur

Aesthetics: There's a brilliance and clarity to the view through an apo that other scopes can only approach.

Geek appeal: An apo combines sophisticated design and exotic materials to produce the maximum available performance per inch of aperture.

Reliability, Availability, Maintainability: Relatively fast cooldown, colimation interval in years or decades, never needs recoating, the last scope on the field to be dewed out.

Not necessarily in that order.