Click here if you are having trouble logging into the forums
Privacy Policy |
Please read our Terms
of Service | Signup and
Troubleshooting FAQ | Problems? PM a Red or a Green Gu.... uh, User
kevinkalich
journeyman
Reged: 10/30/09
Posts: 5
|
|
I've seen plenty of recommendations for getting a Barlow as an early addition, especially for us newcomers that don't have a wide EP selection already.
I fully intend to do that, but one thing I can't seem to get a clear impression on...
Aside from the obvious - being able to Barlow 2" EP's, what else would you gain from buying a 2" body Barlow as opposed to a 1.25"? Since most people seem to accumulate a few EP's over the range of FL's they enjoy... would they ever bother to Barlow a long FL EP instead of just using the equivalent FL direct view EP?
Or... specific example, if someone has both 26mm and 13mm Naglers, is there ever an advantage to using a 2"-2X Barlow on the 26mm instead of just direct view on the 1.25" 13mm? Is the only advantage maintaining eye relief from the bigger body EP's?
Nothing urgent here, and I'm not going to allow myself to buy ANY more stuff until I've thoroughly enjoyed my starter equipment. Just trying to educate myself a bit more.
|
panhard
Mongo
Reged: 01/20/08
Posts: 5226
Loc: Markham Ontario Canada
|
|
More glass in the line of sight, will dim the view slightly. Also the field of view will will be different with a 1.25" ep as opposed to a 2" ep. Don't quote me on this, but this is the way I understand that it works. By the way welcome to the site.
--------------------
|
Midnight Dan
Carpal Tunnel
Reged: 01/23/08
Posts: 2768
Loc: Brockport, NY
|
|
A 2" optical path, including barlow will allow a wider field of view. But that's only for those 2" EPs you mentioned. For me, this particular 2" barlow, http://tinyurl.com/p8e69q , provides me with a 2x barlow plus other features.
Since I have both 2" and 1.25" EPs, I want to standardize on 2" filters but can't do that directly with the EPs. This barlow can also function as a 2" extension tube by unscrewing the lens part at the bottom. I can then add a 2" filter to its bottom, and move from one EP to the next (1.25" or 2") without having to touch the filter.
I can also screw the 2" lens part directly onto the filter threads of a 2" EP and it works as a 1.5x barlow.
Quality is high, price is right. Highly recommended!
-Dan
--------------------
Scopes: Celestron NexStar 8SE, Orion EON 72mm ED/APO, Orion ShortTube 80
Mounts: NexStar Alt/Az GoTo, Orion Astroview (EQ3) w/single axis drive
Eyepieces: Baader Hyperion 36mm (Aspheric), 21mm 13mm, 8mm, 5mm;
Other: 2x & 3x Barlow, 0.63x Focal Reducer, Dew-not strips, DewBuster controller, SQM Meter
|
star drop
Guilty as Charged
Reged: 02/02/08
Posts: 16395
Loc: Snow Plop, WNY
|
|
Hi Kevin and welcome to Cloudy Nights. A 2" set up is also sturdier. A draw back to using a Barlow lens that I encounter is the length of the eyepiece with a Barlow lens stack forced me to constantly reposition my observing ladder when switching the Barlow lens in and out of the light train.
--------------------
Ted
|
David Knisely
Postmaster
Reged: 04/19/04
Posts: 8290
Loc: Beatrice, Nebraska
|
|
Quote:
More glass in the line of sight, will dim the view slightly. Also the field of view will will be different with a 1.25" ep as opposed to a 2" ep. Don't quote me on this, but this is the way I understand that it works. By the way welcome to the site.
With modern coatings and materials, any light transmission difference between an 1.25" Barlow and a 2" model would be so small that it would be totally undetectable visually. To quote a certain Vulcan science officer: "A difference which makes no difference is no difference." Clear skies to you.
--------------------
David W. Knisely
Hyde Memorial Observatory
http://www.hydeobservatory.info
Prairie Astronomy Club
http://www.prairieastronomyclub.org
|
Jim Haley
professor emeritus
Reged: 07/04/07
Posts: 732
Loc: Surrey England (SW of London)
|
|
Most folks try to avoid having a 2x barlow with a 26mm and 13mm eyepiece. For example I have a 13mm ethos. I use it with my 2" barlow to give me 6.5mm but retain 100 degree apparent field of view and long eye relief. I would not purchase a 6 or 8mm ethos... the 2" barlow is much cheaper and does almost exactly the same thing. Same for my 2" 40mm 70 degree eyepiece. I barlow it for 20mm so I don't need to purchase a 20mm 70 degree eyepiece (unless I want one I can stuff in a 1.25" focus)
Other than a bit of weight hanging off the focus, it is best to think of a barlow as just doubling your eyepiece collection while retaining the eye relief of the long focal length eyepiece.
The reason for 2" barlows is to use 2" eyepieces (as well as 1.25" eyepieces with included adapter). Plus they do seem a bit more "stable" in the tube.
--------------------
Jim Haley
12.5" f6 Starsplitter Dob because aperture and focal length rule.
Orion 8" XTi (with computerized object locator) because I view from the city and I won't always lug out the 12.5
Orion 114EQ reflector, Heritage 130P flextub Dob (My super portable dob is always in the car).
80mm f6 refractor (great for daytime use)
76mm Mini Dob (skywatcher brand). Hyper-portable dob base mounts to heavy duty ($100) tripod.
|
Tony Flanders
Post Laureate
Reged: 05/18/06
Posts: 3469
Loc: Cambridge, MA, USA
|
|
Quote:
Aside from the obvious - being able to Barlow 2" EP's, what else would you gain from buying a 2" body Barlow as opposed to a 1.25"?
That's the main reason. Also, 2-inch Barlows are sometimes used for photography, since a 1.25-inch Barlow will clip the corners of a 24x36 mm film frame (or equivalent digital camera sensor).
Most people don't bother with 2-inch Barlows, since the whole idea of Barlows is to get high magnifications, and all really high-mag eyepieces come in 1.25-inch barrels. But there are plenty of people who own beloved EPs in 2-inch barrels and really want the ability to Barlow them.
In general, if you have a 2X Barlow, you try to avoid buying EPs with focal lengths that are double other ones. So you might get EPs with focal lengths of 24, 18, and 6, achieving 24, 18, 12, 9, 6, and 3 in combination with the Barlow.
Barlows are also useful to get truly short focal lengths that are hard to achieve any other way. Selection is pretty limited in EPs with a focal length much below 5 mm.
And as you say, Barlowing an EP with a longer focal length is an easy way to get a short-focal-length EP with long eye relief.
--------------------
Tony Flanders
First and foremost observing love: naked eye.
Second, binoculars.
Last but not least, telescopes.
And I sometimes dabble with cameras.
|
RonBurgundy
sage
Reged: 06/16/09
Posts: 271
Loc: Philadelphia
|
|
I would have to go against the grain here (uh oh)... I'm not a fan of barlows. While I may understand their need for a barlow when the eyepiece selection is rather small, I don't like the extra focusing required with a barlow. On my main scope, I have an electric focuser, and a barlow will require additional manual focusing, involving the mirror lock as well.
I suppose I'm not "barlow-friendly" because my eyepieces are parfocal; it makes a barlow another thing to worry about. And as for short eye relief, I don't find it a problem (lucky me, I don't need glasses, one less fiasco to deal with). Oh well...
So, if you are going to consider a barlow in the future, go with the 2". It will give you more options for the time you decide to get one of the larger eyepieces. Good Luck!
--------------------
Kipp Ginsburg
8" LX200-ACF
Orion 120mm F/5.0 Piggybacked Refractor
Meade UWA Set [4.7mm-30mm]
DSI-II
|
arpruss
scholastic sledgehammer
Reged: 05/23/08
Posts: 858
Loc: Waco, TX
|
|
A (minor?) disadvantage of a larger barlow is more weight, potentially requiring more of a counterweight. I find manufacturing new counterweights to be a big nuisance, and don't want to have switch counterweights to handle different eyepiece combinations.
Personally, I almost never use a Barlow in the normal way--I just use its lens cell as a screw-on 1.5X adapter. For some reason, on my (1.25") Barlow, the quality is visibly better with the latter combination than when using the Barlow in the normal way.
--------------------
Coulter Odyssey 13.1" split-tube
Coulter Odyssey 8"
Home-made 7.8" F/4 dobsonian travel scope
Home-made 68mm F/5.3 achro (typically used as finder on 13.1")
Skymaster 15x70
BPTs4 8x30
32mm Plossl, 30mm Rini, 27mm Kellner, 13mm Hyperion, 6mm TMB/BO Planetary, Owl 2X Barlow
Palm TX with AstroInfo and RescoViewer
|
sixela
Postmaster
Reged: 12/23/04
Posts: 10877
Loc: Boechout, Belgium
|
|
Quote:
Or... specific example, if someone has both 26mm and 13mm Naglers, is there ever an advantage to using a 2"-2X Barlow on the 26mm instead of just direct view on the 1.25" 13mm? Is the only advantage maintaining eye relief from the bigger body EP's?
Yes. A 2" barlow is effective if you plan your eyepiece collection around it (e.g. getting a set of T4 Naglers in 22/17/12 lengths and relying upon a barlow for the smaller focal lengths, giving you six Naglers for the price of three plus a barlow).
Otherwise, most of us end up with one or 2 2" eyepieces on the high end with 1.25" eyepieces that we barlow.
--------------------
400mm f/4.46 self made Dobsonian on Tom Osypowski equatorial platform
Orion Starblast (114mm f/4 reflector, Alt/Az)
|
sixela
Postmaster
Reged: 12/23/04
Posts: 10877
Loc: Boechout, Belgium
|
|
Quote:
A 2" optical path, including barlow will allow a wider field of view.
Nope. Optically, there's not a lot in it. In fact, many 1.25" wide field eyepieces that have a narrow barrel but become "fatter" above it already use something similar to a barlow and a 2" eyepiece behind it (a negative field doublet and then a wider eyepiece section).
--------------------
400mm f/4.46 self made Dobsonian on Tom Osypowski equatorial platform
Orion Starblast (114mm f/4 reflector, Alt/Az)
|
Midnight Dan
Carpal Tunnel
Reged: 01/23/08
Posts: 2768
Loc: Brockport, NY
|
|
Quote:
Quote:
A 2" optical path, including barlow will allow a wider field of view.
Nope. Optically, there's not a lot in it. In fact, many 1.25" wide field eyepieces that have a narrow barrel but become "fatter" above it already use something similar to a barlow and a 2" eyepiece behind it (a negative field doublet and then a wider eyepiece section).
A 2" optical path very definitely increases the maximum true FOV for my scope. With a 1.25" path, I can get to about 1.1° before the image is clipped. with a 2" path I can get to about 1.8°.
-Dan
--------------------
Scopes: Celestron NexStar 8SE, Orion EON 72mm ED/APO, Orion ShortTube 80
Mounts: NexStar Alt/Az GoTo, Orion Astroview (EQ3) w/single axis drive
Eyepieces: Baader Hyperion 36mm (Aspheric), 21mm 13mm, 8mm, 5mm;
Other: 2x & 3x Barlow, 0.63x Focal Reducer, Dew-not strips, DewBuster controller, SQM Meter
|
|
3 registered and 5 anonymous users are browsing this forum.
Moderator: desertstars, werewolf6977, ClownFish
Print Thread
|
Forum Permissions
You cannot start new topics
You cannot reply to topics
HTML is disabled
UBBCode is enabled
|
Thread views: 155
|
|
|
|
|
|
|
Previous
Index
Next
Threaded
Edit
Reply
Quote
