Am i doing something wrong?

WestAusChris (Chris) · #1 25-11-2010, 09:28 AM

Hi All

Finally got my 2x barlow today, nothing expensive Seben brand from Germany.

Put it in with a 10mm to look at Jupiter and the distance looks the same as just having the 10mm in with no barlow

Maybe i was expecting too much from the barlow??

mental4astro (Alexander) · #2 25-11-2010, 09:36 AM

What scope are you using it in? Do you have any other eyepieces and have you tried the barlow with them?

The 2X barlow will make the image bigger, but by how much will also depend on the focal length. Effectively it should 'double' the magnifcation. That it should look the same might be a factor of the quality of you EP, or the scope, or atmospheric conditions.

jjjnettie (Jeanette) · #3 25-11-2010, 09:53 AM

strange, you should see a significant increase in size.

WestAusChris (Chris) · #4 25-11-2010, 09:54 AM

Quote:

Originally Posted by mental4astro

What scope are you using it in? Do you have any other eyepieces and have you tried the barlow with them?

The 2X barlow will make the image bigger, but by how much will also depend on the focal length. Effectively it should 'double' the magnifcation. That it should look the same might be a factor of the quality of you EP, or the scope, or atmospheric conditions.

Hi again

Its a 6' Dob, i did try it looking at some leaves on a tree just then and it did bring the image closer just didnt seem to make a difference with Jupiter.

mental4astro (Alexander) · #5 25-11-2010, 10:05 AM

Well, that it worked on something is a start. Try again on Jupiter, and alternate between with the barlow and without. As JJJ said, there will be a difference.

I'd hate to be a stickler for detail, but are you sure you have Jupiter? The difference would be obvious. Four moons, a clear ovoid disk with banding. Even try it on the Moon.

iceman (Mike) · #6 25-11-2010, 10:08 AM

True - if you were looking at a star, you probably wouldn't notice any difference with or without the barlow.

It might just look a little bit blurrier or wobbly with the barlow, but not much of an increase in size.

WestAusChris (Chris) · #7 25-11-2010, 12:15 PM

Hi all

Definatley Jupiter can see the moons and red cloud belt.

Just looks the same size with the 10mm EP in and with the barlow added.

I will have another go tonight weather permitting and see how i go.

multiweb (Marc) · #8 25-11-2010, 12:16 PM

Quote:

Originally Posted by WestAusChris

Hi all

Definatley Jupiter can see the moons and red cloud belt.

Just looks the same size with the 10mm EP in and with the barlow added.

I will have another go tonight weather permitting and see how i go.

I think you'll need more than a 2x barlow on a 6".

WestAusChris (Chris) · #9 25-11-2010, 12:43 PM

Quote:

Originally Posted by multiweb

I think you'll need more than a 2x barlow on a 6".

Hmmm have to go up to a 3x ??

astro744 · #10 25-11-2010, 12:50 PM

Quote:

Originally Posted by multiweb

I think you'll need more than a 2x barlow on a 6".

6" Dob is typically 1200mm f.l. (f8). Therefore 10mm eyepieces gives 120x mag. 2x Barlow gives 240x with 10mm eyepiece and this is more than enough on most nights and very good seeing is required. Exit pupil for 10mm is 1.25mm and for 2x Barlowed 10mm is 0.625mm with an f8 system. Exit pupil of 0.5mm is about the limit but requires exceptional seeing. This equates to a 4mm eyepiece or 8mm with 2x Barlow with your telescope.

The image should be twice as big with the 2x Barlow as without on any eyepiece.

multiweb (Marc) · #11 25-11-2010, 05:06 PM

Quote:

Originally Posted by WestAusChris

Hmmm have to go up to a 3x ??

Try spacing the 2x barlow cell further from the eyepiece and you'll get a bit more maginification this way as well.

Quote:

Originally Posted by astro744

6" Dob is typically 1200mm f.l. (f8).

Didn't realise his system wasf/8. I thought more like F/5 or about, so yeah 2.4m should be nice with 10mm.

torana68 (Roger) · #12 25-11-2010, 05:38 PM

[QUOTE=WestAusChris;659734]Hi All

Finally got my 2x barlow today, nothing expensive Seben brand from German QUOTE]

I am fairly sure everything they have is Chinese, nothing made in Germany and low quality. Hopefully you work it out

astro744 · #13 25-11-2010, 06:23 PM

Quote:

Originally Posted by multiweb

Try spacing the 2x barlow cell further from the eyepiece and you'll get a bit more maginification this way as well.

Didn't realise his system wasf/8. I thought more like F/5 or about, so yeah 2.4m should be nice with 10mm.

A 3x Barlow would be nice with a 15mm eyepiece giving the same result with better eye relief than a 10mm + 2x. GSO make a nice 3x ED 1.25" Barlow. There are many combinations possible but the same effective focal length produces the same image size.

erick (Eric) · #14 25-11-2010, 09:52 PM

Stupid question - but check there is a lens in it - at the bottom - it isn't just the tube with the lens unscrewed and missing?

WestAusChris (Chris) · #15 25-11-2010, 11:16 PM

Thankyou all very much for the tips, i will try a few different things you have all said on the next good viewing night and see how i go

Eric, checked to make sure the barlow did actually come with the lens attached just incase and it did

Will keep you all informed as to how i get on, the weekend is going to be quiet warm so fingers crossed i will try it out again then.

Thankyou all again

multiweb (Marc) · #16 27-11-2010, 09:15 AM

Quote:

Originally Posted by astro744

A 3x Barlow would be nice with a 15mm eyepiece giving the same result with better eye relief than a 10mm + 2x. GSO make a nice 3x ED 1.25" Barlow. There are many combinations possible but the same effective focal length produces the same image size.

I have both GSO 2" x2 and GSO 1"1/4 x3. The x3 shows a lot of chromatic aberration. The x2 is very nice though.