Jump to content


Photo

24mm Brandon: I think I just figured it out.

  • Please log in to reply
25 replies to this topic

#1 jrbarnett

jrbarnett

    Eyepiece Hooligan

  • *****
  • Posts: 20631
  • Joined: 28 Feb 2006
  • Loc: Petaluma, CA

Posted 03 November 2012 - 06:58 PM

The 24mm Brandon is the "odd man out" in that it has a wider AFOV than the rest. Though they're all putatively 50-degrees, they aren't really. I suspect the "average" is around 43-degees and the 24mm is closer to 53-degrees. Problem is, in anything approaching a "fast" scope (anything faster than f/8) the outer portion of the field is quite astigmatic (:barf:).

But...remember the Dakin! The matched Barlow for the Brandon line is the 2.4x Dakin Barlow. When you mate the 2.4x Dakin with the 24mm Brandon, you're operating at 10mm with a 53-degree fairly well corrected AFOV with ~19mm of eye relief.

In other words, it was a 10mm Radian long before there was a 10mm Radian. :grin:

- Jim

#2 houser23

houser23

    Mariner 2

  • -----
  • Posts: 257
  • Joined: 26 Oct 2009
  • Loc: Rocklin, CA

Posted 03 November 2012 - 07:18 PM

I think applause is in order.

#3 johnnyha

johnnyha

    Fly Me to the Moon

  • *****
  • Posts: 6500
  • Joined: 12 Nov 2006
  • Loc: Sherman Oaks, CA

Posted 03 November 2012 - 07:55 PM

Nice! The Delos are also just Panoptics in TV barlows and the 4.7 Ethos looks suspiciously like the 13 Ethos in a 2.5X Powermate. :grin:

And pssst... the T6 line and 1.25" XW line are each just one eyepiece, with the field lens pulled further and further away from the eye lens for more mag... ;) :lol:

#4 pstarr

pstarr

    Gemini

  • *****
  • Posts: 3047
  • Joined: 17 Sep 2004
  • Loc: NE Ohio

Posted 03 November 2012 - 08:13 PM

So then if you spend $235.00 on the 24mm Brandon and another $185.00 on a Dakin Barlow, you will almost get the equivalent of a 10mm Radian. The fov and eye relief will just be smaller. Huh.

#5 Jim Rosenstock

Jim Rosenstock

    Fly Me to the Moon

  • *****
  • Posts: 6592
  • Joined: 14 Jul 2005
  • Loc: MD, south of the DC Nebula

Posted 03 November 2012 - 09:08 PM

While I'm not naturally drawn to barlows, I gotta admit the Dakin 2.4X also works magic with my Brandon 16 and 12. Oh, I'll still prefer my Brandon 8, 6, and UOHD 5, but for sharing views with my eyeglasses-wearing friends, the Dakined longer-focus Brandons don't give up much!

Also I'm fond of the 2.8X Klee Barlow for more "in-between" magnifications--try that with an old 28mm Ortho or RKE! :jump:

Cheers,

Jim

#6 Jeff Morgan

Jeff Morgan

    Fly Me to the Moon

  • *****
  • Posts: 5788
  • Joined: 28 Sep 2003
  • Loc: Prescott, AZ

Posted 03 November 2012 - 10:04 PM

In other words, it was a 10mm Radian long before there was a 10mm Radian. :grin:

- Jim


Radian?! Yuck.

Some time ago it occurred to me that the 24 Brandon/2.4 Dakin combo was at least a 10 Delos long before there was a 10 Delos.

#7 dscarpa

dscarpa

    Gemini

  • *****
  • Posts: 3006
  • Joined: 15 Mar 2008
  • Loc: San Diego Ca.

Posted 03 November 2012 - 10:20 PM

For $80 less than the Brandon-Dakin barlow one could get a Delos at the sale price. David

#8 Scott in NC

Scott in NC

    80mm Refractor Fanatic

  • *****
  • Administrators
  • Posts: 16686
  • Joined: 05 Mar 2005
  • Loc: NC

Posted 03 November 2012 - 10:28 PM

Some time ago it occurred to me that the 24 Brandon/2.4 Dakin combo was at least a 10 Delos long before there was a 10 Delos.


I think I'd still rather have the Delos, as it'll have a MUCH wider AFOV than the Brandon/Dakin combo.

#9 jrbarnett

jrbarnett

    Eyepiece Hooligan

  • *****
  • Posts: 20631
  • Joined: 28 Feb 2006
  • Loc: Petaluma, CA

Posted 03 November 2012 - 10:52 PM

Yeah, but then you'd be stuck with a Delos and not have either the Brandon or Dakin Barlow. :thinking:

- Jim

#10 jrbarnett

jrbarnett

    Eyepiece Hooligan

  • *****
  • Posts: 20631
  • Joined: 28 Feb 2006
  • Loc: Petaluma, CA

Posted 03 November 2012 - 10:53 PM

What I meant to say was "like a 10mm Radian, only not all sucky like that". :lol:

- Jim

#11 dscarpa

dscarpa

    Gemini

  • *****
  • Posts: 3006
  • Joined: 15 Mar 2008
  • Loc: San Diego Ca.

Posted 04 November 2012 - 12:45 AM

But then again the Delos isn't the least bit sucky. David

#12 johnnyha

johnnyha

    Fly Me to the Moon

  • *****
  • Posts: 6500
  • Joined: 12 Nov 2006
  • Loc: Sherman Oaks, CA

Posted 04 November 2012 - 01:25 AM

Yeah, but then you'd be stuck with a Delos and not have either the Brandon or Dakin Barlow. :thinking:

- Jim

:lol:

#13 johnnyha

johnnyha

    Fly Me to the Moon

  • *****
  • Posts: 6500
  • Joined: 12 Nov 2006
  • Loc: Sherman Oaks, CA

Posted 04 November 2012 - 01:26 AM

Yeah, but then you'd be stuck with a Delos and not have either the Brandon or Dakin Barlow. :thinking:

- Jim

:lol:

:jedi:

#14 Rick Woods

Rick Woods

    Voyager 1

  • *****
  • Posts: 14935
  • Joined: 27 Jan 2005
  • Loc: Inner Solar System

Posted 04 November 2012 - 02:12 AM

The only solution is to get them all.

#15 jrbarnett

jrbarnett

    Eyepiece Hooligan

  • *****
  • Posts: 20631
  • Joined: 28 Feb 2006
  • Loc: Petaluma, CA

Posted 04 November 2012 - 09:33 AM

Rick, you make 'em sound like Pokemon.

:lol:

- Jim

#16 Rick Woods

Rick Woods

    Voyager 1

  • *****
  • Posts: 14935
  • Joined: 27 Jan 2005
  • Loc: Inner Solar System

Posted 04 November 2012 - 08:06 PM

Hey, it's not my money! :D

#17 Metalmanstan

Metalmanstan

    Vostok 1

  • -----
  • Posts: 120
  • Joined: 02 Jul 2012
  • Loc: Oneonta, NY

Posted 04 November 2012 - 08:26 PM

So because I have a f/4.9 telescope I have to probably spend more on the eyepieces then I did on the scope? Just got itbsobim just learning, please bare with me :p

#18 Scott in NC

Scott in NC

    80mm Refractor Fanatic

  • *****
  • Administrators
  • Posts: 16686
  • Joined: 05 Mar 2005
  • Loc: NC

Posted 04 November 2012 - 09:03 PM

So because I have a f/4.9 telescope I have to probably spend more on the eyepieces then I did on the scope?


You *can*, but you really don't *have to*. An inexpensive set of Plossls will do just fine for now, and if you decide to stick with the hobby and wish to upgrade someday, there will be plenty of opportunity to do that later.

#19 Keith

Keith

    Messenger

  • *****
  • Posts: 467
  • Joined: 14 May 2005
  • Loc: Costa Mesa, CA USA

Posted 04 November 2012 - 10:41 PM

So because I have a f/4.9 telescope I have to probably spend more on the eyepieces then I did on the scope? Just got itbsobim just learning, please bare with me :p


Back in the day that was the case, but nowadays there are suitable alternatives, explore scientific comes to mind as a good value that handles fast newtonians well, 82deg especially. Wide fields come in handy if it is a dob, but if it is on a tracking platform or driven mount, good plossls work fine until you get spoiled by darth nagler and emperor ethos. And even then, Explore scientific to the rescue, $299 for a waterproof 100deg 20mm eyepiece, much less than half the price of the ethos, and at least 80% of the performance. $100 a piece for 1.25" 82degs 4.7,6.7,8.8,11,14mm is a bargain too. If I didn't already have a mixed bag of older meade UWA, Nagler and Pentax, I would snatch them up. Note that I DO have both 14mm and 20mm ES100's, and they curb my ethos lust quite well. I have not yet experienced Delos, since I was pulled out of the game just before they hit the market.

#20 LDb

LDb

    Apollo

  • *****
  • Posts: 1039
  • Joined: 01 Feb 2008
  • Loc: Cleveland, Ohio

Posted 07 November 2012 - 11:35 PM

Well Jim,

Once again your insight uncovers an important piece of the riddle of the Brandons.

The Dakin has proven to be an extraordinary barlow (and the only one I have kept) since I got mine in 1985. It's match to the 24mm with its wider FOV is amazing and it does make all of the Brandons a whole "new" set with intermediate mags and virtually no loss or "interference" with the image. Just another one of those interesting little things about how good these "old" deisgns are.

Never giving mine up.

As ever, a humble acolyte of Ordo Brandonensis

#21 Jeff B

Jeff B

    Vanguard

  • *****
  • Posts: 2030
  • Joined: 30 Dec 2006

Posted 08 November 2012 - 03:10 PM

So somebody please explain to me what exactly is a "matched" barlow.

What does it "match"?

Jeff

#22 Rick Woods

Rick Woods

    Voyager 1

  • *****
  • Posts: 14935
  • Joined: 27 Jan 2005
  • Loc: Inner Solar System

Posted 08 November 2012 - 07:36 PM

According to the post, it matches the 24mm Brandon. I interpret that as meaning the combination is greater than the sum of the parts. Or something like that.
The Dakin, with its 2.4x magnification, is intended to complement the Brandons by making a whole new set of eyepieces with no duplications.

I've got a Dakin, but I confess I haven't used it hardly at all (you don't need a barlow in a big SCT), so I can't say from personal experience.

#23 Sarkikos

Sarkikos

    Hubble

  • *****
  • Posts: 17472
  • Joined: 18 Dec 2007
  • Loc: Per sylvam ad astra

Posted 08 November 2012 - 08:46 PM

I hardly ever use a Barlow any more; virtually never for deep sky, hardly ever for planets/Moon. But I do screw on a Barlow lens cell in order to compensate for not enough in-focus when I use a binoviewer or filter wheel on my Newts. Other than that, I'd rather utilize individual eyepieces. I've recently sold a couple of my Barlows. Just wasn't using them. :shrug:

Mike

#24 Jeff B

Jeff B

    Vanguard

  • *****
  • Posts: 2030
  • Joined: 30 Dec 2006

Posted 08 November 2012 - 09:11 PM

According to the post, it matches the 24mm Brandon. I interpret that as meaning the combination is greater than the sum of the parts. Or something like that.
The Dakin, with its 2.4x magnification, is intended to complement the Brandons by making a whole new set of eyepieces with no duplications.

I've got a Dakin, but I confess I haven't used it hardly at all (you don't need a barlow in a big SCT), so I can't say from personal experience.


Ok, so what optical abberations does it correct, if any?

#25 Rick Woods

Rick Woods

    Voyager 1

  • *****
  • Posts: 14935
  • Joined: 27 Jan 2005
  • Loc: Inner Solar System

Posted 09 November 2012 - 03:36 AM

That, I don't know.






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics