Posted 20 October 2013 - 10:30 AM
Posted 20 October 2013 - 10:59 AM
Posted 20 October 2013 - 11:59 AM
Posted 20 October 2013 - 12:22 PM
Posted 20 October 2013 - 12:41 PM
Posted 20 October 2013 - 02:21 PM
Posted 20 October 2013 - 02:31 PM
You can get extension tubes from Astronomics:
and if you bought the Apertura, you probably already have the 35mm extension tube.
Posted 20 October 2013 - 02:55 PM
Yes, they multiply when you stack. eg., 2x barlow and 3x barlow = 6x.
Maybe, but it seems that if one Barlow is 1.5x, and the other is 2x, that you would get a net 3x, rather than 3.5x. I think they would multiply, rather than add.
Posted 20 October 2013 - 08:35 PM
Posted 21 October 2013 - 05:13 AM
An alternative to stacking Barlows is to use an extension tube to increase the spacing between the Barlow lens and eyepiece. If I recall right the amplification scales linearly with the lens/eyepiece separation.
I believe you are correct. The simplest model in stacking Barlows is that you multiply the magnifications, i.e. a 1.5x and a 2x = 3x.
But it's not that simple because the magnification of a Barlow is not fixed but rather depends, as John has said, on the distance between the lens and the focal plane.. So, the actual geometry would need to be understood.