Choice of Barlow for 8" Dobsonian

[sikfish]

Hello all,

My first post and my second scope (prev 80mm refractor) and I want to get a Barlow to go with it and don't know whether to go for a 2.5x or 5x Barlow (both GSO). Anyone have any views on that question? It came with both a 10mm and 26mm eyepeice.

Cheers

Mike

[mark3d]

hi.. a 10mm and 26mm at 5x is 2mm and 5mm .. the former is basically unusable and the latter only on those good nights. on the other hand the 2x barlow gives you 5mm and 13mm which overall gives you a nice range of magnifications 5mm, 10mm, 13mm, 26mm.

sorry just noticed you are looking at 2.5x not 2x

.

[sikfish]

Ok that is useful info.
Many thanks. Tonight is my first go at it and I can't wait.

Mike

:)

[rogerco]

I have a 2.5x Williams Optics barlow that works fine on my ED80 refractor but is unusable on my new bintel 8inch dob as the focuser will not go in far enough to focus. It is a premium one with the ten to one crayfor foucuse. So check that the barlow you buy is going to work before you buy.

[erick]

Go with the 2.5x GSO. I expect it is a 2" diameter design.

Nope, I just looked at GSO's website. It is 1.25" so you cannot use it on your 26mm eyepiece (a 2" kelner design, I believe).

So have a look at the 2" GSO. It is 2" diameter and has an adapter for 1.25" eyepiece use. I have one of the older (like 2006!) models and am happy with it.

GSO barlows should work without a problem on the GSO scopes. (I'm guessing your 8" is a GSO?)

I also bought a Televue 3x barlow (1.25") which I use a lot.

Honestly, 5x barlows are for those folks trying to get Jupiter to fill their CCD chip!

[AlexN]

with an 8" Dob, I've used a 2x and 3x with my 10, 25mm ep's and found the best combination for alot of deep sky stuff was the 25mm + 2x barlow..

This yielded the sharpest, most contrasty image. I would highly recommend a 2x, a 5x would be somewhat overkill, and you would only get real use out of it for planetary viewing on the finest of fine nights...

Erick is right, 5x is really a planetary imaging tool, rather than an observing tool.

Alex.

[sikfish]

Ok I should have mentioned the scope is a Skywatcher 8" with the 1.25" 10mm and 26 mm eyepieces. I don't have any 2" eyepieces at this stage but would consider purchasing if I thought it worth while. The scope comes with a 2" adapter.
It does seem from reading your comments that a 2x seems to be the best bet (I have seen 2, 2.5 and 5 on offer).

Cheers

Mike

[madtuna]

My Televue 4x 2" powermate turned up today.. stick a decent 2" Nagler or the big Andrews 30 in it and you need two beer kegs and a house brick to counter it.

I've got a GSO 2" ED 2x Barlow and for it's price it's very impressive.

[AlexN]

Mike, yeah same setup here, and I made my comparison with the same standard SW Ep's...

2" EP's are awesome if you spend MONEY! dont expect to get away with a quality 2" Ep for less than $200... The 30mm 2" i have was $99, and it gives great views, but its nothing on a Baader Hyperion/TV Nagler/Ethos EP's that range upwards of $450 for certain ones..

[JethroB76]

Actually, the Hyperions/stratus lines, while not really 2" they can be used in 2" mode; can be had for about $200 new (Hyperions) and $160 (Stratus) or if secondhand for less than $160.

Great EPs for the money and barlow well to boot

As for which barlow, I think you'd be best to stick with a 2x or 2.5x

[sikfish]

Brilliant much appreciated

Mike

[pneuman]

Hi guys,

I've just bought an 8" Bintel dob and I'm also looking at a Barlow as my first add-on, mainly so I can get higher magnifications for viewing Jupiter. I'm looking at the 2X Televue Barlow (Bintel has them for $150), because I can see myself getting at least one Televue Plossl in the next few months, and I don't want buy a cheaper Barlow now and feel like I'll have to upgrade it when I start getting quality eyepieces.

Does that sound reasonable, or am I getting a bit ahead of myself for a newbie? :)

[erick]

Sounds good to me, Leigh. Maybe the 3x instead of the 2x - same price? I have the 3x and am happy with it. What do others think?

[AlexN]

yeah I'd go a 3x.. I have one, use it with my 8" and love the view given from my Vixen LV 20mm + 3x!

[pneuman]

Hmm, I hadn't really thought much about the 3X -- that's a lot of magnification, but on an f/6 scope I guess that's not such a bad thing, especially if I'm going to invest in new eyepieces. Right now I have 15mm and 9mm GSO Plossls (and a 26mm 2"), so that's 80X and 133X without a Barlow, or 240X and 400X with the 3X.

If I did go the 3X, and then pick up a Televue Plossl as a first new eyepiece, what size would you recommend? Maybe the 20mm? I think that'd be wide enough for a lot of DSOs, and close enough with the Barlow for some planetary work.

[erick]

I agree with the 20mm Televue plossl. I picked up one second hand and it's a great plossl. Watch the secondhand market, they come up often - put a wanted ad in.

I often get down to my 10mm Vixen LV in the 3x Televue barlow in the 12" f5 - on Moon and planets. That's 450x if my calculation is correct. If seeing is acceptable, it's fine.