Can a 2x barlow be 3x?

[rob7]

I have a Revelation 2" 2x ed barlow and I sort of remember reading something on this forum which briefly said that this barlow would become a '3x' barlow if installed in front of the diagonal. Can't test this poser because I haven't got a 'pushfit' diagonal. Am I talking twaddle? There certainly room in the barlow to stuff a diagonal into it. If by any chance I wasn't seeing things and then out of curiosity, do any other barlows do the same and if so, whats happening?

Regards, Rob.

[Ant]

Hi Rob,

The amount of increase is related to the distance between the barlow (lens part) and the EP or film or CCD. Increase the distance and you increase the "x". So...

If you remove the lens part of the barlow and screw it into the body of an EP, or T Ring adapter, then the increase will be more like x1.6, used normally it'll be around the x2 mark. Screwing it into the diagonal will increase it to above x3, but exactly how much depends on the length of the diagonal. But x3 sounds about right.

Hope that helps.

Ant

[daz]

Rob

Usually when moving the barlow lens closer, the magnification is reduced. Many of the barlow lenses that unscrew will, when fitted directly to the EP barrel, give 1.6x instead of 2.

But now having read your post properly, you will be putting the barlow lens furtheraway from the EP, so, I guess the answer is yes!!

As to how - I'll leave that to someone who knows the physics!!

[daz]

What Ant said...........

[Ant]

[rob7]

Thanks for the replies and explanations guys. So in effect you've saved me form buying a 3x barlow in the future, because I've sort of got one already! [My wife we be grateful to you all ,for that small saving]!. Its a nice surprise to find out a piece of my equipment has another capability. I wish I had the right sort of diagonal at the moment to put it to the test.

Cheers, Rob.

[Ant]

Which Diagonal have you got Rob?

Most diagonals are internally threaded for filters - this is where the barlow(lens part) goes.

Ant

[rob7]

Ant, its an Revelation 'sct' screw fit diagonal. I assumed you had to put the 'non' dismantled barlow into the ota visual back. Then, insert the diagonal into the barlow. Am I barking up the wrong tree here? It wouldn't be the first time or the last!

Rob.

[Ant]

Sorry yeah your right the SCT thread does make life more tricky.

I haven't had an SCT for about 14 years!

Putting the EP into the Barlow into the diagonal will give the standard 2x increase. Screwing the barlow lens part into the EP and putting that in the diagonal will give around 1.6x

I think you need a different diagonal for the x3 option to work.

Ant

[rob7]

I can't have it all my own way I suppose. Thanks for your help, anyhows...

Rob.

[Astroman]

If you place the Barlow in the visual back, then add the diagonal, then an EP, you'll get something like 3x from your Barlow because the lens itself is farther from the EP. I have 2 2x Barlows. I place one in the visual back of my C8, then the diagonal, then the other Barlow, then a 7.5mm EP. I get ~813x I use on the Moon. Puts you right in orbit. 8)