Barlows and f number

[Regulus]

Does a 2x barlow increase the scopes f number the same way a 2x teleconverter does with a camera lens?

Trevor

[Shiraz]

Yes, both are negative lenses and they increase the focal length and hence the fNo. The actual magnification depends on the design type, the negative lens focal length and where you put it relative to the original and final focal planes - this is worth a read: http://www.brayebrookobservatory.org/BrayObsWebSite/BOOKS/BarlowLens.pdf

[Regulus]

Thx Ray.