Barlow before diagonal?

Does anybody use a barlow before the diagonal. I am set to get my first refractor around July. I will be using a 1.25" diagonal. I would like to use my 2x TV barlow before the diagonal for an effective 3x. I will be using orthos. Will I have any issues with focus? Too much in or out focus?
Jason

Jason,
Yes, I have done it. Works O.K.. A nuisance in my scope though.

If the scope can be used in straight through mode (no diag.) you should have no problem with focus travel. The scope will focus as if no diag. were there. If you need extensions for straight through viewing it becomes a pain.

Bob

fwiw: Here is a link to the barlow/distance/mag. calculation.

http://www.astromart.com/forums/viewpost.asp?forum_post_id=14545&poll_id=&news_id=&page=12

Jason,

I have an old C-90 Astroscope where the barlow threads into the diagonal and is inserted into the scope (before the diagonal). There are no focus issues with the Mak., so the configuration is not unheard of. I am not aware of anyone using a barlow before the diagonal in a refractor. I suspect there will be focus issues with a refractor. Maybe using a binoviewer will solve them, if they exist.

Bill

Jason Paoletti said:

Does anybody use a Barlow before the diagonal. I am set to get my first refractor around July. I will be using a 1.25" diagonal. I would like to use my 2x TV Barlow before the diagonal for an effective 3x. I will be using orthos. Will I have any issues with focus? Too much in or out focus?
Jason

Hi Jason,
As noted, the Barlow in front of the eyepiece or Diagonal/eyepiece will work if you have enough focus travel to accommodate the application in your refractor. I have an AP Barcon which is designed to be used in front of or after or even with extension tubes to provide varying magnification. I've used other Barlows in a similar fashion really just to see how it works. On scopes such as TV Genesis, NP-127, AP Traveler, and AP 152 StarFire it works fine. On other scopes such as some of the less expensive wide fields (80mm f/5.6) there isn't enough travel in the focuser to bring them to focus.
So it really depends on your refractor & eyepiece used. Let us know which refractor and what ortho's and we might be able to give you a better idea if it'll work.
Clear Skies, Bill