Tv barlow or powermate in 120ed eon refractor

Hi,
I'm sure that this has been beaten to death but I can't seem to find the threads so here goes.
I have a 1.25 televue everbrite diag which I think is just fantastic. I would like to add som TV plossls but they only go down to 8mm. I was thinking of gettig the 25mm and the 11mm and when I want higher powers to use a 2x or 3x barlow/powermate (2x or 2.5x) which would work best for me. I am strictly visual and have 1.25 diagonal. Also, the tv barlows look long do they go before the diag with the diag inserted into it, or do they go into the diag. as do other barlows?
Thanx

Itz
You should be able to install a barlow either way. Just be aware that installing a 2X barlow before the diag will usually result in about 3X, after the diag in 2X increase. Some scope do not come to focus well with it before the diag, most will after the diag.
Thanks
Steven Jindra

Barlows do not work well with long focal length EP's. They are much worse at blacking them out and move the eye relief back....something you do not want witha 25mm Plossl.

My rule of thumb is to stop using a Barlow at around 15mm with a Plossl. A Powermate will work better from there and longer in FL beacause it does not move the eye relief back, does not cause blackouts, and collimates the light path for maximum light throughput.

With a Plossl shorter than 15mm, you want to increase the eye relief, and a Barlow will do that. At the narrow field stop diameters of short FL EP's, the diverging rays of a Barlow will still be fairly parallel and will not cause optical problems. A Barlow can have higher contrast because it has half as many optical elements as a Powermate.

Barlows are for short FL EP's, and a Powermate is for any FL EP, but best with a moderate to long FL EP.

A Powermate is also a good OCA for a binoviewer, so you can kill two birds with one stone and justify the increased cost relative to most Barlows.

Phil

Hi Itz, unless you are using wide feild ep's greater than 60 degree FOV you really dont need the TV powermate. The Powermate will retain the full FOV on wide feild ep's were standard barlows might restrick some of that FOV. I have a SW120ED and had the powermate 2.5X for years but found that simpler barlows seem to have better brightness compared to the powermate, maybe because less optical elements but when trying to get the highest mags outa my scope the simpler designs seemed brighter. ON a lark I tried a barlow a buddy of mine told me he had which was a Smart Astronomy 2.5X three element barlow made by GSO, it has a compression ring top and is light and small, very well made for the asking price of $50 dollars. Well before I sold my 2.5X powermate I tried the both and compared them on objects like M42, lunar and saturn. They both were very good and on dimer objects the SA barlow seemed to have a little more brightness to the objects observed plus when skweeking the highest power out of the scope on lunar the simple barlow had more brightness at those higher powers and the image sharpness was the same. I think there is also a reveiw on the SA barlows here on AM, you might want to check it out.
regards
Jim

I ran into this problem myself a while back. I have a set of TV smooth sided plossls and both the Klee 2.8x and Celestron Ultima SV 2x barlows were vignetting all of them, not just the longer focal lengths. The thread title was "2.8x Klee Vignettes TV Plossls?" and the comments may help you. I now use a 2.5x Powermate for these eyepieces and have been very happy with it.