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Equipment Discussions >> Reflectors

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auriga
Pooh-Bah


Reged: 03/02/06

just when we thought we were safe
      #5987001 - 07/23/13 10:35 PM

We thought we were safe in needing a ladder with a large scope.

Then the duo struck:

First it was the jpastrocraft/mikelockwood Sweet Sixteen 16"f/4. Seated viewing in all positions.

Then it was the astrocraft/lockwood 14.5" f/2.5. Seated viewing in all positions.

Then is was the 20" f/3 astrocraft/lockwood, which Bob S has. Seated viewing in all positions.

All were no ladder scopes.

Now we have the jpastrocraft/ lookwood 25" f/3, you might have to stand to observe at the zenith, or maybe not, but in any event no ladder is required,

Where will all this end? Doesn't anyone want to catch falling people at public outreach events?

Bill


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frito
Pooh-Bah


Reged: 10/05/12

Loc: Fremont, CA
Re: just when we thought we were safe new [Re: auriga]
      #5987201 - 07/24/13 12:44 AM

ladders are cool and all but if i don't have to climb one then why have to climb one?

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Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: just when we thought we were safe new [Re: frito]
      #5987429 - 07/24/13 07:21 AM

Quote:

ladders are cool and all but if i don't have to climb one then why have to climb one?




- Because F/4 - F/5 is a much nicer place to be than F/3...

- Because an F/4 - F/5 is affordable when compared to an F/3...

- Because you need the exercise.

Jon


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tezster
scholastic sledgehammer
*****

Reged: 07/14/09

Loc: Missisauga, Canada
Re: just when we thought we were safe new [Re: auriga]
      #5987437 - 07/24/13 07:30 AM

The ladder-making industry must be near a point of crisis, indeed, with the increasing number of large scopes now being designed for observing while seated or standing. I'm surprised that the .001% reduction in ladder sales haven't sent the ladder-making interest groups and lobbyists flooding the astronomy community, decrying the introduction of these new-fangled, short focal-length dobs.

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nicknacknock
professor emeritus
*****

Reged: 02/20/12

Loc: In a galaxy far far away...
Re: just when we thought we were safe new [Re: tezster]
      #5987461 - 07/24/13 08:00 AM

Ah, diversification is the key! Them ladder manufacturers are offsetting the dramatic fall in ladder sales with the increase in sales of neat little chairs for us astronuts!

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csrlice12
Postmaster
*****

Reged: 05/22/12

Loc: Denver, CO
Re: just when we thought we were safe new [Re: nicknacknock]
      #5987501 - 07/24/13 08:42 AM

They could always go into the eyepiece cap/cup manufacturing business and make up the difference.......

Imagine, caps/cups that actually fit....


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FJA
Sketcher Extraordinaire
*****

Reged: 11/17/04

Loc: 50.65° N, 1.15° W
Re: just when we thought we were safe new [Re: csrlice12]
      #5987545 - 07/24/13 09:18 AM

With my knees, doing away with ladders or even steps (my 18" is an f/4.3 but even so the eyepiece is about 6ft 5in off the ground) is an attractive idea but bank account says 'no' to buying a fast big dob.

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Cotts
Just Wondering
*****

Reged: 10/10/05

Loc: Toronto, Ontario
Re: just when we thought we were safe new [Re: tezster]
      #5987559 - 07/24/13 09:30 AM

Quote:

The ladder-making industry must be near a point of crisis, indeed, with the increasing number of large scopes now being designed for observing while seated or standing. I'm surprised that the .001% reduction in ladder sales haven't sent the ladder-making interest groups and lobbyists flooding the astronomy community, decrying the introduction of these new-fangled, short focal-length dobs.




Obviously we need a 65+ page thread to discuss this important issue....

Dave


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csrlice12
Postmaster
*****

Reged: 05/22/12

Loc: Denver, CO
Re: just when we thought we were safe new [Re: Cotts]
      #5987644 - 07/24/13 10:34 AM

You do realize that Astro ladders are much more expensive...because it has the word Astro in it.....

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Sean Cunneen
Let Me Think
*****

Reged: 08/01/07

Loc: Blue Island Illinois
Re: just when we thought we were safe new [Re: csrlice12]
      #5987858 - 07/24/13 01:48 PM

I am doing what I can to help, I am building a 16" f7.2. Now won't you please consider a long focus instrument before the industries' bell has rung?

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Jeff Morgan
Postmaster
*****

Reged: 09/28/03

Loc: Prescott, AZ
Re: just when we thought we were safe new [Re: Sean Cunneen]
      #5987879 - 07/24/13 02:04 PM Attachment (31 downloads)

Quote:

I am doing what I can to help, I am building a 16" f7.2. Now won't you please consider a long focus instrument before the industries' bell has rung?




Well I can't top f/7.2, but would still like to think I am doing my part while we patiently wait for monsoon season to end.

The ladder that goes with this scope is even American made!


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Cotts
Just Wondering
*****

Reged: 10/10/05

Loc: Toronto, Ontario
Re: just when we thought we were safe new [Re: Jeff Morgan]
      #5988174 - 07/24/13 05:34 PM

Gorgeous scope! But those six-truss jobs always look lopsided and waaaaay out of collimation.

Of course they aren't, really....

My 16" f/5 requires one step on a stepstool for me so I guess I qualify for something or other...

Dave


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GOLGO13
Carpal Tunnel


Reged: 11/05/05

Loc: St. Louis area
Re: just when we thought we were safe new [Re: auriga]
      #5988830 - 07/25/13 12:52 AM

I have enjoyed looking through scopes which required a ladder. But that experience also made me really appreciate my XT10i and not needing to deal with that. I've decided that I will never go above a point where I would need a ladder. I've also decided that a 10 inch scope is plenty big enough for me, and I'll just mooch off someone else who has a bigger scope when i can.

It's also one thing for the ladder to be a step stool and another thing for it to be one meant for an orchard.


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Peter Natscher
professor emeritus


Reged: 03/28/06

Loc: Central Coast California
Re: just when we thought we were safe new [Re: auriga]
      #5989331 - 07/25/13 11:01 AM

I use a strong 4ft. Werner fiberglass ladder with my 24" f/3.3 dob. I added extra rungs between existing ones so there's now four rungs spaced 6" apart at the lower two feet of the ladder. I only need to use the two or three lower rungs at the most telescope elevation angle. I've added extra rungs to all my past ladders that I've used with my past taller Dobs (5ft. and 6ft. ladders). While observing flat-footed with the dob at 60 or lower angles, I can rest against the 4ft. ladder while observing. Resting against a ladder while observing is comfortable after a few hours of standing at the eyepiece. It steadies my body so that long periods of threshold observing are easier to do and more productive. A 4ft. ladder with extra rungs is relatively small and easy to transport with a larger telescope.

Quote:

We thought we were safe in needing a ladder with a large scope.

Then the duo struck:

First it was the jpastrocraft/mikelockwood Sweet Sixteen 16"f/4. Seated viewing in all positions.

Then it was the astrocraft/lockwood 14.5" f/2.5. Seated viewing in all positions.

Then is was the 20" f/3 astrocraft/lockwood, which Bob S has. Seated viewing in all positions.

All were no ladder scopes.

Now we have the jpastrocraft/ lookwood 25" f/3, you might have to stand to observe at the zenith, or maybe not, but in any event no ladder is required,

Where will all this end? Doesn't anyone want to catch falling people at public outreach events?

Bill




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Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: just when we thought we were safe new [Re: GOLGO13]
      #5989396 - 07/25/13 11:40 AM Attachment (20 downloads)

Quote:


I have enjoyed looking through scopes which required a ladder. But that experience also made me really appreciate my XT10i and not needing to deal with that. I've decided that I will never go above a point where I would need a ladder. I've also decided that a 10 inch scope is plenty big enough for me, and I'll just mooch off someone else who has a bigger scope when i can.




My 12.5 inch Equatorial requires a ladder but not a tall one, I use it at home on my driveway. In my mind, I never wanted another ladder scope, a short step, yes but a true ladder scope, I didn't want one, too much hassle, too much effort transporting it, setting it up.

But about 4 years ago, my wife and I found the place that was our little dream mountain hideaway and after a while I realized that what with the big garage and everything, I didn't need to be thinking portable so much any more so I began keeping a lazy eye open for something larger than my 16 inch, I was thinking 20 inch, something like that.

Well at some point an 25 inch F/5 Obsession showed up on Astromart at a good price and not far away. I realized that just about any 25 inch would require a ladder, certainly any 25 inch I was willing to pay for would so if I wanted a 25 inch, it was not a question of a ladder or not but rather how tall a ladder...

Anyway, I ended up with the scope and eventually, with the help of Jeff Morgan, eventually purchased a rolling ladder for stability and security. It all works. I would not want to be in the position where this was my only larger scope but I am fine with it as a ladder scope.

Jon


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careysub
Carpal Tunnel
*****

Reged: 02/18/11

Loc: Rancho Cucamonga, CA
Re: just when we thought we were safe new [Re: auriga]
      #5989408 - 07/25/13 11:48 AM

Quote:

We thought we were safe in needing a ladder with a large scope.

Then the duo struck:

First it was the jpastrocraft/mikelockwood Sweet Sixteen 16"f/4. Seated viewing in all positions.

Then it was the astrocraft/lockwood 14.5" f/2.5. Seated viewing in all positions.

Then is was the 20" f/3 astrocraft/lockwood, which Bob S has. Seated viewing in all positions.

All were no ladder scopes.

Now we have the jpastrocraft/ lookwood 25" f/3, you might have to stand to observe at the zenith, or maybe not, but in any event no ladder is required,

Where will all this end? Doesn't anyone want to catch falling people at public outreach events?

Bill




What constitutes "ladder-free viewing" is a matter of opinion due to a 12" or so height difference commonly seen in a mixed sex crowd of adults.

However the consensus seems to be that a "height factor" (FL - 0.5*D) of 64" is about that number (an LB-16 for example).

The Lockwood Custom Optics website places the minimum FR for visual use at 2.75 (that Astrocraft seems to be cheating - I wonder how well the EP/eye system is handling that steep visual cone).

So: 64/(2.75 -0.5) = 28.4". If you think your focuser-end optics can handle F/2.5 then it increases to 32".

Could a more exotic optical design handle F/2 for visual use? (No, SCTs don't count - any full aperture corrector will fail as it scales to larger diameters.)


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derangedhermit
Pooh-Bah


Reged: 10/07/09

Loc: USA
Re: just when we thought we were safe new [Re: careysub]
      #5989948 - 07/25/13 05:04 PM

Quote:

Could a more exotic optical design handle F/2 for visual use? (No, SCTs don't count - any full aperture corrector will fail as it scales to larger diameters.)




I've been asking about this. You're going to have a large secondary in any practical solution. I doubt you'll find anyone wanting to make an f/2 paraboloid, hyperboloid, or ellipse, so you're left with the SCT-type spherical mirror. Cheap to make, but very very difficult to correct the tons of spherical aberration for large diameter primaries by using subaperture correctors. At least that's my understanding. CDKs and Cassegrains use higher primary focal ratios, above f/3. Oh, at f/2 you probably need a 3" focuser with 2" adapter to avoid drawtube vignetting.

About the best you can do is f/3 and a Paracorr, and you're still pushing it - there are a few people that know how to make such a mirror and build such a thing, but a lot less than can build at f/5, or even f/4.

Lee


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Mike B
Starstruck
*****

Reged: 04/06/05

Loc: shake, rattle, & roll, CA
Re: just when we thought we were safe new [Re: Jon Isaacs]
      #5990012 - 07/25/13 05:50 PM

Quote:

I would not want to be in the position where this was my only larger scope but I am fine with it as a ladder scope.



Jon, it's good to see at least some of us moving on up in the telescope realm.

Considering the things which go bump in the night, and not wishing to numbered amongst them, i've always been inclined to keep both feet on the ground. So i stopped the fever at 15" F4.5.... however, given the opportunity to keep a larger rig permanently stationed in the boondocks, i think i could manage with a ladder like Jon's.

But until such time, the ladder manuf. crisis will have to be resolved without me; for i feel it's wrong to wring wealth with rungs wielded too widely, so prefer a standing dissent to a decent descent.


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Deep13
Carpal Tunnel
*****

Reged: 01/25/05

Loc: NE Ohio
Re: just when we thought we were safe new [Re: Mike B]
      #5990129 - 07/25/13 07:04 PM

A friend of mine has a home-built 20" f/6. "I don't like coma," he said. I guess he doesn't like coma-correcting lenses either.

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Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: just when we thought we were safe new [Re: Mike B]
      #5990765 - 07/26/13 05:59 AM

Quote:

But until such time, the ladder manuf. crisis will have to be resolved without me; for i feel it's wrong to wring wealth with rungs wielded too widely, so prefer a standing dissent to a decent descent.




I still haven't quite figured it out but is sure is clever.

Jon


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