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Olivier Biot
Amused
*****

Reged: 04/25/05

Loc: 51°N (Belgium)
Stranger than fiction!
      #4071952 - 09/25/10 07:00 AM

Stranger than fiction!

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jrbarnett
Eyepiece Hooligan
*****

Reged: 02/28/06

Loc: Petaluma, CA
Re: Stranger than fiction! new [Re: Olivier Biot]
      #4072182 - 09/25/10 10:53 AM

Did you hear that?

What was that sound?

That was the sound of two or more decades of misconceptions shrieking as they are thrown out of the window.

Truly a modern "magnum opus" and must read for anyone owning or considering a refractor.

Exceptional and well done!

Regards,

Jim


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J_D_Metzger
Carpal Tunnel
*****

Reged: 05/13/04

Loc: Tucson, AZ
Re: Stranger than fiction! new [Re: jrbarnett]
      #4072343 - 09/25/10 12:02 PM

Quote:

Truly a modern "magnum opus" and must read for anyone owning or considering a refractor.




Anyone considering a refractor for visual use, that is...


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City Kid
Carpal Tunnel
*****

Reged: 05/06/09

Loc: Northern Indiana
Re: Stranger than fiction! new [Re: jrbarnett]
      #4072345 - 09/25/10 12:04 PM

I just finished reading this article and all I can say is wow. Extremely well written and very interesting. I will read it again to make sure I am taking in all of the information because it is packed with more info than my humble brain can digest in one reading. My current refractor is a 101mm f5.4 APO. I have been thinking about a larger refractor and only gave cosideration to another APO. This article has caused me to consider a long focus achro as a possibility.

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DaveTinning
super member


Reged: 01/03/09

Loc: Central England
Re: Stranger than fiction! new [Re: City Kid]
      #4072541 - 09/25/10 01:48 PM

I take my hat off to Neil and his valued co-researcher. Being only a layman with a passion for visual astronomy and traditional (and some new) refractors, this is a clearly well researched, well written and very informative piece of work.

It deserves serious study and constructive responses from those academics with a far deeper understanding of the science of optics than I have.

For my own part, I am content to be pleased that my "gut feeling" about long focus refractors being in some way better able to present stable, clear images compared to their very short focus new exotic counterparts, appears to be founded in good science.

Neil, you deserve some kind of public recognition for this piece of work, as does your colleague. Well done!

very best wishes
Dave


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BillP
Postmaster
*****

Reged: 11/26/06

Loc: Vienna, VA
Re: Stranger than fiction! new [Re: jrbarnett]
      #4072591 - 09/25/10 02:21 PM

Quote:

Truly a modern "magnum opus" and must read for anyone owning or considering a refractor.




Neil,

An exceptional effort for sure! It will stand many enjoyable readings and re-readings ... a wealth of both finidngs and implications that I'm sure will bear much fruit. Destined to be a classic reference for the community in the years to come. Hats off to Vlad for the outstanding technical support as well. Quite deserves the coining of the "Sacek Effect" !!



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7331Peg
Sirius Observer
*****

Reged: 09/01/08

Loc: North coast of Oregon
Re: Stranger than fiction! new [Re: jrbarnett]
      #4072614 - 09/25/10 02:34 PM

Quote:

Did you hear that?

What was that sound?

That was the sound of two or more decades of misconceptions shrieking as they are thrown out of the window.

Truly a modern "magnum opus" and must read for anyone owning or considering a refractor.

Exceptional and well done!

Regards,

Jim





And I thought it was a jet!

Yes, very well written and, I might add, very even-handed in it's treatment of achromats and APO's. Neil has established a very solid foundation for future research - although, I'm not sure at this point what else can be added.

In one word - Superb!


John


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Astrojensen
Post Laureate
*****

Reged: 10/05/08

Loc: Bornholm, Denmark
Re: Stranger than fiction! new [Re: Olivier Biot]
      #4072679 - 09/25/10 03:11 PM

So it finally got published!

Excellent! A fine piece of work, Neil. Now, on to the next project!


Clear skies!
Thomas, Denmark


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Ciprian
Vendor (SkyMap)


Reged: 02/25/10

Loc: Seattle, WA
Re: Stranger than fiction! new [Re: Astrojensen]
      #4072688 - 09/25/10 03:15 PM

Great article. Well done!

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Doug76
Long Achro Junkie
*****

Reged: 12/05/07

Loc: Refractor Heaven
Re: Stranger than fiction! new [Re: Ciprian]
      #4073030 - 09/25/10 06:19 PM

I am not surprised by this!
Nice Neil.

Doug


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Achroman
member


Reged: 08/30/10

Loc: Finger Lakes Region, New York ...
Re: Stranger than fiction! new [Re: Doug76]
      #4073299 - 09/25/10 08:53 PM

Excellent article, very well written, and makes the complex science very understandable. I have always had a suspicion that this might be the case, but now there is solid science to explain it. Well done!

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Jeff Morgan
Postmaster
*****

Reged: 09/28/03

Loc: Prescott, AZ
Re: Stranger than fiction! new [Re: Olivier Biot]
      #4073378 - 09/25/10 09:40 PM

Long live long focus telescopes!

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Clive Gibbons
Mostly Harmless
*****

Reged: 05/26/05

Loc: Oort Cloud
Re: Stranger than fiction! new [Re: Olivier Biot]
      #4073547 - 09/25/10 11:35 PM

An impressive read.

This reminds me of folks who swear ol' carbureted engines are somehow superior to the modern fuel-injected powerplants we now enjoy... and how horse drawn transportation is actually far better than motorized vehicles.

I've used long focus achromats and compared them to all manner of doublet and triplet apo optics.

IMO, long achros show less sensitivity to seeing conditions, but that's the only inherent advantage they offer.

If somebody has a vested interest in championing the alleged superiority of a particular design, then it's not surprising that they will continue to promote it. Present lots of convincing looking charts, graphs and statistics, which apparently prove their point.

Can somebody point me to the 4" f/6.3 doublet apo mentioned in this article? I'd like to *actually* compare it to my 4" f/15 achromat.

Then again, I have observed with a 4.3" f/5.95 ED doublet stopped down to 4" F/6.3 and can report that it outperforms the 4" f/15 achro in all respects, except for sensitivity to seeing.


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BillP
Postmaster
*****

Reged: 11/26/06

Loc: Vienna, VA
Re: Stranger than fiction! new [Re: Clive Gibbons]
      #4073625 - 09/26/10 12:25 AM

Quote:

This reminds me of folks who swear ol' carbureted engines are somehow superior to the modern fuel-injected powerplants we now enjoy...




As profession drag racer Warren Johnson characterized it, properly tuned, carburetors make more peak power than EFI in a Pro Stock engine. A carb’s pressure differential atomizes the gas a lot better than spraying fuel through an orifice. And as professional racer Myron Cottrell puts it, if you're looking to drive the family car about 25k miles a year, get EFI; if you are looking to race, get a carb. With every advantage, comes a disadvantage...but this is off topic


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Jeff Morgan
Postmaster
*****

Reged: 09/28/03

Loc: Prescott, AZ
Re: Stranger than fiction! new [Re: BillP]
      #4073666 - 09/26/10 01:10 AM

Quote:

Quote:

This reminds me of folks who swear ol' carbureted engines are somehow superior to the modern fuel-injected powerplants we now enjoy...




As profession drag racer Warren Johnson characterized it, properly tuned, carburetors make more peak power than EFI in a Pro Stock engine. A carb’s pressure differential atomizes the gas a lot better than spraying fuel through an orifice. And as professional racer Myron Cottrell puts it, if you're looking to drive the family car about 25k miles a year, get EFI; if you are looking to race, get a carb. With every advantage, comes a disadvantage...but this is off topic




Moral of the story: Pick your analogies carefully, CN members have diverse and varied experience


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Bob Myler
Pooh-Bah
*****

Reged: 05/18/06

Loc: St Louis, MO
Re: Stranger than fiction! new [Re: Jeff Morgan]
      #4074068 - 09/26/10 10:04 AM

Printing it - then laminating it.

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Dr Morbius
Post Laureate
*****

Reged: 02/06/07

Loc: ManorvilleNY-but not for long
Re: Stranger than fiction! new [Re: Bob Myler]
      #4074575 - 09/26/10 02:39 PM

Don't forget to frame it also!

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banatop
member


Reged: 05/06/07

Re: Stranger than fiction! new [Re: Bob Myler]
      #4074581 - 09/26/10 02:40 PM

Whilst I agree that long focus achromats can be excellent telescopes, one of the main reasons for buying a shorter focal length Apochromat is because of the optical quality, combined with its shorter, more manageable length. This would probably outweigh any slight optical differences for many owners. When I decided to go to a bigger refractor, I chose the 178ed because a similar achro ( probably a DG "8 f15), would have meant going round to knock on my neighbours door every time I wanted to remove the dew shield. I ask, in all humility,that this discovery be called: "the not waking up the neighbour at two in the morning effect".

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Preston Smith
The Travel Scope Guy
*****

Reged: 04/24/05

Loc: Eureka, Pa
Re: Stranger than fiction! new [Re: banatop]
      #4074701 - 09/26/10 03:41 PM Attachment (359 downloads)

The answer is simple folks.

Buy one of each.


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astroneil
Pooh-Bah
*****

Reged: 07/28/09

Loc: res publica caledoniae
Re: Stranger than fiction! new [Re: Preston Smith]
      #4074776 - 09/26/10 04:32 PM

Hello everyone,

Thank you all for the fantastic feedback this article has so far generated. I am overwhelmed, really!

Some folk have kindly contacted me to let me know of a few little errors that have inadvertently crept into the text. Mea culpa! Hope to rectify them soon.

Jim: hope you didn't choke on your roasted chicory

Clive: I need to emphasise that the purpose of the article is to evaluate the performance of fast apos (can I call them that?) and long focus achromats primarily with respect to their perceived image stability. The intention was not to be adversarial but to point out how the respective instruments are likley to perform in the field. There are 4" F/6 doublets already in existence, so F/6.3 was not a fictional scenario in any way, shape or form.

Bill: The Sacek effect is something we all need to talk about sometime soon. It is fascinating to say the least!

Banatop:

"I ask, in all humility,that this discovery be called: "the not waking up the neighbour at two in the morning effect".


Preston: Too right! In fact, I'm out with my TV 76 F/6.3 doublet Apo (oooooh) tonight. Conditions are very calm, cool and stable.

Kind regards,

Neil.

Edited by astroneil (09/26/10 04:42 PM)


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