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Posts Made By: Alan French

December 27, 2006 12:40 AM Forum: Equipment Talk

6" f/8

Posted By Alan French
Magnus Ahrling said:

Can a 6" f/8 Newtonian be as good as a 4" ED/APO when it comes to planetary, binaries and globular clusters?
Has anyone tried this Sky-Watcher (Synta) 6" f/8 OTA? I`d like to buy this OTA and mount it on my EQ3 or possible my Vixen Porta....
/Magnus

A 6" f/8 is a very good alternative to a 4" APO. It does give up the low power, wide field views. If the optics are good it will do better than any 4" scope on the Moon, planets, and most deep sky objects. The good old 6" f/8 is a very cost effective way to get a nice scope.

Things might be a bit closer on double stars - refractors tend to give tighter star images at very high powers, and often split doubles at lower powers than a comparable reflector.

Clear skies, Alan

December 27, 2006 08:48 PM Forum: Chinese Optics Imports

Planet Hunter Part Two?

Posted By Alan French
Jeffrey Kurtz said:

There was a report on the Yahoo Refractors group that Burgess is "preannouncing" (pardon the euphemism) a 91mm F7.6 fluorite doublet refractor using either Ohara S-LAL14 or LZOS CTK12...is this the long lost "son of the Backpacker"...think we should "start the clock" to see how long this one will take to reach actual production.

This is how trouble starts - speculation becomes fact.

Please note that the only thing we know from Burgess is that the scope uses fluorite (CaF2). The use of Ohara S-LAL14 or LZOS CTK12 was just speculation on my part. From the relative partial dispersion diagram these two glasses appear to be good mates for fluorite. I have no idea what other glass is actually used.

Clear skies, Alan

December 28, 2006 07:55 PM Forum: Refractors

Do classic achromats outperform modern APOs?

Posted By Alan French
Doug Peterson said:

A recent ad for a 4" Unitron claims it outperforms modern 4" APOs. I see this claim a lot, usually from someone selling an achromat to buy an APO. Does anyone have any data to support this conclusion?

I've used 4" Unitron and a 4" APO. I'd definitely give the nod to the APO, and it provides low power, wide field views that are simply unavailable through a 4" f/15. It is also a lot more portable. IMHO, the 4" long focus achromat is pretty much a dinosaur. A well maintained Unitron might be a nice collectable, but it wouldn't be the best choice for use by an active observer.

Clear skies, Alan

December 31, 2006 03:58 PM Forum: Birding Optics and Photos

Red-bellied Woodpecker ?????

Posted By Alan French
As Dan posted, it is indeed a Red-bellied Woodpecker, and is the female. The red on the head extends farther forward on the male.

These used to be rare here in upstate NY. We moved into our house in 1985, and I have a note that we spotted one in the yard in 1993 and 1996. In 1998 they started visiting my feeders on a regular basis, and now they are very common in the area. Their range, like the Cardinal and Mockingbird, and more recently the Carolina Wren, has expanded northward.

Clear skies, Alan

January 4, 2007 01:12 AM Forum: Telescope Making

Pyrex drying up?

Posted By Alan French
A nice quartz mirror by one of the top mirror makers would be really, really nice.

Clear skies, Alan

January 4, 2007 10:14 PM Forum: Chinese Optics Imports

Planet Hunter Part Two?

Posted By Alan French
Science has long argued that perpetual motion is impossible. It seems that some forum threads argue against this contention. smile

Clear skies, Alan

January 22, 2007 01:54 AM Forum: Telescope Making

Why Are Rechargable AA Batts 1.2V & Not 1.5V?

Posted By Alan French
Bill Byrd said:

[COLOR="Purple"]Inquiring minds want to know!

The thread about using AA batts to power fans has me wondering: Why are rechargable AA batts rated at 1.2V when disposable AAs are 1.5V?
Curious,
Bill[/COLOR]

Bill,

I believe the voltage is mostly determined by the choice of materials for the cathode and anode, and suspect the choice was largely dictated by the ability to make the battery rechargeable many times - rather than the ability to match the 1.5 volts of one use versions.

Clear skies, Alan

January 23, 2007 10:06 PM Forum: Astro-Physics

AP 9" Folded Apochromatic Refractor for sale on cl

Posted By Alan French
Steven Lynn said:

The seller is asking $65,000.

[SIZE="Small"]I wouldn't pay a dime over $59,000. 8) [/SIZE]

I wonder what other unique or micro-runs of AP scopes are out there?

Speaking of dimes, a unique 1873-CC No-Arrows dime sold for $632,500 back in 1999. With the 9" AP you get something useful for 1/10th the price! Also, you're unlikely to accidentally spend a 9" APO. wink

Clear skies, Alan

February 10, 2007 02:01 AM Forum: Refractors

Guidelines for A comparison

Posted By Alan French
ROBERT MOORE said:

Hi All, I would like, if anyones knows, what type of guidelines should be used for a comparison ( A shoot out ) between TOA-130 & TMB130SS. What I'm looking for is the best way to run such a shoot out & if their is some kind of data sheet to use.

Thanks for any help you can give

Bob

Bob,

First, you have to travel down to the Florida Keys to find some steady skies. smile Comparisons under New York skies can be tough.

Seriously, I think there are some common problems that should be avoided. If it is just you doing the comparison, this isn't a problem, but if you involve more people, insist that everyone quietly go about their business. Absolutely no discussion until the observing is all done and everyone has put together their notes. Agree on the targets ahead of time, but then just do your observations and make careful notes. No changes allowed after you've compared your results.

The other problem common to comparisons is lack of detail. Comparisons should carefully and thoroughly document what was seen in each scope. Seeing and transparency should be included, and how much time was involved.

Given the number of clear nights lately in New York, keep in mind that time doing comparisons IS deducted from your time observing....

Clear skies, Alan




February 20, 2007 02:22 PM Forum: Eyepieces

So when is an Orthoscopic an Orthoscopic?

Posted By Alan French
The word orthoscopic is an adjective with a specific meaning, and is not capitalized. An eyepiece free of rectilinear distortion - or perhaps with a minimum amount - would be called an orthoscopic eyepiece, with no implications of the specific design.

Astronomers seem to have changed orthoscopic to a noun, and often write it as "Orthoscopic," perhaps because many eyepiece designs are named after people, and should start with a capital letter. It is obvious that writing Orthoscopic is confusing, because there are many designs that are orthoscopic. Specifying the design, such as Abbe Orthoscopic, seems to nicely avoid confusion.

Now we should get back to that age old question about angels on the head of a pin.

Clear skies, Alan


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