2x Barlow into 1.5x ?

[johnnyp]

Hi all, Is it true that if i unscrew the lense of my tal 2x barlow and attach it directly to the eyepiece, it makes the magnification 1.5 ?

Or alternatively, Does attaching the barlow before the diagonal achieve the same result?

cheers

John

Im lookin to purchase a paradigm 5mm eyepiece for my 102 slt , which would give 132x, with the barlow at 1.5 this would achieve 198x. (i think)I realise this is the max mag for the scope but id like to give it a try as im off to galloway next month:) Does this sound feasible?

[Merlin66]

It really depends on the focal length of the barlow lens (F) and the distance between the end of the nosepiece and the focal plane of the eyepiece.

If the distance from the barlow to the image plane is B

and the position of the barlow is A inside the telescope prime focus

then:

1/B = 1/A -1/F

for a x2 barlow, B/A = 2

and

A = F/2

Ken

[johnnyp]

Hi Ken, ill be honest im lost with that equation, no idea how to work that out:(

Thanks for tryin to explain it to me though:)

[Rusty Strings]

The Backyard Astronomer book I have says that placing a barlow before the diagonal increases the magnification factor by 50% approx. I tried this with my C80ED and the draw tube was too far out too achieve focus which is pity as I could get loads of useful magnifications with three eyepieces I have and a 2.5x powermate.

John

[johnnyp]

The Backyard Astronomer book I have says that placing a barlow before the diagonal increases the magnification factor by 50% approx. I tried this with my C80ED and the draw tube was too far out too achieve focus which is pity as I could get loads of useful magnifications with three eyepieces I have and a 2.5x powermate.

John

So the further away the barlow is from the eyepiece, increases magnification? Maths isnt my forte:(

[Merlin66]

John,

Yes is the simple answer.

So if you move the barlow lens closer to the eyepiece you will REDUCE the magnification.

( If you can unscrew the lens from your Barlow and then screw it onto the front of your eyepiece, I'm guessing you would get approx x1.5 from a x2 barlow lens.)

Ken

[johnnyp]

Hi Ken

Yes i can unscrew the Barlow lense and attach it to my eyepieces.

Thanks for clearing that up

Regards

John