A Barlow lense isn't the easiest accessory to choose in astronomy. Moreover, it's often a newbies choice to enlarge their eyepieces range. And, in such conditions, it's a bad choice.
How does it work ? That's quite simple if we don't try to enter the whole optic trick which stays behind. So we won't try. We will just say that a Barlow lense is an accessory designed to manifold the focal length of the telescope by a given coefficient. So, when you buy a Barlow lense having three eyepieces, you can have up to six eyepieces, combinating with your new accessory. But things are not all that simple : even if your Barlow lense is really good, its combination with an eyepiece will always result in an eyepiece of lower quality than the initial one. So, it's often better to buy a new eyepiece rather than a Barlow lense. Especially since this last one is an expensive accessory.
The true usefulness of a Barlow lense reveals itself in photography : in this case, you use it without any other accessory, so the resulting image is not worse than the one obtained through an eyepiece. That was my motivation to buy the Celestron Ultima x2, one of the best Barlow lense which could be found in 2004. It's an apochromatic one (hear this way that it should not have too much chromatic aberration) and I didn't notice any geometric aberration. Until now, I think the Ultima is the best Barlow lense I ever use, but, of course, I haven't try every Barlow lenses which could be found !
Now that I have a Barlow lense, I have to acknowledge the fact that I sometimes use it in combination with my eyepieces. But, I repet myself here : this way of use must not be your main motivation for buying such an accessory !
| Flying Jacket |
