Barlow 1.25"v 2"

[slice of heaven]

Just ordered the12" gso from Andrews .What I need to know is;
Is there any benefit in a 2" barlow over a 1.25" barlow?
My old scope has a 1.25" focusser,(rack&pinion,smooth,no slop so I've no mind to change it) so if I go 1.25" I can use it in both .
But if the 2" has some benefit I'd consider that for just the gso. Both scopes are basically the same specs.The gso is more for the kids (yep kids like big buckets too) but being lighter I can see myself grabbing this one for the late night ,on my own viewing.
Also,opinions on a value for money barlow between $100-$200
would be appreciated.

Thanks,Geoff

[Starkler]

Orion Shorty PLUS 1.25"

Same optics as the Celestron Ultima. A great barlow, definately recommended. $150 at Bintel last I saw.
Not to be confused with orion Shorty, get the shorty PLUS.

The answer to the 2" vs 1.25' question is as simple as what eyepieces are you wanting to barlow? A quality 2 inch barlow is going to cost more.

[slice of heaven]

Thanks Starkler,
I have the shorty+ on my short list. 1 to Shorty

All our current ep's are 1.25" ,nothing expensive. So maybe what I should've also asked is what benefits do 2"ep's have over 1.25". I'm looking at upgrading the ep's verrrrrrrry slowly to some top quality but dont want to start off on the wrong foot.

So the new question is ; Is bigger better?????

Geoff

[Striker]

My wife sayed something about bigger is better but I didn't realy understand and sent her back to the Kitchen where she belongs......lol

I know the 2" is obviously better in longer focal length eyepieces but with you having a Dob their probably isn't any use unless your thinking about getting 30-40mm eyepieces for extra wide viewing.....I think its personal.....I like 2" on the basis I see more for my money......eg......A Nagler 11mm 1 1/4 is about $100 cheaper then a Nagler 12mm 2" but is 3 times the size.....if I am spending big dollars on eyepieces I just prefer to see some size to the value....My personal opinion only....I like big.

[ving]

if all of your EPs are 1.25 then you would be better off getting a 1.25 barlow. no sense in getting a 2" barlow if you dont have EPs to go in it.

2" EPs are good for the extra FOV they give you. I have got only one 2" EP (a 30mm GSO SV) and wouldnt dream of barlowing it as it would defeat the purpose of me getting it.

this said, if you plan on getting a collection of 2 inch EPs then go for it. :)

[vindictive666]

gday all

along the same lines can you get a adapter for a 2 inch barlow then will it take 1.25 inch ep's ?

[Exfso]

I have the 2" powermate and it comes standard with the 1.25" adapter, I would think the barlows do likewise. Worth checking though.

[Striker]

I think every 2"Barlow/powermate I have seen comes with a 1 1/4 adapter standard.....I could be wrong...their maybe a model or 2 that dont......

[ving]

ah yes... didnt think of that!
get the 2" and put the adapter in it :)

D'oh!

[slice of heaven]

Thanks Striker (happpy birthday too) and Ving have taken both opinions on board,thanks.
In this situation I'm an absolute newbie as I've never seen a 2" ep let alone looked in one,same goes with ep's with a wide F.O.V. . So everyones opinion is very welcome.
I've no idea on what ep should or shouldn't be barlowed either (thanks Ving , another point I hadn't considerred) .

Geoff

[slice of heaven]

Thanks guys,
Wasn't sure if you could adapt 2" barlows to 1.25".Thats a good option......(Never seen a barlow either).
Powermates.....How much different / better are they to the barlow? .....and price for a 2x?

Geoff

[mch62]

Get the 2" as you will one day want a 2" EP and being able to use that 30mm or 40mm EP with a barlow is an advantage.
A 40mm wide field 2" eyepiece with a 2x barlow gives you a 20mm with similar characteristics of the 40mm. eg wide field , eye relief just higher magnifications.
I use my 2" EP's like this all the time even though I have numerous 11/4"EP that cover that range.
I just enjoy the easier viewing offered this way with the bigger glass.
If your on a budget the 2x GSO 2" barlow's are a bargain and come with a 11/4" adapter.
If your budget can afford it a Televue Powermate is better than a barlow , but they are expensive.
There are copies of a PM from Siebert Optics and Meade not wanting to miss out have jumped on the band wagon as well apparently .
The only reason not to get a 2" barlow would be you only have a 11/4" focuser or weight is a real problem in your scope.
Any others??

[vindictive666]

bintels prices on televue are


1.25 " (2x) $180
2 " big (2x) $335
1.25 " (3X) $180

https://www.bintelshop.com.au/


i followed the link from their page eyepieces and did an televue barlow search and thats what came up

not sure if prices are current though :) looks like the 2" comes with an adapter according to the picture best bet is to email or ring them :)

[ballaratdragons]

Just had a look at Andrews website. He has finally updated it.

He has a 2" 2X barlow for $79. Don't know if it is any good though. It is on the 'Eyepieces' page.

Also just discovered he has a new section: Used and returned stuff. There is an 8" Dob with no base for $199. Be good for a big finder or mount on a GEM, or make a dob base.

[slice of heaven]

Thanks Vin,rang bintel & thats their price $330 for the barlow & $450 for the Powermate 2" 2x.
Has anyone done a comparison on these 2.

mhodson; Thanks for the feedback, easier viewing would be a big plus as my eyes aren't getting any younger and I'm looking for long term benefits.

[ausastronomer]

I have got only one 2" EP (a 30mm GSO SV) and wouldnt dream of barlowing it as it would defeat the purpose of me getting it.

Hi David,

I also own the 2" 30mm GSO Superview and I can tell you that it barlows very nicely in my 2" 1.6X Antares barlow to convert it to a 2" 19mm eyepiece. The barlow actually cleans up the EOF very well by turning the F5 scope into an F8 light cone.

Clear skies
John B

[ausastronomer]

Wasn't sure if you could adapt 2" barlows to 1.25".Thats a good option......(Never seen a barlow either).

Powermates.....How much different / better are they to the barlow? .....and price for a 2x?


Hi Geoff,

In the right telescope and in conjunction with the right eyepieces the powermates can show an improvement over a standard high quality barlow like the Orion Shorty Plus, Celestron Ultima and also the Televue barlows. The powermates are in a different class to the lower quality cheaper chinese/taiwanese barlows, which really I don't recommend if you have a decent scope and eyepieces. Another advantage of the powermate is that it preserves the eye-relief of the eyepiece used in it, whereas a standard barlow will extend the eye-relief by about 20%. If you are using short eye-relief eyepieces like orthos or plossls the extension of eye-relief by a standard barlow can be an advantage. The extension of eye relief on eyepieces with standard long eye-relief like Pentaxes or TV Radians can be a disadvantage and the powermate works best with those. Its really a case of matching the best barlow to your existing or proposed eye piece purchases. Remember however that with astronomical equipment that last 5% performance gain costs a disproportianate amount of money so $300 plus for the 1.25" 2.5X powermate is a lot of extra money for a performance gain of roughly 5% to 10% over the Orion Shorty Plus costing $150 or about $Aus 110 if you bring it in from Canada.

If you care to tell me what scopes and eyepieces you have and will be using the barlow in conjunction with I can advise you further.

Clear Skies
John Bambury

[trufflehunter]

Another thing to remember is some longer focal length 1.25" eyepieces, particularly if they are a wide-field design, will definitely 'vignette' in a 1.25" barlow.

I cannot use my 20mm Meade QX with my current barlow (a 'generic' one, but I suspect it's the same as the Orion Shorty) because of severe vignetting. It looks a bit like this:
<img src="http://www.users.bigpond.net.au/trufflehunter/vignetting.jpg">
The first circle is what it looks like thru the ep w/o the barlow, the second circle with the barlow!

Definitely looking for a decent 2" barlow...

[Starkler]

The Orion Shorty Plus has 27mm of clear aperture, which will handle most anything available in 1.25" format without vignetting.

[ausastronomer]

Hi Truffle,

Geoff is 100% correct there, the Shorty PLUS with 27mm of clear aperture shouldnt present any vignetting issues for visual use. I have used it with my 20mm Pentax XW and the 24mm Panoptic without issue. The Orion Shorty is a cheap barlow and not in the class of the Shorty Plus, its internal field stop is only 22mm which is what causes it to vignette with the 20mm Meade UWA. Most cheap barlows will cause vignetting with long focal length wide field eyepieces. An expensive barlow which also has vignetting issues is the University Optics 2.8X Klee barlow. It only has a 19mm internal field stop and does vignette with "most" long focal length eyepieces (over 15mm FL) , however when used with the appropriate eyepieces, ie short focal length ones, the 2.8X Klee barlow does provide very good on axis performance.

Clear Skies
John Bambury

[slice of heaven]

Thanks Truff thats exactly why I've asked this ,Idont want that view.So I'm leaning heavily towards the 2"powermate for some quality ep's(my eyes only) and also the orion shortyplus for the 1.25"s for general family use.

Hi John, That post(above Truff's) really cleared the fog.
One Question though; how does the f/ratio change with the barlow?

Same specs both scopes 12" f5 .The old one has Park optics Pyrex mirror.No real difference in specs.Have plans to remount the older scope later,one dobs enough. As for 2"ep's that I'll want ,that is another dilemna. At the moment I use 20's<30's for hunting, 15 for general viewing & 6<9 for powering up. But add a wider f.o.v to the equation and this makes it so much harder to decide. With what I've read in this thread Im thinking of going for a 2x powermate & 15mm ep & then maybe a 40? to cover my most used magnifications. Im not looking to build a treasure chest of ep's(be nice though) just trying to get some quality ep's to cover most bases.


Geoff

[trufflehunter]

Thanks for that guys. Think I might have to have a look at the Shorty Plus! Just measured my generic barlow and it's only 22mm aperture!

[ausastronomer]

[QUOTE]Originally posted by slice of heaven

Hi John,

That post(above Truff's) really cleared the fog.
One Question though; how does the f/ratio change with the barlow?


Hi Geoff,

Thats in fact how a barlow works, a barlow is a telenegative lens that increases the effective focal length of the light cone of the original telescope, thereby increasing the magnification of any given eyepiece by the amplification factor of the barlow. The magnification of a given eyepiece in a given telescope is calculated by dividing the focal length of the telescope by the focal length of the eyepiece. The 2X barlow achieves the effective increase in focal length of the light cone by halving its angle of incidence.

Here is a good article explaining how a barlow works by Stephen Tonkin. There is also a good diagram showing the path of the original light cone and what happens after it goes through the barlow.

http://www.astunit.com/tutorials/barlow.htm

Here are a couple of other websites you could look at:

http://astro.isi.edu/notes/barlow.html
http://www.atmsite.org/contrib/Carlin/barlow/
http://www.astrosurf.com/legault/focal.html

Its also worth being aware that the amplification factor (magnification) of a barlow thats quoted (printed on its side) only holds when the barlow is used at a fixed position in the light path. For example a 2X barlow when used in conjunction with a diagonal and a refractor or SCT or MCT will give approximately 2X when used after the diagonal and approximately 3X when used before the diagonal. You can also increase the magnification of a barlow by using an extension tube which moves it further out in the light path. Something else to note is that the stated magnification of the barlow (eg 2X) is only an approximation and the 1 barlow could provide a range of magnifications between about 1.7 and 2.3 depending on the combination of telescope and eyepieces used with it.

There is a way to measure the exact magnification factor that an eyepiece and barlow is giving, I won't bore you with the details but if anyone wants to know out of curiosity to test their barlow let me know and I will tell you how to do it.

Well you wanted to know the time and I just told you how to build a clock, but I guess thats me :)


Clear Skies
John Bambury

[ausastronomer]

[B]Thanks Truff thats exactly why I've asked this ,Idont want that view.So I'm leaning heavily towards the 2"powermate for some quality ep's(my eyes only) and also the orion shortyplus for the 1.25"s for general family use.

Same specs both scopes 12" f5 .The old one has Park optics Pyrex mirror.No real difference in specs.Have plans to remount the older scope later,one dobs enough. As for 2"ep's that I'll want ,that is another dilemna. At the moment I use 20's<30's for hunting, 15 for general viewing & 6<9 for powering up. But add a wider f.o.v to the equation and this makes it so much harder to decide. With what I've read in this thread Im thinking of going for a 2x powermate & 15mm ep & then maybe a 40? to cover my most used magnifications. Im not looking to build a treasure chest of ep's(be nice though) just trying to get some quality ep's to cover most bases.


Geoff,

I replied to this part of your post separately because they are separate issues.

The old scope if it has an old Parks mirror should have damn nice optics, provided all is as it should be, collimation good mirror cell and secondary etc. The old Parks mirrors are excellent.

Don't sell the Shorty Plus short and put it into the poor relations category compared to the Powermate, it is an outstanding barlow and 10 years ago rated with the best available. The powermates are marginally superior but the differences are subtle and it often takes an experienced eye and excellent seeing to even detect a difference.

The only problem I see with your choice of 2 different barrel size 2X barlows is that you are not maximising all available magnification options and there is a lot of overlap. The 2" powermate won't do a lot that the 1.25" Shorty plus can do in terms of 1.25" eyepieces. What are the 2" eyepieces that you own, or plan to buy that you wish to barlow in the 2" powermate ??

The option I took was to buy the 2" 1.6X Antares barlow and the 1.25" 2.5X Powermate. This basically gives me 3 eyepiece sets wheres your option still only gives you 2 eyepiece sets even though you own 2 barlows and the native eyepieces.

Clear Skies
John Bambury

[slice of heaven]

Hi John,
Nice post with nice links...Glad I asked you the time.

It's good to know the theory behind things you dont understand.Will be reading those links in more detail before I ask you some questions on a few points there.(heads a bit foggy, I've been at the hospital nearly all day with my lad who had his tonsils out)

Good point about the having the same Power on 2 different sized barlows. That wasn't a smart choice I made. I was going down the wrong track ,a pretty narrow one at that.
With the 2 different powered barlows / 2 different sizes this would give me :
2 ep sets in the old scope(1.25"focusser)
Barlowed and not barlowed

3 ep sets in the new scope(2 "focusser)
?x 1.25"barlow(adapted)
??x 2" barlow
not barlowed

I dont have any 2" ep's @ the moment simply because the old scope has a 1.25" focusser. Now we'll have the new scope with 2"focusser I have the option of using this size ep. Hopefully with extra benefits e.g. wider fov, easier on the eye.
After considering comments here on the SHORTY PLUS and a few searches elsewhere I ordered one today. It seems to be a decent piece in the price range I was looking at and I can use it in both scopes. So now I have to choose a powermate size to compliment the 2x shorty plus. Hope I haven't stuck my foot too far in the muck. ......More advice please.

The old scope seems to be great. I' ve never compared it to another one so next week will be my first chance to. I enjoy using it... that excludes carrying it...and the large aperture gives the kids a decent view even at twilight. The mirror and certificate of optical precision are hand signed/engraved by George Clements, master optician.


Thanks again , Geoff

[ausastronomer]

Geoff,

On the basis that one of your scopes only has a 1.25" focuser I would just stay with the shorty plus and be done with it.

Clear Skies
John B

[slice of heaven]

Thanks John
. Music to my ears. Just had a peek in the new scope & I cant justify purchasing 2" equipment and only using it in the gs.
If I change to 2" on the Parks then I'll consider it. But that means more $$$ for a top focusser on top of the ep's & barlow.
Now I can leisurely just add some nice 1.25s to the shorty+ for now.
I've enjoyed the chat John Thanks Geoff