Quote:
Originally Posted by morls
....but there's a thought rattling around in my head that a telextender might be a good option, but more expensive... I'm thinking of a relatively high quality barlow as I see this as being something I won't be replacing in the near future, and i hope i'm right in thinking it will not be wasted with the rest of my gear...
|
If you mean the Meade 5000 series telextender then these are 4 element Barlows and were introduced to compete with the Tele Vue Powermates.
I cannot comment on the Meades but the Powermates allow the eyepiece to see the light cone from the telescope as the designer of the eyepiece intended thereby retaining eye relief and maintaining full field without vignetting. Note not all eyepiece/Barlow combinations vignette, some do. No eyepiece/Powermate combinations vignette. To achieve this 4 elements are used in lieu of 2 elements at a negligible loss in light transmission. In essence the Powermates are invisible in the light path. I have not used the Meades so I cannot comment on their performance.
If you intend on Barlowing an eyepiece of 30mm or greater then use a Powermate otherwise the eyerelief will be too long and difficult to use. Note some sizes are avaibale in 2" and some in 1.25" only. A quality 2" 2x Barlow or 2" 2x Powermate is a good investment.
Note Powermates are also used for imaging applications particularly the 4x and 5x as they can extend the focal length of your telescope considerably to give greater image scale for objects such as planets.
Note too Powermates can be heavy and may require counter-balancing. An alternative would be to get a low cost ED Barlow to get a feel for the powers you need and then get a quality eyepiece of the required focal length to give you that power without a Barlow or Powermate.