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Posts Made By: Jon Isaacs

June 12, 2006 01:41 AM Forum: Beginning Astronomy?

Mercury at Sunset

Posted By Jon Isaacs

Mercury should be visable at sunset for the next two weeks or more. Tonite at sunset from San Diego it will be close to 20 degrees above the horizon and close to the ecliptic (path of the sun).

25 minutes after sunset it should be still nearly 15 degrees above the horizon and visable depending on your conditions. I normally start looking 10 or 15 minutes after sunset with binoculars or a scope finder.

Mercury is interesting because if the seeing is decent, you can see the phases, currently it is about 55% illuminated and that will be dropping rather quickly over the next weeks.

I enjoy beginning the evening with Mercury or Venus..

Jon



June 19, 2006 12:33 PM Forum: Eyepieces

Re: threats to the validity of eyepiece comparison

Posted By Jon Isaacs

>>>>6. "Jay Freeman philosphy to excess". Freeman's introductory essay (on excelsis.com) correctly states that much can be gotten from mid price orthos and plossls etc. It's all strictly speaking true, and good advice for people starting out with 1.25" default focusers etc. and limited budgets. And as a pure science matter the ortho within its field of view is conveying as mucy information as a more complex eyepiece. But at some point people need to know they're missing out on the party.
-----

You make some very good points but I have to take issue with this one.

I believe that anyone who is outside looking at the stars with a decent quality eyepiece and a decent quality telescope on a reasoably stable mount is not missing out on any party. I do think that someone who can't enjoy the night sky unless they are using the highest tech latest stuff is on the wrong track.

Widefields of view can be nice but are really only the icing on the cake. It doesn't take a Nagler or a Panoptic to have a great time...

Personally I think one of the biggest issues that you did not mention is that eyepieces are just not that big a deal, that's why there are so many opinions, the differences between a fancy eyepiece (Radian, moncentric, etc)and a decent but simple (Plossl)eyepiece are tiny compared to the differences between telescopes.

Biggest mistake IMHO is to pay too much attention to equipment and not enough to just having a good time with whatever equipment one might have.

When it comes to seeing more, it is not the eyepiece or the telescope that is most important, rather it is the observer, developing observing skills and eyepiece time are far more important than building a collection of eyepieces.

There is a reason that Jay Reynolds Freeman was able to complete the Herschel 400 with a 55mm refractor...


Jon


June 20, 2006 04:59 AM Forum: Refractors

Re: Single-Element "Apo" Lens For Moon?

Posted By Jon Isaacs

>>>>How about it, people? What's the verdict? I hope that it's favorable, because it would be a lot of fun to own a 6-inch apo refractor with a singlet, BK7 objective lens. -- And if we're going to dream a little here, how about a 10-inch lens? Or even 16 inches? Or --- ???
-----

IMHO the better solution is the zero lens solution. It allows for reasonably fast focal ratios so the tube length is not overwhelming, there is no chromatic aberration to deal with and it allows for viewing the full spectrum or any section you might choose...

jon

June 23, 2006 11:10 AM Forum: Beginning Astronomy?

Re: Happy camper with Orion Starblast

Posted By Jon Isaacs

Greg:

Everyone who owns a Starblast seems to say that it is the neatest little thing.

Uncle Rod Mollise, the SCT guru, thinks the Starblast is a modern classic. It will be interesting to see what you have to say once you evaluate the optics but everything I have heard says they are quite good.

Jon

June 24, 2006 11:14 AM Forum: Solar System Observing

Anybody else watching Mercury??

Posted By Jon Isaacs

Hi:

For the past few weeks Mercury has been quite viewable, about 15 degrees altitude 25 minutes after sunset. Tonite is will still be something like 14 degrees or so.

I have been starting out the evening viewing Mercury with my ED-80. Some nights the atmosphere is quite turbulent so the phase is not particularly apparent but the night before last it was quite nice, about 35% illuminated and quite sharp at 125x, not so sharp at 250x but the crescent was still very apparent and larger. The Atmospheric dispersion was quite apparent at 250x.

Mercury does not show the sort of detail of Saturn, Mars and Jupiter but it does show is phases and it is quite close to the sun. I enjoy watching it much the same way I enjoy watching Venus, the challenge is being aware of what it is doing and being there for those minutes when it is at its best.

Best to all...

Jon

PS: I post this in the Beginners section a few weeks ago when Mercury's run was just beginning but did seem to raise any interest...

June 28, 2006 12:30 PM Forum: Beginning Astronomy?

Re: Philosophical Issue: On the Spirit of the Star

Posted By Jon Isaacs

Greg:

1. I calculate the diffraction limited field to be only 0.14 degrees (=1.1mm diameter), if it is not perfectly collimated, it will probably not perform at high magnifications very well, particularly on planets. That has been my experience with F/4 Newts.

2. The Spirit of the Starblast...

The is something schizophrenic about using a $300 eyepiece in a $170 scope, it doesn't quite set right with the cosmic scheme of things...

Still if you have it, why not use it???

If you have a 1.25 Paracorr, why not throw that in there too? it reduces the field of view a bit but in my experience cleans things up with the reduced coma and somewhat slower focal ratio...

jon

June 28, 2006 12:35 PM Forum: Beginning Astronomy?

Re: Guide scopes for beginners

Posted By Jon Isaacs

If I were in your shoes, I would seriously consider the Orion ED-80, it's it a bit bigger than some of the others but for the money, it has the best optics and a decent focuser. There are quite a few nicer looking "achromat/semi-APO" 80mm F6 scopes at the $400 price point but in my experience/opinion, the extra size and money is well worth it to get the color free optics.

jon

July 10, 2006 10:33 PM Forum: Reflectors

Center dotting a Primary, how close???

Posted By Jon Isaacs

I have been pondering how accurately the center ring must be placed in order to accurately collimate using lasers and barlowed lasers.

Most often I seem to get very good results with my normal technique, an computer drawn circle with a center hole, cut out, center dot is then placed and the ring is place around the hole. Nice star tests in F/5 scopes.

However with the realization that the diffraction limited circle of an F4 scope is only 1.1mm, I am wondering if this means that dot needs to place with a high degree of accuracy, maybe 0.1 mm or even less??

I know one can collimate using a star test, probably the best way to go for sure, but I am doing this alone and moving from the eyepiece to the cell, finding the star, well it ain't all that easy.

Any thoughts, experiences, analysis would be appreciated.


Clear skies

jon

July 15, 2006 02:05 PM Forum: AstroMart FAQ

Re: Is there a way to help others ?

Posted By Jon Isaacs

Patrick:

That's what ratings are for... A month with no contact, for me that would be a real problem. Never on astromart I have had anything other than prompt with-in a day or two shipping.

A month, well, a simple factual rating would IMHO, be appropriate. There may be a very good reason why this transaction has not been completed but the reality is that even in the best case scenerio, the other party needs to do some explaining. Let them do it in the ratings section.

Thats my thinking, others may have other ideas...

Jon

July 17, 2006 05:12 PM Forum: Reflectors

Re: please help with new starbuckets dob

Posted By Jon Isaacs

Nils:

It does look beautiful... Have you contacted the seller?

Jon