Barlow-Celestron Ultima 2x VS TeleVue 2x

[shirox]

Hi guys,

I'm thinking about getting either this 2 barlow.

Televue 2 x

Celestron Ultima 2 x

Which one is better?

And comparing this 2 with the Powermate 2.5x, is there really a big difference

[cloud_cover]

There's quite a significant difference in power between 2x and 2.5x.
I have no experience with the Celestron but the Televue is nice and occasionally pops up in the US for less than 70USD, so plus shipping just under $100SGD. You might want to give that a go

[shirox]

icic thanks!

[weixing]

Hi,
I think the Televue 2x is better than Ultima 2x on the edge performance and also it doesn't increase eye relief as much as the Ultima 2x.

The main different between Powermate 2.5x and the other 2 barlow (other than magnification) is Powermate 2.5x won't increase eye relief of eyepiece and provide a flatter view (useful for imaging).

Have a nice day.

[rlow]

If I may broadly catagorise, there are three types of barlows: short barlow, standard barlow and telecentric. 

Short barlows have stronger nagative lens than the standard types, hence the barrels are shorter. This is useful in a star diagonal (for refractors & SCTs etc) and to reduce light-path intrusion in a Newtonian. It also increases the eye-relief more than the standard barlow; this may be good or bad, depending on the eyepiece used. Short barlow are more likely to vignette the light-path of certain eyepieces more than the standard barlows. The Ultima 2x barlow is a short barlow.   

The TV 2x barlow is a standard barlow. Standard barlow generally tend to be of slightly superior optical design than the short barlow. If you use this with a diagonal, check first to make sure it doesnt hit the diagonal mirror or prism.

Speaking of diagonals, if you place the 2x barlow on top of the star diagonal, you get 2x magnification, but if you place the barlow before the diagonal, you get closer to 3x. Similarly one can get various magnification values from a single barlow by adding various lengths of extension tubes.    

Short & standard barlow have 2 element in 1 group, a doublet. There are also barlows with a triplet design which are said to be 'apochromatic' but this is apparently not significant and perhaps more of a marketing ploy.    

Telecentrics have 4 elements in 2 group, ie, a barlow doublet with another doublet. It minimizes vignetting, and preserves the original eye-relief of the eyepiece. Imaging folks tend to prefer using this type, like the Powermates. 

Experienced planetary visual observers prefer NOT to use a barlow. However, if a barlow is necessary, a high-quality standard doublet barlow is preferred. For visual observers, this type is slightly superior to the shorties, triplets and telecentrics in maximising light throughput and contrast, and in minimising light scatter.  The TV 2x barlow is a good barlow for this purpose, though there are better ones, eg. Zeiss barlows.

I hope this help to shed some light on barlows for you (:     

[shirox]

Hi guys, thank you so much for the info and advices. I have decided to get the TV2x from a fellow member here tomorrow.
Thanks alot!