2x Powermate v 2x Big Barlow?

[Rodstar]

My next planned purchase is a 2 inches 2x Big Barlow or 2x Powermate. I currently have a crappy generic one which is best used as a paperweight.

To start with, it will be used in conjunction with my 22 Panoptic to produce 231x, my 13 Ethos to produce 390x, and my 9 Nagler to produce 564x. This will produce some lovely views through the Mary Rose when the conditions are right. When I eventually get a 31 Nagler, the barlow will produce a nice154x.

I am interested to have some feedback on the practical benefits of the TV Powermate over the Big Barlow. Their respective prices are $379 cf $269 at Bintel. If I am to pay the extra $110, I want to know what the benefit will be, and how good the cheaper alternative is likely to be.

The TV blurb re the Powermate speaks of it having an extra element which corrects the path of the light to avoid/reduce vignetting etc. I wonder how bad the vignetting is with the Big Barlow?

What experiences have members of our IIS community had with either of these products?

On Cloudy Nights there seems to be a view that the Ethos does very nicely coupled with the Powermate.

Thanks, in advance, for your input and experiences. :thumbsup:

[Rodstar]

I note that the following appears in a thread on Cloudy Nights, posted by a Televue dealer:

---------------------
Bert,
I'm really sorry I don't normally make recommendations on our product
for TOS reasons. But since both products are our products I don't see a problem.

How Al answered Lawrence in 1999 is exactly our recommendation today.
You didn't say what type of scope you have. If you called Tele Vue, We would have recommended the Big Barlow if you have a Newtonian, and the powermate if you have a refractor. The reason?,
For the Nagler eyepieces the optical benefits of the powermate are invisible, however, ergonomically in a Newtonian both the BB and powermate will reach their parfocal point.
In a refractor, where a diagonal is used, the BB will not come close to reaching it's parfocal point, and an inch or so of in-travel will be required.

--------------------
John Rhodes (TV Rep.)

[janoskiss]

2x big barlow + panoptic barlow interface = 2x powermate. If you can still get the Pano interface that's another option you might like to consider. btw it seems to work well with other 2" barlows also.

[Rodstar]

Thanks Steve,

You are no doubt aware that the CN thread I cut and paste quote from in the second post contains an interesting debate about whether TV ever represented that "2x big barlow + panoptic barlow interface = 2x powermate" ! I think ultimately the position that the TV rep presented was that the two alternatives produce a similar result.

I don't have a Panoptic barlow interface. I wonder how much they cost? If it is more than $100, I would rather go with the Powermate.

[iceman]

I'm keen to get a 2x 2" barlow for my ED80 + 350D, so will watch this thread with interest.

[janoskiss]

Was considerably less than that when I got mine. Afaik they are being phased out by TV but might still be available from some dealers. For high powers (where barlowed eye relief is fine) a plain old well made 2-element barlow is preferable so I like the option of being able to remove the extra two elements that correct for eye relief. On the downside, the interface+barlow is a bulkier package and there is more glass to protect from dust etc.

[§AB]

I think the powermate. I love mine and I swear to god it outperforms the already great TV 2x barlow! As Janoskiss said its less bulky and less glass in the lightpath than the 2x + panoptic interface.

[ausastronomer]

Rod,

On lawyers wages you shouldn't need to ask this question :D

Just go and buy the powermate.

Steve is correct, the 2" 2X Powermate is the equivalent of the 2" 2X Big Barlow plus the Panoptic Interface. The powermate was designed from those two original components because at the time the Powermate was developed the Panoptics accounted for a very major portion of Televues' eyepiece sales.

Cheers,
John B

[dannat]

can I butt in on the thread and ask how you set up a barlow in between an imaging setup of scope & d-slr?
thanks daniel

[astropolak]

Rod

I have the TV Big Barlow, if you are coming to Pony Club this Saturday I will let you play with it...:)

Joe

[Rodstar]

Thanks Joe, that sounds great!

[skwinty]

Hi Daniel
You would need whats called eye piece projection fittings. These fittings require a nose piece to fit in to the telescope, a fitting to hold the barlow and then a fitting to connect the nose piece and eyepiece to the t ring and camera.
I can post a pic of the fittings tomorrow if you'd like.
Regards
Steve:)

[Dazzler]

I have a 2.5x Powermate and use it a lot with my 24 Pan which mates very very well. The pair give approx the same power as my XW10 and I don't see any great difference between the two in my 10" LX200R.

Contrast is very similar and performance is exceptional as you would expect.

I find the powermate very handy with my PST and also the ETX.

Good luck! :thumbsup:

[Rodstar]

Darren. that is huge rap for the Powermate, given how good the Pentax XW is. Do you ever use the Powermate with the 17 Nagler? If so, how does that pairing go?

[dannat]

steve, thanks for the reply - I would really love a pic if you have the time & will
cheers daniel

[skwinty]

Hi Daniel
Will take some pics tonight and start a new thread.
Regards
Steve

[Dazzler]

Rod - the 17 Nagler is a 2" ep and the 2.5 powermate is 1.25".

I was really surprised by how well the 24 pan and powermate performed given I had been using the xw10 a fair bit before getting them. I can even aaaaaaaaaaaaalmost say that I prefer the TV pairing to the XW10. :shrug:

[Zuts]

I have a 2.5 powermate and it is definately a 2 inch though it is sold with an adaptor so can take 1.25 inch ep's

Paul

[Merlin66]

I'm embarrassed! I should have known better! After all these years I'm still stupid!
Like any supplementary lens in the system, the Barlow is designed to give the "design magnification" at a precise back focal distance. Any deviation from this "sweet spot" will affect the amplification factor and possibly the optical performance.
The error I made was to use a TV Big Barlow on an ED80 to "try" and achieve f15 ( ie x2) for the PST etalon....The distance from the barlow lens to the normal eyepiece position is 60+50=110mm (60 to the shoulder, 50mm for eyepiece insertion); when put in my situation I had:
110 +50 (PST to 2" adaptor) + 60 (diagonal +BF) = 220mm. What this means, is that the amplification ratio was more like 5-10!!!
( As the position of the barlow lens approachs its focal length inside the prime focus, the new focus tends to infinity ie parallel beam!)
I had tooooo much back focus on the Barlow.
It made me think about other applications where a camera adaptor + 55mm camera body may be fitted to a Barlow.... the amplification factor will NOT be the same as design ie possibly x4 rather than x2.