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Posts Made By: Dan D DuBal

May 9, 2003 09:08 AM Forum: Maksutovs

Orion Starmax/Apex line and baffling

Posted By Dan D DuBal

Hello, Levente.

I recommend a simple meniscus shield/baffle sleeve (like a dew shield on a refractor). Cardboard, craft foam, felt-lined bubble-wrap -- these materials are fine. Make sure the interior of the shield is flat black (not glossy or shiny or otherwise reflective). The sleeve/shield should project a distance equivalent to at least 1.5x the scope's aperture (up to 2x is also fine -- do not make it much longer). This would mean about 5 to 7 inches for your Apex 90.

All cassegrain designs require some level of compromise with regard to the length and/or shape of the primary baffle tube. If a primary baffle tube is made long enough to strictly/fully baffle the meniscus, then it will end up projecting into the primary light cone, thus *increasing* the effective diameter of the central obstruction. On the other hand, if a baffle tube is made short enough to allow for *zero* additional obstruction, then the meniscus ends up *not* being fully baffled.

A forward shield/sleeve/extension baffle should help quite a bit.

Best wishes.
-Dan

May 9, 2003 09:46 AM Forum: Off Topic Discussions

Ok, I've had enough

Posted By Dan D DuBal

<http://www.seachem.com/en_products/product_pages/049_flourite.html
As you can see it wouldn't make a very good refractor lens :-)>>

Actually that's FLOURITE, Joplin.

Take care.
-Dan


May 14, 2003 08:42 AM Forum: Astro Binoculars

celestron skymaster 15x70's

Posted By Dan D DuBal

They are clones of the ubiquitous Galileo/Barska/Bear/Oberwerk/Burgess 15x70 binoculars. Coatings and cosmetics may vary. Given good collimation, I'd expect essentially identical performance at the eyepiece.

Best wishes.
-Dan

May 17, 2003 08:48 PM Forum: Equipment Talk

Oldie Goldie Laptops?

Posted By Dan D DuBal

I, myself, would expect to find laptops (and usually do see them) in the "Miscellaneous & Other Astronomy" category.

Best wishes.
-Dan

May 18, 2003 10:36 AM Forum: Solar System Observing

Jupiter & Saturn phases?

Posted By Dan D DuBal

Hi Ron. Hope my attempt doesn't furrow your brow too much...

A superior (outer) planet's phase -- relative to Earth view -- occurs at quadrature (planet and Sun at 90 degs. "separation," relative to Earth; planet near zenith at sunrise/sunset). Imagine the Earth as being the 90-deg. vertex of a right triangle; the Sun and outer planet at the other two vertices.

Now imagine the sides of that right triangle, using Earth and Mars:
Assume length of Sun-Earth side = 1.
Sun-Mars length: ~1.5 (mean ~141 million miles)
Mars-Earth: ~1.2
*Sun/Mars/Earth vertex (this is the key): ~51 degs.

Now, let's replace Mars with Jupiter (again, in a right triangle):
Sun-Jupiter length: ~5.2 (mean ~483 million miles)
Jupiter-Earth: ~5.3
*Sun/Jupiter/Earth vertex: ~11 degs.

Theoretically, this might allow for a ~96% illuminated gibbous phase for Jupiter. However, Jupiter's not a terrestrial planet. Factor in it's gasseous nature (and corresponding diffusion of sunlight along its terminator), and we're lucky to "see" a 99% illuminated Jove (which is what Jupiter's gibbous phase *does* present to us, under favorable conditions). Discerning a 99% gibbous phase on an ellipse such as Jupiter... sounds pretty-darn subjective, to me!

How about Saturn?
Sun-Saturn length: ~9.5 (mean ~887 million miles)
Saturn-Earth: ~9.8
*Sun/Saturn/Earth vertex: ~5.9%

Under ideal conditions, Saturn's gibbous phase would be in the realm of ~99.7% illuminated.

Shall we give Jupiter a try? It's around 99.2% illuminated, these days. :-)

Best wishes.
-Dan

May 19, 2003 03:20 PM Forum: Off Topic Discussions

Herb -can you authenticate a users ID?.

Posted By Dan D DuBal

"Larry Stang's Method" was a local band in southern Florida in the '60s. Maybe it's him.

There are plenty of other guys named Larry Stang in the U.S.

Bottom line: he doesn't share your name, and there's zero evidence of impersonation.

Assume the best.
Cheers.
-Dan

May 20, 2003 10:56 PM Forum: Equipment Talk

MK-67 focus queston

Posted By Dan D DuBal

Not sure about "several inches," but my own MK67 does indeed require a 2-inch-long extension tube (plus 1.25-inch adapter) when using 1.25-inch diagonals. This is a common trait amongst many MK67s, it seems.

On the other hand, my 2-inch diagonal requires no extension -- just an adapter to accomodate 1.25-inch eyepieces.

If you can better estimate the distance from the top of the diagonal's eyepiece collar to the bottom of the eyepiece's lens housing (top of the eyepiece barrel), you'll have a fair idea as to how much extension you'll need to allow a 1.25-inch diagonal (& eyepiece) to reach focus. That's ballpark, anyway.

As a last resort, the primary *might* be "pulled" slightly rearward (just a few millimeters) via the collimation screws on the back plate. This would bring the image plane forward -- nearer to the focuser. HOWEVER, I would strongly advise getting a dealer's help before resorting to that sort of "fix" (shifting the primary rearward). Bit tricky, to say the least.

Best wishes and luck.
-Dan

May 22, 2003 07:19 AM Forum: Equipment Talk

Nikon spotting scope 7351 and 7355 difference

Posted By Dan D DuBal

Same base spotter.

The 7355 outfit includes a Slik tripod and the Nikon "view-through" case (zippered flaps allow viewing without removing scope from case).

Anacortes carries both. Check links below:
http://www.buytelescopes.com/product.asp?t=&pid=1928&m=23
http://www.buytelescopes.com/product.asp?t=&pid=1926&m=23

Hope that helps.
Best wishes.
-Dan

May 22, 2003 12:51 PM Forum: Equipment Talk

Question about Field Stops

Posted By Dan D DuBal

Placement/location is also a defining aspect of a field stop. In this regard, a field stop may be considered a specialized baffle.

A field stop is coincident with the eyepiece's image plane. Thus, it remains in sharp focus with the telescopic image and provides/defines the "frame" for that image.

Think of a field stop as being designed to limit the *use-able* field of an eyepiece. In a given eyepiece design (as well as its integration with a given telescope), the image plane *beyond* (outside) the zone defined by the field stop may be significantly aberrated in one or more ways. Astigmatism, distortion, and lateral chroma are perhaps the three "biggest" (most important; most destructive) off-axis aberrations in most eyepiece designs.

Best wishes.
-Dan

May 23, 2003 02:11 PM Forum: Solar System Observing

TV-102 detected Jupiter phase - fact or fiction?

Posted By Dan D DuBal

I'm hopeful for good skies, tonight, Ron. If they pan out, I'll give Big Jove a look-see and report back here.

Assuming you *did* see what your sketch conveys :-)
then I think you *did* see what you thought you saw. ;^)

And hey, at least you're sketching! I'm still slacking off, in that regard :-
Best wishes, and thanks for the update.
-Dan