|
|
Thread Tools | Display Modes |
#1
|
|||
|
|||
Seeking Barlow Recommendation
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! |
#2
|
|||
|
|||
Seeking Barlow Recommendation
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.... |
#3
|
|||
|
|||
Seeking Barlow Recommendation
"Richard Adams" wrote in message oups.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. |
#4
|
|||
|
|||
Seeking Barlow Recommendation
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? |
#5
|
|||
|
|||
Seeking Barlow Recommendation
Joe S. wrote:
"Richard Adams" wrote in message oups.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? |
#6
|
|||
|
|||
Seeking Barlow Recommendation
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" wrote in message oups.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! |
#7
|
|||
|
|||
Seeking Barlow Recommendation
"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! 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 |
#8
|
|||
|
|||
Seeking Barlow Recommendation
Willie R. Meghar 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! 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 |
#9
|
|||
|
|||
Seeking Barlow Recommendation
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" wrote in message oups.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! |
#10
|
|||
|
|||
Seeking Barlow Recommendation
On 2006-09-05, Willie R Meghar 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 |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
XT-8 restricted to short Barlows??? | Starboard | Amateur Astronomy | 4 | May 18th 06 11:45 PM |
Seeking barlow "clear aperture requirement(?)" formula | Lawrence Sayre | Amateur Astronomy | 16 | January 17th 06 11:52 PM |
negative relay lens for a Newt? | David Randell | Amateur Astronomy | 16 | April 7th 05 08:50 PM |
Beagle 2 Commission of Inquiry - Press Release | Keith Dancey | UK Astronomy | 5 | May 25th 04 10:14 PM |
Lessons learnt from Beagle 2 and plans to implement recommendationsfrom the Commission of Inquiry (Forwarded) | Andrew Yee | Astronomy Misc | 0 | May 24th 04 10:52 PM |