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Posts Made By: Jon Isaacs

February 6, 2004 04:52 AM Forum: Equipment Talk

Re: Equatorial Mount

Posted By Jon Isaacs

Have you considered an EQ platform? For a 12.5 inch scope the cost is probably somewhat less than an EQ mount. Seems like a good way to retain the portability and stability of the DOB and still get tracking.

My guess is that your scope is too big for the Atlas mount. Your scope must weigh 60 lbs and be about 60 inches long, its a biggie for an eQ mount..

jon

February 7, 2004 01:02 PM Forum: Chinese Optics Imports

102F6 on its way..

Posted By Jon Isaacs

After I sent an Email to BO and got the reply that they were waiting for my credit card expiration date, they shipped the scope as promised the next day. FedEx sent me a notice that it had been shipped.

So, finally it looks like the wait is over. It is scheduled to arrive on Thursday so I would guess that Southern California will be getting some much needed rain next weekend....

I will probably post a brief comparison of the 102F6 to other small scopes I have, Pronto, ST-80, C5 and the Space Probe 130F5 Newt with the 2 inch focuser. The 130F5 comparison is the one that most interests me, similar focal lengths, the larger aperture should make up for the obstruction. The Newt does have to cool down but there's no "false color."

Should I get excited at the prospect of the scope arriving or should I just play it safe ...
jon

March 7, 2004 07:09 AM Forum: Refractors

Astigmatism Question, back to reality.

Posted By Jon Isaacs

OK, I think the Markus Ludes/TeleVue question has been beat enough to kill a cat, here's a question for you about a scope at the other end of the scale.

The problem:

I received an Achromatic refractor, 102 mm F6, from a vendor with a forum here. I waited quite sometime for this scope and when shipped it was "as is" because of continued problems with the objectives. New ones are supposed to arrive someday.

Mechanically the scope is quite nice, optically, my example is quite disappointing.

Not even requiring a star test, just viewing at any magnification reveals a great deal of what I take to be astigmatism.

Best focus on a star is not a point or even a point with coma, it is a cross. Viewing the double Castor (about 4 arc seconds), the lengths of the lines are sufficient to connect the two and then some. This would be most apparent at 100X. These lines are nice and sharp but of different colors, one is red, one yellow-white. Using Aberator, it seems this would correspond to about 1 wave of astigmatism.

From what I have gather reading the net, astigmatism in a refractor is caused by either pinched optics or bad glass.

I have tried rotating the elements with respect to each other, I have tried to make sure the elements are free and not overly tightened, the problem remains.

The questions:

1. Am I correct in thinking this is astigmatism...

2. Any thoughts on what I might do other than wait for the next round of objectives??

Note: at this point, this is more of an intellectual curiousity to me, and interesting problem to think about and understand, a learning experience. There is some frustration of course, but I have plenty of other scopes to keep me occupied until this one becomes useable.

Thanks for any thoughts or suggestions.

jon isaacs


March 8, 2004 12:42 PM Forum: Equipment Talk

Re: Reasonable price on a Meade 8" starfinder

Posted By Jon Isaacs

What do you hope to get for it? One can buy an Asian 8 inch DOB with a better focuser and a mirror cell that will allow it to cool down for about $400...

jon

March 10, 2004 06:14 AM Forum: Equipment Talk

Re: "Ne Plus Ultra"

Posted By Jon Isaacs

>>>It is possible to enjoy astronomy with inexpensive
equipment. It is also possible to equally enjoy
astronomy with outrageously expensive equipment.
Difference is I'll have more left for food & gas.
-------

I agree it is important to stress that one can enjoy astronomy without spending a great deal of money. I point this out regularly when people are suggesting 31mm Naglers to someone with $400 telescope.

An 8 inch DOB and a few eyepieces will set you back less than $600 and yet can provide years of discovery and enjoyment. On the otherhand, a $400 eyepiece is a lifetime investment, one guy I know spends that much on fuel for his boat for a weekend...

A couple of additional comments:

1. Cycling is quite different than astronomy in that one soon reaches a limit with bicycles, essentially an $800 road bike performs as well as a $2500 road bike. Yeah, one might have 105 and one might have Ultegra, one might weigh a pound or two less, but those factors really don't matter in the big picture.

True Aerowheels like Disks and Hed Trispokes, not the boutique wheels one sees on most new bikes, do make some significant difference if one is time trialling and serious about it.

But for the average everyday cyclist, 36 spoke wheels with SS 14-15 double butted spokes built, stress relieved and properly tensioned are going to provide much better service than some low spoke count jobbers that look snazzy.

The modern road bike uses short reach brakes which provide no advantages over 47mm-57mm "normal reach" brakes except to prevent the use of fenders and 28 mm tires. Thats why with a garage full of bikes, most days I choose my 1984 Specialized Sequioa to ride to work rather than the Paramount or Merckx or one the 15 or 20 bikes plugging up my garage, it does the job.

2. Telescopes on the hand, well the sky is the limit. More money buys more aperture, better optics, better mounts that provide real and useable benefits.

Jon







March 16, 2004 06:23 AM Forum: Equipment Talk

Interesting Astromart Binocular Ad...

Posted By Jon Isaacs

Check out ad #257126

To quote:

"I bought a pair of 12 X 60 and compared them with my 7 X 50's. WHAT A DIFFERENCE! I looked first at the Pleiades. Instead of looking so far away, they looked right up close and filled the field of view. I saw more stars and they were brighter. The 12 X 60s are light and just about as steady and as easy handheld as the 7 X 50. Not much larger either. The FOV is just about the same. 6.4 DEGREES with 12 X 60 as compared to 7 X 50 at 7 degrees."
----

I find it contradictory that the Pleiades can have "filled the Field of View" and yet still have nearly the same field of view. The Pleiades are less than 2 degrees across so its pretty hard for them to fill a 6.4 degree FOV.

Three possibilities come to mind:

1. The Pleiades grew by a factor of two or so during the night.

2. The TFOV of the 12x60s is not 6.4 degrees, this would imply a 77 degree APOV. Wonder if they are "sharp to the edge."

3. A bit of BS/hype is going down here.

I am also curious about why this fellow is selling these fantastic bino's.

jon


March 22, 2004 05:37 AM Forum: Chinese Optics Imports

Any News on the New Objectives?

Posted By Jon Isaacs

Last post here was about a week ago. Just wondering if there has been any news? Scope is still in the closet...

jon

April 16, 2004 05:15 PM Forum: Chinese Optics Imports

May 23, 2004 10:53 AM Forum: Chinese Optics Imports

Re: Astromart ad for 102/f6

Posted By Jon Isaacs

Actually these scopes were stopped down to improve the Chromatic Aberration, not because of "edge" defects.

jon

May 24, 2004 08:00 AM Forum: Chinese Optics Imports

Re: Astromart ad for 102/f6

Posted By Jon Isaacs

From one of the ads:

"This is an extremely well made scope, has very decent images and is an incredible value! (Various reviews in the Astromart Burgess Refractor forum)."

The guy is either bluffing and hoping that a potential buyer will not bother to read this forum or he hasn't bothered to read it himself.

jon