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Main
Date: 02 Sep 2006 15:04:18
From: Richard Adams
Subject: Seeking Barlow Recommendation
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Telescope: Meade LXD75 10" SNT
Eyepieces: Pentax SMC XL 7, 10.5, 14 & 21, Meade Super Plossl 32, 40
It seems the more I read the more confused I become regarding barlows.
I'm looking to get a 2x and want to minimise the amount of trial and
replacement. Please chime in with what you are using and how well it
works with which eyepieces. Thanks!
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Date: 02 Sep 2006 22:19:42
From: Joe S.
Subject: Re: Seeking Barlow Recommendation
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"Richard Adams" <ackthpt@concentric.net > wrote in message
news:1157234657.949155.252990@h48g2000cwc.googlegroups.com...
>
> Telescope: Meade LXD75 10" SNT
> Eyepieces: Pentax SMC XL 7, 10.5, 14 & 21, Meade Super Plossl 32, 40
>
> It seems the more I read the more confused I become regarding barlows.
> I'm looking to get a 2x and want to minimise the amount of trial and
> replacement. Please chime in with what you are using and how well it
> works with which eyepieces. Thanks!
>
TeleVue 2X or 3X -- costs a bit more but worth it.
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Date: 02 Sep 2006 22:51:41
From: Richard Adams
Subject: Re: Seeking Barlow Recommendation
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Joe S. wrote:
> "Richard Adams" <ackthpt@concentric.net> wrote in message
> news:1157234657.949155.252990@h48g2000cwc.googlegroups.com...
>
>>Telescope: Meade LXD75 10" SNT
>>Eyepieces: Pentax SMC XL 7, 10.5, 14 & 21, Meade Super Plossl 32, 40
>>
>>It seems the more I read the more confused I become regarding barlows.
>>I'm looking to get a 2x and want to minimise the amount of trial and
>>replacement. Please chime in with what you are using and how well it
>>works with which eyepieces. Thanks!
>>
>
>
> TeleVue 2X or 3X -- costs a bit more but worth it.
>
>
>
Big Barlow? Powermate? Other models?
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Date: 02 Sep 2006 18:32:09
From: Ben
Subject: Re: Seeking Barlow Recommendation
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Richard Adams wrote:
> Telescope: Meade LXD75 10" SNT
> Eyepieces: Pentax SMC XL 7, 10.5, 14 & 21, Meade Super Plossl 32, 40
>
> It seems the more I read the more confused I become regarding barlows.
> I'm looking to get a 2x and want to minimise the amount of trial and
> replacement. Please chime in with what you are using and how well it
>works with which eyepieces. Thanks
From: Ben
Subject: Barlow choice
This is my first post to the group so I hope I'm doing it
correctly. If not please forgive- I'm new to this stuff.
I purchased a TeleVue 3x several years ago to use in my 10 in Newt
and it's the best investment I've made outside of an O III filter.
When employed with a zoom lens it allows you to tune up the
magnification to match sky conditions. TeleVue is expensive but worth
it.
Will now return to lurking....
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Date: 02 Sep 2006 22:36:09
From: Richard Adams
Subject: Re: Seeking Barlow Recommendation
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Ben wrote:
> Richard Adams wrote:
>
>>Telescope: Meade LXD75 10" SNT
>>Eyepieces: Pentax SMC XL 7, 10.5, 14 & 21, Meade Super Plossl 32, 40
>>
>>It seems the more I read the more confused I become regarding barlows.
>>I'm looking to get a 2x and want to minimise the amount of trial and
>>replacement. Please chime in with what you are using and how well it
>>works with which eyepieces. Thanks
>
>
> From: Ben
> Subject: Barlow choice
>
> This is my first post to the group so I hope I'm doing it
> correctly. If not please forgive- I'm new to this stuff.
> I purchased a TeleVue 3x several years ago to use in my 10 in Newt
> and it's the best investment I've made outside of an O III filter.
> When employed with a zoom lens it allows you to tune up the
> magnification to match sky conditions. TeleVue is expensive but worth
> it.
> Will now return to lurking....
>
Thanks for the feedback. What model Televue did you get? How does it
work with non-zoom eye pieces? i.e. 40mm or 7 mm?
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Date: 04 Sep 2006 19:04:05
From: Willie R. Meghar
Subject: Re: Seeking Barlow Recommendation
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"Richard Adams" <ackthpt@concentric.net > wrote:
>Telescope: Meade LXD75 10" SNT
>Eyepieces: Pentax SMC XL 7, 10.5, 14 & 21, Meade Super Plossl 32, 40
>
>It seems the more I read the more confused I become regarding barlows.
>I'm looking to get a 2x and want to minimise the amount of trial and
>replacement. Please chime in with what you are using and how well it
>works with which eyepieces. Thanks!
Hi Richard,
I've had two Barlows (Japanese made TeleVue 2x and University Optics
2.8x Klee) that I've been using for several years. I recently added a
third Barlow (Orion 2x Shorty-Plus).
Some measurements:
TL = Top Length (portion of Barlow that does *not* go inside focuser)
BL = Bottom Length (length of 1.25" O.D. section of Barlow)
OA = Overall Length of Barlow
------------------------------ TL ------------ BL ----------- OA ---
TV 2x ---------------- 41mm --------- 56 mm ----- 97 mm
2x Shorty-Plus- 42.5 mm ------ 32.5 mm ---- 75 mm
2.8x Klee ---------- 36 mm ------- 26.5 mm -- 62.5 mm
A recent comparison revealed the following details:
The TeleVue was the only Barlow of these three that was threaded for
filters.
Out of 23 eyepieces used, 10 showed absolutely no sign of vignetting
with any of these Barlows.
When vignetting occurred, the TV Barlow was least affected and the
Klee was most affected.
Three eyepieces showed some 'Kidney Beaning' sensitivity with eye
placement when used with each of the three Barlows.
Barlow amplification factors were computed based on field of view
comparisons with and without the Barlows (using the 10 eyepieces that
did *not* result in vignetting). The TV 2x Barlow averaged 2.11x.
The Shorty-Plus averaged 2.19x. The Klee averaged 2.79x. The
difference between the two 2x Barlows (as well as for the Klee) held
for all 23 eyepieces. *All* eyepieces resulted in a little wider true
fields (a little lower magnification) with the TV than they did with
the Shorty-Plus.
On an individual eyepiece basis, two eyepieces (both Naglers) were
consistently on the lower end of the magnification amplification range
for all three Barlows -- probably due to their 'low' lower lens
element being closer to the lens element(s) of the Barlows. Barlows
do *not* amplify all eyepieces equally. My raw data would seem to
indicate that higher power (or perhaps shorter) Barlows result in a
greater range of amplification than do lower power (or perhaps longer)
Barlows.
I've yet to make definitive comparisons of image quality between these
Barlows. Up until the present I was content to use whichever Barlow
was needed to achieve the magnification/field-of-view desired.
The data on which the above is based was collected using a 13cm f/6.4
apochromat refractor. (The scope was originally advertised as "f/6";
but careful measurements of true fields of view and eyepiece field
stop diameters revealed that the scope is more likely f/6.4.) I'm
currently in the process of making additional measurements of
individual eyepiece characteristics as well as comparisons between the
various Barlows. This is likely to take a fair amount of time.
Superficially, other than a bit of vignetting and the magnification
differences, I've noticed no glaring differences in the performance of
these three Barlows; but like I said, I've not yet attempted to make a
(time consuming) critical comparison.
*Perhaps* (just speculation) a good 2" Barlow would avoid all
vignetting situations (at least for 1.25" OD eyepieces) -- if that's a
concern to you.
For most of the above I've not mentioned specific eyepieces or
eyepiece types. This is because of space concerns as well as the fact
that I have none of the same eyepieces that the original poster
mentioned!
Unfortunately I lack the funding to be able to purchase a greater
variety of Barlows, etc. for testing -- besides, I usually prefer
actual observing over equipment testing and measuring. Most of the
testing I do is for my own information -- so I'll be better informed
as to the performance of my own equipment ;-)
Hopefully the above will be of some benefit to some readers -- if not
to the original poster. If nothing else, it shows beyond any doubt
that Barlow amplification factors can vary some with eyepiece choice;
and two "2x" Barlows do not necessary magnify equally even when used
with the same eyepiece and telescope.
Willie R. Meghar
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Date: 04 Sep 2006 21:37:55
From: William Hamblen
Subject: Re: Seeking Barlow Recommendation
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On 2006-09-05, Willie R Meghar <NoMail@thisaddress.net > wrote:
> On an individual eyepiece basis, two eyepieces (both Naglers) were
> consistently on the lower end of the magnification amplification range
> for all three Barlows -- probably due to their 'low' lower lens
> element being closer to the lens element(s) of the Barlows. Barlows
> do *not* amplify all eyepieces equally. My raw data would seem to
> indicate that higher power (or perhaps shorter) Barlows result in a
> greater range of amplification than do lower power (or perhaps longer)
> Barlows.
The magnification of a barlow lens is equal to 1 + d/f, where f
is the focal length of the negative lens expressed as a positive
number and d is the distance from the lens to the focal plane of
the eyepiece. The focal plane is in different places on
different eyepieces, making the magnification vary. The smaller
f is, as on a shorty barlow or a high magnification barlow, the
more the variation of magnification between eyepieces.
Tele Vue Powermates are a different design that reduces the
variation in magnification from eyepiece to eyepiece.
Bud
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Date: 04 Sep 2006 21:24:05
From: Richard Adams
Subject: Re: Seeking Barlow Recommendation
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Willie R. Meghar wrote:
> "Richard Adams" <ackthpt@concentric.net> wrote:
>
>
>>Telescope: Meade LXD75 10" SNT
>>Eyepieces: Pentax SMC XL 7, 10.5, 14 & 21, Meade Super Plossl 32, 40
>>
>>It seems the more I read the more confused I become regarding barlows.
>>I'm looking to get a 2x and want to minimise the amount of trial and
>>replacement. Please chime in with what you are using and how well it
>>works with which eyepieces. Thanks!
>
>
> Hi Richard,
> I've had two Barlows (Japanese made TeleVue 2x and University Optics
> 2.8x Klee) that I've been using for several years. I recently added a
> third Barlow (Orion 2x Shorty-Plus).
>
> Some measurements:
> TL = Top Length (portion of Barlow that does *not* go inside focuser)
> BL = Bottom Length (length of 1.25" O.D. section of Barlow)
> OA = Overall Length of Barlow
>
> ------------------------------ TL ------------ BL ----------- OA ---
> TV 2x ---------------- 41mm --------- 56 mm ----- 97 mm
> 2x Shorty-Plus- 42.5 mm ------ 32.5 mm ---- 75 mm
> 2.8x Klee ---------- 36 mm ------- 26.5 mm -- 62.5 mm
>
> A recent comparison revealed the following details:
>
> The TeleVue was the only Barlow of these three that was threaded for
> filters.
>
> Out of 23 eyepieces used, 10 showed absolutely no sign of vignetting
> with any of these Barlows.
>
> When vignetting occurred, the TV Barlow was least affected and the
> Klee was most affected.
>
> Three eyepieces showed some 'Kidney Beaning' sensitivity with eye
> placement when used with each of the three Barlows.
>
> Barlow amplification factors were computed based on field of view
> comparisons with and without the Barlows (using the 10 eyepieces that
> did *not* result in vignetting). The TV 2x Barlow averaged 2.11x.
> The Shorty-Plus averaged 2.19x. The Klee averaged 2.79x. The
> difference between the two 2x Barlows (as well as for the Klee) held
> for all 23 eyepieces. *All* eyepieces resulted in a little wider true
> fields (a little lower magnification) with the TV than they did with
> the Shorty-Plus.
>
> On an individual eyepiece basis, two eyepieces (both Naglers) were
> consistently on the lower end of the magnification amplification range
> for all three Barlows -- probably due to their 'low' lower lens
> element being closer to the lens element(s) of the Barlows. Barlows
> do *not* amplify all eyepieces equally. My raw data would seem to
> indicate that higher power (or perhaps shorter) Barlows result in a
> greater range of amplification than do lower power (or perhaps longer)
> Barlows.
>
> I've yet to make definitive comparisons of image quality between these
> Barlows. Up until the present I was content to use whichever Barlow
> was needed to achieve the magnification/field-of-view desired.
>
> The data on which the above is based was collected using a 13cm f/6.4
> apochromat refractor. (The scope was originally advertised as "f/6";
> but careful measurements of true fields of view and eyepiece field
> stop diameters revealed that the scope is more likely f/6.4.) I'm
> currently in the process of making additional measurements of
> individual eyepiece characteristics as well as comparisons between the
> various Barlows. This is likely to take a fair amount of time.
>
> Superficially, other than a bit of vignetting and the magnification
> differences, I've noticed no glaring differences in the performance of
> these three Barlows; but like I said, I've not yet attempted to make a
> (time consuming) critical comparison.
>
> *Perhaps* (just speculation) a good 2" Barlow would avoid all
> vignetting situations (at least for 1.25" OD eyepieces) -- if that's a
> concern to you.
>
> For most of the above I've not mentioned specific eyepieces or
> eyepiece types. This is because of space concerns as well as the fact
> that I have none of the same eyepieces that the original poster
> mentioned!
>
> Unfortunately I lack the funding to be able to purchase a greater
> variety of Barlows, etc. for testing -- besides, I usually prefer
> actual observing over equipment testing and measuring. Most of the
> testing I do is for my own information -- so I'll be better informed
> as to the performance of my own equipment ;-)
>
> Hopefully the above will be of some benefit to some readers -- if not
> to the original poster. If nothing else, it shows beyond any doubt
> that Barlow amplification factors can vary some with eyepiece choice;
> and two "2x" Barlows do not necessary magnify equally even when used
> with the same eyepiece and telescope.
>
> Willie R. Meghar
Thanks for your extensive and well considered reply. I performed a lot
of research on Sunday morning and afternoon trying to get the best idea
I could from numerous articles scattered about astronomy sites and old
posts on s.a.a. I've picked out something from TV and will let all
know how it works out with my assortment of eyepieces.
I was excetpionally fortunate last spring to find on eBay the bulk of my
Pentax set at a substantial discount with little competition. Why I got
them for as little as I did I have no clue. They arrived in factory
packaging with all papers. They had seen very little use and were all
immaculate. It would be lovely to have the money to buy these sort of
eps new as I'm often wary of eBay, where people often pass on poorly
treated items as 'mint condition.' This once it did work out.
Thanks again and clear skies,
Richard
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Date: 04 Sep 2006 18:36:44
From: Frank Bov
Subject: Re: Seeking Barlow Recommendation
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Richard,
You have a very nice selection of eyepieces, and a 2-3x Barlow will give you
the ability to use them to explore the limits of an f/4 focal ratio
telescope. As others have recommended, the TeleVue Powermate series are
among the finest Barlows ever offered, with some unique features not found
in a normal Barlow. I have their normal 2.5x and it's quite good.
However, I find something less than satisfying with a Barlow, perhaps its
the long tube sticking out or the need to switch the Barlow in and out to
change power smoothly. With your scope and eyepiece selection, I'd suggest
considering a TeleVue Nagler Zoom, specifically the 3-6mm. It fits right in
below your XL7 (an eyepiece we share) and lets you adjust magnification in a
very sensitive range continuously without focus changes. I got one at NEAF,
and have since sold off everything below 6mm. It's as good at 6mm as the
vaunted Pentax Orthos, and is as comfortable at 3mm as my Takahashi 2.8mm
Hi-O was.
The downside is the cost, and the inability to use the rest of your XLs at
the same time, but I think it's worth it.
HAve fun,
Frank
"Richard Adams" <ackthpt@concentric.net > wrote in message
news:1157234657.949155.252990@h48g2000cwc.googlegroups.com...
>
> Telescope: Meade LXD75 10" SNT
> Eyepieces: Pentax SMC XL 7, 10.5, 14 & 21, Meade Super Plossl 32, 40
>
> It seems the more I read the more confused I become regarding barlows.
> I'm looking to get a 2x and want to minimise the amount of trial and
> replacement. Please chime in with what you are using and how well it
> works with which eyepieces. Thanks!
>
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Date: 04 Sep 2006 21:25:34
From: Richard Adams
Subject: Re: Seeking Barlow Recommendation
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Frank Bov wrote:
> Richard,
> You have a very nice selection of eyepieces, and a 2-3x Barlow will give you
> the ability to use them to explore the limits of an f/4 focal ratio
> telescope. As others have recommended, the TeleVue Powermate series are
> among the finest Barlows ever offered, with some unique features not found
> in a normal Barlow. I have their normal 2.5x and it's quite good.
>
> However, I find something less than satisfying with a Barlow, perhaps its
> the long tube sticking out or the need to switch the Barlow in and out to
> change power smoothly. With your scope and eyepiece selection, I'd suggest
> considering a TeleVue Nagler Zoom, specifically the 3-6mm. It fits right in
> below your XL7 (an eyepiece we share) and lets you adjust magnification in a
> very sensitive range continuously without focus changes. I got one at NEAF,
> and have since sold off everything below 6mm. It's as good at 6mm as the
> vaunted Pentax Orthos, and is as comfortable at 3mm as my Takahashi 2.8mm
> Hi-O was.
>
> The downside is the cost, and the inability to use the rest of your XLs at
> the same time, but I think it's worth it.
>
> HAve fun,
> Frank
Thanks for your reply, Frank. I've settled on a TV Powermate. I'm
hoping it works out well.
> "Richard Adams" <ackthpt@concentric.net> wrote in message
> news:1157234657.949155.252990@h48g2000cwc.googlegroups.com...
>
>>Telescope: Meade LXD75 10" SNT
>>Eyepieces: Pentax SMC XL 7, 10.5, 14 & 21, Meade Super Plossl 32, 40
>>
>>It seems the more I read the more confused I become regarding barlows.
>>I'm looking to get a 2x and want to minimise the amount of trial and
>>replacement. Please chime in with what you are using and how well it
>>works with which eyepieces. Thanks!
>>
>
>
>
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