Barlow - dumb queation

[asset189]

If a barlow effectively doubles the magnification of a eyepiece does that mean using a barlow lense with an EP that has 8mm FL is the same as using a 4mm Ep with out a barlow? or thats my understanding of it.

In essence what im asking is that if i buy a new 15MM eyepiece will it also double as a 7.5mm using the barlow?

[rory]

correct. but a normal barlow will increase eye relief too. so in some cases a 8mm barlowed will be easier on the eye than a 4mm eyepiece.

[rowan46]

yes that's the gist of it i

[asset189]

ideal, thanks

[nephilim]

BUT......Do your research & buy a good barlow as a naff one will not give good views. I use a Revelation 2.5x which is very good value for money.

Steve

[E621Keith]

In terms of magnification a 8mm with a 2x barlow will act like a 4mm. However, the additional glass in the barlow can degrade the image. A barlow can also increase eye relief which can be a valuable feature if you use conventional eyepiece.

An 8mm+barlow has longer ER than an 8mm un-barlowed, which in turn has longer ER than a 4mm.

[russ.will]

There is another factor to consider. Yes, a barlowed 8mm is effectively delivers a 4mm EP magnification. But as the barlow is placed before the EP, it effectively doubles the scope's focal ratio.

Russell

[alan potts]

Can't disagree with Rory and Russell because they are right.

There is a device called a Powermate that doubles the magnification without increasing the eyerelief, however they are rather expensive.

Alan.