What’s the difference...

[rawhead]

...between a Telenegative Barlow and a Focal Reducer?

Cheers

Jon

[EA2007]

..the name

[jgs001]

I thought a telenegative/barlow lens increases the OTA focal lenth/mag, decreasing the FOV and a focal reducer does the opposite, decreases the OTA focal length/mag, increasing the FOV

[John]

I thought a telenegative/barlow lens increases the OTA focal lenth/mag, decreasing the FOV and a focal reducer does the opposite, decreases the OTA focal length/mag, increasing the FOV

Thats my understanding as well

John

[RobH]

Yes, that is correct....barlows increase magnification, with a corresponding reduction in FOV, focal reducers do the opposite.

Cheers

Rob

[rawhead]

A telenegative barlow increases mag?

Therefore 'telenegative barlow' is the same as a 'barlow'?

I'd always assumed the telenegative bit meant it was like a barlow in reverse. Doh! :oops:

[jgs001]

yes, if you prefer, it decreases (negative) the focal length of the eyepiece That one has always been a puzzle to me and the decrease in the effective FL of the ep is the only way I can think the negative comes into play.

[legion48]

A telenegative barlow increases mag?

Yes, and decreases the FOV, hence the teleNEGETIVE.

[GazOC]

IIRC from a book a read a fair while ago (so don't take this as gospel), magnification in a scope is actually a minus value, the larger the minus value the higher the mag. A (say) 9mm eyepiece is actually a -9mm eyepiece but the minus is usually dropped for easy of use.

I'll try and find the book...