More on Barlow lens
I have a SXV-M7 camera mounted on a manual filter wheel inserted by an
extension tube on the Crayford of a 80 mm. APO refractor.
I am now trying to assemble my scope to get more magnification
(resolution). I have a 2.8x Barlow lens, but I have not the right
adaptors to mount it, so I am unable to try something. In the mean
time I've searched documents to get information on the B.L.
amplification factor and the adaptors commonly used.
I feel a little confused by the various opinions one can find all over
the Internet and I'ld like to know which is the most reliable. I think
the following two are the most representative concepts with
contrasting ideas to follow:
1. Basically Ron says that to get a certain amplification factor (e.g.
2x) you must put the Barlow just in front of your camera, to get 3x
use 2"-3" spacers etc. Nothing of more simple;
2. Thiery Legault presents a simple formula to get the Barlow factor
knowing the Barlow lens focal lenght and its distance from the focal
plane (CCD camera or film). The formula shows that when the distance
increases, the amplification factor increases, and that a '2x' Barlow
lens gives a true amplification factor of 2 only if its distance from
the focal plane is equal to its focal length (100 mm in one example he
does). If this distance is doubled, the amplification factor becomes
In conclusion the RW rule simplifies very much my problem, the TL
rule, instead, complicates it since I'ld put the B.L. between the
filter wheel and the scope.
I hope someone has a similar equipment and he is so kind to help me.